Simultaneous Study of Intake and In-Cylinder IC Engine Flow Fields to Provide an Insight into Intake Induced Cyclic Variations

NASA Astrophysics Data System (ADS)

Justham, T.; Jarvis, S.; Clarke, A.; Garner, C. P.; Hargrave, G. K.; Halliwell, N. A.

2006-07-01

Simultaneous intake and in-cylinder digital particle image velocimetry (DPIV) experimental data is presented for a motored spark ignition (SI) optical internal combustion (IC) engine. Two individual DPIV systems were employed to study the inter-relationship between the intake and in-cylinder flow fields at an engine speed of 1500 rpm. Results for the intake runner velocity field at the time of maximum intake valve lift are compared to incylinder velocity fields later in the same engine cycle. Relationships between flow structures within the runner and cylinder were seen to be strong during the intake stroke but less significant during compression. Cyclic variations within the intake runner were seen to affect the large scale bulk flow motion. The subsequent decay of the large scale motions into smaller scale turbulent structures during the compression stroke appear to reduce the relationship with the intake flow variations.

Spatial and temporal variations of the ion velocity measured in the Venus ionosphere

NASA Technical Reports Server (NTRS)

Miller, K. L.; Knudsen, W. C.

1987-01-01

Temporal and spatial deviations of ion velocity from the dominant flow of the Venusian ionosphere were detected in data collected from a retarding potential analyzer (RPA) aboard the Pioneer-Venus orbiter spectrometer. The ion velocity measurements were analyzed for the first 3.5 Venus years of the Pioneer-Venus mission, approximately through orbit 780. The deviations of ion velocity from the dominant velocity of the Venusian ionosphere, which generally flows nightward and is almost symmetric about the sun-Venus axis, affect both the ionospheric structure and dynamics. Two examples of departure from steady symmetric flow that were measured by the RPA are discussed.

Planar Laser-Induced Iodine Fluorescence Measurements in Rarefied Hypersonic Flow

NASA Technical Reports Server (NTRS)

Cecil, Eric; McDaniel, James C.

2005-01-01

A planar laser-induced fluorescence (PLIF) technique is discussed and applied to measurement of time-averaged values of velocity and temperature in an I(sub 2)-seeded N(sub 2) hypersonic free jet facility. Using this technique, a low temperature, non-reacting, hypersonic flow over a simplified model of a reaction control system (RCS) was investigated. Data are presented of rarefied Mach 12 flow over a sharp leading edge flat plate at zero incidence, both with and without an interacting jet issuing from a nozzle built into the plate. The velocity profile in the boundary layer on the plate was resolved. The slip velocity along the plate, extrapolated from the velocity profile data, varied from nearly 100% down to 10% of the freestream value. These measurements are compared with results of a DSMC solution. The velocity variation along the centerline of a jet issuing from the plate was measured and found to match closely with the correlation of Ashkenas and Sherman. The velocity variation in the oblique shock terminating the jet was resolved sufficiently to measure the shock wave thickness.

Numerical solution for the velocity-derivative skewness of a low-Reynolds-number decaying Navier-Stokes flow

NASA Technical Reports Server (NTRS)

Deissler, Robert G.

1990-01-01

The variation of the velocity-derivative skewness of a Navier-Stokes flow as the Reynolds number goes toward zero is calculated numerically. The value of the skewness, which has been somewhat controversial, is shown to become small at low Reynolds numbers.

Receptivity of flat-plate boundary layer in a non-uniform free stream (vorticity normal to the plate)

NASA Technical Reports Server (NTRS)

Kogan, M. N.

1994-01-01

Recent progress in both the linear and nonlinear aspects of stability theory has highlighted the importance of the receptivity problem. One of the most unclear aspects of receptivity study is the receptivity of boundary-layer flow normal to vortical disturbances. Some experimental and theoretical results permit the proposition that quasi-steady outer-flow vortical disturbances may trigger by-pass transition. In present work such interaction is investigated for vorticity normal to a leading edge. The interest in these types of vortical disturbances arise from theoretical work, where it was shown that small sinusoidal variations of upstream velocity along the spanwise direction can produce significant variations in the boundary-layer profile. In the experimental part of this work, such non-uniform flow was created and the laminar-turbulent transition in this flow was investigated. The experiment was carried out in a low-turbulence direct-flow wind tunnel T-361 at the Central Aerohydrodynamic Institute (TsAGI). The non-uniform flow was produced by laminar or turbulent wakes behind a wire placed normal to the plate upstream of the leading edge. The theoretical part of the work is devoted to studying the unstable disturbance evolution in a boundary layer with strongly non-uniform velocity profiles similar to that produced by outer-flow vorticity. Specifically, the Tollmien-Schlichting wave development in the boundary layer flow with spanwise variations of velocity is investigated.

Mafic-crystal distributions, viscosities, and lava structures of some Hawaiian lava flows

NASA Astrophysics Data System (ADS)

Rowland, Scott K.; Walker, George P. L.

1988-09-01

The distribution patterns of mafic phenocrysts in some Hawaiian basalt flows are consistent with simple in situ gravitational settling. We use the patterns to estimate the crystal settling velocity and hence viscosity of the lava, which in turn can be correlated with surface structures. Numerical modeling generates theoretical crystal concentration profiles through lava flow units of different thicknesses for differing settling velocities. By fitting these curves to field data, crystal-settling rates through the lavas can be estimated, from which the viscosities of the flows can be determined using Stokes' Law. Lavas in which the crystal settling velocity was relatively high (on the order of 5 × 10 -4 cm/sec) show great variations in phenocryst content, both from top to bottom of the same flow unit, and from one flow unit to another. Such lava is invariably pahoehoe, flow units of which are usually less than 1 m thick. Lavas in which the crystal-settling velocity was low show a small but measurable variation in phenocryst content. These lavas are part of a progression from a rough pahoehoe to toothpaste lava to a'a. Toothpaste lava is characterized by spiny texture as well as the ability to retain surface grooves during solidification, and flow units are usually thicker than 1 m. In the thickest of Hawaiian a'a flows, those of the distal type, no systematic crystal variations are observed, and high viscosity coupled with a finite yield strength prevented crystal settling. The amount of crystal settling in pahoehoe indicates that the viscosity ranged from 600 to 6000 Pa s. The limited amount of settling in toothpaste lava indicates a viscosity greater than this value, approaching 12,000 Pa s. We infer that distal-type a'a had a higher viscosity still and also possessed a yield strength.

The variation in frequency locations in Doppler ultrasound spectra for maximum blood flow velocities in narrowed vessels.

PubMed

Zhang, Yingyun; Zhang, Yufeng; Gao, Lian; Deng, Li; Hu, Xiao; Zhang, Kexin; Li, Haiyan

2017-11-01

This study assessed the variation in the frequency locations in the Doppler ultrasound spectra for the maximum blood flow velocities of in vessels with different degrees of bilaterally axisymmetric stenosis. This was done by comparing the relationship between the velocity distributions and corresponding Doppler power spectra. First, a geometric vessel model with axisymmetric stenosis was established. This made it possible to obtain the blood flow velocity distributions for different degrees of stenosis from the solutions of the Navier-Stokes equations. Then, the Doppler spectra were calculated for the entire segment of the vessel that was covered by the sound field. Finally, the maximum frequency locations for the spectra were determined based on the intersections of the maximum values chosen from the calculated blood flow velocity distributions and their corresponding spectra. The computational analysis showed that the maximum frequencies, which corresponded to the maximum blood flow velocities for different degrees of stenosis, were located at different positions along the spectral falling edges. The location for a normal (stenosis free) vessel was in the middle of the falling edge. For vessels with increasing degrees of stenosis, this location shifted approximately linearly downward along the falling edge. For 40% stenosis, the location reached a position at the falling edge of 0.32. Results obtained using the Field II simulation tool demonstrated the validity of the theoretical analysis and calculations, and may help to improve the maximum velocity estimation accuracy for Doppler blood flow spectra in stenosed vessels. Copyright © 2017 IPEM. Published by Elsevier Ltd. All rights reserved.

Hydroecological factors governing surface water flow on a low-gradient floodplain

USGS Publications Warehouse

Harvey, J.W.; Schaffranek, R.W.; Noe, G.B.; Larsen, L.G.; Nowacki, D.J.; O'Connor, B.L.

2009-01-01

Interrelationships between hydrology and aquatic ecosystems are better understood in streams and rivers compared to their surrounding floodplains. Our goal was to characterize the hydrology of the Everglades ridge and slough floodplain ecosystem, which is valued for the comparatively high biodiversity and connectivity of its parallel-drainage features but which has been degraded over the past century in response to flow reductions associated with flood control. We measured flow velocity, water depth, and wind velocity continuously for 3 years in an area of the Everglades with well-preserved parallel-drainage features (i.e., 200-m wide sloughs interspersed with slightly higher elevation and more densely vegetated ridges). Mean daily flow velocity averaged 0.32 cm s-1 and ranged between 0.02 and 0.79 cm s-1. Highest sustained velocities were associated with flow pulses caused by water releases from upstream hydraulic control structures that increased flow velocity by a factor of 2-3 on the floodplain for weeks at a time. The highest instantaneous measurements of flow velocity were associated with the passage of Hurricane Wilma in 2005 when the inverse barometric pressure effect increased flow velocity up to 5 cm s-1 for several hours. Time-averaged flow velocities were 29% greater in sloughs compared to ridges because of marginally higher vegetative drag in ridges compared to sloughs, which contributed modestly (relative to greater water depth and flow duration in sloughs compared to ridges) to the predominant fraction (86%) of total discharge through the landscape occurring in sloughs. Univariate scaling relationships developed from theory of flow through vegetation, and our field data indicated that flow velocity increases with the square of water surface slope and the fourth power of stem diameter, decreases in direct proportion with increasing frontal area of vegetation, and is unrelated to water depth except for the influence that water depth has in controlling the submergence height of vegetation that varies vertically in its architectural characteristics. In the Everglades the result of interactions among controlling variables was that flow velocity was dominantly controlled by water surface slope variations responding to flow pulses more than spatial variation in vegetation characteristics or fluctuating water depth. Our findings indicate that floodplain managers could, in addition to managing water depth, manipulate the frequency and duration of inflow pulses to manage water surface slope, which would add further control over flow velocities, water residence times, sediment settling, biogeochemical transformations, and other processes that are important to floodplain function. ?? 2009 by American Geophysical Union.

Interactive Effects of Nutrient and Mechanical Stresses on Plant Morphology

PubMed Central

Puijalon, Sara; Lena, Jean-Paul; Bornette, Gudrun

2007-01-01

Background and Aims Plant species frequently encounter multiple stresses under natural conditions, and the way they cope with these stresses is a major determinant of their ecological breadth. The way mechanical (e.g. wind, current) and resource stresses act simultaneously on plant morphological traits has been poorly addressed, even if both stresses often interact. This paper aims to assess whether hydraulic stress affects plant morphology in the same way at different nutrient levels. Methods An examination was made of morphological variations of an aquatic plant species growing under four hydraulic stress (flow velocity) gradients located in four habitats distributed along a nutrient gradient. Morphological traits covering plant size, dry mass allocation, organ water content and foliage architecture were measured. Key Results Significant interactive effects of flow velocity and nutrient level were observed for all morphological traits. In particular, increased flow velocity resulted in size reductions under low nutrient conditions, suggesting an adaptive response to flow stress (escape strategy). On the other hand, moderate increases in flow velocity resulted in increased size under high nutrient conditions, possibly related to an inevitable growth response to a higher nutrient supply induced by water renewal at the plant surface. For some traits (e.g. dry mass allocation), a consistent sense of variation as a result of increasing flow velocity was observed, but the amount of variation was either reduced or amplified under nutrient-rich compared with nutrient-poor conditions, depending on the traits considered. Conclusions These results suggest that, for a given species, a stress factor may result, in contrasting patterns and hence strategies, depending on a second stress factor. Such results emphasize the relevance of studies on plant responses to multiple stresses for understanding the actual ecological breadth of species. PMID:17913725

Hydrogeological characterization of flow system in a karstic aquifer, Seymareh dam, Iran

NASA Astrophysics Data System (ADS)

Behrouj Peely, Ahmad; Mohammadi, Zargham; Raeisi, Ezzatollah; Solgi, Khashayar; Mosavi, Mohammad J.; Kamali, Majid

2018-07-01

In order to determine the characteristics of the flow system in a karstic aquifer, an extensive hydrogeological study includes dye tracing test was conducted. The aquifer suited left abutment of Seymareh Dam, in Ravandi Anticline and discharges by more than 50 springs in the southern flank. Flow system in the aquifer is mainly controlled by the reservoir of Seymareh Dam. Time variations of the spring discharge and water table in the observation wells were highly correlated with the reservoir water level. The average groundwater velocity ranges from 0.2 to more than 14 m/h based on the dye tracing test. The probable flow paths were differentiated in two groups including the flow paths in the northern and southern flanks of Ravandi Anticline. Types of groundwater flow in the proposed flow paths are determined as diffuse or conduit flow type considering groundwater velocity and shape of the breakthrough curves. An index is proposed for differentiation of diffuse and conduit flow system based on relationship of groundwater velocity and hydraulic gradient. Dominant geometry of the flow routs (e.g., conduit diameter and fracture aperture) is estimated for the groundwater flow paths toward the springs. Based on velocity variations and variance coefficient of the water table and discharge of springs on map view a major karst conduit was probably developed in the aquifer. This research emphasizes applying of an extensive hydrogeological study for characterization of flow system in the karst aquifer.

Transverse radius dependence for transverse velocity and elliptic flow in intermediate energy HIC

NASA Astrophysics Data System (ADS)

Yan, Ting-Zhi; Li, Shan

2011-05-01

The mean transverse velocity and elliptic flow of light fragments (A <= 2) as a function of transverse radius are studied for 25 MeV/nucleon 64Cu+64Cu collisions with impact parameters 3-5 fm by the isospin-dependent quantum molecular dynamics model. By comparison between the in-plane and the out-of-plane transverse velocities, the elliptic flow dependence on the transverse radius can be understood qualitatively, and variation of the direction of the resultant force on the fragments can be investigated qualitatively.

Modeling the effect of varying swim speeds on fish passage through velocity barriers

USGS Publications Warehouse

Castro-Santos, T.

2006-01-01

The distance fish can swim through zones of high-velocity flow is an important factor limiting the distribution and conservation of riverine and diadromous fishes. Often, these barriers are characterized by nonuniform flow conditions, and it is likely that fish will swim at varying speeds to traverse them. Existing models used to predict passage success, however, typically include the unrealistic assumption that fish swim at a constant speed regardless of the speed of flow. This paper demonstrates how the maximum distance of ascent through velocity barriers can be estimated from the swim speed-fatigue time relationship, allowing for variation in both swim speed and water velocity.

Velocity and temperature profiles in near-critical nitrogen flowing past a horizontal flat plate

NASA Technical Reports Server (NTRS)

Simoneau, R. J.

1977-01-01

Boundary layer velocity and temperature profiles were measured for nitrogen near its thermodynamic critical point flowing past a horizontal flat plate. The results were compared measurements made for vertically upward flow. The boundary layer temperatures ranged from below to above the thermodynamic critical temperature. For wall temperatures below the thermodynamic critical temperature there was little variation between the velocity and temperature profiles in three orientations. In all three orientations the point of crossing into the critical temperature region is marked by a significant flattening of the velocity and temperature profiles and also a decrease in heat transfer coefficient.

Analytical solutions for solute transport in groundwater and riverine flow using Green's Function Method and pertinent coordinate transformation method

NASA Astrophysics Data System (ADS)

Sanskrityayn, Abhishek; Suk, Heejun; Kumar, Naveen

2017-04-01

In this study, analytical solutions of one-dimensional pollutant transport originating from instantaneous and continuous point sources were developed in groundwater and riverine flow using both Green's Function Method (GFM) and pertinent coordinate transformation method. Dispersion coefficient and flow velocity are considered spatially and temporally dependent. The spatial dependence of the velocity is linear, non-homogeneous and that of dispersion coefficient is square of that of velocity, while the temporal dependence is considered linear, exponentially and asymptotically decelerating and accelerating. Our proposed analytical solutions are derived for three different situations depending on variations of dispersion coefficient and velocity, respectively which can represent real physical processes occurring in groundwater and riverine systems. First case refers to steady solute transport situation in steady flow in which dispersion coefficient and velocity are only spatially dependent. The second case represents transient solute transport in steady flow in which dispersion coefficient is spatially and temporally dependent while the velocity is spatially dependent. Finally, the third case indicates transient solute transport in unsteady flow in which both dispersion coefficient and velocity are spatially and temporally dependent. The present paper demonstrates the concentration distribution behavior from a point source in realistically occurring flow domains of hydrological systems including groundwater and riverine water in which the dispersivity of pollutant's mass is affected by heterogeneity of the medium as well as by other factors like velocity fluctuations, while velocity is influenced by water table slope and recharge rate. Such capabilities give the proposed method's superiority about application of various hydrological problems to be solved over other previously existing analytical solutions. Especially, to author's knowledge, any other solution doesn't exist for both spatially and temporally variations of dispersion coefficient and velocity. In this study, the existing analytical solutions from previous widely known studies are used for comparison as validation tools to verify the proposed analytical solution as well as the numerical code of the Two-Dimensional Subsurface Flow, Fate and Transport of Microbes and Chemicals (2DFATMIC) code and the developed 1D finite difference code (FDM). All such solutions show perfect match with the respective proposed solutions.

Velocity Measurements in Confined Dual Coaxial Jets Behind an Axisymmetric Bluff Body: Isothermal and Combusting Flows

DTIC Science & Technology

1981-04-01

made of the fuei and air stagnation points along the centerline, in bc-, isothermal and cotnbusting flows. STPi SECURITY CLA~S:FICATIOWII QF T•, PAGE...Flow Rates. 22 The Variation of the Centerline Location (Z.) of the Fuel 33 (f.) and Air (a.) Stuignation Points with the Mean Annulus Air Velocity (WA...Tunnel with No 41 Annular Flow. 31 Flowfield for Annula , Flow in the Combustion Tunnel with 42 No Fuel Flow. S2 Flowfield in the Combustion Tunnel when

The steady inhomogeneous rapid granular shear flow of nearly elastic spheres

NASA Astrophysics Data System (ADS)

Chou, Chuen-Shii

2000-11-01

The steady inhomogeneous rapid granular shear flows of identical, smooth, nearly elastic spheres were considered, which interact with a flat wall to which identical, evenly spaced half-spheres have been attached. The boundary-value problem for the steady inhomogeneous shear flows, which are maintained by the relative motion of parallel bumpy boundaries, was solved by employing the constitutive relations of Jenkins and Richman (Arch. Rational Mech. Anal. 87 (1985) 355) and the boundary conditions of Richman (Acta. Mech. 75 (1988) 227) in the balance equations for mean fields of mass density of flow, velocity, and the granular temperature. How the resulting profiles of velocity, solid fraction, and granular temperature were affected by changes in the geometrical configuration of the boundary and the coefficient of restitution was demonstrated. Additionally, predicting how the slip velocity would vary with the geometrical configuration of the boundary, the coefficient of restitution, the flow depth and the average solid fraction within the flow was under taken. Special emphasis was placed on the manner in which the shear and normal stresses vary with boundary characteristics and the coefficient of restitution, primarily because the stresses are the quantities most easily measured by the experimentalist. Variations in slip velocity were observed to be partially responsible for the corresponding variations in the stresses.

Effects of non-homogeneous flow on ADCP data processing in a hydroturbine forebay

DOE PAGES

Harding, S. F.; Richmond, M. C.; Romero-Gomez, P.; ...

2016-01-02

Accurate modeling of the velocity field in the forebay of a hydroelectric power station is important for both power generation and fish passage, and is able to be increasingly well represented by computational fluid dynamics (CFD) simulations. Acoustic Doppler Current Profiler (ADCP) are investigated herein as a method of validating the numerical flow solutions, particularly in observed and calculated regions of non-homogeneous flow velocity. By using a numerical model of an ADCP operating in a velocity field calculated using CFD, the errors due to the spatial variation of the flow velocity are quantified. Furthermore, the numerical model of the ADCPmore » is referred to herein as a Virtual ADCP (VADCP).« less

DIVERGENT HORIZONTAL SUB-SURFACE FLOWS WITHIN ACTIVE REGION 11158

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jain, Kiran; Tripathy, S. C.; Hill, F., E-mail: kjain@nso.edu, E-mail: stripathy@nso.edu, E-mail: fhill@nso.edu

We measure the horizontal subsurface flow in a fast emerging active region (AR; NOAA 11158) using the ring-diagram technique and the Helioseismic and Magnetic Imager high spatial resolution Dopplergrams. This AR had a complex magnetic structure and displayed significant changes in morphology during its disk passage. Over a period of six days from 2011 February 11 to 16, the temporal variation in the magnitude of the total velocity is found to follow the trend of magnetic field strength. We further analyze regions of individual magnetic polarity within AR 11158 and find that the horizontal velocity components in these sub-regions havemore » significant variation with time and depth. The leading and trailing polarity regions move faster than the mixed-polarity region. Furthermore, both zonal and meridional components have opposite signs for trailing and leading polarity regions at all depths showing divergent flows within the AR. We also find a sharp decrease in the magnitude of total horizontal velocity in deeper layers around major flares. It is suggested that the re-organization of magnetic fields during flares, combined with the sunspot rotation, decreases the magnitude of horizontal flows or that the flow kinetic energy has been converted into the energy released by flares. After the decline in flare activity and sunspot rotation, the flows tend to follow the pattern of magnetic activity. We also observe less variation in the velocity components near the surface but these tend to increase with depth, further demonstrating that the deeper layers are more affected by the topology of ARs.« less

An experimental study of the fluid mechanics associated with porous walls

NASA Technical Reports Server (NTRS)

Ramachandran, N.; Heaman, J.; Smith, A.

1992-01-01

The fluid mechanics associated with the blowing phenomenon from porous walls is measured and characterized. The measurements indicate that the flow exiting a porous wall exhibits a lumpy velocity profile caused by the coalescence effects of smaller jets emerging from the surface. The velocity variations are spatially stable and prevail even at low flow rates. The intensity of this pseudoturbulence is found to be directly proportional to the filter rating of the porous wall and to increase linearly with the mean velocity. Beyond a critical mean velocity, the pseudoturbulence intensity shows a leveling trend with increase in the mean velocity. This critical velocity varies inversely as the filter rating and represents the onset of fully developed jetting action in the flow field. Based on the data, a more appropriate length scale for the flow field is proposed and a correlation is developed that can be used to predict the onset of fully developed jets in the flow emerging from a porous wall.

Landsat imagery and its treatment in a publicly available data portal to monitor flow velocity variations of Greenland outlet glaciers

NASA Astrophysics Data System (ADS)

Scheinert, M.; Rosenau, R.; Ebermann, B.; Horwath, M.

2016-12-01

Utilizing the freely available Landsat archive we have set up a monitoring system to process and provide flow-velocity fields for more than 300 outlet glaciers along the margin of the Greenland ice sheet. We will present major processing steps. These include, among others, an improved orthorectification that is based on the Global Digital Elevation Map V2 (GDEM-V2) of the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER). For those Landsat 7 products which feature the scan line corrector (SLC) failure a destriping correction was applied. An adaptive, recursive filter approach was applied in order to remove outliers. Altogether, the enhanced processing leads to a higher accuracy of the flow-velocity fields. By mid-2016 we succeeded in incorporating more than 37,000 optical multi-sensoral scenes from Landsat 1 to 8. These scenes cover the period from 1972 to 2015. Until now, for almost 300 glaciers we processed more than 100,000 flow-velocity fields for the time span until 2012. For the time until 2015 velocity fields were inferred only for the fastest flowing glaciers. However, new recordings of Landsat 7 and Landsat 8 as well as the availability of further scenes through the Landsat Global Archive Consolidation (LGAC) effort will help to enlarge the database. With a further quality check, we can provide more than 40,000 flow-velocity for public accessibility. More products will be added continuously while the almost automated processing is ongoing. The long time span enables to determine trends of the flow velocity over different (long) periods. A major achievement can be seen in the fact that a high temporal resolution facilitates the analysis of seasonal flow-velocity variations. We will discuss prominent examples of the non-uniform pattern of ice flow velocity changes. For this, a powerful tool is provided by the monitoring system and its web-based data portal. It allows to study the flow-velocity changes in time and space, and to possibly identify distinctive patterns. Rapid changes like surge events can be detected and analyzed in detail. The presentation will demonstrate how the data portal enables to interactively perform the calculation of profiles or time series for locations the user can select on the map. Also, the user can choose from different options to download the examined data.

Forced convective heat transfer in curved diffusers

NASA Technical Reports Server (NTRS)

Rojas, J.; Whitelaw, J. H.; Yianneskis, M.

1987-01-01

Measurements of the velocity characteristics of the flows in two curved diffusers of rectangular cross section with C and S-shaped centerlines are presented and related to measurements of wall heat transfer coefficients along the heated flat walls of the ducts. The velocity results were obtained by laser-Doppler anemometry in a water tunnel and the heat transfer results by liquid crystal thermography in a wind tunnel. The thermographic technique allowed the rapid and inexpensive measurement of wall heat transfer coefficients along flat walls of arbitrary boundary shapes with an accuracy of about 5 percent. The results show that an increase in secondary flow velocities near the heated wall causes an increase in the local wall heat transfer coefficient, and quantify the variation for maximum secondary-flow velocities in a range from 1.5 to 17 percent of the bulk flow velocity.

Variations in Temperature at the Base of the Lithosphere Beneath the Archean Superior Province, Canada

NASA Astrophysics Data System (ADS)

Mareschal, J.; Jaupart, C. P.

2013-12-01

Most of the variations in surface heat flux in stable continents are caused by variations in crustal heat production, with an almost uniform heat flux at the base of the crust ( 15+/-3 mW/m2). Such relatively small differences in Moho heat flux cannot be resolved by heat flow data alone, but they lead to important lateral variations in lithospheric temperatures and thicknesses. In order to better constrain temperatures in the lower lithosphere, we have combined surface heat flow and heat production data from the southern Superior Province in Canada with vertical shear wave velocity profiles obtained from surface wave inversion. We use the Monte-Carlo method to generate lithospheric temperature profiles from which shear wave velocity can be calculated for a given mantle composition. We eliminate thermal models which yield lithospheric and sub-lithospheric velocities that do not fit the shear wave velocity profile. Surface heat flux being constrained, the free parameters of the thermal model are: the mantle heat flux, the mantle heat production, the crustal differentiation index (ratio of surface to bulk crustal heat production) and the temperature of the mantle isentrope. Two conclusions emerge from this study. One is that, for some profiles, the vertical variations in shear wave velocities cannot be accounted for by temperature alone but also require compositional changes within the lithosphere. The second is that there are long wavelength horizontal variations in mantle temperatures (~80-100K) at the base of the lithosphere and in the mantle below

Exploiting LSPIV to assess debris-flow velocities in the field

NASA Astrophysics Data System (ADS)

Theule, Joshua I.; Crema, Stefano; Marchi, Lorenzo; Cavalli, Marco; Comiti, Francesco

2018-01-01

The assessment of flow velocity has a central role in quantitative analysis of debris flows, both for the characterization of the phenomenology of these processes and for the assessment of related hazards. Large-scale particle image velocimetry (LSPIV) can contribute to the assessment of surface velocity of debris flows, provided that the specific features of these processes (e.g. fast stage variations and particles up to boulder size on the flow surface) are taken into account. Three debris-flow events, each of them consisting of several surges featuring different sediment concentrations, flow stages, and velocities, have been analysed at the inlet of a sediment trap in a stream in the eastern Italian Alps (Gadria Creek). Free software has been employed for preliminary treatment (orthorectification and format conversion) of video-recorded images as well as for LSPIV application. Results show that LSPIV velocities are consistent with manual measurements of the orthorectified imagery and with front velocity measured from the hydrographs in a channel recorded approximately 70 m upstream of the sediment trap. Horizontal turbulence, computed as the standard deviation of the flow directions at a given cross section for a given surge, proved to be correlated with surface velocity and with visually estimated sediment concentration. The study demonstrates the effectiveness of LSPIV in the assessment of surface velocity of debris flows and permit the most crucial aspects to be identified in order to improve the accuracy of debris-flow velocity measurements.

Twelve-hour reproducibility of retinal and optic nerve blood flow parameters in healthy individuals.

PubMed

Luksch, Alexandra; Lasta, Michael; Polak, Kaija; Fuchsjäger-Mayrl, Gabriele; Polska, Elzbieta; Garhöfer, Gerhard; Schmetterer, Leopold

2009-11-01

The aim of the present study was to investigate the reproducibility and potential diurnal variation of optic nerve head and retinal blood flow parameters in healthy individuals over a period of 12 hr. We measured optic nerve head and retinal blood flow parameters in 16 healthy male non-smoking individuals at five time-points during the day (08:00, 11:00, 14:00, 17:00 and 20:00 hr). Outcome parameters were perimacular white blood cell flux (as assessed with the blue field entoptic technique), blood velocities in retinal veins (as assessed with bi-directional laser Doppler velocimetry), retinal arterial and venous diameters (as assessed with the retinal vessel analyser), optic nerve head blood flow, volume and velocity (as assessed with single point and scanning laser Doppler flowmetry) and blood velocities in the central retinal artery (as assessed with colour Doppler imaging). The coefficient of variation and the maximum change from baseline in an individual were calculated for each outcome parameter. No diurnal variation in optic nerve head or retinal blood flow was observed with any of the techniques employed. Coefficients of variation were between 1.6% and 18.5% for all outcome parameters. The maximum change from baseline in an individual was much higher, ranging from 3.7% to 78.2%. Our data indicate that in healthy individuals the selected techniques provide adequate reproducibility to be used in clinical studies. However, in patients with eye diseases and reduced vision the reproducibility may be considerably worse.

Environmental controls on drainage behavior of an ephemeral stream

USGS Publications Warehouse

Blasch, K.W.; Ferré, T.P.A.; Vrugt, J.A.

2010-01-01

Streambed drainage was measured at the cessation of 26 ephemeral streamflow events in Rillito Creek, Tucson, Arizona from August 2000 to June 2002 using buried time domain reflectometry (TDR) probes. An unusual drainage response was identified, which was characterized by sharp drainage from saturation to near field capacity at each depth with an increased delay between depths. We simulated the drainage response using a variably saturated numerical flow model representing a two-layer system with a high permeability layer overlying a lower permeability layer. Both the observed data and the numerical simulation show a strong correlation between the drainage velocity and the temperature of the stream water. A linear combination of temperature and the no-flow period preceding flow explained about 90% of the measured variations in drainage velocity. Evaluation of this correlative relationship with the one-dimensional numerical flow model showed that the observed temperature fluctuations could not reproduce the magnitude of variation in the observed drainage velocity. Instead, the model results indicated that flow duration exerts the most control on drainage velocity, with the drainage velocity decreasing nonlinearly with increasing flow duration. These findings suggest flow duration is a primary control of water availability for plant uptake in near surface sediments of an ephemeral stream, an important finding for estimating the ecological risk of natural or engineered changes to streamflow patterns. Correlative analyses of soil moisture data, although easy and widely used, can result in erroneous conclusions of hydrologic cause—effect relationships, and demonstrating the need for joint physically-based numerical modeling and data synthesis for hypothesis testing to support quantitative risk analysis.

Model-based review of Doppler global velocimetry techniques with laser frequency modulation

NASA Astrophysics Data System (ADS)

Fischer, Andreas

2017-06-01

Optical measurements of flow velocity fields are of crucial importance to understand the behavior of complex flow. One flow field measurement technique is Doppler global velocimetry (DGV). A large variety of different DGV approaches exist, e.g., applying different kinds of laser frequency modulation. In order to investigate the measurement capabilities especially of the newer DGV approaches with laser frequency modulation, a model-based review of all DGV measurement principles is performed. The DGV principles can be categorized by the respective number of required time steps. The systematic review of all DGV principle reveals drawbacks and benefits of the different measurement approaches with respect to the temporal resolution, the spatial resolution and the measurement range. Furthermore, the Cramér-Rao bound for photon shot is calculated and discussed, which represents a fundamental limit of the achievable measurement uncertainty. As a result, all DGV techniques provide similar minimal uncertainty limits. With Nphotons as the number of scattered photons, the minimal standard deviation of the flow velocity reads about 106 m / s /√{Nphotons } , which was calculated for a perpendicular arrangement of the illumination and observation direction and a laser wavelength of 895 nm. As a further result, the signal processing efficiencies are determined with a Monte-Carlo simulation. Except for the newest correlation-based DGV method, the signal processing algorithms are already optimal or near the optimum. Finally, the different DGV approaches are compared regarding errors due to temporal variations of the scattered light intensity and the flow velocity. The influence of a linear variation of the scattered light intensity can be reduced by maximizing the number of time steps, because this means to acquire more information for the correction of this systematic effect. However, more time steps can result in a flow velocity measurement with a lower temporal resolution, when operating at the maximal frame rate of the camera. DGV without laser frequency modulation then provides the highest temporal resolutions and is not sensitive with respect to temporal variations but with respect to spatial variations of the scattered light intensity. In contrast to this, all DGV variants suffer from velocity variations during the measurement. In summary, the experimental conditions and the measurement task finally decide about the ideal choice from the reviewed DGV methods.

Canonical fluid thermodynamics. [variational principles of stability for compressible adiabatic flow

NASA Technical Reports Server (NTRS)

Schmid, L. A.

1974-01-01

The space-time integral of the thermodynamic pressure plays in a certain sense the role of the thermodynamic potential for compressible adiabatic flow. The stability criterion can be converted into a variational minimum principle by requiring the molar free-enthalpy and temperature to be generalized velocities. In the fluid context, the definition of proper-time differentiation involves the fluid velocity expressed in terms of three particle identity parameters. The pressure function is then converted into a functional which is the Lagrangian density of the variational principle. Being also a minimum principle, the variational principle provides a means for comparing the relative stability of different flows. For boundary conditions with a high degree of symmetry, as in the case of a uniformly expanding spherical gas box, the most stable flow is a rectilinear flow for which the world-trajectory of each particle is a straight line. Since the behavior of the interior of a freely expanding cosmic cloud may be expected to be similar to that of the fluid in the spherical box of gas, this suggests that the cosmic principle is a consequence of the laws of thermodynamics, rather than just an ad hoc postulate.

CHANGES OF THE SOLAR MERIDIONAL VELOCITY PROFILE DURING CYCLE 23 EXPLAINED BY FLOWS TOWARD THE ACTIVITY BELTS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cameron, R. H.; Schuessler, M., E-mail: cameron@mps.mpg.d

The solar meridional flow is an important ingredient in Babcock-Leighton type models of the solar dynamo. Global variations of this flow have been suggested to explain the variations in the amplitudes and lengths of the activity cycles. Recently, cycle-related variations in the amplitude of the P{sup 1}{sub 2} term in the Legendre decomposition of the observed meridional flow have been reported. The result is often interpreted in terms of an overall variation in the flow amplitude during the activity cycle. Using a semi-empirical model based upon the observed distribution of magnetic flux on the solar surface, we show that themore » reported variations of the P{sup 1}{sub 2} term can be explained by the observed localized inflows into the active region belts. No variation of the overall meridional flow amplitude is required.« less

Application of boundary element method to Stokes flows over a striped superhydrophobic surface with trapped gas bubbles

NASA Astrophysics Data System (ADS)

Ageev, A. I.; Golubkina, I. V.; Osiptsov, A. N.

2018-01-01

A slow steady flow of a viscous fluid over a superhydrophobic surface with a periodic striped system of 2D rectangular microcavities is considered. The microcavities contain small gas bubbles on the curved surface of which the shear stress vanishes. The general case is analyzed when the bubble occupies only a part of the cavity, and the flow velocity far from the surface is directed at an arbitrary angle to the cavity edge. Due to the linearity of the Stokes flow problem, the solution is split into two parts, corresponding to the flows perpendicular and along the cavities. Two variants of a boundary element method are developed and used to construct numerical solutions on the scale of a single cavity with periodic boundary conditions. By averaging these solutions, the average slip velocity and the slip length tensor components are calculated over a wide range of variation of governing parameters for the cases of a shear-driven flow and a pressure-driven channel flow. For a sufficiently high pressure drop in a microchannel of finite length, the variation of the bubble surface shift into the cavities induced by the streamwise pressure variation is estimated from numerical calculations.

Flow variation and substrate type affect dislodgement of the freshwater polychaete, Manayunkia speciosa

USGS Publications Warehouse

Malakauskas, David M.; Wilson, Sarah J.; Wilzbach, Margaret A.; Som, Nicholas A.

2013-01-01

We quantified microscale flow forces and their ability to entrain the freshwater polychaete, Manayunkia speciosa, the intermediate host for 2 myxozoan parasites (Ceratomyxa shasta and Parvicapsula minibicornis) that cause substantial mortalities in salmonid fishes in the Pacific Northwest. In a laboratory flume, we measured the shear stress associated with 2 mean flow velocities and 3 substrates and quantified associated dislodgement of polychaetes, evaluated survivorship of dislodged polychaetes, and observed behavioral responses of the polychaetes in response to increased flow. We used a generalized linear mixed model to estimate the probability of polychaete dislodgement for treatment combinations of velocity (mean flow velocity  =  55 cm/s with a shear velocity  =  3 cm/s, mean flow velocity  =  140 cm/s with a shear velocity  =  5 cm/s) and substrate type (depositional sediments and analogs of rock faces and the filamentous alga, Cladophora). Few polychaetes were dislodged at shear velocities <3 cm/s on any substrate. Above this level of shear, probability of dislodgement was strongly affected by both substrate type and velocity. After accounting for substrate, odds of dislodgement were 8× greater at the higher flow. After accounting for velocity, probability of dislodgement was greatest from fine sediments, intermediate from rock faces, and negligible from Cladophora. Survivorship of dislodged polychaetes was high. Polychaetes exhibited a variety of behaviors for avoiding increases in flow, including extrusion of mucus, burrowing into sediments, and movement to lower-flow microhabitats. Our findings suggest that polychaete populations probably exhibit high resilience to flow-mediated disturbances.

In vitro evaluation of forward and reverse volumetric flow across a regurgitant aortic valve using Doppler power-weighted mean velocities.

PubMed

Minich, L L; Tani, L Y; Pantalos, G M

1997-01-01

To determine the accuracy of using power-weighted mean velocities for quantitating volumetric flow across a cardiac valve, we equipped pulsatile flow-tank systems with a 25 mm porcine or a 27 mm mechanical valve with various sizes of regurgitant orifices. Forward and reverse volumetric flows were measured over a range of hemodynamic conditions using two insonating angles (0 and 45 degrees). Pulsed Doppler power-weighted mean velocity measurements were obtained simultaneously with electromagnetic or ultrasonic transit-time probe measurements. For the porcine valve, Doppler measurements correlated well with electromagnetic flow measurements for all (r = 0.75 to 0.97, p < 0.05) except the smallest (2.7 mm) orifice (r = 0.19). For the mechanical valve, power-weighted mean velocity measurements correlated well with ultrasonic transit-time measurements for each hemodynamic condition defined by pulse rate, mean arterial pressure, and insonating angle (r = 0.93 to 0.99, p < 0.01), but equations varied unpredictably. Thus, although power-weighted mean velocity volumetric flow measurements correlate well with flow probe measurements, equations vary widely as hemodynamic conditions change. Because of this variation, power-weighted mean velocity data are not useful for quantitation of volumetric flow across a cardiac valve at this time. Further investigation may show how different hemodynamic conditions affect power-weighted mean velocity measurements of volumetric flow.

Calculation of gas turbine characteristic

NASA Astrophysics Data System (ADS)

Mamaev, B. I.; Murashko, V. L.

2016-04-01

The reasons and regularities of vapor flow and turbine parameter variation depending on the total pressure drop rate π* and rotor rotation frequency n are studied, as exemplified by a two-stage compressor turbine of a power-generating gas turbine installation. The turbine characteristic is calculated in a wide range of mode parameters using the method in which analytical dependences provide high accuracy for the calculated flow output angle and different types of gas dynamic losses are determined with account of the influence of blade row geometry, blade surface roughness, angles, compressibility, Reynolds number, and flow turbulence. The method provides satisfactory agreement of results of calculation and turbine testing. In the design mode, the operation conditions for the blade rows are favorable, the flow output velocities are close to the optimal ones, the angles of incidence are small, and the flow "choking" modes (with respect to consumption) in the rows are absent. High performance and a nearly axial flow behind the turbine are obtained. Reduction of the rotor rotation frequency and variation of the pressure drop change the flow parameters, the parameters of the stages and the turbine, as well as the form of the characteristic. In particular, for decreased n, nonmonotonic variation of the second stage reactivity with increasing π* is observed. It is demonstrated that the turbine characteristic is mainly determined by the influence of the angles of incidence and the velocity at the output of the rows on the losses and the flow output angle. The account of the growing flow output angle due to the positive angle of incidence for decreased rotation frequencies results in a considerable change of the characteristic: poorer performance, redistribution of the pressure drop at the stages, and change of reactivities, growth of the turbine capacity, and change of the angle and flow velocity behind the turbine.

Intrinsic Flow Behavior During Improved Confinement in MST Reversed-field Pinch

NASA Astrophysics Data System (ADS)

Tan, E.; Craig, D.; Schott, B.; Boguski, J.; Xing, Z. A.; Nornberg, M. D.; Anderson, J. K.

2017-10-01

We used active charge exchange recombination spectroscopy to measure impurity ion flow velocity in high-current plasmas during periods of improved confinement. Velocity measurements througout the core reveal that ion flow parallel to the magnetic field is dominant compared to the perpendicular flow. The poloidal flow profile reverses at r/a = 0.6, and the flow near the core is larger on outboard positions compared to the inboard positions. A strong shear in the toroidal flow develops near the axis as PPCD proceeds. In the past, the mode velocity has been used to infer the toroidal flow based on the `no-slip' assumption that the mode and local plasma co-rotate. We tested this assumption with direct measurements near the m = 1, n = 6 resonant surface. Inboard flow measurements are consistent with the no-slip condition and exhibit a time dependence where the flow decreases together with the n = 6 mode velocity. The outboard flow is consistent in magnitude with the no-slip condition but the variations in time and across shots do not correlate well with the n = 6 mode velocity. Possible reasons why the inboard and outboard flow exhibit different behavior are discussed. This work has been supported by the US DOE and the Wheaton College summer research program.

Temporal variation of chemical and isotopic signals in major discharges of an alpine karst aquifer in Turkey: implications with respect to response of karst aquifers to recharge

NASA Astrophysics Data System (ADS)

Ozyurt, N. Nur; Bayari, C. Serdar

2008-03-01

Proper management of karst aquifers requires a better understanding of flow and transport mechanisms in these systems. Flow in karst aquifers is inherently very complex due to the non-linear and non-stationary relationship between recharge and discharge. Information on this relationship has been acquired for a large (1,000 km2), mountainous (>3,500 m asl) karst aquifer with a deep unsaturated zone (>2,000 m) in the Aladaglar mountain range of south-central Turkey. All major discharges from the aquifer, which drain almost all the recharge, have been observed periodically for specific electrical conductivity, tritium and oxygen-18 variations during a period of 12 months. Observations reveal that the system’s response to recharge depends strongly on the competition between the infiltration and drainage velocities. These velocities, which are controlled by variables such as the time of precipitation, time of infiltration, intensity, and continuity of recharge, determine the degree of dominance of different types of flow mechanisms in the aquifer. Bypass, well-mixed and piston flow mechanisms are used to explain the response of the aquifer to the spatio-temporal variations in recharge. It appears that the aquifer switches among these flow mechanisms depending on the prevailing recharge mode and the competition between infiltration and drainage velocities.

Experimental study of flow distribution and pressure loss with circumferential inlet and outlet manifolds

NASA Technical Reports Server (NTRS)

Dittrich, R. T.

1972-01-01

Water flow tests with circumferential inlet and outlet manifolds were conducted to determine factors affecting fluid distribution and pressure losses. Various orifice sizes and manifold geometries were tested over a range of flow velocities. With inlet manifolds, flow distribution was related directly to orifice discharge coefficients. A correlation indicated that nonuniform distribution resulted when the velocity head ratio at the orifice was not in the range of constant discharge coefficient. With outlet manifolds, nonuniform flow was related to static pressure variations along the manifold. Outlet manifolds had appreciably greater pressure losses than comparable inlet manifolds.

Accounting For Compressibility In Viscous Flow In Pipes

NASA Technical Reports Server (NTRS)

Steinle, Frank W.; Gee, Ken; Murthy, Sreedhara V.

1991-01-01

Method developed to account for effects of compressibility in viscous flows through long, circular pipes of uniform diameter. Based on approximation of variations in density and velocity across pipe cross section by profile equations developed for boundary-layer flow between flat plates.

Numerical simulation of buoyancy peristaltic flow of Johnson-Segalman nanofluid in an inclined channel

NASA Astrophysics Data System (ADS)

Hayat, T.; Ayub, Sadia; Alsaedi, Ahmed; Ahmad, Bashir

2018-06-01

This study addresses mixed convection on peristaltic flow in an inclined channel. The relevant flow problem is developed for MHD Johnson-Segalman nanofluid. Hall current and thermal radiation are discussed. Channel boundaries are compliant in nature. Slip effects for velocity, temperature and concentration are examined. Long wavelength concept is employed. Variations for prominent parameters in velocity, temperature, concentration, heat transfer coefficient and streamlines are obtained via built-in numerical approach. Velocity shows significant decline for larger local temperature Grashof number. Heat transfer slows down for increasing thermophoresis and thermal slip parameters. Increase in bolus is reported for higher Weissenberg number.

Microgravity flame spread over thick solids in low velocity opposed flow

NASA Astrophysics Data System (ADS)

Wang, Shuangfeng; Zhu, Feng

2016-07-01

Motivated primarily by fire safety of spacecraft, a renewed interest in microgravity flame spread over solid materials has arisen. With few exceptions, however, research on microgravity flame spread has been focused on thermally thin fuels due to the constraint on available test time. In this study, two sets of experiments are conducted to examine the flame spread and extinction behavior over thick PMMA in simulated and actual microgravity environments. The low-gravity flame spread environment is produced by a narrow channel apparatus in normal gravity. Extinction limits using flow velocity and oxygen concentration as coordinates are presented, and flame spread rates are determined as a function of the velocity and oxygen concentration of the gas flow. The microgravity experiments are also performed with varying low-velocity flow and varying ambient oxygen concentration. The important observations include flame behavior and appearance as a function of oxygen concentration and flow velocity, temperature variation in gas and solid phases, and flame spread rate. A comparison between simulated and actual microgravity data is made, and general agreement is found. Based on the experimental observations, mechanisms for flame spread and extinction in low velocity opposed flows are discussed.

A dual-phantom system for validation of velocity measurements in stenosis models under steady flow.

PubMed

Blake, James R; Easson, William J; Hoskins, Peter R

2009-09-01

A dual-phantom system is developed for validation of velocity measurements in stenosis models. Pairs of phantoms with identical geometry and flow conditions are manufactured, one for ultrasound and one for particle image velocimetry (PIV). The PIV model is made from silicone rubber, and a new PIV fluid is made that matches the refractive index of 1.41 of silicone. Dynamic scaling was performed to correct for the increased viscosity of the PIV fluid compared with that of the ultrasound blood mimic. The degree of stenosis in the models pairs agreed to less than 1%. The velocities in the laminar flow region up to the peak velocity location agreed to within 15%, and the difference could be explained by errors in ultrasound velocity estimation. At low flow rates and in mild stenoses, good agreement was observed in the distal flow fields, excepting the maximum velocities. At high flow rates, there was considerable difference in velocities in the poststenosis flow field (maximum centreline differences of 30%), which would seem to represent real differences in hydrodynamic behavior between the two models. Sources of error included: variation of viscosity because of temperature (random error, which could account for differences of up to 7%); ultrasound velocity estimation errors (systematic errors); and geometry effects in each model, particularly because of imperfect connectors and corners (systematic errors, potentially affecting the inlet length and flow stability). The current system is best placed to investigate measurement errors in the laminar flow region rather than the poststenosis turbulent flow region.

Spectroscopic Doppler analysis for visible-light optical coherence tomography

NASA Astrophysics Data System (ADS)

Shu, Xiao; Liu, Wenzhong; Duan, Lian; Zhang, Hao F.

2017-12-01

Retinal oxygen metabolic rate can be effectively measured by visible-light optical coherence tomography (vis-OCT), which simultaneously quantifies oxygen saturation and blood flow rate in retinal vessels through spectroscopic analysis and Doppler measurement, respectively. Doppler OCT relates phase variation between sequential A-lines to the axial flow velocity of the scattering medium. The detectable phase shift is between -π and π due to its periodicity, which limits the maximum measurable unambiguous velocity without phase unwrapping. Using shorter wavelengths, vis-OCT is more vulnerable to phase ambiguity since flow induced phase variation is linearly related to the center wavenumber of the probing light. We eliminated the need for phase unwrapping using spectroscopic Doppler analysis. We split the whole vis-OCT spectrum into a series of narrow subbands and reconstructed vis-OCT images to extract corresponding Doppler phase shifts in all the subbands. Then, we quantified flow velocity by analyzing subband-dependent phase shift using linear regression. In the phantom experiment, we showed that spectroscopic Doppler analysis extended the measurable absolute phase shift range without conducting phase unwrapping. We also tested this method to quantify retinal blood flow in rodents in vivo.

Mean velocities and Reynolds stresses in a juncture flow

NASA Technical Reports Server (NTRS)

Mcmahon, H.; Hubbartt, J.; Kubendran, L.

1982-01-01

Values of three mean velocity components and six turbulence stresses measured in a juncture flow are presented and discussed. The juncture flow is generated by a constant thickness body, having an elliptical leading edge, which is mounted perpendicular to a large flat plate along which a turbulent boundary layer is growing. The measurements were carried out at two streamwise stations in the juncture and were made using two single sensor hot-wire probes. The secondary flow in the juncture results in a considerable distortion in the mean velocity profiles. The secondary flow also transports turbulence in the juncture flow and has a large effect on the turbulence stresses. From visual inspection of the results, there is considerable evidence of similarity between the turbulent shear stresses and the mean flow strain rates. There is some evidence of similarity between the variations in the turbulent stress components.

Radiation induced precursor flow field ahead of a Jovian entry body

NASA Technical Reports Server (NTRS)

Tiwari, S.; Szema, K. Y.

1977-01-01

The change in flow properties ahead of the bow shock of a Jovian entry body, resulting from absorption of radiation from the shock layer, is investigated. Ultraviolet radiation is absorbed by the free stream gases, causing dissociation, ionization, and an increase in enthalpy of flow ahead of the shock wave. As a result of increased fluid enthalpy, the entire flow field in the precursor region is perturbed. The variation in flow properties is determined by employing the small perturbation technique of classical aerodynamics as well as the thin layer approximation for the preheating zone. By employing physically realistic models of radiative transfer, solutions are obtained for velocity, pressure, density, temperature, and enthalpy variations. The results indicate that the precursor flow effects, in general, are greater at higher altitudes. Just ahead of the shock, however, the effects are larger at lower altitudes. Pre-heating of the gas significantly increases the static pressure and temperature ahead of the shock for velocities exceeding 36 km/sec.

Twelve hour reproducibility of choroidal blood flow parameters in healthy subjects

PubMed Central

Polska, E; Polak, K; Luksch, A; Fuchsjager-Mayrl, G; Petternel, V; Findl, O; Schmetterer, L

2004-01-01

Aims/background: To investigate the reproducibility and potential diurnal variation of choroidal blood flow parameters in healthy subjects over a period of 12 hours. Methods: The choroidal blood flow parameters of 16 healthy non-smoking subjects were measured at five time points during the day (8:00, 11:00, 14:00, 17:00, and 20:00). Outcome parameters were pulsatile ocular blood flow as assessed by pneumotonometry, fundus pulsation amplitude as assessed by laser interferometry, blood velocities in the opthalmic and posterior ciliary arteries as assessed by colour Doppler imaging, and choroidal blood flow, volume, and velocity as assessed by fundus camera based laser Doppler flowmetry. The coefficient of variation and the maximum change from baseline in an individual were calculated for each outcome parameter. Results: None of the techniques used found a diurnal variation in choroidal blood flow. Coefficients of variation were within 2.9% and 13.6% for all outcome parameters. The maximum change from baseline in an individual was much higher, ranging from 11.2% to 58.8%. Conclusions: These data indicate that in healthy subjects the selected techniques provide adequate reproducibility to be used in clinical studies. Variability may, however, be considerably higher in older subjects or subjects with ocular disease. The higher individual differences in flow parameter readings limit the use of the techniques in clinical practice. To overcome problems with measurement validity, a clinical trial should include as many choroidal blood flow outcome parameters as possible to check for consistency. PMID:15031172

Twelve hour reproducibility of choroidal blood flow parameters in healthy subjects.

PubMed

Polska, E; Polak, K; Luksch, A; Fuchsjager-Mayrl, G; Petternel, V; Findl, O; Schmetterer, L

2004-04-01

To investigate the reproducibility and potential diurnal variation of choroidal blood flow parameters in healthy subjects over a period of 12 hours. The choroidal blood flow parameters of 16 healthy non-smoking subjects were measured at five time points during the day (8:00, 11:00, 14:00, 17:00, and 20:00). Outcome parameters were pulsatile ocular blood flow as assessed by pneumotonometry, fundus pulsation amplitude as assessed by laser interferometry, blood velocities in the opthalmic and posterior ciliary arteries as assessed by colour Doppler imaging, and choroidal blood flow, volume, and velocity as assessed by fundus camera based laser Doppler flowmetry. The coefficient of variation and the maximum change from baseline in an individual were calculated for each outcome parameter. None of the techniques used found a diurnal variation in choroidal blood flow. Coefficients of variation were within 2.9% and 13.6% for all outcome parameters. The maximum change from baseline in an individual was much higher, ranging from 11.2% to 58.8%. These data indicate that in healthy subjects the selected techniques provide adequate reproducibility to be used in clinical studies. Variability may, however, be considerably higher in older subjects or subjects with ocular disease. The higher individual differences in flow parameter readings limit the use of the techniques in clinical practice. To overcome problems with measurement validity, a clinical trial should include as many choroidal blood flow outcome parameters as possible to check for consistency.

Prerequisites for Accurate Monitoring of River Discharge Based on Fixed-Location Velocity Measurements

NASA Astrophysics Data System (ADS)

Kästner, K.; Hoitink, A. J. F.; Torfs, P. J. J. F.; Vermeulen, B.; Ningsih, N. S.; Pramulya, M.

2018-02-01

River discharge has to be monitored reliably for effective water management. As river discharge cannot be measured directly, it is usually inferred from the water level. This practice is unreliable at places where the relation between water level and flow velocity is ambiguous. In such a case, the continuous measurement of the flow velocity can improve the discharge prediction. The emergence of horizontal acoustic Doppler current profilers (HADCPs) has made it possible to continuously measure the flow velocity. However, the profiling range of HADCPs is limited, so that a single instrument can only partially cover a wide cross section. The total discharge still has to be determined with a model. While the limitations of rating curves are well understood, there is not yet a comprehensive theory to assess the accuracy of discharge predicted from velocity measurements. Such a theory is necessary to discriminate which factors influence the measurements, and to improve instrument deployment as well as discharge prediction. This paper presents a generic method to assess the uncertainty of discharge predicted from range-limited velocity profiles. The theory shows that a major source of error is the variation of the ratio between the local and cross-section-averaged velocity. This variation is large near the banks, where HADCPs are usually deployed and can limit the advantage gained from the velocity measurement. We apply our theory at two gauging stations situated in the Kapuas River, Indonesia. We find that at one of the two stations the index velocity does not outperform a simple rating curve.

Monitoring groundwater variation by satellite and implications for in-situ gravity measurements.

PubMed

Fukuda, Yoichi; Yamamoto, Keiko; Hasegawa, Takashi; Nakaegawa, Toshiyuki; Nishijima, Jun; Taniguchi, Makoto

2009-04-15

In order to establish a new technique for monitoring groundwater variations in urban areas, the applicability of precise in-situ gravity measurements and extremely high precision satellite gravity data via GRACE (Gravity Recovery and Climate Experiment) was tested. Using the GRACE data, regional scale water mass variations in four major river basins of the Indochina Peninsula were estimated. The estimated variations were compared with Soil-Vegetation-Atmosphere Transfer Scheme (SVATS) models with a river flow model of 1) globally uniform river velocity, 2) river velocity tuned by each river basin, 3) globally uniform river velocity considering groundwater storage, and 4) river velocity tuned by each river basin considering groundwater storage. Model 3) attained the best fit to the GRACE data, and the model 4) yielded almost the same values. This implies that the groundwater plays an important role in estimating the variation of total terrestrial storage. It also indicates that tuning river velocity, which is based on the in-situ measurements, needs further investigations in combination with the GRACE data. The relationships among GRACE data, SVATS models, and in-situ measurements were also discussed briefly.

Magnetosheath Flow Anomalies in 3-D

NASA Technical Reports Server (NTRS)

Vaisberg, O. L.; Burch, J. L.; Smirnov, V. N.; Avanov, L. A.; Moore, T. E.; Waite, J. H., Jr.; Skalsky, A. A.; Borodkova, N. L.; Coffey, V. N.; Gallagher, D. L.;

Performance characterization of a cross-flow hydrokinetic turbine in sheared inflow

DOE Office of Scientific and Technical Information (OSTI.GOV)

Forbush, Dominic; Polagye, Brian; Thomson, Jim

2016-12-01

A method for constructing a non-dimensional performance curve for a cross-flow hydrokinetic turbine in sheared flow is developed for a natural river site. The river flow characteristics are quasi-steady, with negligible vertical shear, persistent lateral shear, and synoptic changes dominated by long time scales (days to weeks). Performance curves developed from inflow velocities measured at individual points (randomly sampled) yield inconclusive turbine performance characteristics because of the spatial variation in mean flow. Performance curves using temporally- and spatially-averaged inflow velocities are more conclusive. The implications of sheared inflow are considered in terms of resource assessment and turbine control.

Simultaneous three-dimensional velocity and mixing measurements by use of laser Doppler velocimetry and fluorescence probes in a water tunnel

NASA Technical Reports Server (NTRS)

Neuhart, Dan H.; Wing, David J.; Henderson, Uleses C., Jr.

1994-01-01

A water tunnel investigation was conducted to demonstrate the capabilities of a laser-based instrument that can measure velocity and fluorescence intensity simultaneously. Fluorescence intensity of an excited fluorescent dye is directly related to concentration level and is used to indicate the extent of mixing in flow. This instrument is a three-dimensional laser Doppler velocimeter (LDV) in combination with a fluorometer for measuring fluorescence intensity variations. This capability allows simultaneous flow measurements of the three orthogonal velocity components and mixing within the same region. Two different flows which were generated by two models were studied: a generic nonaxisymmetric nozzle propulsion simulation model with an auxiliary internal water source that generated a jet flow and an axisymmetric forebody model with a circular sector strake that generated a vortex flow. The off-body flow fields around these models were investigated in the Langley 16- by 24-Inch Water Tunnel. The experimental results were used to calculate 17 quantities that included mean and fluctuating velocities, Reynolds stresses, mean and fluctuating dye fluorescence intensities (proportional to concentration), and fluctuating velocity and dye concentration correlations. An uncertainty analysis was performed to establish confidence levels in the experimental results. In general, uncertainties in mean velocities varied between 1 and 7 percent of free-stream velocity; uncertainties in fluctuating velocities varied between 1 and 5 percent of reference values. The results show characteristics that are unique to each type of flow.

Quantification of the transient mass flow rate in a simplex swirl injector

NASA Astrophysics Data System (ADS)

Khil, Taeock; Kim, Sunghyuk; Cho, Seongho; Yoon, Youngbin

2009-07-01

When a heat release and acoustic pressure fluctuations are generated in a combustor by irregular and local combustions, these fluctuations affect the mass flow rate of the propellants injected through the injectors. In addition, variations of the mass flow rate caused by these fluctuations bring about irregular combustion, which is associated with combustion instability, so it is very important to identify a mass variation through the pressure fluctuation on the injector and to investigate its transfer function. Therefore, quantification of the variation of the mass flow rate generated in a simplex swirl injector via the injection pressure fluctuation was the subject of an initial study. To acquire the transient mass flow rate in the orifice with time, the axial velocity of flows and the liquid film thickness in the orifice were measured. The axial velocity was acquired through a theoretical approach after measuring the pressure in the orifice. In an effort to understand the flow area in the orifice, the liquid film thickness was measured by an electric conductance method. In the results, the mass flow rate calculated from the axial velocity and the liquid film thickness measured by the electric conductance method in the orifice was in good agreement with the mass flow rate acquired by the direct measuring method in a small error range within 1% in the steady state and within 4% for the average mass flow rate in a pulsated state. Also, the amplitude (gain) of the mass flow rate acquired by the proposed direct measuring method was confirmed using the PLLIF technique in the low pressure fluctuation frequency ranges with an error under 6%. This study shows that our proposed method can be used to measure the mass flow rate not only in the steady state but also in the unsteady state (or the pulsated state). Moreover, this method shows very high accuracy based on the experimental results.

Proper orthogonal decomposition analysis for cycle-to-cycle variations of engine flow. Effect of a control device in an inlet pipe

NASA Astrophysics Data System (ADS)

Vu, Trung-Thanh; Guibert, Philippe

2012-06-01

This paper aims to investigate cycle-to-cycle variations of non-reacting flow inside a motored single-cylinder transparent engine in order to judge the insertion amplitude of a control device able to displace linearly inside the inlet pipe. Three positions corresponding to three insertion amplitudes are implemented to modify the main aerodynamic properties from one cycle to the next. Numerous particle image velocimetry (PIV) two-dimensional velocity fields following cycle database are post-treated to discriminate specific contributions of the fluctuating flow. We performed a multiple snapshot proper orthogonal decomposition (POD) in the tumble plane of a pent roof SI engine. The analytical process consists of a triple decomposition for each instantaneous velocity field into three distinctive parts named mean part, coherent part and turbulent part. The 3rd- and 4th-centered statistical moments of the proper orthogonal decomposition (POD)-filtered velocity field as well as the probability density function of the PIV realizations proved that the POD extracts different behaviors of the flow. Especially, the cyclic variability is assumed to be contained essentially in the coherent part. Thus, the cycle-to-cycle variations of the engine flows might be provided from the corresponding POD temporal coefficients. It has been shown that the in-cylinder aerodynamic dispersions can be adapted and monitored by controlling the insertion depth of the control instrument inside the inlet pipe.

DNS of helicity-induced stratified turbulent flow

NASA Astrophysics Data System (ADS)

Chandy, Abhilash J.; Rahimi, Abbas

2013-11-01

Helical flows undergoing density stratification have wide applications in meteorological phenomena such as dust devils, tornadoes, and hurricanes due to the complexity and disasters caused by them. Direct numerical simulations (DNS) of transition to turbulence in a stably stratified Boussinesq fluid are presented for different rotation and stratification intensities. In order to understand the effect of velocity on the energy cascade, comparisons are made between helicity initiated and non-helical flows. Results show that stratification decelerates the helicity decay and causes velocity and vorticity to align with each other. With respect to the helical and non-helical flow comparisons, the total energy in the presence of stratification decays faster with helicity. In addition, the behavior of length scales were examined by comparing temporal variations of the vertical shearing of velocities. Results showed a growing asymmetry with time in the case of helical flow, while non-helical flow stayed close to begin symmetric.

An improved car-following model with multiple preceding cars' velocity fluctuation feedback

NASA Astrophysics Data System (ADS)

Guo, Lantian; Zhao, Xiangmo; Yu, Shaowei; Li, Xiuhai; Shi, Zhongke

2017-04-01

In order to explore and evaluate the effects of velocity variation trend of multiple preceding cars used in the Cooperative Adaptive Cruise Control (CACC) strategy on the dynamic characteristic, fuel economy and emission of the corresponding traffic flow, we conduct a study as follows: firstly, with the real-time car-following (CF) data, the close relationship between multiple preceding cars' velocity fluctuation feedback and the host car's behaviors is explored, the evaluation results clearly show that multiple preceding cars' velocity fluctuation with different time window-width are highly correlated to the host car's acceleration/deceleration. Then, a microscopic traffic flow model is proposed to evaluate the effects of multiple preceding cars' velocity fluctuation feedback in the CACC strategy on the traffic flow evolution process. Finally, numerical simulations on fuel economy and exhaust emission of the traffic flow are also implemented by utilizing VT-micro model. Simulation results prove that considering multiple preceding cars' velocity fluctuation feedback in the control strategy of the CACC system can improve roadway traffic mobility, fuel economy and exhaust emission performance.

Numerical studies of asymmetric adiabatic accretion flow - The effect of velocity gradients

NASA Technical Reports Server (NTRS)

Taam, Ronald E.; Fryxell, B. A.

1989-01-01

A numerical study of the time variation of the angular momentum and mass capture rates for a central object accreting from a uniform medium with a velocity gradient transverse to the direction of the mean flow is presented, covering a range of velocity asymmetries and Mach numbers in the incident flow. It is found that the mass accretion rate in a given evolutionary sequence varies in an irregular manner, with the matter accreting onto the central object from either a continuously moving accretion wake or from an accretion disk. The implications of the results from the study of short-term fluctuations observed in the pulse period and luminosity of X-ray pulsars are discussed.

Intra-individual variation in blood flow velocities in cerebral arteries of children with sickle cell disease.

PubMed

Brambilla, Donald J; Miller, Scott T; Adams, Robert J

2007-09-01

Children with sickle cell disease (SCD) are at elevated risk of stroke. Risk increases with blood flow velocity in selected cerebral arteries, as measured by transcranial Doppler (TCD) ultrasound, and use of TCD to screen these patients is widely recommended. Interpretation of TCD results should be based on knowledge of intra-individual variation in blood flow velocity, information not currently available for sickle cell patients. Between 1995 and 2002, 4,141 subjects, 2-16 years old, with homozygous SCD or Sbeta0-thalasemmia and no history of stroke were screened with TCD, including 2,018 subjects screened in one clinical trial (STOP), 1,816 screened in another (STOP 2), and 307 screened in an interim ancillary prospective study. The 812 subjects with >or=2 examinations<6 months apart were selected for analysis, including 242 (29.8%) subjects with normal average velocities (i.e., <170 cm/sec), 350 (43.1%) subjects with conditional velocities (i.e., 170-199 cm/sec), and 220 (27.1%) subjects with abnormal velocities (i.e., >or=200 cm/sec). The intra-subject standard deviation of TCD velocity was estimated from the difference between velocities at the first two interpretable examinations on each subject. An intra-subject standard deviation of 14.9 cm/sec was obtained. Seven (0.9%) subjects had unusually large and unexplained differences between velocities at the two examinations (range of absolute differences: 69-112 cm/sec). While stroke risk is well demonstrated to increase with increasingly abnormal TCD velocity, given the relatively large intra-subject variability, one TCD examination is generally not sufficient to characterize stroke risk in this patient population. Copyright (c) 2007 Wiley-Liss, Inc.

CFD and PTV steady flow investigation in an anatomically accurate abdominal aortic aneurysm.

PubMed

Boutsianis, Evangelos; Guala, Michele; Olgac, Ufuk; Wildermuth, Simon; Hoyer, Klaus; Ventikos, Yiannis; Poulikakos, Dimos

2009-01-01

There is considerable interest in computational and experimental flow investigations within abdominal aortic aneurysms (AAAs). This task stipulates advanced grid generation techniques and cross-validation because of the anatomical complexity. The purpose of this study is to examine the feasibility of velocity measurements by particle tracking velocimetry (PTV) in realistic AAA models. Computed tomography and rapid prototyping were combined to digitize and construct a silicone replica of a patient-specific AAA. Three-dimensional velocity measurements were acquired using PTV under steady averaged resting boundary conditions. Computational fluid dynamics (CFD) simulations were subsequently carried out with identical boundary conditions. The computational grid was created by splitting the luminal volume into manifold and nonmanifold subsections. They were filled with tetrahedral and hexahedral elements, respectively. Grid independency was tested on three successively refined meshes. Velocity differences of about 1% in all three directions existed mainly within the AAA sack. Pressure revealed similar variations, with the sparser mesh predicting larger values. PTV velocity measurements were taken along the abdominal aorta and showed good agreement with the numerical data. The results within the aneurysm neck and sack showed average velocity variations of about 5% of the mean inlet velocity. The corresponding average differences increased for all velocity components downstream the iliac bifurcation to as much as 15%. The two domains differed slightly due to flow-induced forces acting on the silicone model. Velocity quantification through narrow branches was problematic due to decreased signal to noise ratio at the larger local velocities. Computational wall pressure and shear fields are also presented. The agreement between CFD simulations and the PTV experimental data was confirmed by three-dimensional velocity comparisons at several locations within the investigated AAA anatomy indicating the feasibility of this approach.

Experimental analysis of thermo-acoustic instabilities in a generic gas turbine combustor by phase-correlated PIV, chemiluminescence, and laser Raman scattering measurements

NASA Astrophysics Data System (ADS)

Arndt, Christoph M.; Severin, Michael; Dem, Claudiu; Stöhr, Michael; Steinberg, Adam M.; Meier, Wolfgang

2015-04-01

A gas turbine model combustor for partially premixed swirl flames was equipped with an optical combustion chamber and operated with CH4 and air at atmospheric pressure. The burner consisted of two concentric nozzles for separately controlled air flows and a ring of holes 12 mm upstream of the nozzle exits for fuel injection. The flame described here had a thermal power of 25 kW, a global equivalence ratio of 0.7, and exhibited thermo-acoustic instabilities at a frequency of approximately 400 Hz. The phase-dependent variations in the flame shape and relative heat release rate were determined by OH* chemiluminescence imaging; the flow velocities by stereoscopic particle image velocimetry (PIV); and the major species concentrations, mixture fraction, and temperature by laser Raman scattering. The PIV measurements showed that the flow field performed a "pumping" mode with varying inflow velocities and extent of the inner recirculation zone, triggered by the pressure variations in the combustion chamber. The flow field oscillations were accompanied by variations in the mixture fraction in the inflow region and at the flame root, which in turn were mainly caused by the variations in the CH4 concentration. The mean phase-dependent changes in the fluxes of CH4 and N2 through cross-sectional planes of the combustion chamber at different heights above the nozzle were estimated by combining the PIV and Raman data. The results revealed a periodic variation in the CH4 flux by more than 150 % in relation to the mean value, due to the combined influence of the oscillating flow velocity, density variations, and CH4 concentration. Based on the experimental results, the feedback mechanism of the thermo-acoustic pulsations could be identified as a periodic fluctuation of the equivalence ratio and fuel mass flow together with a convective delay for the transport of fuel from the fuel injector to the flame zone. The combustor and the measured data are well suited for the validation of numerical combustion simulations.

An in vitro experimental study of flow past aortic valve under varied pulsatile conditions

NASA Astrophysics Data System (ADS)

Zhang, Ruihang; Zhang, Yan

2017-11-01

Flow past aortic valve represents a complex fluid-structure interaction phenomenon that involves pulsatile, vortical, and turbulent conditions. The flow characteristics immediately downstream of the valve, such as the variation of pulsatile flow velocity, formation of vortices, distribution of shear stresses, are of particular interest to further elucidate the role of hemodynamics in various aortic diseases. However, the fluid dynamics of a realistic aortic valve is not fully understood. Particularly, it is unclear how the flow fields downstream of the aortic valve would change under varied pulsatile inlet boundary conditions. In this study, an in vitro experiment has been conducted to investigate the flow fields downstream of a silicone aortic valve model within a cardiovascular flow simulator. Phased-locked Particle Image Velocimetry measurements were performed to map the velocity fields and Reynolds normal and shear stresses at different phases in a cardiac cycle. Temporal variations of pressure across the valve model were measured using high frequency transducers. Results have been compared for different pulsatile inlet conditions, including varied frequencies (heart rates), magnitudes (stroke volumes), and cardiac contractile functions (shapes of waveforms).

Time Resolved Digital PIV Measurements of Flow Field Cyclic Variation in an Optical IC Engine

NASA Astrophysics Data System (ADS)

Jarvis, S.; Justham, T.; Clarke, A.; Garner, C. P.; Hargrave, G. K.; Halliwell, N. A.

2006-07-01

Time resolved digital particle image velocimetry (DPIV) experimental data is presented for the in-cylinder flow field development of a motored four stroke spark ignition (SI) optical internal combustion (IC) engine. A high speed DPIV system was employed to quantify the velocity field development during the intake and compression stroke at an engine speed of 1500 rpm. The results map the spatial and temporal development of the in-cylinder flow field structure allowing comparison between traditional ensemble average and cycle average flow field structures. Conclusions are drawn with respect to engine flow field cyclic variations.

Photoballistics of volcanic jet activity at Stromboli, Italy

NASA Technical Reports Server (NTRS)

Chouet, B.; Hamisevicz, N.; Mcgetchin, T. R.

1974-01-01

Two night eruptions of the volcano Stromboli were studied through 70-mm photography. Single-camera techniques were used. Particle sphericity, constant velocity in the frame, and radial symmetry were assumed. Properties of the particulate phase found through analysis include: particle size, velocity, total number of particles ejected, angular dispersion and distribution in the jet, time variation of particle size and apparent velocity distribution, averaged volume flux, and kinetic energy carried by the condensed phase. The frequency distributions of particle size and apparent velocities are found to be approximately log normal. The properties of the gas phase were inferred from the fact that it was the transporting medium for the condensed phase. Gas velocity and time variation, volume flux of gas, dynamic pressure, mass erupted, and density were estimated. A CO2-H2O mixture is possible for the observed eruptions. The flow was subsonic. Velocity variations may be explained by an organ pipe resonance. Particle collimation may be produced by a Magnus effect.

Fish responses to flow velocity and turbulence in relation to size, sex and parasite load

PubMed Central

Hockley, F. A.; Wilson, C. A. M. E.; Brew, A.; Cable, J.

2014-01-01

Riverine fish are subjected to heterogeneous flow velocities and turbulence and may use this to their advantage by selecting regions that balance energy expenditure for station holding while maximizing energy gain through feeding opportunities. This study investigated microhabitat selection by guppies Poecilia reticulata in terms of flow characteristics generated by hemisphere boulders in an open channel flume. Velocity and turbulence influenced the variation in swimming behaviour with respect to size, sex and parasite intensity. With increasing body length, fish swam further and more frequently between boulder regions. Larger guppies spent more time in the areas of high-velocity and low-turbulence regions beside the boulders, whereas smaller guppies frequented the low-velocity and high-turbulence regions directly behind the boulders. Male guppies selected the regions of low velocity, indicating possible reduced swimming ability owing to hydrodynamic drag imposed by their fins. With increasing Gyrodactylus turnbulli burden, fish spent more time in regions with moderate velocity and lowest turbulent kinetic energy which were the most spatially and temporally homogeneous in terms of velocity and turbulence. These findings highlight the importance of heterogeneous flow conditions in river channel design owing to the behavioural variability within a species in response to velocity and turbulence. PMID:24284893

Fish responses to flow velocity and turbulence in relation to size, sex and parasite load.

PubMed

Hockley, F A; Wilson, C A M E; Brew, A; Cable, J

2014-02-06

Riverine fish are subjected to heterogeneous flow velocities and turbulence and may use this to their advantage by selecting regions that balance energy expenditure for station holding while maximizing energy gain through feeding opportunities. This study investigated microhabitat selection by guppies Poecilia reticulata in terms of flow characteristics generated by hemisphere boulders in an open channel flume. Velocity and turbulence influenced the variation in swimming behaviour with respect to size, sex and parasite intensity. With increasing body length, fish swam further and more frequently between boulder regions. Larger guppies spent more time in the areas of high-velocity and low-turbulence regions beside the boulders, whereas smaller guppies frequented the low-velocity and high-turbulence regions directly behind the boulders. Male guppies selected the regions of low velocity, indicating possible reduced swimming ability owing to hydrodynamic drag imposed by their fins. With increasing Gyrodactylus turnbulli burden, fish spent more time in regions with moderate velocity and lowest turbulent kinetic energy which were the most spatially and temporally homogeneous in terms of velocity and turbulence. These findings highlight the importance of heterogeneous flow conditions in river channel design owing to the behavioural variability within a species in response to velocity and turbulence.

Do Doppler color flow algorithms for mapping disturbed flow make sense?

PubMed

Gardin, J M; Lobodzinski, S M

1990-01-01

It has been suggested that a major advantage of Doppler color flow mapping is its ability to visualize areas of disturbed ("turbulent") flow, for example, in valvular stenosis or regurgitation and in shunts. To investigate how various color flow mapping instruments display disturbed flow information, color image processing was used to evaluate the most common velocity-variance color encoding algorithms of seven commercially available ultrasound machines. In six of seven machines, green was reportedly added by the variance display algorithms to map areas of disturbed flow. The amount of green intensity added to each pixel along the red and blue portions of the velocity reference color bar was calculated for each machine. In this study, velocities displayed on the reference color bar ranged from +/- 46 to +/- 64 cm/sec, depending on the Nyquist limit. Of note, changing the Nyquist limits depicted on the color reference bars did not change the distribution of the intensities of red, blue, or green within the contour of the reference map, but merely assigned different velocities to the pixels. Most color flow mapping algorithms in our study added increasing intensities of green to increasing positive (red) or negative (blue) velocities along their color reference bars. Most of these machines also added increasing green to red and blue color intensities horizontally across their reference bars as a marker of increased variance (spectral broadening). However, at any given velocity, marked variations were noted between different color flow mapping instruments in the amount of green added to their color velocity reference bars.(ABSTRACT TRUNCATED AT 250 WORDS)

Shunt flow evaluation in congenital heart disease based on two-dimensional speckle tracking.

PubMed

Fadnes, Solveig; Nyrnes, Siri Ann; Torp, Hans; Lovstakken, Lasse

2014-10-01

High-frame-rate ultrasound speckle tracking was used for quantification of peak velocity in shunt flows resulting from septal defects in congenital heart disease. In a duplex acquisition scheme implemented on a research scanner, unfocused transmit beams and full parallel receive beamforming were used to achieve a frame rate of 107 frames/s for full field-of-view flow images with high accuracy, while also ensuring high-quality focused B-mode tissue imaging. The setup was evaluated in vivo for neonates with atrial and ventricular septal defects. The shunt position was automatically tracked in B-mode images and further used in blood speckle tracking to obtain calibrated shunt flow velocities throughout the cardiac cycle. Validation toward color flow imaging and pulsed wave Doppler with manual angle correction indicated that blood speckle tracking could provide accurate estimates of shunt flow velocities. The approach was less biased by clutter filtering compared with color flow imaging and was able to provide velocity estimates beyond the Nyquist range. Possible placements of sample volumes (and angle corrections) for conventional Doppler resulted in a peak shunt velocity variations of 0.49-0.56 m/s for the ventricular septal defect of patient 1 and 0.38-0.58 m/s for the atrial septal defect of patient 2. In comparison, the peak velocities found from speckle tracking were 0.77 and 0.33 m/s for patients 1 and 2, respectively. Results indicated that complex intraventricular flow velocity patterns could be quantified using high-frame-rate speckle tracking of both blood and tissue movement. This could potentially help increase diagnostic accuracy and decrease inter-observer variability when measuring peak velocity in shunt flows. Copyright © 2014 World Federation for Ultrasound in Medicine & Biology. Published by Elsevier Inc. All rights reserved.

Experimental study of overland flow resistance coefficient model of grassland based on BP neural network

NASA Astrophysics Data System (ADS)

Jiao, Peng; Yang, Er; Ni, Yong Xin

2018-06-01

The overland flow resistance on grassland slope of 20° was studied by using simulated rainfall experiments. Model of overland flow resistance coefficient was established based on BP neural network. The input variations of model were rainfall intensity, flow velocity, water depth, and roughness of slope surface, and the output variations was overland flow resistance coefficient. Model was optimized by Genetic Algorithm. The results show that the model can be used to calculate overland flow resistance coefficient, and has high simulation accuracy. The average prediction error of the optimized model of test set is 8.02%, and the maximum prediction error was 18.34%.

Investigation of the tip clearance flow inside and at the exit of a compressor rotor passage

NASA Technical Reports Server (NTRS)

Pandya, A.; Lakshminarayana, B.

1982-01-01

The nature of the tip clearance flow in a moderately loaded compressor rotor is studied. The measurements were taken inside the clearance between the annulus-wall casing and the rotor blade tip. These measurements were obtained using a stationary two-sensor hot-wire probe in combination with an ensemble averaging technique. The flowfield was surveyed at various radial locations and at ten axial locations, four of which were inside the blade passage in the clearance region and the remaining six outside the passage. Variations of the mean flow properties in the tangential and the radial directions at various axial locations were derived from the data. Variation of the leakage velocity at different axial stations and the annulus-wall boundary layer profiles from passage-averaged mean velocities were also estimated.

Transport of magneto-nanoparticles during electro-osmotic flow in a micro-tube in the presence of magnetic field for drug delivery application

NASA Astrophysics Data System (ADS)

Mondal, A.; Shit, G. C.

2017-11-01

In this paper, we have examined the motion of magnetic-nanoparticles and the flow characteristics of biofluid in a micro-tube in the presence of externally applied magnetic field and electrokinetic effects. In the drug delivery system, the motion of the magnetic nanoparticles as carriers is important for therapeutic procedure in the treatment of tumor cells, infections and removing blood clots. The unidirectional electro-osmotic flow of biofluid is driven by the combined effects of pulsatile pressure gradient and electrokinetic force. The governing equation for unsteady electromagnetohydrodynamic flow subject to the no-slip boundary condition has been solved numerically by using Crank-Nicolson implicit finite difference scheme. We have analyzed the variation of axial velocity, velocity distribution of magnetic nanoparticles, volumetric flow rate and wall shear stress for various values of the non-dimensional parameters. The study reveals that blood flow velocity, carriers velocity and flow rate are strongly influenced by the electro-osmotic parameter as well as the Hartmann number. The particle mass parameter as well as the particle concentration parameter have efficient capturing effect on magnetic nanoparticles during blood flow through a micro-tube for drug delivery.

Determination of mean pressure from PIV in compressible flows using the Reynolds-averaging approach

NASA Astrophysics Data System (ADS)

van Gent, Paul L.; van Oudheusden, Bas W.; Schrijer, Ferry F. J.

2018-03-01

The feasibility of computing the flow pressure on the basis of PIV velocity data has been demonstrated abundantly for low-speed conditions. The added complications occurring for high-speed compressible flows have, however, so far proved to be largely inhibitive for the accurate experimental determination of instantaneous pressure. Obtaining mean pressure may remain a worthwhile and realistic goal to pursue. In a previous study, a Reynolds-averaging procedure was developed for this, under the moderate-Mach-number assumption that density fluctuations can be neglected. The present communication addresses the accuracy of this assumption, and the consistency of its implementation, by evaluating of the relevance of the different contributions resulting from the Reynolds-averaging. The methodology involves a theoretical order-of-magnitude analysis, complemented with a quantitative assessment based on a simulated and a real PIV experiment. The assessments show that it is sufficient to account for spatial variations in the mean velocity and the Reynolds-stresses and that temporal and spatial density variations (fluctuations and gradients) are of secondary importance and comparable order-of-magnitude. This result permits to simplify the calculation of mean pressure from PIV velocity data and to validate the approximation of neglecting temporal and spatial density variations without having access to reference pressure data.

Liquid Jet Cavitation via Molecular Dynamics

NASA Astrophysics Data System (ADS)

Ashurst, W. T.

1997-11-01

A two-dimensional molecular dynamics simulation of a liquid jet is used to investigate cavitation in a diesel-like fuel injector. A channel with a length four times its width has been examined at various system sizes (widths of 20 to 160 σ, where σ is the zero energy location in the Lennard-Jones potential). The wall boundary condition is Maxwell's diffuse reflection, similar to the work by Sun & Ebner (Phys. Rev A 46, 4813, 1992). Currently, the jet exhausts into a vacuum, but a second, low density gas will be incorporated to represent the compressed air in a diesel chamber. Four different flow rates are examined. With ρ U equal to √mɛ/σ^2 (the largest flow rate) the static pressure decreases by a factor of twenty between the channel entrance and exit. The largest flow rate has a parabolic velocity profile with almost constant density across the channel. The smallest flow rate has the same velocity profile but the density exhibits a large variation, with the minimum value in the channel center. Thus, the product ρ U is nearly constant across the channel at this flow rate. The discharge coefficient CD has a small variation with flow rate, but the velocity coefficient CV varies with the amount of two-phase fluid within the channel. The ratio of CV to CD varies from 1.3 (largest flow rate) to 2.0 (the smallest flow rate, which is one-eighth of the largest).

The 6dFGS Peculiar Velocity Field

NASA Astrophysics Data System (ADS)

Springob, Chris M.; Magoulas, C.; Colless, M.; Mould, J.; Erdogdu, P.; Jones, D. H.; Lucey, J.; Campbell, L.; Merson, A.; Jarrett, T.

2012-01-01

The 6dF Galaxy Survey (6dFGS) is an all southern sky galaxy survey, including 125,000 redshifts and a Fundamental Plane (FP) subsample of 10,000 peculiar velocities, making it the largest peculiar velocity sample to date. We have fit the FP using a maximum likelihood fit to a tri-variate Gaussian. We subsequently compute a Bayesian probability distribution for every possible peculiar velocity for each of the 10,000 galaxies, derived from the tri-variate Gaussian probability density distribution, accounting for our selection effects and measurement errors. We construct a predicted peculiar velocity field from the 2MASS redshift survey, and compare our observed 6dFGS velocity field to the predicted field. We discuss the resulting agreement between the observed and predicted fields, and the implications for measurements of the bias parameter and bulk flow.

Investigation of distributor vane jets to decrease the unsteady load on hydro turbine runner blades

NASA Astrophysics Data System (ADS)

Lewis, B. J.; Cimbala, J. M.; Wouden, A. M.

2012-11-01

As the runner blades of a Francis hydroturbine pass though the wakes created from the wicket gates, they experience a significant change in absolute velocity, flow angle, and pressure. The concept of adding jets to the trailing edge of the wicket gates is proposed as a method for reducing the dynamic load on the hydroturbine runner blades. Computational experiments show a decrease in velocity variation experienced by the runner blade with the addition of the jets. The decrease in velocity variation resulted in a 43% decrease in global torque variation at the runner passing frequency. However, an increased variation was observed at the wicket gate passing frequency. Also, a 5.7% increase in average global torque was observed with the addition of blowing from the trailing-edge of the wicket gates.

Length-scales of Slab-induced Asthenospheric Deformation from Geodynamic Modeling, Mantle Deformation Fabric, and Synthetic Shear Wave Splitting

NASA Astrophysics Data System (ADS)

Jadamec, M. A.; MacDougall, J.; Fischer, K. M.

2017-12-01

The viscosity structure of the Earth's interior is critically important, because it places a first order constraint on plate motion and mantle flow rates. Geodynamic models using a composite viscosity based on experimentally derived flow laws for olivine aggregates show that lateral viscosity variations emerge in the upper mantle due to the subduction dynamics. However, the length-scale of this transition is still not well understood. Two-dimensional numerical models of subduction are presented that investigate the effect of initial slab dip, maximum yield stress (slab strength), and viscosity formulation (Newtonian versus composite) on the emergent lateral viscosity variations in the upper-mantle and magnitude of slab-driven mantle flow velocity. Significant viscosity reductions occur in regions of large flow velocity gradients due to the weakening effect of the dislocation creep deformation mechanism. The dynamic reductions in asthenospheric viscosity (less than 1018 Pa s) occur within approximately 500 km from driving force of the slab, with peak flow velocities occurring in models with a lower yield stress (weaker slab) and higher stress exponent. This leads to a sharper definition of the rheological base of the lithosphere and implies lateral variability in tractions along the base of the lithosphere. As the dislocation creep mechanism also leads to mantle deformation fabric, we then examine the spatial variation in the LPO development in the asthenosphere and calculate synthetic shear wave splitting. The models show that olivine LPO fabric in the asthenosphere generally increases in alignment strength with increased proximity to the slab, but can be transient and spatially variable on small length scales. The vertical flow fields surrounding the slab tip can produce shear-wave splitting variations with back-azimuth that deviate from the predictions of uniform trench-normal anisotropy, a result that bears on the interpretation of complexity in shear-wave splitting observed in real subduction zones.

Sakiadis flow of Maxwell fluid considering magnetic field and convective boundary conditions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mustafa, M., E-mail: meraj-mm@hotmail.com; Khan, Junaid Ahmad; Hayat, T.

2015-02-15

In this paper we address the flow of Maxwell fluid due to constantly moving flat radiative surface with convective condition. The flow is under the influence of non-uniform transverse magnetic field. The velocity and temperature distributions have been evaluated numerically by shooting approach. The solution depends on various interesting parameters including local Deborah number De, magnetic field parameter M, Prandtl number Pr and Biot number Bi. We found that variation in velocity with an increase in local Deborah number De is non-monotonic. However temperature is a decreasing function of local Deborah number De.

Magnetic resonance imaging of convection in laser-polarized xenon

NASA Technical Reports Server (NTRS)

Mair, R. W.; Tseng, C. H.; Wong, G. P.; Cory, D. G.; Walsworth, R. L.

2000-01-01

We demonstrate nuclear magnetic resonance (NMR) imaging of the flow and diffusion of laser-polarized xenon (129Xe) gas undergoing convection above evaporating laser-polarized liquid xenon. The large xenon NMR signal provided by the laser-polarization technique allows more rapid imaging than one can achieve with thermally polarized gas-liquid systems, permitting shorter time-scale events such as rapid gas flow and gas-liquid dynamics to be observed. Two-dimensional velocity-encoded imaging shows convective gas flow above the evaporating liquid xenon, and also permits the measurement of enhanced gas diffusion near regions of large velocity variation.

Influence of thermal stratification and slip conditions on stagnation point flow towards variable thicked Riga plate

NASA Astrophysics Data System (ADS)

Anjum, A.; Mir, N. A.; Farooq, M.; Khan, M. Ijaz; Hayat, T.

2018-06-01

This article addresses thermally stratified stagnation point flow of viscous fluid induced by a non-linear variable thicked Riga plate. Velocity and thermal slip effects are incorporated to disclose the flow analysis. Solar thermal radiation phenomenon is implemented to address the characteristics of heat transfer. Variations of different physical parameters on the horizontal velocity and temperature distributions are described through graphs. Graphical interpretations of skin friction coefficient (drag force at the surface) and Nusselt number (rate of heat transfer) are also addressed. Modified Hartman number and thermal stratification parameter result in reduction of temperature distribution.

Dynamic PIV measurement of a compressible flow issuing from an airbag inflator nozzle

NASA Astrophysics Data System (ADS)

Lee, Sang Joon; Jang, Young Gil; Kim, Seok; Kim, Chang Soo

2006-12-01

Among many equipment for passenger safety, the air bag system is the most fundamental and effective device for an automobile. The inflator housing is a main part of the curtain-type air bag system, which supplies high-pressure gases in pumping up the air bag-curtain which is increasingly being adapted in deluxe cars for protecting passengers from the danger of side clash. However, flow information on the inflator housing is very limited. In this study, we measure the instantaneous velocity fields of a high-speed compressible flow issuing from the exit nozzle of an inflator housing using a dynamic PIV system. From the velocity field data measured at a high frame-rate, we evaluate the variation of the mass flow rate with time. The dynamic PIV system consists of a high-repetition Nd:YLF laser, a high-speed CMOS camera, and a delay generator. The flow images are taken at 4000 fps with synchronization of the trigger signal for inflator ignition. From the instantaneous velocity field data of flow ejecting from the airbag inflator housing at the initial stage, we can see a flow pattern of broken shock wave front and its downward propagation. The flow ejecting from the inflator housing is found to have very high velocity fluctuations, with the maximum velocity at about 700 m/s. The time duration of the high-speed flow is very short, and there is no perceptible flow after 100 ms.

Experimental and analytical study of water pipe's rupture for damage identification purposes

NASA Astrophysics Data System (ADS)

Papakonstantinou, Konstantinos G.; Shinozuka, Masanobu; Beikae, Mohsen

2011-04-01

A malfunction, local damage or sudden pipe break of a pipeline system can trigger significant flow variations. As shown in the paper, pressure variations and pipe vibrations are two strongly correlated parameters. A sudden change in the flow velocity and pressure of a pipeline system can induce pipe vibrations. Thus, based on acceleration data, a rapid detection and localization of a possible damage may be carried out by inexpensive, nonintrusive monitoring techniques. To illustrate this approach, an experiment on a single pipe was conducted in the laboratory. Pressure gauges and accelerometers were installed and their correlation was checked during an artificially created transient flow. The experimental findings validated the correlation between the parameters. The interaction between pressure variations and pipe vibrations was also theoretically justified. The developed analytical model explains the connection among flow pressure, velocity, pressure wave propagation and pipe vibration. The proposed method provides a rapid, efficient and practical way to identify and locate sudden failures of a pipeline system and sets firm foundations for the development and implementation of an advanced, new generation Supervisory Control and Data Acquisition (SCADA) system for continuous health monitoring of pipe networks.

Mean flow field and surface heating produced by unequal shock interactions at hypersonic speeds

NASA Technical Reports Server (NTRS)

Birch, S. F.; Rudy, D. H.

1975-01-01

Mean velocity profiles were measured in a free shear layer produced by the interaction of two unequal strength shock waves at hypersonic free-stream Mach numbers. Measurements were made over a unit Reynolds number range of 3,770,000 per meter to 17,400,000 per meter based on the flow on the high velocity side of the shear layer. The variation in measured spreading parameters with Mach number for the fully developed flows is consistent with the trend of the available zero velocity ratio data when the Mach numbers for the data given in this study are taken to be characteristic Mach numbers based on the velocity difference across the mixing layer. Surface measurements in the shear-layer attachment region of the blunt-body model indicate peak local heating and static pressure consistent with other published data. Transition Reynolds numbers were found to be significantly lower than those found in previous data.

Measurement of filtration rates by infaunal bivalves in a recirculating flume

USGS Publications Warehouse

Cole, B.E.; Thompson, J.K.; Cloern, J.E.

1992-01-01

A flume system and protocol for measuring the filtration rate of infaunal bivalves is described. Assemblages of multi-sized clams, at natural densities and in normal filter-feeding positions, removed phytoplankton suspended in a unidirectional flow of water. The free-stream velocity and friction velocity of the flow, and bottom roughness height were similar to those in natural estuarine waters. Continuous variations in phytoplankton (Chroomonas salinay) cell density were used to measure the filtration rate of the suspension-feeding clam Potamocorbula amurensis for periods of 2 to 28 h. Filtration rates of P. amurensis varied from 100 to 580 liters (gd)-1 over a free-stream velocity range of 9 to 25 cm s-1. Phytoplankton loss rates were usually constant throughout the experiments. Our results suggest that suspension-feeding by infaunal bivalves is sensitive to flow velocity. ?? 1992 Springer-Verlag.

The ground vortex flow field associated with a jet in a cross flow impinging on a ground plane for uniform and annular turbulent axisymmetric jets. M.S. Thesis

NASA Technical Reports Server (NTRS)

Cavage, William M.; Kuhlman, John M.

1993-01-01

An experimental study was conducted of the impingement of a single circular jet on a ground plane in a cross flow. This geometry is a simplified model of the interaction of propulsive jet exhaust from a V/STOL aircraft with the ground in forward flight. Jets were oriented normal to the cross flow and ground plane. Jet size, cross flow-to-jet velocity ratio, ground plane-to-jet board spacing, and jet exit turbulence level and mean velocity profile shape were all varied to determine their effects on the size of the ground vortex interaction region which forms on the ground plane, using smoke injection into the jet. Three component laser Doppler velocimeter measurements were made with a commercial three color system for the case of a uniform jet with exit spacing equal to 5.5 diameters and cross flow-to-jet velocity ratio equal to 0.11. The flow visualization data compared well for equivalent runs of the same nondimensional jet exit spacing and the same velocity ratio for different diameter nozzles, except at very low velocity ratios and for the larger nozzle, where tunnel blockage became significant. Variation of observed ground vortex size with cross flow-to-jet velocity ratio was consistent with previous studies. Observed effects of jet size and ground plane-to-jet board spacing were relatively small. Jet exit turbulence level effects were also small. However, an annular jet with a low velocity central core was found to have a significantly smaller ground vortex than an equivalent uniform jet at the same values of cross flow-to-jet velocity ratio and jet exit-to-ground plane spacing. This may suggest a means of altering ground vortex behavior somewhat, and points out the importance of proper simulation of jet exit velocity conditions. LV data indicated unsteady turbulence levels in the ground vortex in excess of 70 percent.

Analysis and testing of high entrainment single nozzle jet pumps with variable mixing tubes

NASA Technical Reports Server (NTRS)

Hickman, K. E.; Hill, P. G.; Gilbert, G. B.

1972-01-01

An analytical model was developed to predict the performance characteristics of axisymmetric single-nozzle jet pumps with variable area mixing tubes. The primary flow may be subsonic or supersonic. The computer program uses integral techniques to calculate the velocity profiles and the wall static pressures that result from the mixing of the supersonic primary jet and the subsonic secondary flow. An experimental program was conducted to measure mixing tube wall static pressure variations, velocity profiles, and temperature profiles in a variable area mixing tube with a supersonic primary jet. Static pressure variations were measured at four different secondary flow rates. These test results were used to evaluate the analytical model. The analytical results compared well to the experimental data. Therefore, the analysis is believed to be ready for use to relate jet pump performance characteristics to mixing tube design.

Experimental Study on Effects of Ground Roughness on Flow Characteristics of Tornado-Like Vortices

NASA Astrophysics Data System (ADS)

Wang, Jin; Cao, Shuyang; Pang, Weichiang; Cao, Jinxin

2017-02-01

The three-dimensional wind velocity and dynamic pressure for stationary tornado-like vortices that developed over ground of different roughness categories were investigated to clarify the effects of ground roughness. Measurements were performed for various roughness categories and two swirl ratios. Variations of the vertical and horizontal distributions of velocity and pressure with roughness are presented, with the results showing that the tangential, radial, and axial velocity components increase inside the vortex core near the ground under rough surface conditions. Meanwhile, clearly decreased tangential components are found outside the core radius at low elevations. The high axial velocity inside the vortex core over rough ground surface indicates that roughness produces an effect similar to a reduced swirl ratio. In addition, the pressure drop accompanying a tornado is more significant at elevations closer to the ground under rough compared with smooth surface conditions. We show that the variations of the flow characteristics with roughness are dependent on the vortex-generating mechanism, indicating the need for appropriate modelling of tornado-like vortices.

Comparative study of the discrete velocity and lattice Boltzmann methods for rarefied gas flows through irregular channels

NASA Astrophysics Data System (ADS)

Su, Wei; Lindsay, Scott; Liu, Haihu; Wu, Lei

2017-08-01

Rooted from the gas kinetics, the lattice Boltzmann method (LBM) is a powerful tool in modeling hydrodynamics. In the past decade, it has been extended to simulate rarefied gas flows beyond the Navier-Stokes level, either by using the high-order Gauss-Hermite quadrature, or by introducing the relaxation time that is a function of the gas-wall distance. While the former method, with a limited number of discrete velocities (e.g., D2Q36), is accurate up to the early transition flow regime, the latter method (especially the multiple relaxation time (MRT) LBM), with the same discrete velocities as those used in simulating hydrodynamics (i.e., D2Q9), is accurate up to the free-molecular flow regime in the planar Poiseuille flow. This is quite astonishing in the sense that less discrete velocities are more accurate. In this paper, by solving the Bhatnagar-Gross-Krook kinetic equation accurately via the discrete velocity method, we find that the high-order Gauss-Hermite quadrature cannot describe the large variation in the velocity distribution function when the rarefaction effect is strong, but the MRT-LBM can capture the flow velocity well because it is equivalent to solving the Navier-Stokes equations with an effective shear viscosity. Since the MRT-LBM has only been validated in simple channel flows, and for complex geometries it is difficult to find the effective viscosity, it is necessary to assess its performance for the simulation of rarefied gas flows. Our numerical simulations based on the accurate discrete velocity method suggest that the accuracy of the MRT-LBM is reduced significantly in the simulation of rarefied gas flows through the rough surface and porous media. Our simulation results could serve as benchmarking cases for future development of the LBM for modeling and simulation of rarefied gas flows in complex geometries.

Comparative study of the discrete velocity and lattice Boltzmann methods for rarefied gas flows through irregular channels.

PubMed

Su, Wei; Lindsay, Scott; Liu, Haihu; Wu, Lei

2017-08-01

Rooted from the gas kinetics, the lattice Boltzmann method (LBM) is a powerful tool in modeling hydrodynamics. In the past decade, it has been extended to simulate rarefied gas flows beyond the Navier-Stokes level, either by using the high-order Gauss-Hermite quadrature, or by introducing the relaxation time that is a function of the gas-wall distance. While the former method, with a limited number of discrete velocities (e.g., D2Q36), is accurate up to the early transition flow regime, the latter method (especially the multiple relaxation time (MRT) LBM), with the same discrete velocities as those used in simulating hydrodynamics (i.e., D2Q9), is accurate up to the free-molecular flow regime in the planar Poiseuille flow. This is quite astonishing in the sense that less discrete velocities are more accurate. In this paper, by solving the Bhatnagar-Gross-Krook kinetic equation accurately via the discrete velocity method, we find that the high-order Gauss-Hermite quadrature cannot describe the large variation in the velocity distribution function when the rarefaction effect is strong, but the MRT-LBM can capture the flow velocity well because it is equivalent to solving the Navier-Stokes equations with an effective shear viscosity. Since the MRT-LBM has only been validated in simple channel flows, and for complex geometries it is difficult to find the effective viscosity, it is necessary to assess its performance for the simulation of rarefied gas flows. Our numerical simulations based on the accurate discrete velocity method suggest that the accuracy of the MRT-LBM is reduced significantly in the simulation of rarefied gas flows through the rough surface and porous media. Our simulation results could serve as benchmarking cases for future development of the LBM for modeling and simulation of rarefied gas flows in complex geometries.

An experimental study of the fluid mechanics associated with porous walls

NASA Technical Reports Server (NTRS)

Ramachandran, N.; Heaman, J.; Smith, A.

1992-01-01

The fluid mechanics of air exiting from a porous material is investigated. The experiments are filter rating dependent, as porous walls with filter ratings differing by about three orders of magnitude are studied. The flow behavior is investigated for its spatial and temporal stability. The results from the investigation are related to jet behavior in at least one of the following categories: (1) jet coalescence effects with increasing flow rate; (2) jet field decay with increasing distance from the porous wall; (3) jet field temporal turbulence characteristics; and (4) single jet turbulence characteristics. The measurements show that coalescence effects cause jet development, and this development stage can be traced by measuring the pseudoturbulence (spatial velocity variations) at any flow rate. The pseudoturbulence variation with increasing mass flow reveals an initial increasing trend followed by a leveling trend, both of which are directly proportional to the filter rating. A critical velocity begins this leveling trend and represents the onset of fully developed jetting action in the flow field. A correlation is developed to predict the onset of fully developed jets in the flow emerging from a porous wall. The data further show that the fully developed jet dimensions are independent of the filter rating, thus providing a length scale for this type of flow field (1 mm). Individual jet characteristics provide another unifying trend with similar velocity decay behavior with distance; however, the respective turbulence magnitudes show vast differences between jets from the same sample. Measurements of the flow decay with distance from the porous wall show that the higher spatial frequency components of the jet field dissipate faster than the lower frequency components. Flow turbulence intensity measurements show an out of phase behavior with the velocity field and are generally found to increase as the distance from the wall is increased.

Macroscopic momentum and mechanical energy equations for incompressible single-phase flow in porous media.

PubMed

Paéz-García, Catherine Teresa; Valdés-Parada, Francisco J; Lasseux, Didier

2017-02-01

Modeling flow in porous media is usually focused on the governing equations for mass and momentum transport, which yield the velocity and pressure at the pore or Darcy scales. However, in many applications, it is important to determine the work (or power) needed to induce flow in porous media, and this can be achieved when the mechanical energy equation is taken into account. At the macroscopic scale, this equation may be postulated to be the result of the inner product of Darcy's law and the seepage velocity. However, near the porous medium boundaries, this postulate seems questionable due to the spatial variations of the effective properties (velocity, permeability, porosity, etc.). In this work we derive the macroscopic mechanical energy equation using the method of volume averaging for the simple case of incompressible single-phase flow in porous media. Our analysis shows that the result of averaging the pore-scale version of the mechanical energy equation at the Darcy scale is not, in general, the expected product of Darcy's law and the seepage velocity. As a matter of fact, this result is only applicable in the bulk region of the porous medium and, in the derivation of this result, the properties of the permeability tensor are determinant. Furthermore, near the porous medium boundaries, a more novel version of the mechanical energy equation is obtained, which incorporates additional terms that take into account the rapid variations of structural properties taking place in this particular portion of the system. This analysis can be applied to multiphase and compressible flows in porous media and in many other multiscale systems.

Turbulence Statistics in the Coastal Ocean Bottom Boundary Layer

NASA Astrophysics Data System (ADS)

Nayak, A. R.; Hackett, E. E.; Luznik, L.; Katz, J.; Osborn, T. R.

2010-12-01

A submersible particle image velocimetry (PIV) system was deployed off the coast of New Jersey, near the LEO-15 site, to characterize the flow and turbulence in the inner part of the continental shelf bottom boundary layer. The measurement domain extended from 5 mm at the bottom up to an elevation of 51 cm in different datasets. The flow comprised of a mean current and wave-induced flow with a period of 10 s. The ratio of wave velocity amplitude to mean current magnitude varied over the tidal cycle and with elevation, with a maximum of 2.35. Their relative orientation also varied. Large databases of time-resolved, high resolution, 2D velocity distributions enabled us to calculate the instantaneous spatial velocity gradients, and from them, the statistically converged vertical dissipation rate profiles. Reynolds Stresses were estimated using the Shaw & Trowbridge technique outside of the wave boundary layer (WBL), and directly, using the instantaneous spatial variations in velocity, near the wall. Results were utilized for calculating the shear production profiles. Hilbert Transforms were utilized for calculating the wave phase of each velocity distribution, and performing conditional sampling of data to determine variations in flow and turbulence parameters during a wave cycle. The mean velocity profiles indicated the presence of a wave boundary layer, followed by a transition region, and a log layer above it. The datasets extending to the wall show that there is no clear log layer within the WBL, but, as expected, profiles vary substantially with location relative to the ripples. Phase dependent variations in mean flow and dissipation rate occurred only in the WBL and transition region, but vanished at higher elevations. The dissipation rate typically peaked during acceleration phases of wave-induced motion, especially near the wall, but it sometimes peaked during wave-crest phases. Below the transition region, the dissipation rate increased rapidly as the wall was approached all the way to the ripple crest, presumably due to the increasing presence of eddies with characteristic size of 1-3 times the ripple height that fell in the dissipation range of the energy spectra. Shear production also peaked at the ripple crest, consistent with laboratory data for rough wall boundary layers. Acknowledgements : NSF

The relationship between VHF radar auroral backscatter amplitude and Doppler velocity: a statistical study

NASA Astrophysics Data System (ADS)

Shand, B. A.; Lester, M.; Yeoman, T. K.

1996-08-01

A statistical investigation of the relationship between VHF radar auroral backscatter intensity and Doppler velocity has been undertaken with data collected from 8 years operation of the Wick site of the Sweden And Britain Radar-auroral Experiment (SABRE). The results indicate three different regimes within the statistical data set; firstly, for Doppler velocities <200 m s-1, the backscatter intensity (measured in decibels) remains relatively constant. Secondly, a linear relationship is observed between the backscatter intensity (in decibels) and Doppler velocity for velocities between 200 m s-1 and 700 m s-1. At velocities greater than 700 m s-1 the backscatter intensity saturates at a maximum value as the Doppler velocity increases. There are three possible geophysical mechanisms for the saturation in the backscatter intensity at high phase speeds: a saturation in the irregularity turbulence level, a maximisation of the scattering volume, and a modification of the local ambient electron density. There is also a difference in the dependence of the backscatter intensity on Doppler velocity for the flow towards and away from the radar. The results for flow towards the radar exhibit a consistent relationship between backscatter intensity and measured velocities throughout the solar cycle. For flow away from the radar, however, the relationship between backscatter intensity and Doppler velocity varies during the solar cycle. The geometry of the SABRE system ensures that flow towards the radar is predominantly associated with the eastward electrojet, and flow away is associated with the westward electrojet. The difference in the backscatter intensity variation as a function of Doppler velocity is attributed to asymmetries between the eastward and westward electrojets and the geophysical parameters controlling the backscatter amplitude.

The noise and flow characteristics of inverted-profile coannular jets

NASA Technical Reports Server (NTRS)

Tanna, H. K.; Tester, B. J.; Lau, J. C.

1979-01-01

A basic understanding of the noise reduction mechanisms in shock-free inverted-velocity-profile coannular jets was studied. Acoustic measurements are first conducted in an anechoic facility to isolate the effects of inverted velocity and inverted temperature for coannular jets having constant total thrust, mass flow rate and exit area. To obtain physical explanations of the measured noise changes, several types of experiments are conducted. These include (1) source location experiments using the polar correlation technique, (2) mean flow surveys using a combination pressure/temperature probe, and (3) detailed mean flow and turbulence measurements using a two-point four-channel laser velocimeter. The results from these experiments are presented and discussed in detail. Finally, the measured variations of coannular jet mixing noise with fan-to-primary velocity ratio and static temperature ratio are interpreted by utilizing the results from the various experimental phases in conjunction with the existing Lockheed single jet noise prediction model.

Three-dimensional lattice Boltzmann model for compressible flows.

PubMed

Sun, Chenghai; Hsu, Andrew T

2003-07-01

A three-dimensional compressible lattice Boltzmann model is formulated on a cubic lattice. A very large particle-velocity set is incorporated in order to enable a greater variation in the mean velocity. Meanwhile, the support set of the equilibrium distribution has only six directions. Therefore, this model can efficiently handle flows over a wide range of Mach numbers and capture shock waves. Due to the simple form of the equilibrium distribution, the fourth-order velocity tensors are not involved in the formulation. Unlike the standard lattice Boltzmann model, no special treatment is required for the homogeneity of fourth-order velocity tensors on square lattices. The Navier-Stokes equations were recovered, using the Chapman-Enskog method from the Bhatnagar-Gross-Krook (BGK) lattice Boltzmann equation. The second-order discretization error of the fluctuation velocity in the macroscopic conservation equation was eliminated by means of a modified collision invariant. The model is suitable for both viscous and inviscid compressible flows with or without shocks. Since the present scheme deals only with the equilibrium distribution that depends only on fluid density, velocity, and internal energy, boundary conditions on curved wall are easily implemented by an extrapolation of macroscopic variables. To verify the scheme for inviscid flows, we have successfully simulated a three-dimensional shock-wave propagation in a box and a normal shock of Mach number 10 over a wedge. As an application to viscous flows, we have simulated a flat plate boundary layer flow, flow over a cylinder, and a transonic flow over a NACA0012 airfoil cascade.

A microscopic lane changing process model for multilane traffic

NASA Astrophysics Data System (ADS)

Lv, Wei; Song, Wei-guo; Liu, Xiao-dong; Ma, Jian

2013-03-01

In previous simulations lane-changing behavior is usually assumed as an instantaneous action. However, in real traffic, lane changing is a continuing process which can seriously affect the following cars. In this paper, a microscopic lane-changing process (LCP) model is clearly described. A new idea of simplifying the lane-changing process to the car-following framework is presented by controlling fictitious cars. To verify the model, the results of flow, lane-changing frequency, and single-car velocity are extracted from experimental observations and are compared with corresponding simulation. It is found that the LCP model agrees well with actual traffic flow and lane-changing behaviors may induce a 12%-18% reduction of traffic flow. The results also reflect that most of the drivers on the two roads in a city are conservative but not aggressive to change lanes. Investigation of lane-changing frequency shows that the largest lane-changing frequency occurs at a medium density range from 15 vehs km lane to 35 vehs km lane. It also implies that the lane-changing process might strengthen velocity variation at medium density and weaken velocity variation at high density. It is hoped that the idea of this study may be helpful to promote the modeling and simulation study of traffic flow.

Water velocity, turbulence, and migration rate of subyearling fall Chinook salmon in the free-flowing and impounded Snake River

USGS Publications Warehouse

Tiffan, Kenneth F.; Kock, Tobias J.; Haskell, Craig A.; Connor, William P.; Steinhorst, R. Kirk

2009-01-01

We studied the migratory behavior of subyearling fall Chinook salmon Oncorhynchus tshawytscha in free-flowing and impounded reaches of the Snake River to evaluate the hypothesis that velocity and turbulence are the primary causal mechanisms of downstream migration. The hypothesis states that impoundment reduces velocity and turbulence and alters the migratory behavior of juvenile Chinook salmon as a result of their reduced perception of these cues. At a constant flow (m3 /s), both velocity (km/d) and turbulence (the SD of velocity) decreased from riverine to impounded habitat as cross-sectional areas increased. We found evidence for the hypothesis that subyearling Chinook salmon perceive velocity and turbulence cues and respond to these cues by varying their behavior. The percentage of the subyearlings that moved faster than the average current speed decreased as fish made the transition from riverine reaches with high velocities and turbulence to upper reservoir reaches with low velocities and turbulence but increased to riverine levels again as the fish moved further down in the reservoir, where velocity and turbulence remained low. The migration rate (km/d) decreased in accordance with longitudinal reductions in velocity and turbulence, as predicted by the hypothesis. The variation in migration rate was better explained by a repeatedmeasures regression model containing velocity (Akaike’s information criterion ¼ 1,769.0) than a model containing flow (2,232.6). We conclude that subyearling fall Chinook salmon respond to changes in water velocity and turbulence, which work together to affect the migration rate.

Lateral variations in upper-mantle seismic anisotropy in the Pacific from inversion of a surface-wave dispersion dataset

NASA Astrophysics Data System (ADS)

Eddy, C. L.; Ekstrom, G.; Nettles, M.; Gaherty, J. B.

2017-12-01

We present a three-dimensional model of the anisotropic velocity structure of the Pacific lithosphere and asthenosphere. The presence of seismic anisotropy in the oceanic upper mantle provides information about the geometry of flow in the mantle, the nature of the lithosphere-asthenosphere boundary, and the possible presence of partial melt in the asthenosphere. Our dataset consists of fundamental-mode dispersion for Rayleigh and Love waves measured between 25-250 s with paths crossing the Pacific Ocean. We invert the phase anomaly measurements directly for three-dimensional anisotropic velocity structure. Our models are radially anisotropic and include the full set of elastic parameters that describe azimuthal variations in velocity (e.g. Gc, Gs). We investigate the age dependence of seismic velocity and radial anisotropy and find that there are significant deviations from the velocities predicted by a simple oceanic plate cooling model. We observe strong radial anisotropy with vsh > vsv in the asthenosphere of the central Pacific. We investigate the radial anisotropy in the shallow lithosphere, where previous models have reported conflicting results. There is a contrast in both upper-mantle isotropic velocities and radial anisotropy between the Pacific and Nazca plates, across the East Pacific Rise. We also investigate lateral variations in azimuthal anisotropy throughout the Pacific upper mantle and find that there are large areas over which the anisotropy fast axis does not align with absolute plate motion, suggesting the presence of small-scale convection or pressure-driven flow beneath the base of the oceanic plate.

Estimating vertical velocity and radial flow from Doppler radar observations of tropical cyclones

NASA Astrophysics Data System (ADS)

Lee, J. L.; Lee, W. C.; MacDonald, A. E.

2006-01-01

The mesoscale vorticity method (MVM) is used in conjunction with the ground-based velocity track display (GBVTD) to derive the inner-core vertical velocity from Doppler radar observations of tropical cyclone (TC) Danny (1997). MVM derives the vertical velocity from vorticity variations in space and in time based on the mesoscale vorticity equation. The use of MVM and GBVTD allows us to derive good correlations among the eye-wall maximum wind, bow-shaped updraught and echo east of the eye-wall in Danny. Furthermore, we demonstrate the dynamically consistent radial flow can be derived from the vertical velocity obtained from MVM using the wind decomposition technique that solves the Poisson equations over a limited-area domain. With the wind decomposition, we combine the rotational wind which is obtained from Doppler radar wind observations and the divergent wind which is inferred dynamically from the rotational wind to form the balanced horizontal wind in TC inner cores, where rotational wind dominates the divergent wind. In this study, we show a realistic horizontal and vertical structure of the vertical velocity and the induced radial flow in Danny's inner core. In the horizontal, the main eye-wall updraught draws in significant surrounding air, converging at the strongest echo where the maximum updraught is located. In the vertical, the main updraught tilts vertically outwards, corresponding very well with the outward-tilting eye-wall. The maximum updraught is located at the inner edge of the eye-wall clouds, while downward motions are found at the outer edge. This study demonstrates that the mesoscale vorticity method can use high-temporal-resolution data observed by Doppler radars to derive realistic vertical velocity and the radial flow of TCs. The vorticity temporal variations crucial to the accuracy of the vorticity method have to be derived from a high-temporal-frequency observing system such as state-of-the-art Doppler radars.

Source Distribution Method for Unsteady One-Dimensional Flows With Small Mass, Momentum, and Heat Addition and Small Area Variation

NASA Technical Reports Server (NTRS)

Mirels, Harold

1959-01-01

A source distribution method is presented for obtaining flow perturbations due to small unsteady area variations, mass, momentum, and heat additions in a basic uniform (or piecewise uniform) one-dimensional flow. First, the perturbations due to an elemental area variation, mass, momentum, and heat addition are found. The general solution is then represented by a spatial and temporal distribution of these elemental (source) solutions. Emphasis is placed on discussing the physical nature of the flow phenomena. The method is illustrated by several examples. These include the determination of perturbations in basic flows consisting of (1) a shock propagating through a nonuniform tube, (2) a constant-velocity piston driving a shock, (3) ideal shock-tube flows, and (4) deflagrations initiated at a closed end. The method is particularly applicable for finding the perturbations due to relatively thin wall boundary layers.

Droplet-based magnetically activated cell separation: analysis of separation efficiency based on the variation of flow-induced circulation in a pendent drop.

PubMed

Kim, Youngho; Lee, Sang Ho; Kim, Byungkyu

2009-12-01

Under the assumption that separation efficiencies are mainly affected by the velocity of flow-induced circulation due to buffer injection in a pendent drop, this paper describes an analysis of the separation efficiency of a droplet-based magnetically activated cell separation (DMACS) system. To investigate the velocity of the flow-induced circulation, we supposed that numerous flows in a pendent drop could be considered as a "theoretically normalized" flow (or conceptually normalized flow, CNF) based on the Cauchy-Goursat theorem. With the morphological characteristics (length and duration time) of a pendent drop depending on the initial volume, we obtained the velocities of the CNF. By measuring the separation efficiencies for different initial volumes and by analyzing the separation efficiency in terms of the velocity of the CNF, we found that the separation efficiencies (in the case of a low rate of buffer injection; 5 and 15 microl x min(-1)) are mainly affected by the velocity of the CNF. Moreover, we confirmed that the phenomenological features of a pendent drop cause a fluctuation of its separation efficiencies over a range of specific volumes (initial volumes ranging from 40 to 80 microl), because of the "sweeping-off" phenomenon, that is, positive cells gathered into the positive fraction are forced to move away from the magnetic side by flow-induced circulation due to buffer injection. In addition, from the variation of the duration time, that is, the interval between the beginning of injection of the buffer solution and the time at which a pendent drop detaches, it could also be confirmed that a shorter duration time leads to decrease of the number of positive cells in negative fraction regardless of the rate of buffer injection (5, 15, and 50 microl x min(-1)). Therefore, if a DMACS system is operated with a 15 microl x min(-1) buffer injection flow rate and an initial volume of 80 microl or more, we would have the best efficiency of separation in the negative fraction.

Cross-Effects in Microgravity Flows

NASA Technical Reports Server (NTRS)

Loyalka, Sudarshan K.; Tompson, R. V.; Ivchenko, I. N.; Ghosh, T. K.; Hamoodi, S. A.; Hickey, K. A.; Huang, C. M.; Tebbe, Patrick A.; Gabis, D. H.; Tekasakul, P.;

Inferring crustal viscosity from seismic velocity: Application to the lower crust of Southern California

NASA Astrophysics Data System (ADS)

Shinevar, William J.; Behn, Mark D.; Hirth, Greg; Jagoutz, Oliver

2018-07-01

We investigate the role of composition on the viscosity of the lower crust through a joint inversion of seismic P-wave (Vp) and S-wave (Vs) velocities. We determine the efficacy of using seismic velocity to constrain viscosity, extending previous research demonstrating robust relationships between seismic velocity and crustal composition, as well as crustal composition and viscosity. First, we calculate equilibrium mineral assemblages and seismic velocities for a global compilation of crustal rocks at relevant pressures and temperatures. Second, we use a rheological mixing model that incorporates single-phase flow laws for major crust-forming minerals to calculate aggregate viscosity from predicted mineral assemblages. We find a robust correlation between crustal viscosity and Vp together with Vs in the α-quartz regime. Using seismic data, geodetic surface strain rates, and heat flow measurements from Southern California, our method predicts that lower crustal viscosity varies regionally by four orders of magnitude, and lower crustal stress varies by three orders of magnitude at 25 km depth. At least half of the total variability in stress can be attributed to composition, implying that regional lithology has a significant effect on lower crustal geodynamics. Finally, we use our method to predict the depth of the brittle-ductile transition and compare this to regional variations of the seismic-aseismic transition. The variations in the seismic-aseismic transition are not explained by the variations in our model rheology inferred from the geophysical observations. Thus, we conclude that fabric development, in conjunction with compositional variations (i.e., quartz and mica content), is required to explain the regional changes in the seismic-aseismic transition.

The flow structure of jets from transient sources and implications for modeling short-duration explosive volcanic eruptions

NASA Astrophysics Data System (ADS)

Chojnicki, K. N.; Clarke, A. B.; Adrian, R. J.; Phillips, J. C.

2014-12-01

We used laboratory experiments to examine the rise process in neutrally buoyant jets that resulted from an unsteady supply of momentum, a condition that defines plumes from discrete Vulcanian and Strombolian-style eruptions. We simultaneously measured the analog-jet discharge rate (the supply rate of momentum) and the analog-jet internal velocity distribution (a consequence of momentum transport and dilution). Then, we examined the changes in the analog-jet velocity distribution over time to assess the impact of the supply-rate variations on the momentum-driven rise dynamics. We found that the analog-jet velocity distribution changes significantly and quickly as the supply rate varied, such that the whole-field distribution at any instant differed considerably from the time average. We also found that entrainment varied in space and over time with instantaneous entrainment coefficient values ranging from 0 to 0.93 in an individual unsteady jet. Consequently, we conclude that supply-rate variations exert first-order control over jet dynamics, and therefore cannot be neglected in models without compromising their capability to predict large-scale eruption behavior. These findings emphasize the fundamental differences between unsteady and steady jet dynamics, and show clearly that: (i) variations in source momentum flux directly control the dynamics of the resulting flow; (ii) impulsive flows driven by sources of varying flux cannot reasonably be approximated by quasi-steady flow models. New modeling approaches capable of describing the time-dependent properties of transient volcanic eruption plumes are needed before their trajectory, dilution, and stability can be reliably computed for hazards management.

Preliminary interpretation of thermal data from the Nevada Test Site

USGS Publications Warehouse

Sass, John Harvey; Lachenbruch, Arthur H.

1982-01-01

Analysis of data from 60 wells in and around the Nevada Test Site, including 16 in the Yucca Mountain area, indicates a thermal regime characterized by large vertical and lateral gradients in heat flow. Estimates of heat flow indicate considerable variation on both regional and local scales. The variations are attributable primarily to hydrologic processes involving interbasin flow with a vertical component of (seepage) velocity (volume flux) of a few mm/yr. Apart from indicating a general downward movement of water at a few mm/yr, the results from Yucca Mountain are as yet inconclusive.

Ambient seismic noise monitoring of a clay landslide: Toward failure prediction

NASA Astrophysics Data System (ADS)

Mainsant, Guénolé; Larose, Eric; Brönnimann, Cornelia; Jongmans, Denis; Michoud, Clément; Jaboyedoff, Michel

2012-03-01

Given that clay-rich landslides may become mobilized, leading to rapid mass movements (earthflows and debris flows), they pose critical problems in risk management worldwide. The most widely proposed mechanism leading to such flow-like movements is the increase in water pore pressure in the sliding mass, generating partial or complete liquefaction. This solid-to-liquid transition results in a dramatic reduction of mechanical rigidity in the liquefied zones, which could be detected by monitoring shear wave velocity variations. With this purpose in mind, the ambient seismic noise correlation technique has been applied to measure the variation in the seismic surface wave velocity in the Pont Bourquin landslide (Swiss Alps). This small but active composite earthslide-earthflow was equipped with continuously recording seismic sensors during spring and summer 2010. An earthslide of a few thousand cubic meters was triggered in mid-August 2010, after a rainy period. This article shows that the seismic velocity of the sliding material, measured from daily noise correlograms, decreased continuously and rapidly for several days prior to the catastrophic event. From a spectral analysis of the velocity decrease, it was possible to determine the location of the change at the base of the sliding layer. These results demonstrate that ambient seismic noise can be used to detect rigidity variations before failure and could potentially be used to predict landslides.

Mantle shear-wave tomography and the fate of subducted slabs.

PubMed

Grand, Steven P

2002-11-15

A new seismic model of the three-dimensional variation in shear velocity throughout the Earth's mantle is presented. The model is derived entirely from shear bodywave travel times. Multibounce shear waves, core-reflected waves and SKS and SKKS waves that travel through the core are used in the analysis. A unique aspect of the dataset used in this study is the use of bodywaves that turn at shallow depths in the mantle, some of which are triplicated. The new model is compared with other global shear models. Although competing models show significant variations, several large-scale structures are common to most of the models. The high-velocity anomalies are mostly associated with subduction zones. In some regions the anomalies only extend into the shallow lower mantle, whereas in other regions tabular high-velocity structures seem to extend to the deepest mantle. The base of the mantle shows long-wavelength high-velocity zones also associated with subduction zones. The heterogeneity seen in global tomography models is difficult to interpret in terms of mantle flow due to variations in structure from one subduction zone to another. The simplest interpretation of the seismic images is that slabs in general penetrate to the deepest mantle, although the flow is likely to be sporadic. The interruption in slab sinking is likely to be associated with the 660 km discontinuity.

A method for modifying two-dimensional adaptive wind-tunnel walls including analytical and experimental verification

NASA Technical Reports Server (NTRS)

Everhart, J. L.

1983-01-01

The theoretical development of a simple and consistent method for removing the interference in adaptive-wall wind tunnels is reported. A Cauchy integral formulation of the velocities in an imaginary infinite extension of the real wind-tunnel flow is obtained and evaluated on a closed contour dividing the real and imaginary flow. The contour consists of the upper and lower effective wind-tunnel walls (wall plus boundary-layer displacement thickness) and upstream and downstream boundaries perpendicular to the axial tunnel flow. The resulting integral expressions for the streamwise and normal perturbation velocities on the contour are integrated by assuming a linear variation of the velocities between data-measurement stations along the contour. In an iterative process, the velocity components calculated on the upper and lower boundaries are then used to correct the shape of the wall to remove the interference. Convergence of the technique is shown numerically for the cases of a circular cylinder and a lifting and nonlifting NACA 0012 airfoil in incompressible flow. Experimental convergence at a transonic Mach number is demonstrated by using an NACA 0012 airfoil at zero lift.

Extreme-scale motions in turbulent plane Couette flows

NASA Astrophysics Data System (ADS)

Lee, Myoungkyu; Moser, Robert D.

2018-05-01

We study the size of large-scale motions in turbulent plane Couette flows at moderate Reynolds number up to $Re_\\tau$ = 500. Direct numerical simulation domains were as large as $100\\pi\\delta\\times2\\delta\\times5\\pi\\delta$, where $\\delta$ is half the distance between the walls. The results indicate that there are structures with streamwise extent, as measured by the wavelength, as long as 78$\\delta$ and at least 310$\\delta$ at $Re_\\tau$ = 220 and 500, respectively. The presence of these very long structures is apparent in the spectra of all three velocity components and the Reynolds stress. In DNS using a smaller domain, the large structures are constrained, eliminating the streamwise variations present in the larger domain. Effects of a smaller domain are also present in the mean velocity and the streamwise velocity variance in the outer flow.

Effect of coolant flow ejection on aerodynamic performance of low-aspect-ratio vanes. 1: Performance with coolant ejection holes plugged

NASA Technical Reports Server (NTRS)

Haas, J. E.; Kofskey, M. G.

1976-01-01

The aerodynamic performance of a low aspect ratio turbine vane designed with coolant flow ejection holes on the vane surfaces was experimentally determined in a full-annular cascade with the coolant ejection holes plugged. The purpose was to establish a baseline for comparison with tests where flow is ejected from the vane surfaces. The vanes were tested over a mean-section ideal critical velocity ratio range of 0.64 to 0.98. This ideal critical velocity ratio corresponds to the vane inlet total to vane aftermixed static pressure ratio at the mean section. The variations in vane efficiency and aftermixed flow conditions with circumferential and radial position were obtained.

Dynamic Response of a High Arctic Glacier to Melt and Runoff Variations

NASA Astrophysics Data System (ADS)

van Pelt, Ward J. J.; Pohjola, Veijo A.; Pettersson, Rickard; Ehwald, Lena E.; Reijmer, Carleen H.; Boot, Wim; Jakobs, Constantijn L.

2018-05-01

The dynamic response of High Arctic glaciers to increased runoff in a warming climate remains poorly understood. We analyze a 10-year record of continuous velocity data collected at multiple sites on Nordenskiöldbreen, Svalbard, and study the connection between ice flow and runoff within and between seasons. During the melt season, the sensitivity of ice motion to runoff at sites in the ablation and lower accumulation zone drops by a factor of 3 when cumulative runoff exceeds a local threshold, which is likely associated with a transition from inefficient (distributed) to efficient (channelized) drainage. Average summer (June-August) velocities are found to increase with summer ablation, while subsequent fall (September-November) velocities decrease. Spring (March-May) velocities are largely insensitive to summer ablation, which suggests a short-lived impact of summer melt on ice flow during the cold season. The net impact of summer ablation on annual velocities is found to be insignificant.

Velocity-Vorticity Correlation Structure in Turbulent Channel Flow

NASA Astrophysics Data System (ADS)

Chen, J.; Pei, J.; She, Z. S.; Hussain, F.

2011-09-01

We present a new definition of statistical structure — velocity-vorticity correlation structure (VVCS) — based on amplitude distributions of the tensor field of normalized velocity-vorticity correlation (uiωj), and show that it displays the geometry of the statistical structure relevant to a given reference point, and it effectively captures coherent motions in inhomogeneous shear flows. The variation of the extracted objects moving with the reference point yr+ then presents a full picture of statistical structures for the flow, which goes beyond the traditional view of searching for reference-independent structures. Application to turbulent channel flow simulation data at Reτ = 180 demonstrates that the VVCS successfully captures, qualitatively and quantitatively, the near-wall streaks, the streamwise vortices [1,2], and their extensions up to yr+ = 110 with variations of their length and inclination angle. More interestingly, the VVCS associated with the streamwise velocity component (particularly (uωx ( and (uωz) displays topological change at four distances from the wall (with transitions at yr+≈20,40,60,110), giving rise to a geometrical interpretation of the multi-layer structure of wall-bounded turbulence. Specifically, we find that the VVCS of (uωz( bifurcates at yr+ = 40 with one attached to the wall and the other near the reference location. The VVCS of (uωx) is blob-like in the center region, quite different from a pair of elongated and inclined objects near the wall. The propagation speeds of the velocity components in the near-wall region, y+ ≤ 10, is found to be characterized by the same stream-wise correlation structures of (uωx) and (uωz), whose core is located at y+≈20. As a result, the convection of the velocity fluctuations always reveal the constant propagation speeds in the near-wall region. The coherent motions parallel to the wall plays an important role in determining the propagation of the velocity fluctuations. This study suggests that a variable set of geometrical structures should be invoked for the study of turbulence structures and for modeling mean flow properties in terms of structures. The method and the concept presented here are general for the study of other flow systems (like boundary or mixing layer), as long as ensemble averaging is well-defined.

Velocity fields and optical turbulence near the boundary in a strongly convective laboratory flow

NASA Astrophysics Data System (ADS)

Matt, Silvia; Hou, Weilin; Goode, Wesley; Hellman, Samuel

2016-05-01

Boundary layers around moving underwater vehicles or other platforms can be a limiting factor for optical communication. Turbulence in the boundary layer of a body moving through a stratified medium can lead to small variations in the index of refraction, which impede optical signals. As a first step towards investigating this boundary layer effect on underwater optics, we study the flow near the boundary in the Rayleigh-Bénard laboratory tank at the Naval Research Laboratory Stennis Space Center. The tank is set up to generate temperature-driven, i.e., convective turbulence, and allows control of the turbulence intensity. This controlled turbulence environment is complemented by computational fluid dynamics simulations to visualize and quantify multi-scale flow patterns. The boundary layer dynamics in the laboratory tank are quantified using a state-of-the-art Particle Image Velocimetry (PIV) system to examine the boundary layer velocities and turbulence parameters. The velocity fields and flow dynamics from the PIV are compared to the numerical model and show the model to accurately reproduce the velocity range and flow dynamics. The temperature variations and thus optical turbulence effects can then be inferred from the model temperature data. Optical turbulence is also visible in the raw data from the PIV system. The newly collected data are consistent with previously reported measurements from high-resolution Acoustic Doppler Velocimeter profilers (Nortek Vectrino), as well as fast thermistor probes and novel next-generation fiber-optics temperature sensors. This multi-level approach to studying optical turbulence near a boundary, combining in-situ measurements, optical techniques, and numerical simulations, can provide new insight and aid in mitigating turbulence impacts on underwater optical signal transmission.

Laminar boundary layer near the rotating end wall of a confined vortex

NASA Astrophysics Data System (ADS)

Shakespeare, W. J.; Levy, E. K.

1982-06-01

The results of an experimental and theoretical investigation of the fluid mechanics in a confined vortex are discussed with particular emphasis on behavior away from the axis of symmetry and near the end walls. The vortex is generated in a rotating cylindrical chamber with an exit opening in one end. Both end walls rotate. For the range of flow rates and swirl ratios (S between 1 and 5) of interest here, the flow field far from the end walls behaves as inviscid and irrotational; and the end wall boundary layers are thin and laminar. Measurements and calculations of tangential and radial velocity in the end wall region show the development of a secondary flow resulting in a strong velocity 'overshoot' in the radial component. Results illustrating the nature of the velocity variations on the end walls are presented; and it is shown that the mass flow rate through the end wall boundary layers, while only a small fraction of the total flow, increases with increasing swirl and with decreasing total flow rate through the chamber.

In vitro evaluation of flow patterns and turbulent kinetic energy in trans-catheter aortic valve prostheses.

PubMed

Giese, Daniel; Weiss, Kilian; Baeßler, Bettina; Madershahian, Navid; Choi, Yeong-Hoon; Maintz, David; Bunck, Alexander C

2018-02-01

The objective of the current work was to evaluate flow and turbulent kinetic energy in different transcatheter aortic valve implants using highly undersampled time-resolved multi-point 3-directional phase-contrast measurements (4D Flow MRI) in an in vitro setup. A pulsatile flow setup was used with a compliant tubing mimicking a stiff left ventricular outflow tract and ascending aorta. Five different implants were measured using a highly undersampled multi-point 4D Flow MRI sequence. Velocities and turbulent kinetic energy values were analysed and compared. Strong variations of turbulent kinetic energy distributions between the valves were observed. Maximum turbulent kinetic energy values ranged from 100 to over 500 J/m 3 while through-plane velocities were similar between all valves. Highly accelerated 4D Flow MRI for the measurement of velocities and turbulent kinetic energy values allowed for the assessment of hemodynamic parameters in five different implant models. The presented setup, measurement protocol and analysis methods provides an efficient approach to compare different valve implants and could aid future novel valve designs.

A Froude-scaled model of a bedrock-alluvial channel reach: 1. Hydraulics

NASA Astrophysics Data System (ADS)

Hodge, Rebecca A.; Hoey, Trevor B.

2016-09-01

The controls on hydraulics in bedrock-alluvial rivers are relatively poorly understood, despite the importance of the flow in determining rates and patterns of sediment transport and consequent erosion. To measure hydraulics within a bedrock-alluvial channel, we developed a 1:10 Froude-scaled laboratory model of an 18 × 9 m bedrock-alluvial river reach using terrestrial laser scanning and 3-D printing. In the reported experiments, water depth and velocity were recorded at 18 locations within the channel at each of five different discharges. Additional data from runs with sediment cover in the flume were used to evaluate the hydraulic impact of sediment cover; the deposition and erosion of sediment patches in these runs are analyzed in the companion paper. In our data (1) spatial variation in both flow velocity and Froude number increases with discharge; (2) bulk flow resistance and Froude number become independent of discharge at higher discharges; (3) local flow velocity and Reynolds stress are correlated to the range of local bed topography at some, but not most, discharges; (4) at lower discharges, local topography induces vertical flow structures and slower velocities, but these effects decrease at higher discharges; and (5) there is a relationship between the linear combination of bed and sediment roughness and local flow velocity. These results demonstrate the control that bedrock topography exerts over both local and reach-scale flow conditions, but spatially distributed hydraulic data from bedrock-alluvial channels with different topographies are needed to generalize these findings.

Development of flow in a square mini-channel: Effect of flow oscillation

NASA Astrophysics Data System (ADS)

Lobo, Oswald Jason; Chatterjee, Dhiman

2018-04-01

In this research paper, we present a numerical prediction of steady and fully oscillatory flows in a square mini-channel connected between two plenums. Flow separation occurs at the contraction of the plenum into the channel which causes an asymmetry in the development of flow in the entrance region. The entrance length and recirculation length are found, for both steady and fully oscillatory flows. It is shown that the maximum entrance length decreases with an increase in the oscillating frequency while the maximum recirculation length and recirculation area increase with an increase in oscillating frequency. The phase of a velocity signal is shown to be a strong function of its location. The phase difference between the velocities with respect to the different points along the centerline and those at the middle of the channel show a significant dependence on the driving frequency. There is a significant variation in the phase angles of the velocity signals computed between a point near the wall and that at the centerline. This phase difference decreases along the channel length and does not change beyond the entrance length. This feature can then be used to determine the maximum entrance length, which is otherwise problematic to ascertain in the case of fully oscillatory flows. The entrance length, thus obtained, is compared with that obtained from the velocity profile consideration and shows good similarity. The phase difference between pressure and velocity is also brought out in this work.

SuperDARN convection and Sondrestrom plasma drift

NASA Astrophysics Data System (ADS)

Xu, L.; Koustov, A. V.; Thayer, J.; McCready, M. A.

2001-07-01

Plasma convection measurements by the Goose Bay and Stokkseyri SuperDARN radar pair and the Sondrestrom incoherent scatter radar are compared in three different ways, by looking at the line-of-sight (l-o-s) velocities, by comparing the SuperDARN vectors and corresponding Sondrestrom l-o-s velocities and by comparing the end products of the instruments, the convection maps. All three comparisons show overall reasonable agreement of the convection measurements though the data spread is significant and for some points a strong disagreement is obvious. The convection map comparison shows a tendency for the SuperDARN velocities to be often less than the Sondrestrom drifts for strong flows (velocities > 1000 m/s) and larger for weak flows (velocities < 500 m/s). On average, both effects do not exceed 35%. Data indicate that inconsistencies between the two data sets occur largely at times of fast temporal variations of the plasma drift and for strongly irregular flow ac-cording to the SuperDARN convection maps. These facts indicate that the observed discrepancies are in many cases a result of the different spatial and temporal resolutions of the instruments.

Effect of heat transfer on rotating electroosmotic flow through a micro-vessel: haemodynamical applications

NASA Astrophysics Data System (ADS)

Sinha, A.; Mondal, A.; Shit, G. C.; Kundu, P. K.

2016-08-01

This paper theoretically analyzes the heat transfer characteristics associated with electroosmotic flow of blood through a micro-vessel having permeable walls. The analysis is based on the Debye-Hückel approximation for charge distributions and the Navier-Stokes equations are assumed to represent the flow field in a rotating system. The velocity slip condition at the vessel walls is taken into account. The essential features of the rotating electroosmotic flow of blood and associated heat transfer characteristics through a micro-vessel are clearly highlighted by the variation in the non-dimensional flow velocity, volumetric flow rate and non-dimensional temperature profiles. Moreover, the effect of Joule heating parameter and Prandtl number on the thermal transport characteristics are discussed thoroughly. The study reveals that the flow of blood is appreciably influenced by the elctroosmotic parameter as well as rotating Reynolds number.

Theoretical and Experimental Investigation of the Subsonic-Flow Fields Beneath Swept and Unswept Wings with Tables or Vortex-induced Velocities

NASA Technical Reports Server (NTRS)

Alford, William J , Jr

1957-01-01

The flow-field characteristics beneath swept and unswept wings as determined by potential-flow theory are compared with the experimentally determined flow fields beneath swept and unswept wing-fuselage combinations. The potential-flow theory utilized considered both spanwise and chordwise distributions of vorticity as well as the wing-thickness effects. The perturbation velocities induced by a unit horseshoe vortex are included in tabular form. The theoretical predictions of the flow-field characteristics were qualitatively correct in all cases considered, although there were indications that the magnitudes of the downwash angles tended to be overpredicted as the tip of the swept wing was approached and that the sidewash angles ahead of the unswept wing were underpredicted. The calculated effects of compressibility indicated that significant increases in the chordwise variation of flow angles and dynamic-pressure ratios should be expected in going from low to high subsonic speeds.

Mooring Measurements of the Abyssal Circulations in the Western Pacific Ocean

NASA Astrophysics Data System (ADS)

Wang, J.; Wang, F.

2016-12-01

A scientific observing network in the western tropical Pacific has initially been established by the Institute of Oceanology, Chinese Academy of Sciences (IOCAS). Using fifteen moorings that gives unprecedented measurements in the intermediate and abyssal layers, we present multi-timescale variations of the deep ocean circulations prior to and during 2015 El Niño event. The deep ocean velocities increase equatorward with high standard deviation and nearly zero mean. The deep ocean currents mainly flow in meridional direction in the central Philippine Basin, and are dominated by a series of alternating westward and eastward zonal jets in the Caroline Basin. The currents in the deep channel connecting the East and West Mariana Basins mainly flow southeastward. Seasonal variation is only present in the deep jets in the Caroline Basin, associating with vertical propagating annual Rossby wave. The high-frequency flow bands are dominated by diurnal, and semi-diurnal tidal currents, and near-inertial currents. The rough topography has a strong influence on the abyssal circulations, including the intensifications in velocity and internal tidal energy, and the formation of upwelling flow.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Michael, A. T.; Opher, M.; Provornikova, E.

In the heliosheath (HS), Voyager 2 has observed a flow with constant radial velocity and magnetic flux conservation. Voyager 1, however, has observed a decrease in the flow’s radial velocity and an order of magnitude decrease in magnetic flux. We investigate the role of the 11 yr solar cycle variation of the magnetic field strength on the magnetic flux within the HS using a global 3D magnetohydrodynamic model of the heliosphere. We use time and latitude-dependent solar wind velocity and density inferred from Solar and Heliospheric Observatory/SWAN and interplanetary scintillations data and implemented solar cycle variations of the magnetic fieldmore » derived from 27 day averages of the field magnitude average of the magnetic field at 1 AU from the OMNI database. With the inclusion of the solar cycle time-dependent magnetic field intensity, the model matches the observed intensity of the magnetic field in the HS along both Voyager 1 and 2. This is a significant improvement from the same model without magnetic field solar cycle variations, which was over a factor of two larger. The model accurately predicts the radial velocity observed by Voyager 2; however, the model predicts a flow speed ∼100 km s{sup −1} larger than that derived from LECP measurements at Voyager 1. In the model, magnetic flux is conserved along both Voyager trajectories, contrary to observations. This implies that the solar cycle variations in solar wind magnetic field observed at 1 AU does not cause the order of magnitude decrease in magnetic flux observed in the Voyager 1 data.« less

Augmenting two-dimensional hydrodynamic simulations with measured velocity data to identify flow paths as a function of depth on Upper St. Clair River in the Great Lakes basin

USGS Publications Warehouse

Holtschlag, D.J.; Koschik, J.A.

2005-01-01

Upper St. Clair River, which receives outflow from Lake Huron, is characterized by flow velocities that exceed 7 feet per second and significant channel curvature that creates complex flow patterns downstream from the Blue Water Bridge in the Port Huron, Michigan, and Sarnia, Ontario, area. Discrepancies were detected between depth-averaged velocities previously simulated by a two-dimensional (2D) hydrodynamic model and surface velocities determined from drifting buoy deployments. A detailed ADCP (acoustic Doppler current profiler) survey was done on Upper St. Clair River during July 1–3, 2003, to help resolve these discrepancies. As part of this study, a refined finite-element mesh of the hydrodynamic model used to identify source areas to public water intakes was developed for Upper St. Clair River. In addition, a numerical procedure was used to account for radial accelerations, which cause secondary flow patterns near channel bends. The refined model was recalibrated to better reproduce local velocities measured in the ADCP survey. ADCP data also were used to help resolve the remaining discrepancies between simulated and measured velocities and to describe variations in velocity with depth. Velocity data from ADCP surveys have significant local variability, and statistical processing is needed to compute reliable point estimates. In this study, velocity innovations were computed for seven depth layers posited within the river as the differences between measured and simulated velocities. For each layer, the spatial correlation of velocity innovations was characterized by use of variogram analysis. Results were used with kriging to compute expected innovations within each layer at applicable model nodes. Expected innovations were added to simulated velocities to form integrated velocities, which were used with reverse particle tracking to identify the expected flow path near a sewage outfall as a function of flow depth. Expected particle paths generated by use of the integrated velocities showed that surface velocities in the upper layers tended to originate nearer the Canadian shoreline than velocities near the channel bottom in the lower layers. Therefore, flow paths to U.S. public water intakes located on the river bottom are more likely to be in the United States than withdrawals near the water surface. Integrated velocities in the upper layers are generally consistent with the surface velocities indicated by drifting-buoy deployments. Information in the 2D hydrodynamic model and the ADCP measurements was insufficient to describe the vertical flow component. This limitation resulted in the inability to account for vertical movements on expected flow paths through Upper St. Clair River. A three dimensional hydrodynamic model would be needed to account for these effects.

Electrokinetically driven active micro-mixers utilizing zeta potential variation induced by field effect

NASA Astrophysics Data System (ADS)

Lee, Chia-Yen; Lee, Gwo-Bin; Fu, Lung-Ming; Lee, Kuo-Hoong; Yang, Ruey-Jen

2004-10-01

This paper presents a new electrokinetically driven active micro-mixer which uses localized capacitance effects to induce zeta potential variations along the surface of silica-based microchannels. The mixer is fabricated by etching bulk flow and shielding electrode channels into glass substrates and then depositing Au/Cr thin films within the latter to form capacitor electrodes, which establish localized zeta potential variations near the electrical double layer (EDL) region of the electroosmotic flow (EOF) within the microchannels. The potential variations induce flow velocity changes within a homogeneous fluid and a rapid mixing effect if an alternating electric field is provided. The current experimental data confirm that the fluid velocity can be actively controlled by using the capacitance effect of the buried shielding electrodes to vary the zeta potential along the channel walls. While compared with commonly used planar electrodes across the microchannels, the buried shielding electrodes prevent current leakage caused by bad bonding and allow direct optical observation during operation. It also shows that the buried shielding electrodes can significantly induce the field effect, resulting in higher variations of zeta potential. Computational fluid dynamic simulations are also used to study the fluid characteristics of the developed active mixers. The numerical and experimental results demonstrate that the developed microfluidic device permits a high degree of control over the fluid flow and an efficient mixing effect. Moreover, the developed device could be used as a pumping device as well. The development of the active electrokinetically driven micro-mixer could be crucial for micro-total-analysis-systems.

Constraints on upper mantle Vp/Vs ratio variations beneath eastern North China from receiver function tomography

NASA Astrophysics Data System (ADS)

Si, Shaokun; Tian, Xiaobo; Gao, Rui

2017-05-01

To detect the thinning, modification, and replacement of the basement of the lithosphere is a key step in understanding the destruction mechanism of the North China lithosphere. The difference of the basement of the lithosphere is mainly displayed by the variation of the peridotite composition and its physical state. Vp/Vs ratio (hereafter referred to as velocity ratio) is more sensitive to this change than Vp or Vs alone. By means of the strong dependence of the travel-time of the wave converted at the 410-km discontinuity (P410s) observed in the receiver function (RF) on the velocity ratio in the upper mantle, we developed a new mapping method to constrain the velocity ratio between the Moho and 410-km discontinuity. Using the RFs extracted from 246 broadband stations beneath the North China Craton (NCC), we obtained a high-resolution velocity ratio image of the upper mantle. The abnormal velocity ratio indicates a strong lateral variation of the mineral composition in the upper mantle beneath North China. Two low-velocity-ratio patches are imaged at the top of the upper mantle and the 410 km depth, respectively. The former may be related to the orthopyroxene enrichment in the lithospheric mantle, and the latter may reflect the stagnant Pacific slab in the mantle transition zone (MTZ). A prominent high-velocity-ratio anomaly is also imaged in the upper mantle beneath the Shaanxi-Shanxi rift system in the central NCC, with the highest anomaly reaching 10%. We speculate that the high velocity ratio of upper mantle is related to convective flow due to slab dehydration in the MTZ. The dehydration of the retained slab in the MTZ results in partial melting and upwelling of upper mantle materials. Such convective flow and their melting are closely related to the Cenozoic basalt eruption in the northern section of the Shaanxi-Shanxi rift system.

Rheology of surface granular flows

NASA Astrophysics Data System (ADS)

Orpe, Ashish V.; Khakhar, D. V.

Surface granular flow, comprising granular material flowing on the surface of a heap of the same material, occurs in several industrial and natural systems. The rheology of such a flow was investigated by means of measurements of velocity and number-density profiles in a quasi-two-dimensional rotating cylinder, half-filled with a model granular material monosize spherical stainless-steel particles. The measurements were made at the centre of the cylinder, where the flow is fully developed, using streakline photography and image analysis. The stress profile was computed from the number-density profile using a force balance which takes into account wall friction. Mean-velocity and root-mean-square (r.m.s.)-velocity profiles are reported for different particle sizes and cylinder rotation speeds. The profiles for the mean velocity superimpose when distance is scaled by the particle diameter d and velocity by a characteristic shear rate dot{gamma}_C = [gsin(beta_m-beta_s)/dcosbeta_s](1/2) and the particle diameter, where beta_m is the maximum dynamic angle of repose and beta_s is the static angle of repose. The maximum dynamic angle of repose is found to vary with the local flow rate. The scaling is also found to work for the r.m.s. velocity profiles. The mean velocity is found to decay exponentially with depth in the bed, with decay length lambda=1.1d. The r.m.s. velocity shows similar behaviour but with lambda=1.7d. The r.m.s. velocity profile shows two regimes: near the free surface the r.m.s. velocity is nearly constant and below a transition point it decays linearly with depth. The shear rate, obtained by numerical differentiation of the velocity profile, is not constant anywhere in the layer and has a maximum which occurs at the same depth as the transition in the r.m.s. velocity profile. Above the transition point the velocity distributions are Gaussian and below the transition point the velocity distributions gradually approach a Poisson distribution. The shear stress increases roughly linearly with depth. The variation in the apparent viscosity eta with r.m.s. velocity u shows a relatively sharp transition at the shear-rate maximum, and in the region below this point the apparent viscosity eta˜ u(-1.5) . The measurements indicate that the flow comprises two layers: an upper low-viscosity layer with a nearly constant r.m.s. velocity and a lower layer of increasing viscosity with a decreasing r.m.s. velocity. The thickness of the upper layer depends on the local flow rate and is independent of particle diameter while the reverse is found to hold for the lower-layer thickness. The experimental data is compared with the predictions of three models for granular flow.

Erosion by an Alpine glacier.

PubMed

Herman, Frédéric; Beyssac, Olivier; Brughelli, Mattia; Lane, Stuart N; Leprince, Sébastien; Adatte, Thierry; Lin, Jiao Y Y; Avouac, Jean-Philippe; Cox, Simon C

2015-10-09

Assessing the impact of glaciation on Earth's surface requires understanding glacial erosion processes. Developing erosion theories is challenging because of the complex nature of the erosion processes and the difficulty of examining the ice/bedrock interface of contemporary glaciers. We demonstrate that the glacial erosion rate is proportional to the ice-sliding velocity squared, by quantifying spatial variations in ice-sliding velocity and the erosion rate of a fast-flowing Alpine glacier. The nonlinear behavior implies a high erosion sensitivity to small variations in topographic slope and precipitation. A nonlinear rate law suggests that abrasion may dominate over other erosion processes in fast-flowing glaciers. It may also explain the wide range of observed glacial erosion rates and, in part, the impact of glaciation on mountainous landscapes during the past few million years. Copyright © 2015, American Association for the Advancement of Science.

Simultaneous Right and Left Heart Real-Time, Free-Breathing CMR Flow Quantification Identifies Constrictive Physiology

PubMed Central

Thavendiranathan, Paaladinesh; Verhaert, David; Walls, Michael C.; Bender, Jacob A.; Rajagopalan, Sanjay; Chung, Yiu-Cho; Simonetti, Orlando P.; Raman, Subha V.

2015-01-01

OBJECTIVES The purpose of this study was to evaluate the ability of a novel cardiac magnetic resonance (CMR) real-time phase contrast (RT-PC) flow measurement technique to reveal the discordant respirophasic changes in mitral and tricuspid valve in flow indicative of the abnormal hemodynamics seen in constrictive pericarditis (CP). BACKGROUND Definitive diagnosis of CP requires identification of constrictive hemodynamics with or without pericardial thickening. CMR to date has primarily provided morphological assessment of the pericardium. METHODS Sixteen patients (age 57 ± 13 years) undergoing CMR to assess known or suspected CP and 10 controls underwent RT-PC that acquired simultaneous mitral valve and tricuspid valve inflow velocities over 10 s of unrestricted breathing. The diagnosis of CP was confirmed via clinical history, diagnostic imaging, cardiac catheterization, intraoperative findings, and histopathology. RESULTS Ten patients had CP, all with increased pericardial thickness (6.2 ± 1.0 mm). RT-PC imaging demonstrated discordant respirophasic changes in atrioventricular valve inflow velocities in all CP patients, with mean ± SD mitral valve and tricuspid valve inflow velocity variation of 46 ± 20% and 60 ± 15%, respectively, compared with 16 ± 8% and 24 ± 11% in patients without CP (p < 0.004 vs. patients with CP for both) and 17 ± 5% and 31 ± 13% in controls (p < 0.001 vs. patients with CP for both). There was no difference in atrioventricular valve inflow velocity variation between patients without CP compared with controls (p > 0.3 for both). Respiratory variation exceeding 25% across the mitral valve yielded a sensitivity of 100%, a specificity of 100%, and an area under the receiver-operating characteristic curve of 1.0 to detect CP physiology. Using a cutoff of 45%, variation of transtricuspid valve velocity had a sensitivity of 90%, a specificity of 88%, and an area under the receiver-operating characteristic curve of 0.98. CONCLUSIONS Accentuated and discordant respirophasic changes in mitral valve and tricuspid valve inflow velocities characteristic of CP can be identified noninvasively with RT-PC CMR. When incorporated into existing CMR protocols for imaging pericardial morphology, RT-PC CMR provides important hemodynamic evidence with which to make a definite diagnosis of CP. PMID:22239888

Effects of forward velocity on turbulent jet mixing noise

NASA Technical Reports Server (NTRS)

Plumblee, H. E., Jr. (Editor)

1976-01-01

Flight simulation experiments were conducted in an anechoic free jet facility over a broad range of model and free jet velocities. The resulting scaling laws were in close agreement with scaling laws derived from theoretical and semiempirical considerations. Additionally, measurements of the flow structure of jets were made in a wind tunnel by using a laser velocimeter. These tests were conducted to describe the effects of velocity ratio and jet exit Mach number on the development of a jet in a coflowing stream. These turbulence measurements and a simplified Lighthill radiation model were used in predicting the variation in radiated noise at 90 deg to the jet axis with velocity ratio. Finally, the influence of forward motion on flow-acoustic interactions was examined through a reinterpretation of the 'static' numerical solutions to the Lilley equation.

DSMC simulations of leading edge flat-plate boundary layer flows at high Mach number

NASA Astrophysics Data System (ADS)

Pradhan, Sahadev, , Dr.

2017-04-01

The flow over a 2D leading-edge flat plate is studied at Mach number Ma =(Uinf / \\setmn √{kBTinf / m}) in the range

DSMC simulations of leading edge flat-plate boundary layer flows at high Mach number

NASA Astrophysics Data System (ADS)

Pradhan, Sahadev, , Dr.

2016-11-01

The flow over a 2D leading-edge flat plate is studied at Mach number Ma = (Uinf /√{kBTinf / m }) in the range

DSMC simulations of leading edge flat-plate boundary layer flows at high Mach number

NASA Astrophysics Data System (ADS)

Pradhan, Sahadev, , Dr.

2017-01-01

The flow over a 2D leading-edge flat plate is studied at Mach number Ma = (Uinf /√{kBTinf / m }) in the range

DSMC simulations of leading edge flat-plate boundary layer flows at high Mach number

NASA Astrophysics Data System (ADS)

Pradhan, Sahadev

2016-10-01

The flow over a 2D leading-edge flat plate is studied at Mach number Ma = (Uinf / {kBTinf /m}) in the range

DSMC simulations of leading edge flat-plate boundary layer flows at high Mach number

NASA Astrophysics Data System (ADS)

Pradhan, Sahadev, , Dr.

The flow over a 2D leading-edge flat plate is studied at Mach number Ma = (Uinf / ∖ sqrt{kBTinf / m})in the range

A revised velocity-reversal and sediment-sorting model for a high-gradient, pool-riffle stream

USGS Publications Warehouse

Thompson, D.M.; Wohl, E.E.; Jarrett, R.D.

1996-01-01

Sediment-sorting processes related to varying channel-bed morphology were investigated from April to November 1993 along a 1-km pool-riffle and step-pool reach of North Saint Vrain Creek, a small mountain stream in the Rocky Mountains of northern Colorado. Measured cross-sectional areas of flow were used to suggest higher velocities in pools than in riffles at high flow. Three hundred and sixteen tracer particles, ranging in size from 16 mm to 256 mm, were placed in two separate pool-riffle-pool sequences and used to assess sediment-sorting patterns and sediment-transport competence variations. Tracer-particle depositional evidence indicated higher sediment-transport competence in pools than in riffles at high flow. Pool-riffle sediment sorting may be created by velocity reversals, and more localized sorting results from gravitational forces along the upstream sloping portion of the channel bed located at the downstream end of pools.

Micro PIV Measurements of the Internal Flow of an Amoeba proteus

NASA Astrophysics Data System (ADS)

Resagk, Christian; Lobutova, Elka; Li, Ling; Voges, Danja

2011-11-01

We report about micro PIV measurements of the internal flow in the protoplasm of an amoeba. The velocity data shall give information about the mechanism of the change of amoeba's contour during its locomotion in water. The experimental data is used for an analytical modeling of the locomotion mechanism with the help of a variable contour and finally for the development of locomotion principles for micro robots. The experimental set-up consists of a microscope and a CCD camera with 12 frames per second and image analysis software. The illumination of the amoeba was done by the built-in microscope halogen lamp. We use the phase contrast configuration to capture images of the amoeba moving in water. We applied an electrical field to the water channel in order to control the movement of the amoeba in one direction. During this motion we measured time dependent velocity vector fields of the protoplasm flow, estimated velocity profiles and analyzed time series of the maximum velocity. The velocity vector plots are calculated from the images by using cross correlation and naturally occurring particles in the protoplasm. Beside the analyses of the internal flow we recorded the motion of the center of gravity and the variation of the sectional area.

Directional synthetic aperture flow imaging.

PubMed

Jensen, Jørgen Arendt; Nikolov, Svetoslav Ivanov

2004-09-01

A method for flow estimation using synthetic aperture imaging and focusing along the flow direction is presented. The method can find the correct velocity magnitude for any flow angle, and full color flow images can be measured using only 32 to 128 pulse emissions. The approach uses spherical wave emissions with a number of defocused elements and a linear frequency-modulated pulse (chirp) to improve the signal-to-noise ratio. The received signals are dynamically focused along the flow direction and these signals are used in a cross-correlation estimator for finding the velocity magnitude. The flow angle is manually determined from the B-mode image. The approach can be used for both tissue and blood velocity determination. The approach was investigated using both simulations and a flow system with a laminar flow. The flow profile was measured with a commercial 7.5 MHz linear array transducer. A plastic tube with an internal diameter of 17 mm was used with an EcoWatt 1 pump generating a laminar, stationary flow. The velocity profile was measured for flow angles of 90 and 60 degrees. The RASMUS research scanner was used for acquiring radio frequency (RF) data from 128 elements of the array, using 8 emissions with 11 elements in each emission. A 20-micros chirp was used during emission. The RF data were subsequently beamformed off-line and stationary echo canceling was performed. The 60-degree flow with a peak velocity of 0.15 m/s was determined using 16 groups of 8 emissions, and the relative standard deviation was 0.36% (0.65 mm/s). Using the same setup for purely transverse flow gave a standard deviation of 1.2% (2.1 mm/s). Variation of the different parameters revealed the sensitivity to number of lines, angle deviations, length of correlation interval, and sampling interval. An in vivo image of the carotid artery and jugular vein of a healthy 29-year-old volunteer was acquired. A full color flow image using only 128 emissions could be made with a high-velocity precision.

Particle imaging velocimetry evaluation of intracranial stents in sidewall aneurysm: hemodynamic transition related to the stent design.

PubMed

Bouillot, Pierre; Brina, Olivier; Ouared, Rafik; Lovblad, Karl-Olof; Farhat, Mohamed; Pereira, Vitor Mendes

2014-01-01

We investigated the flow modifications induced by a large panel of commercial-off-the-shelf (COTS) intracranial stents in an idealized sidewall intracranial aneurysm (IA). Flow velocities in IA silicone model were assessed with and without stent implantation using particle imaging velocimetry (PIV). The use of the recently developed multi-time-lag method has allowed for uniform and precise measurements of both high and low velocities at IA neck and dome, respectively. Flow modification analysis of both regular (RSs) and flow diverter stents (FDSs) was subsequently correlated with relevant geometrical stent parameters. Flow reduction was found to be highly sensitive to stent porosity variations for regular stents RSs and moderately sensitive for FDSs. Consequently, two distinct IA flow change trends, with velocity reductions up to 50% and 90%, were identified for high-porosity RS and low-porosity FDS, respectively. The intermediate porosity (88%) regular braided stent provided the limit at which the transition in flow change trend occurred with a flow reduction of 84%. This transition occurred with decreasing stent porosity, as the driving force in IA neck changed from shear stress to differential pressure. Therefore, these results suggest that stents with intermediate porosities could possibly provide similar flow change patterns to FDS, favourable to curative thrombogenesis in IAs.

Theoretical modeling of electroosmotic flow in soft microchannels: A variational approach applied to the rectangular geometry

NASA Astrophysics Data System (ADS)

Sadeghi, Arman

2018-03-01

Modeling of fluid flow in polyelectrolyte layer (PEL)-grafted microchannels is challenging due to their two-layer nature. Hence, the pertinent studies are limited only to circular and slit geometries for which matching the solutions for inside and outside the PEL is simple. In this paper, a simple variational-based approach is presented for the modeling of fully developed electroosmotic flow in PEL-grafted microchannels by which the whole fluidic area is considered as a single porous medium of variable properties. The model is capable of being applied to microchannels of a complex cross-sectional area. As an application of the method, it is applied to a rectangular microchannel of uniform PEL properties. It is shown that modeling a rectangular channel as a slit may lead to considerable overestimation of the mean velocity especially when both the PEL and electric double layer (EDL) are thick. It is also demonstrated that the mean velocity is an increasing function of the fixed charge density and PEL thickness and a decreasing function of the EDL thickness and PEL friction coefficient. The influence of the PEL thickness on the mean velocity, however, vanishes when both the PEL thickness and friction coefficient are sufficiently high.

Pilot model expansion tunnel test flow properties obtained from velocity, pressure, and probe measurements

NASA Technical Reports Server (NTRS)

Friesen, W. J.; Moore, J. A.

1973-01-01

Velocity-profile, pitot-pressure, and supplemental probe measurements were made at the nozzle exist of an expansion tunnel (a modification to the Langley pilot model expansion tube) for a nozzle net condition of a nitrogen test sample with a velocity of 4.5 km/sec and a density 0.005 times the density of nitrogen at standard conditions, both with the nozzle initially immersed in a helium atmosphere and with the nozzle initially evacuated. The purpose of the report is to present the results of these measurements and some of the physical properties of the nitrogen test sample which can be inferred from the measured results. The main conclusions reached are that: the velocity profiles differ for two nozzle conditions; regions of the flow field can be found where the velocity is uniform to within 5 percent and constant for several hundred microseconds; the velocity of the nitrogen test sample is reduced due to passage through the nozzle; and the velocity profiles do not significantly reflect the large variations which occur in the inferred density profiles.

The Effect of Area Variation on Wave Rotor Elements

NASA Technical Reports Server (NTRS)

Wilson, Jack

1997-01-01

The effect of varying the cross-sectional flow area of the passages of a wave rotor is examined by means of the method of characteristics. An idealized expansion wave, an idealized inlet port, and an idealized compression stage are considered. It is found that area variation does not have a very significant effect on the expansion wave, nor on the compression stage. For the expansion wave, increasing the passage area in the flow direction has the same effect as a diffuser, so that the flow emerges at a lower velocity than it would for the constant area case. This could be advantageous. The inlet is strongly affected by the area variation, as it changes the strength of the hammer shock wave, thereby changing the pressure behind it. In this case, reduction in the passage area in the flow direction leads to increased pressure. However, this result is dependent on the assumption that the inlet conditions remain constant with area variation. This may not be the case.

Slip flow through a converging microchannel: experiments and 3D simulations

NASA Astrophysics Data System (ADS)

Varade, Vijay; Agrawal, Amit; Pradeep, A. M.

2015-02-01

An experimental and 3D numerical study of gaseous slip flow through a converging microchannel is presented in this paper. The measurements reported are with nitrogen gas flowing through the microchannel with convergence angles (4°, 8° and 12°), hydraulic diameters (118, 147 and 177 µm) and lengths (10, 20 and 30 mm). The measurements cover the entire slip flow regime and a part of the continuum and transition regimes (the Knudsen number is between 0.0004 and 0.14); the flow is laminar (the Reynolds number is between 0.5 and 1015). The static pressure drop is measured for various mass flow rates. The overall pressure drop increases with a decrease in the convergence angle and has a relatively large contribution of the viscous component. The numerical solutions of the Navier-Stokes equations with Maxwell’s slip boundary condition explore two different flow behaviors: uniform centerline velocity with linear pressure variation in the initial and the middle part of the microchannel and flow acceleration with nonlinear pressure variation in the last part of the microchannel. The centerline velocity and the wall shear stress increase with a decrease in the convergence angle. The concept of a characteristic length scale for a converging microchannel is also explored. The location of the characteristic length is a function of the Knudsen number and approaches the microchannel outlet with rarefaction. These results on gaseous slip flow through converging microchannels are observed to be considerably different than continuum flow.

Flow Environment Study Near the Empennage of a 15-Percent Scale Helicopter Model

NASA Technical Reports Server (NTRS)

Gorton, Susan Althoff; Berry, John D.; Hodges, W. Todd; Reis, Deane G.

2000-01-01

Development of advanced rotorcraft configurations has highlighted a need for high-quality experimental data to support the development of flexible and accurate analytical design tools. To provide this type of data, a test program was conducted in the Langley 14- by 22-Foot Subsonic Tunnel to measure the flow near the empennage of a 15-percent scale powered helicopter model with an operating tail fan. Three-component velocity profiles were measured with laser velocimetry (LV) one chord forward of the horizontal tail for four advance ratios to evaluate the effect of the rotor wake impingement on the horizontal tail angle of attack. These velocity data indicate the horizontal tail can experience unsteady angle of attack variations of over 30 degrees due to the rotor wake influence. The horizontal tail is most affected by the rotor wake above advance ratios of 0.10. Velocity measurements of the flow on the inlet side of the tail fan were made for a low-speed flight condition using conventional LV techniques. The velocity data show an accelerated flow near the tail fan duct, and vorticity calculations track the passage of main rotor wake vortices through the measurement plane.

Impact experiments in viscous fluid media

NASA Technical Reports Server (NTRS)

Greeley, R.

1984-01-01

Available phase and group velocity data are inverted by a procedure which includes the effects of transverse anisotropy, anelastic dispersion, sphericity, and gravity. The resulting models, for average Earth, average ocean, and oceanic regions divided according to the age of the ocean floor, are quite different from previous results which ignore the above effects. The models show a low-veocity zone with age dependent anisotropy and velocities higher than derived in previous surface wave studied. The correspondence between the anisotropy variation with age and a physical model based on flow aligned olivine is suggestive. For most of the Earth SHSV in the vicinity of the low-velocity zone. Near the East Pacific Rise, however, SVSH at depth, consistent with ascending flow. Anisotropy is as important as temperature in causing radial and lateral variations in velocity. The models have a high velocity nearly isotropic layer at the top of the mantle that thickens with age. This layer defines the LID, or seismic lithosphere. In the Pacific, the LID thickens with age to a maximum thickness of about 50 km. This thickness is comparable to the thickness of the elastic lithosphere. The LID thickness is thinner than derived using isotropic or pseudo-isotropic procedures A new model for Average Earth is obtained which includes a thin LID. This model extends the fit of a P.R.E.M. type model to shorter period surface waves.

Active and hibernating turbulence in minimal channel flow of newtonian and polymeric fluids.

PubMed

Xi, Li; Graham, Michael D

2010-05-28

Turbulent channel flow of drag-reducing polymer solutions is simulated in minimal flow geometries. Even in the Newtonian limit, we find intervals of "hibernating" turbulence that display many features of the universal maximum drag reduction asymptote observed in polymer solutions: weak streamwise vortices, nearly nonexistent streamwise variations, and a mean velocity gradient that quantitatively matches experiments. As viscoelasticity increases, the frequency of these intervals also increases, while the intervals themselves are unchanged, leading to flows that increasingly resemble maximum drag reduction.

Fish Passage in Large Culverts with Low Flows

DOT National Transportation Integrated Search

2014-08-01

A series of physical and numerical modeling runs were completed to support the development of a design procedure for characterizing the variation in velocity within non-embedded and embedded culverts. Physical modeling of symmetrical half-section cir...

Flow-Tagging Velocimetry for Hypersonic Flows Using Fluorescence of Nitric Oxide

NASA Technical Reports Server (NTRS)

Danehy, Paul M.; OByrne, Sean; Houwing, A. Frank P.; Fox, Jodie S.; Smith, Daniel R.

2003-01-01

We demonstrate a new variation of molecular-tagging velocimetry for hypersonic flows based on laser-induced fluorescence. A thin line of nitric-oxide molecules is excited with a laser beam and then, after a time delay, a fluorescence image of the displaced line is acquired. One component of velocity is determined from the time of flight. This method is applied to measure the velocity profile in a Mach 8.5 laminar, hypersonic boundary layer in the Australian National University s T2 free-piston shock tunnel. The single-shot velocity measurement uncertainty in the freestream was found to be 3.5%, based on 90% confidence. The method is also demonstrated in the separated flow region forward of a blunt fin attached to a flat plate in a Mach 7.4 flow produced by the Australian National University s T3 free-piston shock tunnel. The measurement uncertainty in the blunt fin experiment is approximately 30%, owing mainly to low fluorescence intensities, which could be improved significantly in future experiments. This velocimetry method is applicable to very high-speed flows that have low collisional quenching of the fluorescing species. It is particularly convenient in facilities where planar laser-induced fluorescence is already being performed.

Modified pressure loss model for T-junctions of engine exhaust manifold

NASA Astrophysics Data System (ADS)

Wang, Wenhui; Lu, Xiaolu; Cui, Yi; Deng, Kangyao

2014-11-01

The T-junction model of engine exhaust manifolds significantly influences the simulation precision of the pressure wave and mass flow rate in the intake and exhaust manifolds of diesel engines. Current studies have focused on constant pressure models, constant static pressure models and pressure loss models. However, low model precision is a common disadvantage when simulating engine exhaust manifolds, particularly for turbocharged systems. To study the performance of junction flow, a cold wind tunnel experiment with high velocities at the junction of a diesel exhaust manifold is performed, and the variation in the pressure loss in the T-junction under different flow conditions is obtained. Despite the trend of the calculated total pressure loss coefficient, which is obtained by using the original pressure loss model and is the same as that obtained from the experimental results, large differences exist between the calculated and experimental values. Furthermore, the deviation becomes larger as the flow velocity increases. By improving the Vazsonyi formula considering the flow velocity and introducing the distribution function, a modified pressure loss model is established, which is suitable for a higher velocity range. Then, the new model is adopted to solve one-dimensional, unsteady flow in a D6114 turbocharged diesel engine. The calculated values are compared with the measured data, and the result shows that the simulation accuracy of the pressure wave before the turbine is improved by 4.3% with the modified pressure loss model because gas compressibility is considered when the flow velocities are high. The research results provide valuable information for further junction flow research, particularly the correction of the boundary condition in one-dimensional simulation models.

On the relationship between the tree and its environment, based on electrical potential difference monitoring on trunk of trees

NASA Astrophysics Data System (ADS)

Koppan, A.; Fenyvesi, A.; Szarka, L.; Wesztergom, V.

2002-05-01

Electrical potential differences (EPD) in the trunk of a Turkey oak tree (measured by using non-polarising electrodes deepened in the sap wood) have been continuously recorded in the Geophysical Observatory "Istv n Széchenyi" of the Hungarian Academy of Sciences since 1997. Besides of various geophysical observations, meteorological and direct sap-flow measurements have also been carried out in the observatory. As it was found (Kopp n A., Szarka L., Wesztergom V., 2000: Annual fluctuation in amplitudes of daily variations of electrical signals measured in the trunk of a standing tree. C.R. Acad. Sci. Paris, Life Sciences 323, 559-563), the measured electric potential difference data have a characteristic sinusoidal daily fluctuation, and the intensity of the diurnal variations has a double-peak annual characteristics, which coincides with the life activity maximums of the tree. We have found a remarkable inter-correlation between trunk EPD, water potential of air (derived from meteorological data), and direct sap flow velocity data from a neighboring tree. All these results clearly demonstrate that the sap streaming due to the transpiration and root pressure generates the largest part of measured potential differences. The ratio of the flow velocity of a diluted solution forced through stems and the potential differences was found to be constant (Gindl, W., L”ppert, H.-G., Wimmer, R., 1999: Relationship between streaming potential and sap velocity in Salix alba L. Phyton, 39, 217-224.). On the contrary in our in-vivo experiments the relationship between the measured sap flow velocity and EPD is non-linear, which means that the conductivity (i.e. ion concentration) of the xylem sap itself also has a daily fluctuation.

A MEMS-based Air Flow Sensor with a Free-standing Micro-cantilever Structure

PubMed Central

Wang, Yu-Hsiang; Lee, Chia-Yen; Chiang, Che-Ming

2007-01-01

This paper presents a micro-scale air flow sensor based on a free-standing cantilever structure. In the fabrication process, MEMS techniques are used to deposit a silicon nitride layer on a silicon wafer. A platinum layer is deposited on the silicon nitride layer to form a piezoresistor, and the resulting structure is then etched to create a freestanding micro-cantilever. When an air flow passes over the surface of the cantilever beam, the beam deflects in the downward direction, resulting in a small variation in the resistance of the piezoelectric layer. The air flow velocity is determined by measuring the change in resistance using an external LCR meter. The experimental results indicate that the flow sensor has a high sensitivity (0.0284 Ω/ms-1), a high velocity measurement limit (45 ms-1) and a rapid response time (0.53 s). PMID:28903233

Decoupling structural and environmental determinants of sap velocity

NASA Astrophysics Data System (ADS)

Caylor, K. K.; Dragoni, D.

2007-12-01

Characterization of transpiration based on the water use of individual tress has the advantage of preserving vital information on the plant-environment functional links and flux partitioning between species and landscape areas. Whole-tree transpiration has been estimated by means of sap velocity probes, which offer the dual advantages of practicality and repeatability. However, the assumptions underlying the technique require careful verification in order to determine total sap flow from point-based estimates of sap velocity. Our work presents a novel theoretical framework for the study of individual tree sap flow that incorporates both spatial and temporal variability in sap velocities. The instantaneous sap velocity at any point in the radial profile of xylem tissue is defined as the product of two components: (1) a time-invariant sap velocity distribution linked to the species- specific anatomical and structural properties of the conducting xylem, and (2) a time-varying term linked to the dynamics of the atmospheric water demand and available soil moisture. The separation of structural and temporal variation in sap velocity observations provides a direct mechanism for investigating how sap flow is governed by variation in environmental conditions as well as a means for comparing characteristic rates of plant water use among individuals of varying size. Most critically, this approach allows for a consistent and physically meaningful method for extrapolating point observations of sap velocity across the entire depth of conducting xylem. Experimental evidence supports our theoretical framework in the case of a population of sugar maples in a mixed deciduous forest, where observations were taken from a wide range of tree sizes, under varying soil water availability and atmospheric transpiration demand. We have also applied our approach to a small homogeneous sample of dwarf apple trees in a managed orchard, with favorable results. While these results require further confirmation in order to be generalized, they nevertheless offer the basis to improve both the specific sampling strategies used to estimate whole-tree transpiration using sap velocity probes as well as methods employed to upscale water use of individual trees to larger scales for evaluation of landscape water balance.

Ion concentrations and velocity profiles in nanochannel electroosmotic flows

NASA Astrophysics Data System (ADS)

Qiao, R.; Aluru, N. R.

2003-03-01

Ion distributions and velocity profiles for electroosmotic flow in nanochannels of different widths are studied in this paper using molecular dynamics and continuum theory. For the various channel widths studied in this paper, the ion distribution near the channel wall is strongly influenced by the finite size of the ions and the discreteness of the solvent molecules. The classical Poisson-Boltzmann equation fails to predict the ion distribution near the channel wall as it does not account for the molecular aspects of the ion-wall and ion-solvent interactions. A modified Poisson-Boltzmann equation based on electrochemical potential correction is introduced to account for ion-wall and ion-solvent interactions. The electrochemical potential correction term is extracted from the ion distribution in a smaller channel using molecular dynamics. Using the electrochemical potential correction term extracted from molecular dynamics (MD) simulation of electroosmotic flow in a 2.22 nm channel, the modified Poisson-Boltzmann equation predicts the ion distribution in larger channel widths (e.g., 3.49 and 10.00 nm) with good accuracy. Detailed studies on the velocity profile in electro-osmotic flow indicate that the continuum flow theory can be used to predict bulk fluid flow in channels as small as 2.22 nm provided that the viscosity variation near the channel wall is taken into account. We propose a technique to embed the velocity near the channel wall obtained from MD simulation of electroosmotic flow in a narrow channel (e.g., 2.22 nm wide channel) into simulation of electroosmotic flow in larger channels. Simulation results indicate that such an approach can predict the velocity profile in larger channels (e.g., 3.49 and 10.00 nm) very well. Finally, simulation of electroosmotic flow in a 0.95 nm channel indicates that viscosity cannot be described by a local, linear constitutive relationship that the continuum flow theory is built upon and thus the continuum flow theory is not applicable for electroosmotic flow in such small channels.

Quantitative characterization of color Doppler images: reproducibility, accuracy, and limitations.

PubMed

Delorme, S; Weisser, G; Zuna, I; Fein, M; Lorenz, A; van Kaick, G

1995-01-01

A computer-based quantitative analysis for color Doppler images of complex vascular formations is presented. The red-green-blue-signal from an Acuson XP10 is frame-grabbed and digitized. By matching each image pixel with the color bar, color pixels are identified and assigned to the corresponding flow velocity (color value). Data analysis consists of delineation of a region of interest and calculation of the relative number of color pixels in this region (color pixel density) as well as the mean color value. The mean color value was compared to flow velocities in a flow phantom. The thyroid and carotid artery in a volunteer were repeatedly examined by a single examiner to assess intra-observer variability. The thyroids in five healthy controls were examined by three experienced physicians to assess the extent of inter-observer variability and observer bias. The correlation between the mean color value and flow velocity ranged from 0.94 to 0.96 for a range of velocities determined by pulse repetition frequency. The average deviation of the mean color value from the flow velocity was 22% to 41%, depending on the selected pulse repetition frequency (range of deviations, -46% to +66%). Flow velocity was underestimated with inadequately low pulse repetition frequency, or inadequately high reject threshold. An overestimation occurred with inadequately high pulse repetition frequency. The highest intra-observer variability was 22% (relative standard deviation) for the color pixel density, and 9.1% for the mean color value. The inter-observer variation was approximately 30% for the color pixel density, and 20% for the mean color value. In conclusion, computer assisted image analysis permits an objective description of color Doppler images. However, the user must be aware that image acquisition under in vivo conditions as well as physical and instrumental factors may considerably influence the results.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jackson, Scott I.

As detonation is a coupled fluid-chemical process, flow divergence inside the detonation reaction zone can strongly influence detonation velocity and energy release. Such divergence is responsible for the diameter-effect and failure-diameter phenomena in condensed-phase explosives and particularly dominant in detonation of nonideal explosives such as Ammonium Nitrate and Fuel Oil (ANFO). In this study, the effect of reaction zone flow divergence on ANFO detonation was explored through variation of the inert confinement and explosive diameter in the rate-stick geometry with cylinder expansion experiments. New tests are discussed and compared to prior experiments. Presented results include the detonation velocity as amore » function of diameter and confinement, reaction zone times, detonation product isentropes and energies, as well as sonic surface pressures and velocities. Product energy densities and isentropes were found to increase with detonation velocity, indicating more complete chemical reaction with increased detonation velocity. In addition, detonation reaction zone times were found to scale with the acoustic transit time of the confiner wall and used to show that the ANFO diameter effect scaled with the reaction zone time for a particle along the flow centerline, regardless of the confinement. Such a result indicates that the ANFO reaction mechanisms are sufficiently slow that the centerline fluid expansion timescale is a limiting factor controlling detonation velocity and energy release.« less

DSMC simulations of leading edge flat-plate boundary layer flows at high Mach number

NASA Astrophysics Data System (ADS)

Pradhan, Sahadev

2016-09-01

The flow over a 2D leading-edge flat plate is studied at Mach number Ma = (Uinf /√{kBTinf / m }) in the range

Discharge estimation from H-ADCP measurements in a tidal river subject to sidewall effects and a mobile bed

NASA Astrophysics Data System (ADS)

Sassi, M. G.; Hoitink, A. J. F.; Vermeulen, B.; Hidayat, null

2011-06-01

Horizontal acoustic Doppler current profilers (H-ADCPs) can be employed to estimate river discharge based on water level measurements and flow velocity array data across a river transect. A new method is presented that accounts for the dip in velocity near the water surface, which is caused by sidewall effects that decrease with the width to depth ratio of a channel. A boundary layer model is introduced to convert single-depth velocity data from the H-ADCP to specific discharge. The parameters of the model include the local roughness length and a dip correction factor, which accounts for the sidewall effects. A regression model is employed to translate specific discharge to total discharge. The method was tested in the River Mahakam, representing a large river of complex bathymetry, where part of the flow is intrinsically three-dimensional and discharge rates exceed 8000 m3 s-1. Results from five moving boat ADCP campaigns covering separate semidiurnal tidal cycles are presented, three of which are used for calibration purposes, whereas the remaining two served for validation of the method. The dip correction factor showed a significant correlation with distance to the wall and bears a strong relation to secondary currents. The sidewall effects appeared to remain relatively constant throughout the tidal cycles under study. Bed roughness length is estimated at periods of maximum velocity, showing more variation at subtidal than at intratidal time scales. Intratidal variations were particularly obvious during bidirectional flow conditions, which occurred only during conditions of low river discharge. The new method was shown to outperform the widely used index velocity method by systematically reducing the relative error in the discharge estimates.

Canonical fluid thermodynamics

NASA Technical Reports Server (NTRS)

Schmid, L. A.

1972-01-01

The space-time integral of the thermodynamic pressure plays the role of the thermodynamic potential for compressible, adiabatic flow in the sense that the pressure integral for stable flow is less than for all slightly different flows. This stability criterion can be converted into a variational minimum principle by requiring the molar free-enthalpy and the temperature, which are the arguments of the pressure function, to be generalized velocities, that is, the proper-time derivatives of scalar spare-time functions which are generalized coordinates in the canonical formalism. In a fluid context, proper-time differentiation must be expressed in terms of three independent quantities that specify the fluid velocity. This can be done in several ways, all of which lead to different variants (canonical transformations) of the same constraint-free action integral whose Euler-Lagrange equations are just the well-known equations of motion for adiabatic compressible flow.

The coupling between hydrodynamic and purification efficiencies of ecological porous spur-dike in field drainage ditch

NASA Astrophysics Data System (ADS)

Rao, Lei; Wang, Pei-fang; Dai, Qing-song; Wang, Chao

2018-05-01

In this study, a series of ecological porous spur-dikes are arranged in an experiment channel to simulate a real field drainage ditch. The inside and outside flow fields of spur-dikes are determined by numerical simulations and experimental methods. An Ammonia-Nitrogen (NH3-N) degradation evaluation model is built to calculate the pollution removal rate by coupling with the inner flow field of the porous spur-dikes. The variations of the total pollutant removal rate in the channel are discussed in terms of different porosities and gap distances between spur-dikes and inlet flow velocities. It is indicated that a reasonable parameter matching of the porosity and the gap distance with the flow velocity of the ditch can bring about a satisfactory purification efficiency with a small delivery quantity of ecological porous materials.

A MEMS-based Air Flow Sensor with a Free-standing Micro-cantilever Structure.

PubMed

Wang, Yu-Hsiang; Lee, Chia-Yen; Chiang, Che-Ming

2007-10-17

This paper presents a micro-scale air flow sensor based on a free-standingcantilever structure. In the fabrication process, MEMS techniques are used to deposit asilicon nitride layer on a silicon wafer. A platinum layer is deposited on the silicon nitridelayer to form a piezoresistor, and the resulting structure is then etched to create afreestanding micro-cantilever. When an air flow passes over the surface of the cantileverbeam, the beam deflects in the downward direction, resulting in a small variation in theresistance of the piezoelectric layer. The air flow velocity is determined by measuring thechange in resistance using an external LCR meter. The experimental results indicate that theflow sensor has a high sensitivity (0.0284 ω/ms -1 ), a high velocity measurement limit (45ms -1 ) and a rapid response time (0.53 s).

Temperature, Velocity, and Mean Turbulence Structure in Stongly-Heated Internal Gas Flows

DOE Office of Scientific and Technical Information (OSTI.GOV)

McEligot, Donald Marinus; Mikielewicz, D. P.; Shehata, A. M.

2002-10-01

The main objective of the present study is to examine whether "simple" turbulence models (i.e., models requiring two partial differential equations or less for turbulent transport) are suitable for use under conditions of forced flow of gas at low Reynolds numbers in tubes with intense heating, leading to large variations of fluid properties and considerable modification of turbulence. Eleven representative models are considered. The ability of such models to handle such flows was assessed by means of computational simulations of the carefully designed experiments of Shehata and McEligot (IJHMT 41 (1998) 4297) at heating rates of q+in˜0.0018, 0.0035 and 0.0045,more » yielding flows ranging from essentially turbulent to laminarized. The resulting comparisons of computational results with experiments showed that the model by Launder and Sharma (Lett. Heat Transfer 1 (1974) 131) performed best in predicting axial wall temperature profiles. Overall, agreement between the measured velocity and temperature distributions and those calculated using the Launder–Sharma model is good, which gives confidence in the values forecast for the turbulence quantities produced. These have been used to assist in arriving at a better understanding of the influences of intense heating, and hence strong variation of fluid properties, on turbulent flow in tubes.« less

Control of topography gradients on residence time distributions, mixing dynamics and reactive hotspot development

NASA Astrophysics Data System (ADS)

Bandopadhyay, Aditya; Le Borgne, Tanguy; Davy, Philippe

2017-04-01

Topography-driven subsurface flows are thought to play a central role in determining solute turnover and biogeochemical processes at different scales in the critical zone, including river-hyporheic zone exchanges, hillslope solute transport and reactions, and catchment biogeochemical cycles. Hydraulic head gradients, induced by topography gradients at different scales, generate a distribution of streamlines at depth, dictating the spatial distribution of redox sensitive species, the magnitude of surface water - ground water exchanges and ultimately the source/sink function of the subsurface. Flow velocities generally decrease with depth, leading to broad residence time distributions, which have been shown to affect river chemistry and geochemical reactions in catchments. In this presentation, we discuss the impact of topography-driven flows on mixing processes and the formation of localized reactive hotspots. For this, we solve analytically the coupled flow, mixing and reaction equations in two-dimensional vertical cross-sections of subsurface domains with different topography gradients. For a given topography gradient, we derive the spatial distribution of subsurface velocities, the rates of solute mixing accross streamlines and the induced kinetics of redox, precipitation and dissolution reactions using a Lagrangian approach (Le Borgne et al. 2014). We demonstrate that vertical velocity profiles driven by topography variations, act effectively as shear flows, hence stretching continuously the mixing fronts between recently infiltrated and resident water (Bandopadhyay et al. 2017). We thus derive analytical expressions for residence time distributions, mixing rates and kinetics of chemical reactions as a function of the topography gradients. We show that the rates dissolution and precipitation reactions are significantly enhanced by the existence of vertical velocity gradients and that reaction rates reach a maximum in a localized subsurface reactive layer, whose location and intensity depends on topography gradients. As a consequence of these findings, we discuss the links between topography variations, subsurface velocity gradients and biogeochemical processes in the critical zone. References: Bandopadhyay A., T. Le Borgne, Y. Méheust and M. Dentz (2017) Enhanced reaction kinetics and reactive mixing scale dynamics in mixing fronts under shear flow for arbitrary Damkohler numbers, Adv. in Water Resour. Vol. 100, p. 78-95 Le Borgne T., T. Ginn and M. Dentz (2014) Impact of Fluid Deformation on Mixing-Induced Chemical Reactions in Heterogeneous Flows, Geophys. Res. Lett., Vol. 41, 22, p. 7898-790

The Influence of Relative Submergence on the Near-bed Flow Field: Implications for Bed-load Transport

NASA Astrophysics Data System (ADS)

Cooper, J.; Tait, S.; Marion, A.

2005-12-01

Bed-load is governed by interdependent mechanisms, the most significant being the interaction between bed roughness, surface layer composition and near-bed flow. Despite this, practically all transport rate equations are described as a function of average bed shear stress. Some workers have examined the role of turbulence in sediment transport (Nelson et al. 1995) but have not explored the potential significance of spatial variations in the near-bed flow field. This is unfortunate considering evidence showing that transport is spatially heterogeneous and could be linked to the spatial nature of the near-bed flow (Drake et al., 1988). An understanding is needed of both the temporal and spatial variability in the near-bed flow field. This paper presents detailed spatial velocity measurements of the near-bed flow field over a gravel-bed, obtained using Particle Image Velocimetry. These data have been collected in a laboratory flume under two regimes: (i) tests with one bed slope and different flow depths; and (ii) tests with a combination of flow depths and slopes at the same average bed shear stress. Results indicate spatial variation in the streamwise velocities of up to 45 per cent from the double-averaged velocity (averaged in both time and space). Under both regimes, as the depth increased, spatial variability in the flow field increased. The probability distributions of near-bed streamwise velocities became progressively more skewed towards the higher velocities. This change was more noticeable under regime (i). This has been combined with data from earlier tests in which the near-bed velocity close to an entraining grain was measured using a PIV/image analysis system (Chegini et al, 2002). This along with data on the shape of the probability density function of velocities capable of entraining individual grains derived from a discrete-particle model (Heald et al., 2004) has been used to estimate the distribution of local velocities required for grain motion in the above tests. The overlap between this distribution and the measured velocities are used to estimate entrainment rates. Predicted entrainment rates increase with relative submergence, even for similar bed shear stress. Assuming bed-load rate is the product of entrainment rate and hop length, and that hop lengths are sensibly stable, suggests that transport rate has a dependence on relative submergence. This demonstrates that transport rate is not a direct function of average bed shear stress. The results describe a mechanism that will cause river channels with contrasting morphologies (and different relative submergence) but similar levels of average bed stress to experience different levels of sediment mobility. Chegini A. Tait S. Heald J. McEwan I. 2002 The development of an automated system for the measurement of near bed turbulence and grain motion. Proc. ASCE Conf. on Hydraulic Measurements and Experimental Methods, ISBN 0-7844-0655-3. Drake T.G. Shreve R.L. Dietrich W.E. Whiting P.J. Leopold L.B. 1988 Bedload transport of fine gravel observed by motion-picture photography, J. Fluid Mech., 192, 193-217. Heald J. McEwan I. Tait, S. 2004 Sediment transport over a flat bed in a unidirectional flow: simulations and validation, Phil. Trans. Roy. Soc. of London A, 362, 1973-1986. Nelson J.M. Shreve R.L. McLean S.R. Drake T.G. 1995 Role of near-bed turbulence structure in bed-load transport and bed form mechanics, Water. Res. Res., 31, 8, 2071-2086.

Hydrodynamics and inundation of a tidal saltmarsh in Kent County, Delaware

NASA Astrophysics Data System (ADS)

Pieterse, A.; Puleo, J. A.; McKenna, T. E.

2013-12-01

A 2-week field experiment was conducted in March and April 2013 in a tidal wetland in Kent County, Delaware. The study area was a tidal flat fed by a secondary channel of a small tributary of Delaware Bay. The goal of the field study was to investigate spatio-temporal variability in the hydrodynamics of the saltmarsh and tidal flat, over the period of one spring-neap tidal cycle. The experiment combined remotely-sensed imagery with high-frequency in-situ measurements. A tower with imagers (RGB, NIR, TIR) was deployed to quantify the spatial variations of inundation of the channels, flat and marsh. In-situ sensors that measured flow velocity, sediment concentration and water depth were deployed on the tidal flat and in the channels. At three locations, a Nortek Vectrino II - profiling velocimeter was deployed that measured a 30 mm velocity profile at 1 mm vertical increments at 100 Hz. These velocity profiles are used to compute turbulent kinetic energy, energy dissipation and stress profiles close to the bed. Preliminary results of the experiment show that peak velocities occur at the beginning of the rising and end of ebbing tide, when the water levels are low. At these instances, peaks in turbulence and bed stress also occur, which coincides with the largest sediment concentrations that were observed. During both rising and falling tide, flow velocities up to 0.4 m/s were observed in the main channel leading to the tidal flat. After these initial large flow velocities, the flat inundated very quickly, and flow velocities decreased. Furthermore, due to the large flow velocities, bed erosion often took place in the channel at the beginning of each high tide, while deposition occurred during ebbing tide, resulting in small net changes over the tidal cycle. The velocities in the channel relative to those on the adjacent flat were investigated. Furthermore, the relationship between near-bed turbulence and suspended sediment concentration and an analysis of the near-bed turbulence budget will be discussed.

Eta Carinae: X-ray Line Variations during the 2003 X-ray Minimum, and the Orbit Orientation

NASA Technical Reports Server (NTRS)

Corcoran, M. F.; Henley, D.; Hamaguchi, K.; Khibashi, K.; Pittard, J. M.; Stevens, I. R.; Gull, T. R.

2007-01-01

The future evolution of Eta Carinae will be as a supernova (or hypernova) and black hole. The evolution is highly contingent on mass and angular momentum changes and instabilities. The presence of a companion can serve to trigger instabilities and provide pathways for mass and angular momentum exchange loss. X-rays can be used a a key diagnostic tool: x-ray temperatures trace pre-shock wind velocities, periodic x-ray variability traces the orbit, and x-ray line variations traces the flow and orientation of shocked gas. This brief presentation highlights x-ray line variations from the HETG and presents a model of the colliding wind flow.

Variational analysis of drifter positions and model outputs for the reconstruction of surface currents in the central Adriatic during fall 2002

USGS Publications Warehouse

Taillandier, V.; Griffa, A.; Poulain, P.-M.; Signell, R.; Chiggiato, J.; Carniel, S.

2008-01-01

In this paper we present an application of a variational method for the reconstruction of the velocity field in a coastal flow in the central Adriatic Sea, using in situ data from surface drifters and outputs from the ROMS circulation model. The variational approach, previously developed and tested for mesoscale open ocean flows, has been improved and adapted to account for inhomogeneities on boundary current dynamics over complex bathymetry and coastline and for weak Lagrangian persistence in coastal flows. The velocity reconstruction is performed using nine drifter trajectories over 45 d, and a hierarchy of indirect tests is introduced to evaluate the results as the real ocean state is not known. For internal consistency and impact of the analysis, three diagnostics characterizing the particle prediction and transport, in terms of residence times in various zones and export rates from the boundary current toward the interior, show that the reconstruction is quite effective. A qualitative comparison with sea color data from the MODIS satellite images shows that the reconstruction significantly improves the description of the boundary current with respect to the ROMS model first guess, capturing its main features and its exchanges with the interior when sampled by the drifters. Copyright 2008 by the American Geophysical Union.

Tidal variations of flow convergence, shear, and stratification at the Rio de la Plata estuary turbidity front

NASA Astrophysics Data System (ADS)

FramiñAn, Mariana B.; Valle-Levinson, Arnoldo; Sepúlveda, HéCtor H.; Brown, Otis B.

2008-08-01

Intratidal variability of density and velocity fields is investigated at the turbidity front of the Río de la Plata Estuary, South America. Current velocity and temperature-salinity profiles collected in August 1999 along a repeated transect crossing the front are analyzed. Horizontal and vertical gradients, stability of the front, convergence zones, and transverse flow associated to the frontal boundary are described. Strong horizontal convergence of the across-front velocity and build up of along-front velocity shear were observed at the front. In the proximity of the front, enhanced transverse (or along-front) flow created jet-like structures at the surface and near the bottom flowing in opposite directions. These structures persisted throughout the tidal cycle and were advected upstream (downstream) by the flood (ebb) current through a distance of ˜10 km. During peak flood, the upper layer flow reversed from its predominant downstream direction and upstreamflow occupied the entire water column; outside the peak flood, two-layer estuarine circulation dominated. Changes in density field were observed in response to tidal straining, tidal advection, and wind-induced mixing, but stratification remained throughout the tidal cycle. This work demonstrates the large spatial variability of the velocity field at the turbidity front; it provides evidence of enhanced transverse circulation along the frontal boundary; and reveals the importance of advective and frictional intratidal processes in the dynamics of the central part of the estuary.

Effect of film slicks on near-surface wind

NASA Astrophysics Data System (ADS)

Charnotskii, Mikhail; Ermakov, Stanislav; Ostrovsky, Lev; Shomina, Olga

2016-09-01

The transient effects of horizontal variation of sea-surface wave roughness due to surfactant films on near-surface turbulent wind are studied theoretically and experimentally. Here we suggest two practical schemes for calculating variations of wind velocity profiles near the water surface, the average short-wave roughness of which is varying in space and time when a film slick is present. The schemes are based on a generalized two-layer model of turbulent air flow over a rough surface and on the solution of the continuous model involving the equation for turbulent kinetic energy of the air flow. Wave tank studies of wind flow over wind waves in the presence of film slicks are described and compared with theory.

Non-Axisymmetric Line Driven Disc Winds II - Full Velocity Gradient

NASA Astrophysics Data System (ADS)

Dyda, Sergei; Proga, Daniel

2018-05-01

We study non-axisymetric features of 3D line driven winds in the Sobolev approximation, where the optical depth is calculated using the full velocity gradient. We find that non-axisymmetric density features, so called clumps, form primarily at the base of the wind on super-Sobolev length scales. The density of clumps differs by a factor of ˜3 from the azimuthal average, the magnitude of their velocity dispersion is comparable to the flow velocity and they produce ˜20% variations in the column density. Clumps may be observable because differences in density produce enhancements in emission and absorption profiles or through their velocity dispersion which enhances line broadening.

Dense flow around a sphere moving into a cloud of grains

NASA Astrophysics Data System (ADS)

Gondret, Philippe; Faure, Sylvain; Lefebvre-Lepot, Aline; Seguin, Antoine

2017-06-01

A bidimensional simulation of a sphere moving at constant velocity into a cloud of smaller spherical grains without gravity is presented with a non-smooth contact dynamics method. A dense granular "cluster" zone of about constant solid fraction builds progressively around the moving sphere until a stationary regime appears with a constant upstream cluster size that increases with the initial solid fraction ϕ0 of the cloud. A detailed analysis of the local strain rate and local stress fields inside the cluster reveals that, despite different spatial variations of strain and stresses, the local friction coeffcient μ appears to depend only on the local inertial number I as well as the local solid fraction ϕ, which means that a local rheology does exist in the present non parallel flow. The key point is that the spatial variations of I inside the cluster does not depend on the sphere velocity and explore only a small range between about 10-2 and 10-1. The influence of sidewalls is then investigated on the flow and the forces.

An automated cell analysis sensing system based on a microfabricated rheoscope for the study of red blood cells physiology.

PubMed

Bransky, Avishay; Korin, Natanel; Nemirovski, Yael; Dinnar, Uri

2006-08-15

An automated rheoscope has been developed, utilizing a microfabricated glass flow cell, high speed camera and advanced image-processing software. RBCs suspended in a high viscosity medium were filmed flowing through a microchannel. Under these conditions, RBCs exhibit different orientations and deformations according to their location in the velocity profile. The rheoscope system produces valuable data such as velocity profile of RBCs, spatial distribution within a microchannel and deformation index (DI) curves. The variation of DI across the channel height, due to change in shear stress, was measured carrying implications for diffractometry methods. These curves of DI were taken at a constant flow rate and cover most of the relevant shear stress spectrum. This is an improvement of the existing techniques for deformability measurements and may serve as a diagnostic tool for certain blood disorders. The DI curves were compared to measurements of the flowing RBCs velocity profile. In addition, we found that RBCs flowing in a microchannel are mostly gathered in the center of the flow and maintain a characteristic spatial distribution. The spatial distribution in this region changes slightly with increasing flow rate. Hence, the system described, provides means for examining the behavior of individual RBCs, and may serve as a microfabricated diagnostic device for deformability measurement.

Optimal energy harvesting from vortex-induced vibrations of cables.

PubMed

Antoine, G O; de Langre, E; Michelin, S

2016-11-01

Vortex-induced vibrations (VIV) of flexible cables are an example of flow-induced vibrations that can act as energy harvesting systems by converting energy associated with the spontaneous cable motion into electricity. This work investigates the optimal positioning of the harvesting devices along the cable, using numerical simulations with a wake oscillator model to describe the unsteady flow forcing. Using classical gradient-based optimization, the optimal harvesting strategy is determined for the generic configuration of a flexible cable fixed at both ends, including the effect of flow forces and gravity on the cable's geometry. The optimal strategy is found to consist systematically in a concentration of the harvesting devices at one of the cable's ends, relying on deformation waves along the cable to carry the energy towards this harvesting site. Furthermore, we show that the performance of systems based on VIV of flexible cables is significantly more robust to flow velocity variations, in comparison with a rigid cylinder device. This results from two passive control mechanisms inherent to the cable geometry: (i) the adaptability to the flow velocity of the fundamental frequencies of cables through the flow-induced tension and (ii) the selection of successive vibration modes by the flow velocity for cables with gravity-induced tension.

Optimal energy harvesting from vortex-induced vibrations of cables

PubMed Central

de Langre, E.; Michelin, S.

2016-01-01

Vortex-induced vibrations (VIV) of flexible cables are an example of flow-induced vibrations that can act as energy harvesting systems by converting energy associated with the spontaneous cable motion into electricity. This work investigates the optimal positioning of the harvesting devices along the cable, using numerical simulations with a wake oscillator model to describe the unsteady flow forcing. Using classical gradient-based optimization, the optimal harvesting strategy is determined for the generic configuration of a flexible cable fixed at both ends, including the effect of flow forces and gravity on the cable’s geometry. The optimal strategy is found to consist systematically in a concentration of the harvesting devices at one of the cable’s ends, relying on deformation waves along the cable to carry the energy towards this harvesting site. Furthermore, we show that the performance of systems based on VIV of flexible cables is significantly more robust to flow velocity variations, in comparison with a rigid cylinder device. This results from two passive control mechanisms inherent to the cable geometry: (i) the adaptability to the flow velocity of the fundamental frequencies of cables through the flow-induced tension and (ii) the selection of successive vibration modes by the flow velocity for cables with gravity-induced tension. PMID:27956880

Optimal energy harvesting from vortex-induced vibrations of cables

NASA Astrophysics Data System (ADS)

Antoine, G. O.; de Langre, E.; Michelin, S.

2016-11-01

Vortex-induced vibrations (VIV) of flexible cables are an example of flow-induced vibrations that can act as energy harvesting systems by converting energy associated with the spontaneous cable motion into electricity. This work investigates the optimal positioning of the harvesting devices along the cable, using numerical simulations with a wake oscillator model to describe the unsteady flow forcing. Using classical gradient-based optimization, the optimal harvesting strategy is determined for the generic configuration of a flexible cable fixed at both ends, including the effect of flow forces and gravity on the cable's geometry. The optimal strategy is found to consist systematically in a concentration of the harvesting devices at one of the cable's ends, relying on deformation waves along the cable to carry the energy towards this harvesting site. Furthermore, we show that the performance of systems based on VIV of flexible cables is significantly more robust to flow velocity variations, in comparison with a rigid cylinder device. This results from two passive control mechanisms inherent to the cable geometry: (i) the adaptability to the flow velocity of the fundamental frequencies of cables through the flow-induced tension and (ii) the selection of successive vibration modes by the flow velocity for cables with gravity-induced tension.

The flame structure and vorticity generated by a chemically reacting transverse jet

NASA Technical Reports Server (NTRS)

Karagozian, A. R.

1986-01-01

An analytical model describing the behavior of a turbulent fuel jet injected normally into a cross flow is developed. The model places particular emphasis on the contrarotating vortex pair associated with the jet, and predicts the flame length and shape based on entrainment of the oxidizer by the fuel jet. Effects of buoyancy and density variations in the flame are neglected in order to isolate the effects of large-scale mixing. The results are compared with a simulation of the transverse reacting jet in a liquid (acid-base) system. For a wide range of ratios of the cross flow to jet velocity, the model predicts flame length quite well. In particular, the observed transitional behavior in the flame length between cross-flow velocity to jet velocity of orifice ratios of 0.0 to 0.1, yielding an approximate minimum at the ratio 0.05, is reproduced very clearly by the present model. The transformation in flow structure that accounts for this minimum arises from the differing components of vorticity dominant in the near-field and far-field regions of the jet.

Performance of a Compression-ignition Engine with a Precombustion Chamber Having High-Velocity Air Flow

NASA Technical Reports Server (NTRS)

Spanogle, J A; Moore, C S

1931-01-01

Presented here are the results of performance tests made with a single-cylinder, four stroke cycle, compression-ignition engine. These tests were made on a precombustion chamber type of cylinder head designed to have air velocity and tangential air flow in both the chamber and cylinder. The performance was investigated for variable load and engine speed, type of fuel spray, valve opening pressure, injection period and, for the spherical chamber, position of the injection spray relative to the air flow. The pressure variations between the pear-shaped precombustion chamber and the cylinder for motoring and full load conditions were determined with a Farnboro electric indicator. The combustion chamber designs tested gave good mixing of a single compact fuel spray with the air, but did not control the ensuing combustion sufficiently. Relative to each other, the velocity of air flow was too high, the spray dispersion by injection too great, and the metering effect of the cylinder head passage insufficient. The correct relation of these factors is of the utmost importance for engine performance.

On the Kolmogorov constant in stochastic turbulence models

NASA Astrophysics Data System (ADS)

Heinz, Stefan

2002-11-01

The Kolmogorov constant is fundamental in stochastic models of turbulence. To explain the reasons for observed variations of this quantity, it is calculated for two flows by various methods and data. Velocity fluctuations are considered as the sum of contributions due to anisotropy, acceleration fluctuations and stochastic forcing that is controlled by the Kolmogorov constant. It is shown that the effects of anisotropy and acceleration fluctuations are responsible for significant variations of the Kolmogorov constant. It is found near 2 for flows where anisotropy and acceleration fluctuations contribute to the energy budget, and near 6 if such contributions disappear.

Mathematical Simulation of Convective Processes in the Liquid Core of the Earth and Implications for the Interpretation of Geomagnetic Field Variations in Polar Latitudes

NASA Astrophysics Data System (ADS)

Abakumov, M. V.; Chechetkin, V. M.; Shalimov, S. L.

2018-05-01

The flow structure induced by thermal convection in a rotating spherical shell with viscous boundary conditions is considered under the assumption that the differential rotation of the core relative to the mantle is absent. The radial, azimuthal, and meridional components of the flow's velocity and helicity are studied. With the magnetic field assumed to be frozen into a liquid (frozen-flux hypothesis), it is shown that the numerical results fit the observations of the geomagnetic field variations close to the pole.

CFD analyses of coolant channel flowfields

NASA Technical Reports Server (NTRS)

Yagley, Jennifer A.; Feng, Jinzhang; Merkle, Charles L.

1993-01-01

The flowfield characteristics in rocket engine coolant channels are analyzed by means of a numerical model. The channels are characterized by large length to diameter ratios, high Reynolds numbers, and asymmetrical heating. At representative flow conditions, the channel length is approximately twice the hydraulic entrance length so that fully developed conditions would be reached for a constant property fluid. For the supercritical hydrogen that is used as the coolant, the strong property variations create significant secondary flows in the cross-plane which have a major influence on the flow and the resulting heat transfer. Comparison of constant and variable property solutions show substantial differences. In addition, the property variations prevent fully developed flow. The density variation accelerates the fluid in the channels increasing the pressure drop without an accompanying increase in heat flux. Analyses of the inlet configuration suggest that side entry from a manifold can affect the development of the velocity profile because of vortices generated as the flow enters the channel. Current work is focused on studying the effects of channel bifurcation on the flow field and the heat transfer characteristics.

Blood Flow Characterization According to Linear Wall Models of the Carotid Bifurcation

NASA Astrophysics Data System (ADS)

Williamson, Shobha; Rayz, Vitaliy; Berger, Stanley; Saloner, David

2004-11-01

Previous studies of the arterial wall include linearly isotropic, isotropic with residual stresses, and anisotropic models. This poses the question of how the results of each method differ when coupled with flow. Hence, the purpose of this study was to compare flow for these material models and subsequently determine if variations exist. Results show that displacement at the bifurcation and internal carotid bulb was noticeably larger in the orthotropic versus the isotropic model with subtle differences toward the inlet and outlets, which are fixed in space. In general, the orthotropic wall is further distended than the isotropic wall for the entire cycle. This apparent distention of the orthotropic wall clearly affects the flow. In diastole, the combination of slower flow and larger wall distention due to lumen pressure creates a sinuous velocity profile, particularly in the orthotropic model where the recirculation zone created displaces the core flow to a smaller area thereby increasing the velocity magnitudes nearly 60

Advection of nematic liquid crystals by chaotic flow

NASA Astrophysics Data System (ADS)

O'Náraigh, Lennon

2017-04-01

Consideration is given to the effects of inhomogeneous shear flow (both regular and chaotic) on nematic liquid crystals in a planar geometry. The Landau-de Gennes equation coupled to an externally prescribed flow field is the basis for the study: this is solved numerically in a periodic spatial domain. The focus is on a limiting case where the advection is passive, such that variations in the liquid-crystal properties do not feed back into the equation for the fluid velocity. The main tool for analyzing the results (both with and without flow) is the identification of the fixed points of the dynamical equations without flow, which are relevant (to varying degrees) when flow is introduced. The fixed points are classified as stable/unstable and further as either uniaxial or biaxial. Various models of passive shear flow are investigated. When tumbling is present, the flow is shown to have a strong effect on the liquid-crystal morphology; however, the main focus herein is on the case without tumbling. Accordingly, the main result of the work is that only the biaxial fixed point survives as a solution of the Q-tensor dynamics under the imposition of a general flow field. This is because the Q-tensor experiences not only transport due to advection but also co-rotation relative to the local vorticity field. A second result is that all families of fixed points survive for certain specific velocity fields, which we classify. We single out for close study those velocity fields for which the influence of co-rotation effectively vanishes along the Lagrangian trajectories of the imposed velocity field. In this scenario, the system exhibits coarsening arrest, whereby the liquid-crystal domains are "frozen in" to the flow structures, and the growth in their size is thus limited.

An inverse inviscid method for the design of quasi-three dimensional rotating turbomachinery cascades

NASA Technical Reports Server (NTRS)

Bonataki, E.; Chaviaropoulos, P.; Papailiou, K. D.

1991-01-01

A new inverse inviscid method suitable for the design of rotating blade sections lying on an arbitrary axisymmetric stream-surface with varying streamtube width is presented. The geometry of the axisymmetric stream-surface and the streamtube width variation with meridional distance, the number of blades, the inlet flow conditions, the rotational speed and the suction and pressure side velocity distributions as functions of the normalized arc-length are given. The flow is considered irrotational in the absolute frame of reference and compressible. The output of the computation is the blade section that satisfies the above data. The method solves the flow equations on a (phi 1, psi) potential function-streamfunction plane for the velocity modulus, W and the flow angle beta; the blade section shape can then be obtained as part of the physical plane geometry by integrating the flow angle distribution along streamlines. The (phi 1, psi) plane is defined so that the monotonic behavior of the potential function is guaranteed, even in cases with high peripheral velocities. The method is validated on a rotating turbine case and used to design new blades. To obtain a closed blade, a set of closure conditions were developed and referred.

Flow Control Application on a Submerged Inlet Characterized by Three-Component LDV

DTIC Science & Technology

2010-12-01

boundary layer deficit accounted for less variation in stresses experienced by the compressor blades . These studies demonstrate the effect of geometry on... deficit region provided the best results. The airspeed and inlet velocity simulated takeoff and landing conditions; velocities ranged from Mach 0.1-0.3...uniformity of the total pressure profile at the compressor face prevents fatigue loading of the blades as they rotate.(5) Pressure recovery directly

Influence of bulk turbulence and entrance boundary layer thickness on the curved duct flow field

NASA Technical Reports Server (NTRS)

Crawford, R. A.

1988-01-01

The influence of bulk turbulence and boundary layer thickness on the secondary flow development in a square, 90 degree turning duct was investigated. A three-dimensional laser velocimetry system was utilized to measure the mean and fluctuating components of velocity at six cross-planes in the duct. The results from this investigation, with entrance boundary layer thickness of 20 percent, were compared with the thin boundary layer results documented in NASA CR-174811. The axial velocity profiles, cross-flow velocities, and turbulence intensities were compared and evaluated with regard to the influence of bulk turbulence intensity and boundary layer thickness, and the influence was significant. The results of this investigation expand the 90 degree curved duct experimental data base to higher turbulence levels and thicker entrance boundary layers. The experimental results provide a challenging benchmark data base for computational fluid dynamics code development and validation. The variation of inlet bulk turbulence intensity provides additional information to aid in turbulence model evaluation.

An a-posteriori finite element error estimator for adaptive grid computation of viscous incompressible flows

NASA Astrophysics Data System (ADS)

Wu, Heng

2000-10-01

In this thesis, an a-posteriori error estimator is presented and employed for solving viscous incompressible flow problems. In an effort to detect local flow features, such as vortices and separation, and to resolve flow details precisely, a velocity angle error estimator e theta which is based on the spatial derivative of velocity direction fields is designed and constructed. The a-posteriori error estimator corresponds to the antisymmetric part of the deformation-rate-tensor, and it is sensitive to the second derivative of the velocity angle field. Rationality discussions reveal that the velocity angle error estimator is a curvature error estimator, and its value reflects the accuracy of streamline curves. It is also found that the velocity angle error estimator contains the nonlinear convective term of the Navier-Stokes equations, and it identifies and computes the direction difference when the convective acceleration direction and the flow velocity direction have a disparity. Through benchmarking computed variables with the analytic solution of Kovasznay flow or the finest grid of cavity flow, it is demonstrated that the velocity angle error estimator has a better performance than the strain error estimator. The benchmarking work also shows that the computed profile obtained by using etheta can achieve the best matching outcome with the true theta field, and that it is asymptotic to the true theta variation field, with a promise of fewer unknowns. Unstructured grids are adapted by employing local cell division as well as unrefinement of transition cells. Using element class and node class can efficiently construct a hierarchical data structure which provides cell and node inter-reference at each adaptive level. Employing element pointers and node pointers can dynamically maintain the connection of adjacent elements and adjacent nodes, and thus avoids time-consuming search processes. The adaptive scheme is applied to viscous incompressible flow at different Reynolds numbers. It is found that the velocity angle error estimator can detect most flow characteristics and produce dense grids in the regions where flow velocity directions have abrupt changes. In addition, the e theta estimator makes the derivative error dilutely distribute in the whole computational domain and also allows the refinement to be conducted at regions of high error. Through comparison of the velocity angle error across the interface with neighbouring cells, it is verified that the adaptive scheme in using etheta provides an optimum mesh which can clearly resolve local flow features in a precise way. The adaptive results justify the applicability of the etheta estimator and prove that this error estimator is a valuable adaptive indicator for the automatic refinement of unstructured grids.

An initial investigation of multidimensional flow and transverse mixing characteristics of the Ohio River near Cincinnati, Ohio

USGS Publications Warehouse

Holtschlag, David J.

2009-01-01

Two-dimensional hydrodynamic and transport models were applied to a 34-mile reach of the Ohio River from Cincinnati, Ohio, upstream to Meldahl Dam near Neville, Ohio. The hydrodynamic model was based on the generalized finite-element hydrodynamic code RMA2 to simulate depth-averaged velocities and flow depths. The generalized water-quality transport code RMA4 was applied to simulate the transport of vertically mixed, water-soluble constituents that have a density similar to that of water. Boundary conditions for hydrodynamic simulations included water levels at the U.S. Geological Survey water-level gaging station near Cincinnati, Ohio, and flow estimates based on a gate rating at Meldahl Dam. Flows estimated on the basis of the gate rating were adjusted with limited flow-measurement data to more nearly reflect current conditions. An initial calibration of the hydrodynamic model was based on data from acoustic Doppler current profiler surveys and water-level information. These data provided flows, horizontal water velocities, water levels, and flow depths needed to estimate hydrodynamic parameters related to channel resistance to flow and eddy viscosity. Similarly, dye concentration measurements from two dye-injection sites on each side of the river were used to develop initial estimates of transport parameters describing mixing and dye-decay characteristics needed for the transport model. A nonlinear regression-based approach was used to estimate parameters in the hydrodynamic and transport models. Parameters describing channel resistance to flow (Manning’s “n”) were estimated in areas of deep and shallow flows as 0.0234, and 0.0275, respectively. The estimated RMA2 Peclet number, which is used to dynamically compute eddy-viscosity coefficients, was 38.3, which is in the range of 15 to 40 that is typically considered appropriate. Resulting hydrodynamic simulations explained 98.8 percent of the variability in depth-averaged flows, 90.0 percent of the variability in water levels, 93.5 percent of the variability in flow depths, and 92.5 percent of the variability in velocities. Estimates of the water-quality-transport-model parameters describing turbulent mixing characteristics converged to different values for the two dye-injection reaches. For the Big Indian Creek dye-injection study, an RMA4 Peclet number of 37.2 was estimated, which was within the recommended range of 15 to 40, and similar to the RMA2 Peclet number. The estimated dye-decay coefficient was 0.323. Simulated dye concentrations explained 90.2 percent of the variations in measured dye concentrations for the Big Indian Creek injection study. For the dye-injection reach starting downstream from Twelvemile Creek, however, an RMA4 Peclet number of 173 was estimated, which is far outside the recommended range. Simulated dye concentrations were similar to measured concentration distributions at the first four transects downstream from the dye-injection site that were considered vertically mixed. Farther downstream, however, simulated concentrations did not match the attenuation of maximum concentrations or cross-channel transport of dye that were measured. The difficulty of determining a consistent RMA4 Peclet was related to the two-dimension model assumption that velocity distributions are closely approximated by their depth-averaged values. Analysis of velocity data showed significant variations in velocity direction with depth in channel reaches with curvature. Channel irregularities (including curvatures, depth irregularities, and shoreline variations) apparently produce transverse currents that affect the distribution of constituents, but are not fully accounted for in a two-dimensional model. The two-dimensional flow model, using channel resistance to flow parameters of 0.0234 and 0.0275 for deep and shallow areas, respectively, and an RMA2 Peclet number of 38.3, and the RMA4 transport model with a Peclet number of 37.2, may have utility for emergency-planning purposes. Emergency-response efforts would be enhanced by continuous streamgaging records downstream from Meldahl Dam, real-time water-quality monitoring, and three-dimensional modeling. Decay coefficients are constituent specific.

Prediction of aerodynamic noise in a ring fan based on wake characteristics

NASA Astrophysics Data System (ADS)

Sasaki, Soichi; Fukuda, Masaharu; Tsujino, Masao; Tsubota, Haruhiro

2011-06-01

A ring fan is a propeller fan that applies an axial-flow impeller with a ring-shaped shroud on the blade tip side. In this study, the entire flow field of the ring fan is simulated using computational fluid dynamics (CFD); the accuracy of the CFD is verified through a comparison with the aerodynamic characteristics of a propeller fan of current model. Moreover, the aerodynamic noise generated by the fan is predicted on the basis of the wake characteristics. The aerodynamic characteristic of the ring fan based on CFD can represent qualitatively the variation in the measured value. The main flow domain of the ring fan is formed at the tip side of the blade because blade tip vortex is not formed at that location. Therefore, the relative velocity of the ring fan is increased by the circumferential velocity. The sound pressure levels of the ring fan within the frequency band of less than 200 Hz are larger than that of the propeller fan. In the analysis of the wake characteristics, it revealed that Karman vortex shedding occurred in the main flow domain in the frequency domain lower than 200 Hz; the aerodynamic noise of the ring fan in the vortex shedding frequency enlarges due to increase in the relative velocity and the velocity fluctuation.

Computational Fluid Dynamics Analysis of Flexible Duct Junction Box Design

DOE Office of Scientific and Technical Information (OSTI.GOV)

Beach, Robert; Prahl, Duncan; Lange, Rich

2013-12-01

IBACOS explored the relationships between pressure and physical configurations of flexible duct junction boxes by using computational fluid dynamics (CFD) simulations to predict individual box parameters and total system pressure, thereby ensuring improved HVAC performance. Current Air Conditioning Contractors of America (ACCA) guidance (Group 11, Appendix 3, ACCA Manual D, Rutkowski 2009) allows for unconstrained variation in the number of takeoffs, box sizes, and takeoff locations. The only variables currently used in selecting an equivalent length (EL) are velocity of air in the duct and friction rate, given the first takeoff is located at least twice its diameter away frommore » the inlet. This condition does not account for other factors impacting pressure loss across these types of fittings. For each simulation, the IBACOS team converted pressure loss within a box to an EL to compare variation in ACCA Manual D guidance to the simulated variation. IBACOS chose cases to represent flows reasonably correlating to flows typically encountered in the field and analyzed differences in total pressure due to increases in number and location of takeoffs, box dimensions, and velocity of air, and whether an entrance fitting is included. The team also calculated additional balancing losses for all cases due to discrepancies between intended outlet flows and natural flow splits created by the fitting. In certain asymmetrical cases, the balancing losses were significantly higher than symmetrical cases where the natural splits were close to the targets. Thus, IBACOS has shown additional design constraints that can ensure better system performance.« less

Navier-Stokes Computations With One-Equation Turbulence Model for Flows Along Concave Wall Surfaces

NASA Technical Reports Server (NTRS)

Wang, Chi R.

2005-01-01

This report presents the use of a time-marching three-dimensional compressible Navier-Stokes equation numerical solver with a one-equation turbulence model to simulate the flow fields developed along concave wall surfaces without and with a downstream extension flat wall surface. The 3-D Navier- Stokes numerical solver came from the NASA Glenn-HT code. The one-equation turbulence model was derived from the Spalart and Allmaras model. The computational approach was first calibrated with the computations of the velocity and Reynolds shear stress profiles of a steady flat plate boundary layer flow. The computational approach was then used to simulate developing boundary layer flows along concave wall surfaces without and with a downstream extension wall. The author investigated the computational results of surface friction factors, near surface velocity components, near wall temperatures, and a turbulent shear stress component in terms of turbulence modeling, computational mesh configurations, inlet turbulence level, and time iteration step. The computational results were compared with existing measurements of skin friction factors, velocity components, and shear stresses of the developing boundary layer flows. With a fine computational mesh and a one-equation model, the computational approach could predict accurately the skin friction factors, near surface velocity and temperature, and shear stress within the flows. The computed velocity components and shear stresses also showed the vortices effect on the velocity variations over a concave wall. The computed eddy viscosities at the near wall locations were also compared with the results from a two equation turbulence modeling technique. The inlet turbulence length scale was found to have little effect on the eddy viscosities at locations near the concave wall surface. The eddy viscosities, from the one-equation and two-equation modeling, were comparable at most stream-wise stations. The present one-equation turbulence model is an effective approach for turbulence modeling in the near solid wall surface region of flow over a concave wall.

A measurement of perpendicular current density in an aurora

NASA Technical Reports Server (NTRS)

Bering, E. A.; Mozer, F. S.

1975-01-01

A Nike Tomahawk sounding rocket was launched into a 400-gamma auroral substorm from Esrange, Kiruna, Sweden. The rocket instrumentation included a split Langmuir-probe plasma-velocity detector and a double-probe electric-field detector. Above 140-km altitude, the electric field deduced from the ion-flow velocity measurement and the electric field measured by the double probe agree to an accuracy within the uncertainties of the two measurements. The difference between the two measurements at altitudes below 140 km provides an in situ measurement of current density and conductivity. Alternatively, if values for the conductivity are assumed, the neutral-wind velocity can be deduced. The height-integrated current was 0.11 A/m flowing at an azimuth angle of 276 deg. The neutral winds were strong, exhibited substantial altitude variation in the east-west component, and were predominantly southward.

Noninvasive assessment of normal carotid bifurcation hemodynamics with color-flow ultrasound imaging.

PubMed

Zierler, R E; Phillips, D J; Beach, K W; Primozich, J F; Strandness, D E

1987-08-01

The combination of a B-mode imaging system and a single range-gate pulsed Doppler flow velocity detector (duplex scanner) has become the standard noninvasive method for assessing the extracranial carotid artery. However, a significant limitation of this approach is the small area of vessel lumen that can be evaluated at any one time. This report describes a new duplex instrument that displays blood flow as colors superimposed on a real-time B-mode image. Returning echoes from a linear array of transducers are continuously processed for amplitude and phase. Changes in phase are produced by tissue motion and are used to calculate Doppler shift frequency. This results in a color assignment: red and blue indicate direction of flow with respect to the ultrasound beam, and lighter shades represent higher velocities. The carotid bifurcations of 10 normal subjects were studied. Changes in flow velocities across the arterial lumen were clearly visualized as varying shades of red or blue during the cardiac cycle. A region of flow separation was observed in all proximal internal carotids as a blue area located along the outer wall of the bulb. Thus, it is possible to detect the localized flow patterns that characterize normal carotid arteries. Other advantages of color-flow imaging include the ability to rapidly identify the carotid bifurcation branches and any associated anatomic variations.

Parametric Study of Sealant Nozzle

NASA Astrophysics Data System (ADS)

Yamamoto, Yoshimi

It has become apparent in recent years the advancement of manufacturing processes in the aerospace industry. Sealant nozzles are a critical device in the use of fuel tank applications for optimal bonds and for ground service support and repair. Sealants has always been a challenging area for optimizing and understanding the flow patterns. A parametric study was conducted to better understand geometric effects of sealant flow and to determine whether the sealant rheology can be numerically modeled. The Star-CCM+ software was used to successfully develop the parametric model, material model, physics continua, and simulate the fluid flow for the sealant nozzle. The simulation results of Semco sealant nozzles showed the geometric effects of fluid flow patterns and the influences from conical area reduction, tip length, inlet diameter, and tip angle parameters. A smaller outlet diameter induced maximum outlet velocity at the exit, and contributed to a high pressure drop. The conical area reduction, tip angle and inlet diameter contributed most to viscosity variation phenomenon. Developing and simulating 2 different flow models (Segregated Flow and Viscous Flow) proved that both can be used to obtain comparable velocity and pressure drop results, however; differences are seen visually in the non-uniformity of the velocity and viscosity fields for the Viscous Flow Model (VFM). A comprehensive simulation setup for sealant nozzles was developed so other analysts can utilize the data.

Computational Fluid Dynamics Study of Swimmer's Hand Velocity, Orientation, and Shape: Contributions to Hydrodynamics

PubMed Central

Bilinauskaite, Milda; Mantha, Vishveshwar Rajendra; Rouboa, Abel Ilah; Ziliukas, Pranas; Silva, Antonio Jose

2013-01-01

The aim of this paper is to determine the hydrodynamic characteristics of swimmer's scanned hand models for various combinations of both the angle of attack and the sweepback angle and shape and velocity of swimmer's hand, simulating separate underwater arm stroke phases of freestyle (front crawl) swimming. Four realistic 3D models of swimmer's hand corresponding to different combinations of separated/closed fingers positions were used to simulate different underwater front crawl phases. The fluid flow was simulated using FLUENT (ANSYS, PA, USA). Drag force and drag coefficient were calculated using (computational fluid dynamics) CFD in steady state. Results showed that the drag force and coefficient varied at the different flow velocities on all shapes of the hand and variation was observed for different hand positions corresponding to different stroke phases. The models of the hand with thumb adducted and abducted generated the highest drag forces and drag coefficients. The current study suggests that the realistic variation of both the orientation angles influenced higher values of drag, lift, and resultant coefficients and forces. To augment resultant force, which affects swimmer's propulsion, the swimmer should concentrate in effectively optimising achievable hand areas during crucial propulsive phases. PMID:23691493

Performance tests for the NASA Ames Research Center 20 cm x 40 cm oscillating flow wind tunnel

NASA Technical Reports Server (NTRS)

Cook, W. J.; Giddings, T. A.

1984-01-01

An evaluation is presented of initial tests conducted to assess the performance of the NASA Ames 20 cm x 40 cm oscillating flow wind tunnel. The features of the tunnel are described and two aspects of tunnel operation are discussed. The first is an assessment of the steady mainstream and boundary layer flows and the second deals with oscillating mainstream and boundary layer flows. Experimental results indicate that in steady flow the test section mainstream velocity is uniform in the flow direction and in cross section. The freestream turbulence intensity is about 0.2 percent. With minor exceptions the steady turbulent boundary layer generated on the top wall of the test section exhibits the characteristics of a zero pressure gradient turbulent boundary layer generated on a flat plate. The tunnel was designed to generate sinusoidal oscillating mainstream flows. Experiments confirm that the tunnel produces sinusoidal mainstream velocity variations for the range of frequencies (up to 15 Hz). The results of this study demonstrate that the tunnel essentially produces the flows that it was designed to produce.

Theoretical and Experimental Investigation of the Subsonic-Flow Fields Beneath Swept and Unswept Wings with Tables of Vortex-Induced Velocities

NASA Technical Reports Server (NTRS)

Alford, William J., Jr.

1956-01-01

The flow-field characteristics beneath swept and unswept wings as determined by potential-flow theory are compared with the experimentally determined flow fields beneath swept and unswept wing-fuselage combinations. The potential-flow theory utilized considered both spanwise and chordwise distributions of vorticity as well as the wing-thickness effects. The perturbation velocities induced by a unit horseshoe vortex are included in tabular form. The results indicated that significant chordwise flow gradients existed beneath both swept and unswept wings at zero lift and throughout the lift range. The theoretical predictions of the flow-field characteristics were qualitatively correct in all cases considered, although there were indications that the magnitudes of the downwash angles tended to be overpredicted as the tip of the swept wing was approached and that the sidewash angles ahead of the unswept wing were underpredicted. The calculated effects of compressibility indicated that significant increases in the chordwise variation of flow angles and dynamic-pressure ratios should be expected in going from low to high subsonic speeds.

Nonparallel stability of three-dimensional compressible boundary layers. Part 1: Stability analysis

NASA Technical Reports Server (NTRS)

El-Hady, N. M.

1980-01-01

A compressible linear stability theory is presented for nonparallel three-dimensional boundary-layer flows, taking into account the normal velocity component as well as the streamwise and spanwise variations of the basic flow. The method of multiple scales is used to account for the nonparallelism of the basic flow, and equations are derived for the spatial evolution of the disturbance amplitude and wavenumber. The numerical procedure for obtaining the solution of the nonparallel problem is outlined.

Effect of Intense Sound Waves on a Stationary Gas Flame

NASA Technical Reports Server (NTRS)

Hahnemann, H; Ehret, L

1950-01-01

Intense sound waves with a resonant frequency of 5000 cycles per second were imposed on a stationary propane-air flame issuing from a nozzle. In addition to a slight increase of the flame velocity, a fundamental change both in the shape of the burning zone and in the flow pattern could be observed. An attempt is made to explain the origin of the variations in the flame configuration on the basis of transition at the nozzle from jet flow to potential flow.

Simultaneous velocity and pressure quantification using pressure-sensitive flow tracers in air

NASA Astrophysics Data System (ADS)

Zhang, Peng; Peterson, Sean; Porfiri, Maurizio

2017-11-01

Particle-based measurement techniques for assessing the velocity field of a fluid have advanced rapidly over the past two decades. Full-field pressure measurement techniques have remained elusive, however. In this work, we aim to demonstrate the possibility of direct simultaneous planar velocity and pressure measurement of a high speed aerodynamic flow by employing novel pressure-sensitive tracer particles for particle image velocimetry (PIV). Specifically, the velocity and pressure variations of an airflow through a converging-diverging channel are studied. Polystyrene microparticles embedded with a pressure-sensitive phosphorescent dye-platinum octaethylporphyrin (PtOEP)-are used as seeding particles. Due to the oxygen quenching effect, the emission lifetime of PtOEP is highly sensitive to the oxygen concentration, that is, the partial pressure of oxygen, in the air. Since the partial pressure of oxygen is linearly proportional to the air pressure, we can determine the air pressure through the phosphorescence emission lifetime of the dye. The velocity field is instead obtained using traditional PIV methods. The particles have a pressure resolution on the order of 1 kPa, which may be improved by optimizing the particle size and dye concentration to suit specific flow scenarios. This work was supported by the National Science Foundation under Grant Number CBET-1332204.

The dependence of Ammonium-Nitrate Fuel-Oil (ANFO) detonation on confinement

DOE PAGES

Jackson, Scott I.

2016-11-17

As detonation is a coupled fluid-chemical process, flow divergence inside the detonation reaction zone can strongly influence detonation velocity and energy release. Such divergence is responsible for the diameter-effect and failure-diameter phenomena in condensed-phase explosives and particularly dominant in detonation of nonideal explosives such as Ammonium Nitrate and Fuel Oil (ANFO). In this study, the effect of reaction zone flow divergence on ANFO detonation was explored through variation of the inert confinement and explosive diameter in the rate-stick geometry with cylinder expansion experiments. New tests are discussed and compared to prior experiments. Presented results include the detonation velocity as amore » function of diameter and confinement, reaction zone times, detonation product isentropes and energies, as well as sonic surface pressures and velocities. Product energy densities and isentropes were found to increase with detonation velocity, indicating more complete chemical reaction with increased detonation velocity. In addition, detonation reaction zone times were found to scale with the acoustic transit time of the confiner wall and used to show that the ANFO diameter effect scaled with the reaction zone time for a particle along the flow centerline, regardless of the confinement. Such a result indicates that the ANFO reaction mechanisms are sufficiently slow that the centerline fluid expansion timescale is a limiting factor controlling detonation velocity and energy release.« less

Impact of Variations on 1-D Flow in Gas Turbine Engines via Monte Carlo Simulations

NASA Technical Reports Server (NTRS)

Ngo, Khiem Viet; Tumer, Irem

2004-01-01

The unsteady compressible inviscid flow is characterized by the conservations of mass, momentum, and energy; or simply the Euler equations. In this paper, a study of the subsonic one-dimensional Euler equations with local preconditioning is presented using a modal analysis approach. Specifically, this study investigates the behavior of airflow in a gas turbine engine using the specified conditions at the inflow and outflow boundaries of the compressor, combustion chamber, and turbine, to determine the impact of variations in pressure, velocity, temperature, and density at low Mach numbers. Two main questions motivate this research: 1) Is there any aerodynamic problem with the existing gas turbine engines that could impact aircraft performance? 2) If yes, what aspect of a gas turbine engine could be improved via design to alleviate that impact and to optimize aircraft performance? This paper presents an initial attempt to model the flow behavior in terms of their eigenfrequencies subject to the assumption of the uncertainty or variation (perturbation). The flow behavior is explored using simulation outputs from a customer-deck model obtained from Pratt & Whitney. Variations of the main variables (i.e., pressure, temperature, velocity, density) about their mean states at the inflow and outflow boundaries of the compressor, combustion chamber, and turbine are modeled. Flow behavior is analyzed for the high-pressure compressor and combustion chamber utilizing the conditions on their left and right boundaries. In the same fashion, similar analyses are carried out for the high-pressure and low-pressure turbines. In each case, the eigenfrequencies that are obtained for different boundary conditions are examined closely based on their probabilistic distributions, a result of a Monte Carlo 10,000 sample simulation. Furthermore, the characteristic waves and wave response are analyzed and contrasted among different cases, with and without preconditioners. The results reveal the existence of flow instabilities due to the combined effect of variations and excessive pressures in the case of the combustion chamber and high-pressure turbine. Finally, a discussion is presented on potential impacts of the instabilities and what can be improved via design to alleviate them for a better aircraft performance.

Towards a Copernicus Service for Monitoring Polar Ice Sheet Velocity and Discharge using Sentinel-1A and 1B SAR

NASA Astrophysics Data System (ADS)

Wuite, Jan; Nagler, Thomas; Hetzenecker, Markus; Blumthaler, Ursula; Ossowska, Joanna; Rott, Helmut

2017-04-01

The enhanced imaging capabilities of Sentinel-1A and 1B and the systematic acquisition planning of polar regions by ESA form the basis for the development and implementation of an operational system for monitoring ice dynamics and discharge of Antarctica, Greenland and other polar ice caps. Within the framework of the ESA CCI and the Austrian ASAP/FFG programs we implemented an automatic system for generation of ice velocity maps from repeat pass Sentinel-1 Terrain Observation by Progressive Scans (TOPS) mode data applying iterative offset tracking using both coherent and incoherent image cross-correlation. Greenland's margins are monitored by 6 tracks continuously since mid of 2015 with 12 days repeat observations using Sentinel-1A. With the twin satellite Sentinel-1B, launched in April 2016, the repeat acquisition period is reduced to only 6 days allowing frequent velocity retrievals - even in regions with high accumulation rates and very fast flow - and providing insight for studying short-term variations of ice flow and discharge. The Sentinel-1 ice velocity products continue the sparse coverage in time and space of previous velocity mapping efforts. The annual Greenland wide winter acquisition campaigns of 4 to 6 repeat track observations, acquired within a few weeks, provide nearly gapless and seamless ice sheet wide flow velocity maps on a yearly basis which are important for ice sheet modelling purposes and accurate mass balance assessments. An Antarctic ice sheet wide ice velocity map (with polar gap) was generated from Sentinel-1A data, acquired within 8 months, providing an important benchmark for gauging future changes in ice dynamics. For regions with significant warming continuous monitoring of ice streams with 6 to 12-day repeat intervals, exploiting both satellites, is ongoing to detect changes of ice flow as indicators of climate change. We present annual ice sheet wide velocity maps of Greenland from 2014/15 to 2016/17 and Antarctica from 2015/16 as well as dense time series of short-term velocity changes of outlet glaciers since 2014. We will highlight the improvements of the dual satellite constellation of Sentinel-1A and 1B, in particular for fast moving glaciers and regions with high accumulation rates. Derived surface velocities are combined with ice thickness from airborne Radio Echo Sounding data to compute ice discharge and its short-term variation across flux gates of major outlet glaciers in Greenland and Antarctica. Ice velocity maps, including dense time series for outlet glaciers, and ice discharge products are made available to registered users through our webtool at cryoportal.enveo.at.

Two-phase flow characteristics of liquid nitrogen in vertically upward 0.5 and 1.0 mm micro-tubes: Visualization studies

NASA Astrophysics Data System (ADS)

Zhang, P.; Fu, X.

2009-10-01

Application of liquid nitrogen to cooling is widely employed in many fields, such as cooling of the high temperature superconducting devices, cryosurgery and so on, in which liquid nitrogen is generally forced to flow inside very small passages to maintain good thermal performance and stability. In order to have a full understanding of the flow and heat transfer characteristics of liquid nitrogen in micro-tube, high-speed digital photography was employed to acquire the typical two-phase flow patterns of liquid nitrogen in vertically upward micro-tubes of 0.531 and 1.042 mm inner diameters. It was found from the experimental results that the flow patterns were mainly bubbly flow, slug flow, churn flow and annular flow. And the confined bubble flow, mist flow, bubble condensation and flow oscillation were also observed. These flow patterns were characterized in different types of flow regime maps. The surface tension force and the size of the diameter were revealed to be the major factors affecting the flow pattern transitions. It was found that the transition boundaries of the slug/churn flow and churn/annular flow of the present experiment shifted to lower superficial vapor velocity; while the transition boundary of the bubbly/slug flow shifted to higher superficial vapor velocity compared to the results of the room-temperature fluids in the tubes with the similar hydraulic diameters. The corresponding transition boundaries moved to lower superficial velocity when reducing the inner diameter of the micro-tubes. Time-averaged void fraction and heat transfer characteristics for individual flow patterns were presented and special attention was paid to the effect of the diameter on the variation of void fraction.

Spontaneous fluctuations in cerebral blood flow: insights from extended-duration recordings in humans

NASA Technical Reports Server (NTRS)

Zhang, R.; Zuckerman, J. H.; Levine, B. D.; Blomqvist, C. G. (Principal Investigator)

2000-01-01

To determine the dependence of cerebral blood flow (CBF) on arterial pressure over prolonged time periods, we measured beat-to-beat changes in mean CBF velocity in the middle cerebral artery (transcranial Doppler) and mean arterial pressure (Finapres) continuously for 2 h in six healthy subjects (5 men and 1 woman, 18-40 yr old) during supine rest. Fluctuations in velocity and pressure were quantified by the range [(peak - trough)/mean] and coefficients of variation (SD/mean) in the time domain and by spectral analysis in the frequency domain. Mean velocity and pressure over the 2-h recordings were 60 +/- 7 cm/s and 83 +/- 8 mmHg, associated with ranges of 77 +/- 8 and 89 +/- 10% and coefficients of variation of 9.3 +/- 2.2 and 7.9 +/- 2.3%, respectively. Spectral power of the velocity and pressure was predominantly distributed in the frequency range of 0.00014-0.1 Hz and increased inversely with frequency, indicating characteristics of an inverse power law (1/f(alpha)). However, linear regression on a log-log scale revealed that the slope of spectral power of pressure and velocity was steeper in the high-frequency (0.02-0.5 Hz) than in the low-frequency range (0.002-0.02 Hz), suggesting different regulatory mechanisms in these two frequency ranges. Furthermore, the spectral slope of pressure was significantly steeper than that of velocity in the low-frequency range, consistent with the low transfer function gain and low coherence estimated at these frequencies. We conclude that 1) long-term fluctuations in CBF velocity are prominent and similar to those observed in arterial pressure, 2) spectral power of CBF velocity reveals characteristics of 1/f(alpha), and 3) cerebral attenuation of oscillations in CBF velocity in response to changes in pressure may be more effective at low than that at high frequencies, emphasizing the frequency dependence of cerebral autoregulation.

Hydrogen and deuterium in the local interstellar medium

DOE Office of Scientific and Technical Information (OSTI.GOV)

Murthy, J.N.

1987-01-01

This work reports on the results of a series of IUE observations of interstellar HI and DI Ly..cap alpha.. absorption against the chromospheric Ly..cap alpha.. emission of the nearby late-type stars ..cap alpha.. Cen B(1.3 pc), epsilon Eri (3.3 pc), Procyon (3.5 pc), Altair (5.1 pc), Capella (13.2 pc), and HR 1099 (33 pc). The density, velocity dispersion, and bulk velocity of the neutral hydrogen along the line of sight to each of these stars was derived. Lower limits were placed on the deuterium-to-hydrogen (D/H) ratio towards the same stars. These IUE results are generally consistent with previous observations ofmore » the same stars with the Copernicus satellite showing that this modeling procedure is independent of stellar variations over a period of several years. The HI absorption profile towards Altair shows a broad saturated core and steep line wings, consistent with a multicomponent interstellar medium in that direction. The bulk velocities towards the other stars are consistent with a bulk flow from the approximate direction of the galactic center but do show local variations from a uniform flow, possibly indicating a complicated velocity structure even in the solar neighborhood. Interstellar deuterium is detected towards every star except Altair and the derived values for the D/H ratio are consistent with those previously found with Copernicus.« less

Colour flow and motion imaging.

PubMed

Evans, D H

2010-01-01

Colour flow imaging (CFI) is an ultrasound imaging technique whereby colour-coded maps of tissue velocity are superimposed on grey-scale pulse-echo images of tissue anatomy. The most widespread use of the method is to image the movement of blood through arteries and veins, but it may also be used to image the motion of solid tissue. The production of velocity information is technically more demanding than the production of the anatomical information, partly because the target of interest is often blood, which backscatters significantly less power than solid tissues, and partly because several transmit-receive cycles are necessary for each velocity estimate. This review first describes the various components of basic CFI systems necessary to generate the velocity information and to combine it with anatomical information. It then describes a number of variations on the basic autocorrelation technique, including cross-correlation-based techniques, power Doppler, Doppler tissue imaging, and three-dimensional (3D) Doppler imaging. Finally, a number of limitations of current techniques and some potential solutions are reviewed.

Ultrasound Velocity Measurements in High-Chromium Steel Under Plastic Deformation

NASA Astrophysics Data System (ADS)

Lunev, Aleksey; Bochkareva, Anna; Barannikova, Svetlana; Zuev, Lev

2016-04-01

In the present study, the variation of the propagation velocity of ultrasound in the plastic deformation of corrosion-resistant high-chromium steel 40X13 with ferrite-carbide (delivery status), martensitic (quenched) and sorbitol (after high-temperature tempering) structures have beem studied/ It is found that each state shows its view of the loading curve. In the delivery state diagram loading is substantially parabolic throughout, while in the martensitic state contains only linear strain hardening step and in the sorbitol state the plastic flow curve is three-step. The velocity of ultrasonic surface waves (Rayleigh waves) was measured simultaneously with the registration of the loading curve in the investigated steel in tension. It is shown that the dependence of the velocity of ultrasound in active loading is determined by the law of plastic flow, that is, the staging of the corresponding diagram of loading. Structural state of the investigated steel is not only changing the type of the deformation curve under uniaxial tension, but also changes the nature of ultrasound speed of deformation.

In vivo quantification of intraventricular flow during left ventricular assist device support

NASA Astrophysics Data System (ADS)

Vu, Vi; Wong, Kin; Del Alamo, Juan; Aguilo, Pablo M. L.; May-Newman, Karen; Department of Bioengineering, San Diego State University Collaboration; Department of Mechanical; Aerospace Engineering, University of California San Diego Collaboration; Mechanical Assist Device Program, Sharp Memorial Hospital Collaboration

2014-11-01

Left ventricular assist devices (LVADs) are mechanical pumps that are surgically connected to the left ventricle (LV) and aorta to increase aortic flow and end-organ perfusion. Clinical studies have demonstrated that LVADs improve patient health and quality of life and significantly reduce the mortality of cardiac failure. However, In the presence of left ventricular assisted devices (LVAD), abnormal flow patterns and stagnation regions are often linked to thrombosis. The aim of our study is to evaluate the flow patterns in the left ventricle of the LVAD-assisted heart, with a focus on alterations in vortex development and blood stasis. To this aim, we applied color Doppler echocardiography to measure 2D, time resolved velocity fields in patients before and after implantation of LVADs. In agreement with our previous in vitro studies (Wong et al., Journal of Biomechanics 47, 2014), LVAD implantation resulted in decreased flow velocities and increased blood residence time near the outflow tract. The variation of residence time changes with LVAD operational speed was characterized for each patient.

Measurement uncertainty budget of an interferometric flow velocity sensor

NASA Astrophysics Data System (ADS)

Bermuske, Mike; Büttner, Lars; Czarske, Jürgen

2017-06-01

Flow rate measurements are a common topic for process monitoring in chemical engineering and food industry. To achieve the requested low uncertainties of 0:1% for flow rate measurements, a precise measurement of the shear layers of such flows is necessary. The Laser Doppler Velocimeter (LDV) is an established method for measuring local flow velocities. For exact estimation of the flow rate, the flow profile in the shear layer is of importance. For standard LDV the axial resolution and therefore the number of measurement points in the shear layer is defined by the length of the measurement volume. A decrease of this length is accompanied by a larger fringe distance variation along the measurement axis which results in a rise of the measurement uncertainty for the flow velocity (uncertainty relation between spatial resolution and velocity uncertainty). As a unique advantage, the laser Doppler profile sensor (LDV-PS) overcomes this problem by using two fan-like fringe systems to obtain the position of the measured particles along the measurement axis and therefore achieve a high spatial resolution while it still offers a low velocity uncertainty. With this technique, the flow rate can be estimated with one order of magnitude lower uncertainty, down to 0:05% statistical uncertainty.1 And flow profiles especially in film flows can be measured more accurately. The problem for this technique is, in contrast to laboratory setups where the system is quite stable, that for industrial applications the sensor needs a reliable and robust traceability to the SI units, meter and second. Small deviations in the calibration can, because of the highly position depending calibration function, cause large systematic errors in the measurement result. Therefore, a simple, stable and accurate tool is needed, that can easily be used in industrial surroundings to check or recalibrate the sensor. In this work, different calibration methods are presented and their influences to the measurement uncertainty budget of the sensor is discussed. Finally, generated measurement results for the film flow of an impinging jet cleaning experiment are presented.

Variability of sap flow on forest hillslopes: patterns and controls

NASA Astrophysics Data System (ADS)

Hassler, Sibylle; Blume, Theresa

2013-04-01

Sap flow in trees is an essential variable in integrated studies of hydrologic fluxes. It gives indication of transpiration rates for single trees and, with a suitable method of upscaling, for whole stands. This information is relevant for hydrologic and climate models, especially for the prediction of change in water fluxes in the soil-plant-atmosphere continuum under climate change. To this end, we do not only need knowledge concerning the response of sapflow to atmospheric forcing but also an understanding of the main controls on its spatial variability. Our study site consists of several subcatchments of the Attert basin in Luxembourg underlain by schists of the Ardennes massif. Within these subcatchments we measure sap flow in more than 20 trees on a range of forested hillslopes covered by a variety of temperate deciduous tree species such as beech, oak, hornbeam and maple as well as conifers such as firs. Our sap flow sensors are based on the heat pulse velocity method and consist of three needles, one needle acting as the heating device and the other two holding three thermistors each, enabling us to simultaneously measure sap flow velocity at three different depths within the tree. In close proximity to the trees we collect additional data on soil moisture, matric potential and groundwater levels. First results show that the sensor design seems promising for an upscaling of the measured sap flow velocities to sap flow at the tree level. The maximum depth of actively used sapwood as well as the decrease in sap flow velocity with increasing depth in the tree can be determined by way of the three thermistors. Marked differences in sap flow velocity profiles are visible between the different species, resulting in differences in sap flow for trees of similar diameter. We examine the range of tree sap flow values and variation due to species, size class, slope position and exposition and finally relate them to the dynamics of soil moisture conditions with the goal to identify the most important controls of sap flow at our study site.

Inverse methods-based estimation of plate coupling in a plate motion model governed by mantle flow

NASA Astrophysics Data System (ADS)

Ratnaswamy, V.; Stadler, G.; Gurnis, M.

2013-12-01

Plate motion is primarily controlled by buoyancy (slab pull) which occurs at convergent plate margins where oceanic plates undergo deformation near the seismogenic zone. Yielding within subducting plates, lateral variations in viscosity, and the strength of seismic coupling between plate margins likely have an important control on plate motion. Here, we wish to infer the inter-plate coupling for different subduction zones, and develop a method for inferring it as a PDE-constrained optimization problem, where the cost functional is the misfit in plate velocities and is constrained by the nonlinear Stokes equation. The inverse models have well resolved slabs, plates, and plate margins in addition to a power law rheology with yielding in the upper mantle. Additionally, a Newton method is used to solve the nonlinear Stokes equation with viscosity bounds. We infer plate boundary strength using an inexact Gauss-Newton method with line search for backtracking. Each inverse model is applied to two simple 2-D scenarios (each with three subduction zones), one with back-arc spreading and one without. For each case we examine the sensitivity of the inversion to the amount of surface velocity used: 1) full surface velocity data and 2) surface velocity data simplified using a single scalar average (2-D equivalent to an Euler pole) for each plate. We can recover plate boundary strength in each case, even in the presence of highly nonlinear flow with extreme variations in viscosity. Additionally, we ascribe an uncertainty in each plate's velocity and perform an uncertainty quantification (UQ) through the Hessian of the misfit in plate velocities. We find that as plate boundaries become strongly coupled, the uncertainty in the inferred plate boundary strength decreases. For very weak, uncoupled subduction zones, the uncertainty of inferred plate margin strength increases since there is little sensitivity between plate margin strength and plate velocity. This result is significant because it implies we can infer which plate boundaries are more coupled (seismically) for a realistic dynamic model of plates and mantle flow.

The effect of atmospheric diabatic heating on low-frequency oscillations

NASA Astrophysics Data System (ADS)

Yen, Ming-Cheng

A diagnostic scheme is devised to illustrate a chain relationship between diabatic heating and planetary-scale divergent and rotational circulations. The scheme consists of the velocity-potential maintenance equation, which relates diabatic heating and velocity potential, and the streamfunction budget equation, which depicts the streamfunction tendency caused by the imbalance between streamfunction tendencies induced by vorticity advection and source. The proposed scheme is employed to examine the effect of tropical diabatic heating on the annual variation of subtropical jet streams. It was found that annual variations of both tropical diabatic heating and planetary-scale divergent circulation exhibit an annual in-phase seesaw oscillation between the winter and summer hemispheres. The annual variation of subtropical jet streams is caused by the adjustment of atmospheric rotational flow through planetary-scale divergent circulation in response to the annual cycle of tropical diabatic heating.

Conceptual definition of porosity function for coarse granular porous media with fixed texture

NASA Astrophysics Data System (ADS)

Shokri, Morteza

2018-06-01

Porous media's porosity value is commonly taken as a constant for a given granular texture free from any type of imposed loads. Although such definition holds for those media at hydrostatic equilibrium, it might not be hydrodynamically true for media subjected to the flow of fluids. This article casts light on an alternative vision describing porosity as a function of fluid velocity, though the media's solid skeleton does not undergo any changes and remain essentially intact. Carefully planned laboratory experiments support such as hypothesis and may help reducing reported disagreements between observed and actual behaviors of nonlinear flow regimes. Findings indicate that the so-called Stephenson relationship that enables estimating actual flow velocity is a case that holds true only for the Darcian conditions. In order to investigate the relationship, an accurate permeability should be measured. An alternative relationship, therefore, has been proposed to estimate actual pore flow velocity. On the other hand, with introducing the novel concept of effective porosity, that should be determined not only based on geotechnical parameters, but also it has to be regarded as a function of the flow regime. Such a porosity may be affected by the flow regime through variations in the effective pore volume and effective shape factor. In a numerical justification of findings, it is shown that unsatisfactory results, obtained from nonlinear mathematical models of unsteady flow, may be due to unreliable porosity estimates.

Backarc spreading and mantle wedge flow beneath the Japan Sea: insight from Rayleigh-wave anisotropic tomography

NASA Astrophysics Data System (ADS)

Liu, Xin; Zhao, Dapeng

2016-10-01

We present the first high-resolution Rayleigh-wave phase-velocity azimuthal anisotropy tomography of the Japan subduction zone at periods of 20-150 s, which is determined using a large number of high-quality amplitude and phase data of teleseismic fundamental-mode Rayleigh waves. The obtained 2-D anisotropic phase-velocity models are then inverted for a 3-D shear-wave velocity azimuthal anisotropy tomography down to a depth of ˜300 km beneath Japan. The subducting Pacific slab is imaged as a dipping high-velocity zone with trench-parallel fast-velocity directions (FVDs) which may indicate the anisotropy arising from the normal faults produced at the outer-rise area near the Japan trench axis, overprinting the slab fossil fabric, whereas the mantle wedge generally exhibits lower velocities with trench-normal FVDs which reflect subduction-driven corner flow and anisotropy. Depth variations of azimuthal anisotropy are revealed in the big mantle wedge beneath the Japan Sea, which may reflect past deformations in the Eurasian lithosphere related to backarc spreading during 21 to 15 Ma and complex current convection in the asthenosphere induced by active subductions of both the Pacific and Philippine Sea plates.

Method of model reduction and multifidelity models for solute transport in random layered porous media

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xu, Zhijie; Tartakovsky, Alexandre M.

This work presents a hierarchical model for solute transport in bounded layered porous media with random permeability. The model generalizes the Taylor-Aris dispersion theory to stochastic transport in random layered porous media with a known velocity covariance function. In the hierarchical model, we represent (random) concentration in terms of its cross-sectional average and a variation function. We derive a one-dimensional stochastic advection-dispersion-type equation for the average concentration and a stochastic Poisson equation for the variation function, as well as expressions for the effective velocity and dispersion coefficient. We observe that velocity fluctuations enhance dispersion in a non-monotonic fashion: the dispersionmore » initially increases with correlation length λ, reaches a maximum, and decreases to zero at infinity. Maximum enhancement can be obtained at the correlation length about 0.25 the size of the porous media perpendicular to flow.« less

Solar Radiation Patterns and Glaciers in the Western Himalaya

NASA Astrophysics Data System (ADS)

Dobreva, I. D.; Bishop, M. P.

2013-12-01

Glacier dynamics in the Himalaya are poorly understood, in part due to variations in topography and climate. It is well known that solar radiation is the dominant surface-energy component governing ablation, although the spatio-temporal patterns of surface irradiance have not been thoroughly investigated given modeling limitations and topographic variations including altitude, relief, and topographic shielding. Glaciation and topographic conditions may greatly influence supraglacial characteristics and glacial dynamics. Consequently, our research objectives were to develop a GIS-based solar radiation model that accounts for Earth's orbital, spectral, atmospheric and topographic dependencies, in order to examine the spatio-temporal surface irradiance patterns on glaciers in the western Himalaya. We specifically compared irradiance patterns to supraglacial characteristics and ice-flow velocity fields. Shuttle Radar Mapping Mission (SRTM) 90 m data were used to compute geomorphometric parameters that were input into the solar radiation model. Simulations results for 2013 were produced for the summer ablation season. Direct irradiance, diffuse-skylight, and total irradiance variations were compared and related to glacier altitude profiles of ice velocity and land-surface topographic parameters. Velocity and surface information were derived from analyses of ASTER satellite data. Results indicate that the direct irradiance significantly varies across the surface of glaciers given local topography and meso-scale relief conditions. Furthermore, the magnitude of the diffuse-skylight irradiance varies with altitude and as a result, glaciers in different topographic settings receive different amounts of surface irradiance. Spatio-temporal irradiance patterns appear to be related to glacier surface conditions including supraglacial lakes, and are spatially coincident with ice-flow velocity conditions on some glaciers. Collectively, our results demonstrate that glacier sensitivity to climate change is also locally controlled by numerous multi-scale topographic parameters.

Turbulence modeling in three-dimensional stenosed arterial bifurcations.

PubMed

Banks, J; Bressloff, N W

2007-02-01

Under normal healthy conditions, blood flow in the carotid artery bifurcation is laminar. However, in the presence of a stenosis, the flow can become turbulent at the higher Reynolds numbers during systole. There is growing consensus that the transitional k-omega model is the best suited Reynolds averaged turbulence model for such flows. Further confirmation of this opinion is presented here by a comparison with the RNG k-epsilon model for the flow through a straight, nonbifurcating tube. Unlike similar validation studies elsewhere, no assumptions are made about the inlet profile since the full length of the experimental tube is simulated. Additionally, variations in the inflow turbulence quantities are shown to have no noticeable affect on downstream turbulence intensity, turbulent viscosity, or velocity in the k-epsilon model, whereas the velocity profiles in the transitional k-omega model show some differences due to large variations in the downstream turbulence quantities. Following this validation study, the transitional k-omega model is applied in a three-dimensional parametrically defined computer model of the carotid artery bifurcation in which the sinus bulb is manipulated to produce mild, moderate, and severe stenosis. The parametric geometry definition facilitates a powerful means for investigating the effect of local shape variation while keeping the global shape fixed. While turbulence levels are generally low in all cases considered, the mild stenosis model produces higher levels of turbulent viscosity and this is linked to relatively high values of turbulent kinetic energy and low values of the specific dissipation rate. The severe stenosis model displays stronger recirculation in the flow field with higher values of vorticity, helicity, and negative wall shear stress. The mild and moderate stenosis configurations produce similar lower levels of vorticity and helicity.

Calculations on the forces and moments for an oscillating wing-aileron combination in two-dimensional potential flow at sonic speed

NASA Technical Reports Server (NTRS)

Nelson, Herbert C; Berman, Julian H

1953-01-01

The linearized theory for compressible unsteady flow is used, as suggested in recent contributions to the subject, to obtain the velocity potential and the lift and moment for a thin harmonically oscillating, two-dimensional wing-aileron combination moving at sonic speed. The velocity potential is derived by considering the sonic case as the limit of the linearized supersonic theory. From the velocity potential explicit expressions for the lift and moment are developed for vertical translation and pitching of the wing and rotation of the aileron. The sonic results are compared and found to be consistent with previously obtained subsonic and supersonic results. Several figures are presented showing the variation of lift and moment with reduced frequency and Mach number and the influence of Mach number on some cases of bending-torsion flutter.

Heart rate and blood pressure variations after transvascular patent ductus arteriosus occlusion in dogs.

PubMed

De Monte, Valentina; Staffieri, Francesco; Caivano, Domenico; Nannarone, Sara; Birettoni, Francesco; Porciello, Francesco; Di Meo, Antonio; Bufalari, Antonello

2017-08-01

The objective of the study was to retrospectively analyse the cardiovascular effects that occurs following the transvascular occlusion of patent ductus arteriosus in dogs. Sixteen anaesthesia records were included. Variables were recorded at the time of placing the arterial introducer, occlusion of the ductus, and from 5 to 60min thereafter, including, among the other, heart rate, systolic, diastolic and mean arterial blood pressure. The maximal percentage variation of the aforementioned physiological parameters within 60min of occlusion, compared with the values recorded at the introducer placing, was calculated. The time at which maximal variation occurred was also computed. Correlations between maximal percentage variation of physiological parameters and the diameter of the ductus and systolic and diastolic flow velocity through it were evaluated with linear regression analysis. Heart rate decreased after occlusion of the ductus with a mean maximal percentage variation of 41.0±14.8% after 21.2±13.7min. Mean and diastolic arterial blood pressure increased after occlusion with a mean maximal percentage variation of 30.6±18.1 and 55.4±27.1% after 19.6±12.1 and 15.7±10.8min, respectively. Mean arterial blood pressure variation had a significant and moderate inverse correlation with diastolic and systolic flow velocity through the ductus. Transvascular patent ductus arteriosus occlusion in anaesthetised dogs causes a significant reduction in heart rate and an increase in diastolic and mean blood arterial pressure within 20min of closure of the ductus. Copyright © 2017 Elsevier Ltd. All rights reserved.

A temporal PIV study of flame/obstacle generated vortex interactions within a semi-confined combustion chamber

NASA Astrophysics Data System (ADS)

Jarvis, S.; Hargrave, G. K.

2006-01-01

Experimental data obtained using a new multiple-camera digital particle image velocimetry (PIV) technique are presented for the interaction between a propagating flame and the turbulent recirculating velocity field generated during flame-solid obstacle interaction. The interaction between the gas movement and the obstacle creates turbulence by vortex shedding and local wake recirculations. The presence of turbulence in a flammable gas mixture can wrinkle a flame front, increasing the flame surface area and enhancing the burning rate. To investigate propagating flame/turbulence interaction, a novel multiple-camera digital PIV technique was used to provide high spatial and temporal characterization of the phenomenon for the turbulent flow field in the wake of three sequential obstacles. The technique allowed the quantification of the local flame speed and local flow velocity. Due to the accelerating nature of the explosion flow field, the wake flows develop 'transient' turbulent fields. Multiple-camera PIV provides data to define the spatial and temporal variation of both the velocity field ahead of the propagating flame and the flame front to aid the understanding of flame-vortex interaction. Experimentally obtained values for flame displacement speed and flame stretch are presented for increasing vortex complexity.

Finite Element Solution of Unsteady Mixed Convection Flow of Micropolar Fluid over a Porous Shrinking Sheet

PubMed Central

Gupta, Diksha; Singh, Bani

2014-01-01

The objective of this investigation is to analyze the effect of unsteadiness on the mixed convection boundary layer flow of micropolar fluid over a permeable shrinking sheet in the presence of viscous dissipation. At the sheet a variable distribution of suction is assumed. The unsteadiness in the flow and temperature fields is caused by the time dependence of the shrinking velocity and surface temperature. With the aid of similarity transformations, the governing partial differential equations are transformed into a set of nonlinear ordinary differential equations, which are solved numerically, using variational finite element method. The influence of important physical parameters, namely, suction parameter, unsteadiness parameter, buoyancy parameter and Eckert number on the velocity, microrotation, and temperature functions is investigated and analyzed with the help of their graphical representations. Additionally skin friction and the rate of heat transfer have also been computed. Under special conditions, an exact solution for the flow velocity is compared with the numerical results obtained by finite element method. An excellent agreement is observed for the two sets of solutions. Furthermore, to verify the convergence of numerical results, calculations are conducted with increasing number of elements. PMID:24672310

Computational Modeling of Seismic Wave Propagation Velocity-Saturation Effects in Porous Rocks

NASA Astrophysics Data System (ADS)

Deeks, J.; Lumley, D. E.

2011-12-01

Compressional and shear velocities of seismic waves propagating in porous rocks vary as a function of the fluid mixture and its distribution in pore space. Although it has been possible to place theoretical upper and lower bounds on the velocity variation with fluid saturation, predicting the actual velocity response of a given rock with fluid type and saturation remains an unsolved problem. In particular, we are interested in predicting the velocity-saturation response to various mixtures of fluids with pressure and temperature, as a function of the spatial distribution of the fluid mixture and the seismic wavelength. This effect is often termed "patchy saturation' in the rock physics community. The ability to accurately predict seismic velocities for various fluid mixtures and spatial distributions in the pore space of a rock is useful for fluid detection, hydrocarbon exploration and recovery, CO2 sequestration and monitoring of many subsurface fluid-flow processes. We create digital rock models with various fluid mixtures, saturations and spatial distributions. We use finite difference modeling to propagate elastic waves of varying frequency content through these digital rock and fluid models to simulate a given lab or field experiment. The resulting waveforms can be analyzed to determine seismic traveltimes, velocities, amplitudes, attenuation and other wave phenomena for variable rock models of fluid saturation and spatial fluid distribution, and variable wavefield spectral content. We show that we can reproduce most of the published effects of velocity-saturation variation, including validating the Voigt and Reuss theoretical bounds, as well as the Hill "patchy saturation" curve. We also reproduce what has been previously identified as Biot dispersion, but in fact in our models is often seen to be wave multi-pathing and broadband spectral effects. Furthermore, we find that in addition to the dominant seismic wavelength and average fluid patch size, the smoothness of the fluid patches are a critical factor in determining the velocity-saturation response; this is a result that we have not seen discussed in the literature. Most importantly, we can reproduce all of these effects using full elastic wavefield scattering, without the need to resort to more complicated squirt-flow or poroelastic models. This is important because the physical properties and parameters we need to model full elastic wave scattering, and predict a velocity-saturation curve, are often readily available for projects we undertake; this is not the case for poroelastic or squirt-flow models. We can predict this velocity saturation curve for a specific rock type, fluid mixture distribution and wavefield spectrum.

Leukocyte adhesion: High-speed cells with ABS.

PubMed

van der Merwe, P A

1999-06-03

In order to decide where to exit blood vessels and enter tissues, leukocytes roll along endothelial surfaces. Recent studies suggest that an 'automatic braking system' (ABS), involving selectin cell-adhesion molecules, enables leukocytes to roll at a fairly constant velocity despite large variations in blood flow rate.

Erratum: Evidence That a Deep Meridional Flow Sets the Sunspot Cycle Period

NASA Technical Reports Server (NTRS)

Hathaway, David H.; Nandy, Dibyendu; Wilson, Robert M.; Reichmann, Edwin J.

2004-01-01

An error was made in entering the data. This changes the results concerning the length of the time lag between the variations in the meridional flow speed and those in the cycle amplitude. The final paragraph on page 667 should read: Finally, we study the relationship between the drift velocities and the amplitudes of the hemisphere/cycles. We compare the drift velocity at the maximum of the cycle to the amplitude of that cycle for that hemisphere. There is a positive (0.5) and significant (95%) correlation between the two. However, an even stronger relationship is found between the drift velocity and the amplitude of the N + 2 cycle. The correlation is stronger (0.7) and more significant (99%), as shown. This relationship is suggestive of a "memory" in the solar cycle, again a property of dynamo models that use meridional circulation. Indeed, the two-cycle lag is precisely the relationship found by Charbonneau & Dikpati. This behavior is, however, more difficult to interpret, and we elaborate on this in the next section. In either case, these correlations only explain part of the variance in cycle amplitude (25% for the current cycle and 50% for the N + 2 cycle). Obviously, other mechanisms, such as variations in the gradient in the rotation rate, also contribute to the cycle amplitude variations. Our investigation of possible connections between drift rates and the amplitudes of the N + 1 and N + 3 cycles gives no significant correlations at these alternative time lags.

[The assessment of ultrasonic measurement of superior vena cava blood flow for the volume responsiveness of patients with mechanical ventilation].

PubMed

Guo, Zhe; He, Wei; Hou, Jing; Li, Tong; Zhou, Hua; Xu, Yuan; Xi, Xiuming

2014-09-01

To approach the evaluative effect of respiratory variation of superior vena cava peak flow velocity measured using transthoracic echocardiography (TTE) on fluid responsiveness in patients with mechanical ventilation. A prospective cohort study was conducted. All mechanical ventilated critically ill patients whose fluid therapy was planned due to hypovolemia in Department of Critical Care Medicine of Beijing Tongren Hospital of Capital Medical University from April 2011 to April 2013 were enrolled. Volume expansion was performed with 500 mL Linger solution within 30 minutes. Patients were classified as responders if pulse pressure variation (PPV) increased ≥ 13% before volume expansion. The respiratory variation in superior vena cava peak velocity was calculated as the difference between maximum and minimum values of velocity in peak A, peak S and peak D over a single respiratory circle, and their variations (ΔA, ΔS, ΔD) were also calculated. The receiver operating characteristic curve (ROC curve) was plotted to assess the evaluative effect of respiratory variation of superior vena cava peak velocity on fluid responsiveness. Twenty-seven patients were enrolled in this study. Volume expansion increased PPV ≥ 13% happened in 14 patients (responders). The velocity of superior vena cava in peak A, peak S, peak D was significantly increased after volume expansion compared with that before volume expansion in responders [peak A (cm/s): 34.6 ± 2.2 vs. 31.3 ± 2.1, t=-2.493, P=0.027; peak S (cm/s): 39.1 ± 1.3 vs. 35.3 ± 2.1, t=-2.564, P=0.024; peak D (cm/s): 28.1 ± 1.2 vs. 23.3 ± 1.4, t=-4.995, P=0.000], but there was no significant difference in ΔA, ΔS and ΔD between before and after volume expansion. The ΔA, ΔS and ΔD were positively correlated with PPV (r=0.040, P=0.854; r=0.350, P=0.074; r=0.749, P=0.000). The area under ROC curve (AUC) of peak S was 0.36 [95% confidence interval (95%CI): 0.11-0.52], but the AUC of ΔS was 0.68 (95%CI 0.47-0.89), the AUC of peak D was 0.41 (95%CI 0.19-0.63), but the AUC of ΔD was 0.95 (95%CI 0.86-1.00), so the aberration rate of superior vena cava in respiration was better than the flow rate in superior vena cava. When the cut-off value of ΔS was 20.7% for predicting fluid responsiveness, the sensitivity was 78.6% and the specificity was 61.5%. When the cut-off value of ΔD was 12.7% for predicting fluid responsiveness, the sensitivity was 92.0% and the specificity was 92.3%. Respiratory variations in superior vena cava peak velocity measured by TTE could assess fluid responsiveness in patients with mechanical ventilation.

Experimental study of a vertical jet in a vegetated crossflow.

PubMed

Ben Meftah, Mouldi; De Serio, Francesca; Malcangio, Daniela; Mossa, Michele; Petrillo, Antonio Felice

2015-12-01

Aquatic ecosystems have long been used as receiving environments of wastewater discharges. Effluent discharge in a receiving water body via single jet or multiport diffuser, reflects a number of complex phenomena, affecting the ecosystem services. Discharge systems need to be designed to minimize environmental impacts. Therefore, a good knowledge of the interaction between effluents, discharge systems and receiving environments is required to promote best environmental management practice. This paper reports innovative 3D flow velocity measurements of a jet discharged into an obstructed crossflow, simulating natural vegetated channel flows for which correct environmental management still lacks in literature. In recent years, numerous experimental and numerical studies have been conducted on vegetated channels, on the one hand, and on turbulent jets discharged into unvegetated crossflows, on the other hand. Despite these studies, however, there is a lack of information regarding jets discharged into vegetated crossflow. The present study aims at obtaining a more thorough understanding of the interaction between a turbulent jet and an obstructed crossflow. In order to achieve such an objective, a series of laboratory experiments was carried out in the Department of Civil, Environmental, Building Engineering and Chemistry of the Technical University of Bari - Italy. The physical model consists of a vertical jet discharged into a crossflow, obstructed by an array of vertical, rigid, circular and threaded steel cylinders. Analysis of the measured flow velocities shows that the array of emergent rigid vegetation significantly affects the jet and the ambient flow structures. It reduces the mean channel velocity, allowing the jet to penetrate higher into the crossflow. It significantly increases the transversal flow motion, promoting a major lateral spreading of the jet within the crossflow. Due to the vegetation array effects, the jet undergoes notable variations in its vortical structure. The variation of the flow patterns affects the mixing process and consequently the dilution of pollutants discharged in receiving water bodies. Copyright © 2015 Elsevier Ltd. All rights reserved.

A study of flow in alluvial channels: the effect of large concentrations of fine sediment on the mechanics of flow in a small flume

USGS Publications Warehouse

Haushild, William Leland; Simons, Daryl Baldwin; Richadrson, Everett V.

1961-01-01

concentration with the dune bed form and was increased by as much as 550 percent for the transition, standing wave, and antidune forms of bed roughness. Resistance to flow was less (C/√ g increased by 45 percent) with fine sediment-laden flow than with clear-water flow for the dune, and transition bed forms; and was greater (C/√ g   reduced by 25 percent) for the standing waves and the antidunes. A narrow range of bentonite concentration for each form of bed roughness was established as a limit below which only minor changes in bed form, bed material transport, and resistance to flow occurred. The variation of the liquid properties, specific weight and viscosity, for water-bentonite dispersions were studied and their effect on the properties of the bed material particles measured. The fall velocity of the particles in a dispersion of 100, 000 parts per million fine sediment in water was reduced to about one-half their fall velocity in clear water.

CFD analyses of coolant channel flowfields

NASA Technical Reports Server (NTRS)

Yagley, J. A.; Feng, J.; Merkle, Charles L.

1993-01-01

The flowfield characteristics in a rocket engine coolant channels are analyzed by means of a numerical model. The channels are characterized by large length to diameter ratios, high Reynolds numbers, and asymmetrical heating. At representative flow conditions, the channel length is approximately twice the hydraulic entrance length so fully developed conditions are reached. The supercritical hydrogen coolant introduces strong property variations that have a major influence on the developing flow and the resulting heat transfer. Comparisons of constant and variable property solutions show substantial differences. The density variation accelerates the fluid in the channels increasing the pressure drop without an accompanying increase in heat flux. Analyses of the inlet configuration suggest that side entry from a manifold can affect the development of the velocity profile because of vortices generated as the flow enters the channel.

Vertical variations of coral reef drag forces

NASA Astrophysics Data System (ADS)

Asher, Shai; Niewerth, Stephan; Koll, Katinka; Shavit, Uri; LWI Collaboration; Technion Collaboration

2017-11-01

Corals rely on water flow for the supply of nutrients, particles and energy. Therefore, modeling of processes that take place inside the reef, such as respiration and photosynthesis, relies on models that describe the flow and concentration fields. Due to the high spatial heterogeneity of branched coral reefs, depth average models are usually applied. Such an average approach is insufficient when the flow spatial variation inside the reef is of interest. We report on measurements of vertical variations of drag force that are needed for developing 3D flow models. Coral skeletons were densely arranged along a laboratory flume. Two corals were CT-scanned and replaced with horizontally sliced 3D printed replicates. Drag profiles were measured by connecting the slices to costume drag sensors and velocity profiles were measured using a LDV. The measured drag of whole colonies was in excellent agreement with previous studies; however, these studies never showed how drag varies inside the reef. In addition, these distributions of drag force showed an excellent agreement with momentum balance calculations. Based on the results, we propose a new drag model that includes the dispersive stresses, and consequently displays reduced vertical variations of the drag coefficient.

Sequence optimization to reduce velocity offsets in cardiovascular magnetic resonance volume flow quantification - A multi-vendor study

PubMed Central

2011-01-01

Purpose Eddy current induced velocity offsets are of concern for accuracy in cardiovascular magnetic resonance (CMR) volume flow quantification. However, currently known theoretical aspects of eddy current behavior have not led to effective guidelines for the optimization of flow quantification sequences. This study is aimed at identifying correlations between protocol parameters and the resulting velocity error in clinical CMR flow measurements in a multi-vendor study. Methods Nine 1.5T scanners of three different types/vendors were studied. Measurements were performed on a large stationary phantom. Starting from a clinical breath-hold flow protocol, several protocol parameters were varied. Acquisitions were made in three clinically relevant orientations. Additionally, a time delay between the bipolar gradient and read-out, asymmetric versus symmetric velocity encoding, and gradient amplitude and slew rate were studied in adapted sequences as exploratory measurements beyond the protocol. Image analysis determined the worst-case offset for a typical great-vessel flow measurement. Results The results showed a great variation in offset behavior among scanners (standard deviation among samples of 0.3, 0.4, and 0.9 cm/s for the three different scanner types), even for small changes in the protocol. Considering the absolute values, none of the tested protocol settings consistently reduced the velocity offsets below the critical level of 0.6 cm/s neither for all three orientations nor for all three scanner types. Using multilevel linear model analysis, oblique aortic and pulmonary slices showed systematic higher offsets than the transverse aortic slices (oblique aortic 0.6 cm/s, and pulmonary 1.8 cm/s higher than transverse aortic). The exploratory measurements beyond the protocol yielded some new leads for further sequence development towards reduction of velocity offsets; however those protocols were not always compatible with the time-constraints of breath-hold imaging and flow-related artefacts. Conclusions This study showed that with current systems there was no generic protocol which resulted into acceptable flow offset values. Protocol optimization would have to be performed on a per scanner and per protocol basis. Proper optimization might make accurate (transverse) aortic flow quantification possible for most scanners. Pulmonary flow quantification would still need further (offline) correction. PMID:21388521

A method to validate quantitative high-frequency power doppler ultrasound with fluorescence in vivo video microscopy.

PubMed

Pinter, Stephen Z; Kim, Dae-Ro; Hague, M Nicole; Chambers, Ann F; MacDonald, Ian C; Lacefield, James C

2014-08-01

Flow quantification with high-frequency (>20 MHz) power Doppler ultrasound can be performed objectively using the wall-filter selection curve (WFSC) method to select the cutoff velocity that yields a best-estimate color pixel density (CPD). An in vivo video microscopy system (IVVM) is combined with high-frequency power Doppler ultrasound to provide a method for validation of CPD measurements based on WFSCs in mouse testicular vessels. The ultrasound and IVVM systems are instrumented so that the mouse remains on the same imaging platform when switching between the two modalities. In vivo video microscopy provides gold-standard measurements of vascular diameter to validate power Doppler CPD estimates. Measurements in four image planes from three mice exhibit wide variation in the optimal cutoff velocity and indicate that a predetermined cutoff velocity setting can introduce significant errors in studies intended to quantify vascularity. Consistent with previously published flow-phantom data, in vivo WFSCs exhibited three characteristic regions and detectable plateaus. Selection of a cutoff velocity at the right end of the plateau yielded a CPD close to the gold-standard vascular volume fraction estimated using IVVM. An investigator can implement the WFSC method to help adapt cutoff velocity to current blood flow conditions and thereby improve the accuracy of power Doppler for quantitative microvascular imaging. Copyright © 2014 World Federation for Ultrasound in Medicine & Biology. Published by Elsevier Inc. All rights reserved.

Laminar flow in a microchannel with superhydrophobic walls exhibiting transverse ribs

NASA Astrophysics Data System (ADS)

Davies, J.; Maynes, D.; Webb, B. W.; Woolford, B.

2006-08-01

One approach recently proposed for reducing the frictional resistance to liquid flow in microchannels is the patterning of microribs and cavities on the channel walls. When treated with a hydrophobic coating, the liquid flowing in the microchannel wets only the surfaces of the ribs, and does not penetrate the cavities, provided the pressure is not too high. The net result is a reduction in the surface contact area between channel walls and the flowing liquid. For microribs and cavities that are aligned normal to the channel axis (principal flow direction), these micropatterns form a repeating, periodic structure. This paper presents results of a study exploring the momentum transport in a parallel-plate microchannel with such microengineered walls. The investigation explored the entire laminar flow Reynolds number range and characterized the influence of the vapor cavity depth on the overall flow field. The liquid-vapor interface (meniscus) in the cavity regions is treated as flat in the numerical analysis and two conditions are explored with regard to the cavity region: (1) The liquid flow at the liquid-vapor interface is treated as shear-free (vanishing viscosity in the vapor region), and (2) the liquid flow in the microchannel core and the vapor flow within the cavity are coupled by matching the velocity and shear stress at the interface. Regions of slip and no-slip behavior exist and the velocity field shows distinct variations from classical laminar flow in a parallel-plate channel. The local streamwise velocity profiles, interfacial velocity distributions, and maximum interfacial velocities are presented for a number of scenarios and provide a sound understanding of the local flow physics. The predictions and accompanying measurements reveal that significant reductions in the frictional pressure drop (enhancement in effective fluid slip at the channel walls) can be achieved relative to the classical smooth-channel Stokes flow. Reductions in the friction factor and enhancements in the fluid slip are greater as the cavity-to-rib length ratio is increased (increasing shear-free fraction) and as the channel hydraulic diameter is decreased. The results also show that the slip length and average friction factor-Reynolds number product exhibit a flow Reynolds dependence. Furthermore, the predictions reveal the global impact of the vapor cavity depth on the overall frictional resistance.

The influence of slope-angle ratio on the dynamics of granular flows: insights from laboratory experiments

NASA Astrophysics Data System (ADS)

Sulpizio, R.; Castioni, D.; Rodriguez-Sedano, L. A.; Sarocchi, D.; Lucchi, F.

2016-11-01

Laboratory experiments on granular flows using natural material were carried out in order to investigate the behaviour of granular flows passing over a break in slope. Sensors in the depositional area recorded the flow kinematics, while video footage permitted reconstruction of the deposit formation, which allowed investigation of the deposit shape as a function of the change in slope. We defined the slope-angle ratio as the proportion between slope angle in the depositional area and that of the channel. When the granular flow encounters the break in slope part of the flow front forms a bouncing clast zone due to elastic impact with the expansion box floor. During this process, part of the kinetic energy of the dense granular flow is transferred to elutriating fine ash, which subsequently forms turbulent ash cloud accompanying the granular flow until it comes to rest. Morphometric analysis of the deposits shows that they are all elliptical, with an almost constant minor axis and a variable major axis. The almost constant value of the minor axis relates to the spreading angle of flow at the end of the channel, which resembles the basal friction angle of the material. The variation of the major axis is interpreted to relate to the effect of competing inertial and frictional forces. This effect also reflects the partitioning of centripetal and tangential velocities, which changes as the flow passes over the break in slope. After normalization, morphometric data provided empirical relationships that highlight the dependence of runout from the product of slope-angle ratio and the difference in height between granular material release and deposit. The empirical relationships were tested against the runouts of hot avalanches formed during the 1944 ad eruption at Vesuvius, with differences among actual and calculated values are between 1.7 and 15 %. Velocity measurements of laboratory granular flows record deceleration paths at different breaks in slope. When normalized, the velocity data show third-order polynomial fit, highlighting a complex behaviour involving interplay between inertial and frictional forces. The theoretical velocity decays were tested against the data published for volcaniclastic debris flows of the 5-6 May 1998 event in the Sarno area. The comparison is very good for non-channelized debris flows, with significant differences between actual and calculated velocities for the channelized debris flows.

Toward predicting clay landslide with ambient seismic noise

NASA Astrophysics Data System (ADS)

Larose, E. F.; Mainsant, G.; Carriere, S.; Chambon, G.; Michoud, C.; Jongmans, D.; Jaboyedoff, M.

2013-12-01

Clay-rich pose critical problems in risk management worldwide. The most widely proposed mechanism leading to such flow-like movements is the increase in water pore pressure in the sliding mass, generating partial or complete liquefaction. This solid-to-liquid transition results in a dramatic reduction of mechanical rigidity, which could be detected by monitoring shear wave velocity variations, The ambient seismic noise correlation technique has been applied to measure the variation in the seismic surface wave velocity in the Pont Bourquin landslide (Swiss Alps). This small but active composite earthslide-earthflow was equipped with continuously recording seismic sensors during spring and summer 2010, and then again from fall 2011 on. An earthslide of a few thousand cubic meters was triggered in mid-August 2010, after a rainy period. This article shows that the seismic velocity of the sliding material, measured from daily noise correlograms, decreased continuously and rapidly for several days prior to the catastrophic event. From a spectral analysis of the velocity decrease, it was possible to determine the location of the change at the base of the sliding layer. These results are confirmed by analogous small-scale experiments in the laboratory. These results demonstrate that ambient seismic noise can be used to detect rigidity variations before failure and could potentially be used to predict landslides.

Flow behind an exponential shock wave in a rotational axisymmetric perfect gas with magnetic field and variable density.

PubMed

Nath, G; Sahu, P K

2016-01-01

A self-similar model for one-dimensional unsteady isothermal and adiabatic flows behind a strong exponential shock wave driven out by a cylindrical piston moving with time according to an exponential law in an ideal gas in the presence of azimuthal magnetic field and variable density is discussed in a rotating atmosphere. The ambient medium is assumed to possess radial, axial and azimuthal component of fluid velocities. The initial density, the fluid velocities and magnetic field of the ambient medium are assumed to be varying with time according to an exponential law. The gas is taken to be non-viscous having infinite electrical conductivity. Solutions are obtained, in both the cases, when the flow between the shock and the piston is isothermal or adiabatic by taking into account the components of vorticity vector. The effects of the variation of the initial density index, adiabatic exponent of the gas and the Alfven-Mach number on the flow-field behind the shock wave are investigated. It is found that the presence of the magnetic field have decaying effects on the shock wave. Also, it is observed that the effect of an increase in the magnetic field strength is more impressive in the case of adiabatic flow than in the case of isothermal flow. The assumption of zero temperature gradient brings a profound change in the density, non-dimensional azimuthal and axial components of vorticity vector distributions in comparison to those in the case of adiabatic flow. A comparison is made between isothermal and adiabatic flows. It is obtained that an increase in the initial density variation index, adiabatic exponent and strength of the magnetic field decrease the shock strength.

Flow pattern changes influenced by variation of viscosities of a heterogeneous gas-liquid mixture flow in a vertical channel

DOE Office of Scientific and Technical Information (OSTI.GOV)

Keska, Jerry K.; Hincapie, Juan; Jones, Richard

In the steady-state flow of a heterogeneous mixture such as an air-liquid mixture, the velocity and void fraction are space- and time-dependent parameters. These parameters are the most fundamental in the analysis and description of a multiphase flow. The determination of flow patterns in an objective way is extremely critical, since this is directly related to sudden changes in spatial and temporal changes of the random like characteristic of concentration. Flow patterns can be described by concentration signals in time, amplitude, and frequency domains. Despite the vital importance and countless attempts to solve or incorporate the flow pattern phenomena intomore » multiphase models, it has still been a very challenging topic in the scientific community since the 1940's and has not yet reached a satisfactory solution. This paper reports the experimental results of the impact of fluid viscosity on flow patterns for two-phase flow. Two-phase flow was created in laboratory equipment using air and liquid as phase medium. The liquid properties were changed by using variable concentrations of glycerol in water mixture which generated a wide-range of dynamic viscosities ranging from 1 to 1060 MPa s. The in situ spatial concentration vs. liquid viscosity and airflow velocity of two-phase flow in a vertical ID=50.8 mm pipe were measured using two concomitant computer-aided measurement systems. After acquiring data, the in situ special concentration signals were analyzed in time (spatial concentration and RMS of spatial concentration vs. time), amplitude (PDF and CPDF), and frequency (PSD and CPSD) domains that documented broad flow pattern changes caused by the fluid viscosity and air velocity changes. (author)« less

Measuring retinal blood flow in rats using Doppler optical coherence tomography without knowing eyeball axial length

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Wenzhong; Yi, Ji; Chen, Siyu

Purpose: Doppler optical coherence tomography (OCT) is widely used for measuring retinal blood flow. Existing Doppler OCT methods require the eyeball axial length, in which empirical values are usually used. However, variations in the axial length can create a bias unaccounted for in the retinal blood flow measurement. The authors plan to develop a Doppler OCT method that can measure the total retinal blood flow rate without requiring the eyeball axial length. Methods: The authors measured the retinal blood flow rate using a dual-ring scanning protocol. The small and large scanning rings entered the eye at different incident angles (smallmore » ring: 4°; large ring: 6°), focused on different locations on the retina, and detected the projected velocities/phase shifts along the probing beams. The authors calculated the ratio of the projected velocities between the two rings, and then used this ratio to estimate absolute flow velocity. The authors tested this method in both Intralipid phantoms and in vivo rats. Results: In the Intralipid flow phantom experiments, the preset and measured flow rates were consistent with the coefficient of determination as 0.97. Linear fitting between preset and measured flow rates determined the fitting slope as 1.07 and the intercept as −0.28. In in vivo rat experiments, the measured average total retinal blood flow was 7.02 ± 0.31μl/min among four wild-type rats. The authors’ measured flow rates were consistent with results in the literature. Conclusions: By using a dual-ring scanning protocol with carefully controlled incident angle difference between the two scanning rings in Doppler OCT, the authors demonstrated that it is feasible to measure the absolute retinal blood flow without knowing the eyeball axial length.« less

Measuring retinal blood flow in rats using Doppler optical coherence tomography without knowing eyeball axial length

PubMed Central

Liu, Wenzhong; Yi, Ji; Chen, Siyu; Jiao, Shuliang; Zhang, Hao F.

2015-01-01

Purpose: Doppler optical coherence tomography (OCT) is widely used for measuring retinal blood flow. Existing Doppler OCT methods require the eyeball axial length, in which empirical values are usually used. However, variations in the axial length can create a bias unaccounted for in the retinal blood flow measurement. The authors plan to develop a Doppler OCT method that can measure the total retinal blood flow rate without requiring the eyeball axial length. Methods: The authors measured the retinal blood flow rate using a dual-ring scanning protocol. The small and large scanning rings entered the eye at different incident angles (small ring: 4°; large ring: 6°), focused on different locations on the retina, and detected the projected velocities/phase shifts along the probing beams. The authors calculated the ratio of the projected velocities between the two rings, and then used this ratio to estimate absolute flow velocity. The authors tested this method in both Intralipid phantoms and in vivo rats. Results: In the Intralipid flow phantom experiments, the preset and measured flow rates were consistent with the coefficient of determination as 0.97. Linear fitting between preset and measured flow rates determined the fitting slope as 1.07 and the intercept as −0.28. In in vivo rat experiments, the measured average total retinal blood flow was 7.02 ± 0.31μl/min among four wild-type rats. The authors’ measured flow rates were consistent with results in the literature. Conclusions: By using a dual-ring scanning protocol with carefully controlled incident angle difference between the two scanning rings in Doppler OCT, the authors demonstrated that it is feasible to measure the absolute retinal blood flow without knowing the eyeball axial length. PMID:26328984

Measuring retinal blood flow in rats using Doppler optical coherence tomography without knowing eyeball axial length.

PubMed

Liu, Wenzhong; Yi, Ji; Chen, Siyu; Jiao, Shuliang; Zhang, Hao F

2015-09-01

Doppler optical coherence tomography (OCT) is widely used for measuring retinal blood flow. Existing Doppler OCT methods require the eyeball axial length, in which empirical values are usually used. However, variations in the axial length can create a bias unaccounted for in the retinal blood flow measurement. The authors plan to develop a Doppler OCT method that can measure the total retinal blood flow rate without requiring the eyeball axial length. The authors measured the retinal blood flow rate using a dual-ring scanning protocol. The small and large scanning rings entered the eye at different incident angles (small ring: 4°; large ring: 6°), focused on different locations on the retina, and detected the projected velocities/phase shifts along the probing beams. The authors calculated the ratio of the projected velocities between the two rings, and then used this ratio to estimate absolute flow velocity. The authors tested this method in both Intralipid phantoms and in vivo rats. In the Intralipid flow phantom experiments, the preset and measured flow rates were consistent with the coefficient of determination as 0.97. Linear fitting between preset and measured flow rates determined the fitting slope as 1.07 and the intercept as -0.28. In in vivo rat experiments, the measured average total retinal blood flow was 7.02 ± 0.31 μl/min among four wild-type rats. The authors' measured flow rates were consistent with results in the literature. By using a dual-ring scanning protocol with carefully controlled incident angle difference between the two scanning rings in Doppler OCT, the authors demonstrated that it is feasible to measure the absolute retinal blood flow without knowing the eyeball axial length.

River banks and channel axis curvature: Effects on the longitudinal dispersion in alluvial rivers

NASA Astrophysics Data System (ADS)

Lanzoni, Stefano; Ferdousi, Amena; Tambroni, Nicoletta

2018-03-01

The fate and transport of soluble contaminants released in natural streams are strongly dependent on the spatial variations of the flow field and of the bed topography. These variations are essentially related to the presence of the channel banks and to the planform configuration of the channel. Large velocity gradients arise near to the channel banks, where the flow depth decreases to zero. Moreover, single thread alluvial rivers are seldom straight, and usually exhibit meandering planforms and a bed topography that deviates from the plane configuration. Channel axis curvature and movable bed deformations drive secondary helical currents which enhance both cross sectional velocity gradients and transverse mixing, thus crucially influencing longitudinal dispersion. The present contribution sets up a rational framework which, assuming mild sloping banks and taking advantage of the weakly meandering character often exhibited by natural streams, leads to an analytical estimate of the contribution to longitudinal dispersion associated with spatial non-uniformities of the flow field. The resulting relationship stems from a physics-based modeling of the flow in natural rivers, and expresses the bend averaged longitudinal dispersion coefficient as a function of the relevant hydraulic and morphologic parameters. The treatment of the problem is river specific, since it relies on an explicit spatial description, although linearized, of the flow field that establishes in the investigated river. Comparison with field data available from tracer tests supports the robustness of the proposed framework, given also the complexity of the processes that affect dispersion dynamics in real streams.

Simultaneous imaging of blood flow dynamics and vascular remodelling during development.

PubMed

Ghaffari, Siavash; Leask, Richard L; Jones, Elizabeth A V

2015-12-01

Normal vascular development requires blood flow. Time-lapse imaging techniques have revolutionised our understanding of developmental biology, but measuring changes in blood flow dynamics has met with limited success. Ultrasound biomicroscopy and optical coherence tomography can concurrently image vascular structure and blood flow velocity, but these techniques lack the resolution to accurately calculate fluid forces such as shear stress. This is important because hemodynamic forces are biologically active and induce changes in the expression of genes important for vascular development. Regional variations in shear stress, rather than the overall level, control processes such as vessel enlargement and regression during vascular remodelling. We present a technique to concurrently visualise vascular remodelling and blood flow dynamics. We use an avian embryonic model and inject an endothelial-specific dye and fluorescent microspheres. The motion of the microspheres is captured with a high-speed camera and the velocity of the blood flow in and out of the region of interest is quantified by micro-particle image velocitymetry (µPIV). The vessel geometry and flow are used to numerically solve the flow physics with computational fluid dynamics (CFD). Using this technique, we can analyse changes in shear stress, pressure drops and blood flow velocities over a period of 10 to 16 h. We apply this to study the relationship between shear stress and chronic changes in vessel diameter during embryonic development, both in normal development and after TGFβ stimulation. This technique allows us to study the interaction of biomolecular and biomechanical signals during vascular remodelling using an in vivo developmental model. © 2015. Published by The Company of Biologists Ltd.

Time-dependent onshore tsunami response

USGS Publications Warehouse

Apotsos, Alex; Gelfenbaum, Guy R.; Jaffe, Bruce E.

2012-01-01

While bulk measures of the onshore impact of a tsunami, including the maximum run-up elevation and inundation distance, are important for hazard planning, the temporal evolution of the onshore flow dynamics likely controls the extent of the onshore destruction and the erosion and deposition of sediment that occurs. However, the time-varying dynamics of actual tsunamis are even more difficult to measure in situ than the bulk parameters. Here, a numerical model based on the non-linear shallow water equations is used to examine the effects variations in the wave characteristics, bed slope, and bottom roughness have on the temporal evolution of the onshore flow. Model results indicate that the onshore flow dynamics vary significantly over the parameter space examined. For example, the flow dynamics over steep, smooth morphologies tend to be temporally symmetric, with similar magnitude velocities generated during the run-up and run-down phases of inundation. Conversely, on shallow, rough onshore topographies the flow dynamics tend to be temporally skewed toward the run-down phase of inundation, with the magnitude of the flow velocities during run-up and run-down being significantly different. Furthermore, for near-breaking tsunami waves inundating over steep topography, the flow velocity tends to accelerate almost instantaneously to a maximum and then decrease monotonically. Conversely, when very long waves inundate over shallow topography, the flow accelerates more slowly and can remain steady for a period of time before beginning to decelerate. These results indicate that a single set of assumptions concerning the onshore flow dynamics cannot be applied to all tsunamis, and site specific analyses may be required.

Application of computational fluid dynamics to closed-loop bioreactors: I. Characterization and simulation of fluid-flow pattern and oxygen transfer.

PubMed

Littleton, Helen X; Daigger, Glen T; Strom, Peter F

2007-06-01

A full-scale, closed-loop bioreactor (Orbal oxidation ditch, Envirex brand technologies, Siemens, Waukesha, Wisconsin), previously examined for simultaneous biological nutrient removal (SBNR), was further evaluated using computational fluid dynamics (CFD). A CFD model was developed first by imparting the known momentum (calculated by tank fluid velocity and mass flowrate) to the fluid at the aeration disc region. Oxygen source (aeration) and sink (consumption) terms were introduced, and statistical analysis was applied to the CFD simulation results. The CFD model was validated with field data obtained from a test tank and a full-scale tank. The results indicated that CFD could predict the mixing pattern in closed-loop bioreactors. This enables visualization of the flow pattern, both with regard to flow velocity and dissolved-oxygen-distribution profiles. The velocity and oxygen-distribution gradients suggested that the flow patterns produced by directional aeration in closed-loop bioreactors created a heterogeneous environment that can result in dissolved oxygen variations throughout the bioreactor. Distinct anaerobic zones on a macroenvironment scale were not observed, but it is clear that, when flow passed around curves, a secondary spiral flow was generated. This second current, along with the main recirculation flow, could create alternating anaerobic and aerobic conditions vertically and horizontally, which would allow SBNR to occur. Reliable SBNR performance in Orbal oxidation ditches may be a result, at least in part, of such a spatially varying environment.

Phase diagram of congested traffic flow: An empirical study

PubMed

Lee; Lee; Kim

2000-10-01

We analyze traffic data from a highway section containing one effective on-ramp. Based on two criteria, local velocity variation patterns and expansion (or nonexpansion) of congested regions, three distinct congested traffic states are identified. These states appear at different levels of the upstream flux and the on-ramp flux, thereby generating a phase digram of the congested traffic flow. Observed traffic states are compared with recent theoretical analyses and both agreeing and disagreeing features are found.

A scientific report on heat transfer analysis in mixed convection flow of Maxwell fluid over an oscillating vertical plate.

PubMed

Khan, Ilyas; Shah, Nehad Ali; Dennis, L C C

2017-03-15

This scientific report investigates the heat transfer analysis in mixed convection flow of Maxwell fluid over an oscillating vertical plate with constant wall temperature. The problem is modelled in terms of coupled partial differential equations with initial and boundary conditions. Some suitable non-dimensional variables are introduced in order to transform the governing problem into dimensionless form. The resulting problem is solved via Laplace transform method and exact solutions for velocity, shear stress and temperature are obtained. These solutions are greatly influenced with the variation of embedded parameters which include the Prandtl number and Grashof number for various times. In the absence of free convection, the corresponding solutions representing the mechanical part of velocity reduced to the well known solutions in the literature. The total velocity is presented as a sum of both cosine and sine velocities. The unsteady velocity in each case is arranged in the form of transient and post transient parts. It is found that the post transient parts are independent of time. The solutions corresponding to Newtonian fluids are recovered as a special case and comparison between Newtonian fluid and Maxwell fluid is shown graphically.

Verification of drag-reduction capabilities of stiff compliant coatings in air flow at moderate speeds

NASA Astrophysics Data System (ADS)

Boiko, Andrey V.; Kulik, Victor M.; Chun, Ho-Hwan; Lee, Inwon

2011-12-01

Skin frictional drag reduction efficiency of "stiff" compliant coating was investigated in a wind tunnel experiment. Flat plate compliant coating inserts were installed in a wind tunnel and the measurements of skin frictional drag and velocity field were carried out. The compliant coatings with varying viscoelastic properties had been prepared using different composition. In order to optimize the coating thickness, the most important design parameter, the dynamic viscoelastic properties had been determined experimentally. The aging of the materials (variation of their properties) during half a year was documented as well. A design procedure proposed by Kulik et al. (2008) was applied to get an optimal value for the coating thickness. Along with the drag measurement using the strain balance, velocity and pressure were measured for different coatings. The compliant coatings with the thickness h = 7mm achieved 4~5% drag reduction within a velocity range 30~40 m/s. The drag reduction mechanism of the attenuation of turbulence velocity fluctuations due to the compliant coating was demonstrated. It is envisioned that larger drag reduction effect is obtainable at higher flow velocities for high speed trains and subsonic aircrafts.

A scientific report on heat transfer analysis in mixed convection flow of Maxwell fluid over an oscillating vertical plate

NASA Astrophysics Data System (ADS)

Khan, Ilyas; Shah, Nehad Ali; Dennis, L. C. C.

2017-03-01

This scientific report investigates the heat transfer analysis in mixed convection flow of Maxwell fluid over an oscillating vertical plate with constant wall temperature. The problem is modelled in terms of coupled partial differential equations with initial and boundary conditions. Some suitable non-dimensional variables are introduced in order to transform the governing problem into dimensionless form. The resulting problem is solved via Laplace transform method and exact solutions for velocity, shear stress and temperature are obtained. These solutions are greatly influenced with the variation of embedded parameters which include the Prandtl number and Grashof number for various times. In the absence of free convection, the corresponding solutions representing the mechanical part of velocity reduced to the well known solutions in the literature. The total velocity is presented as a sum of both cosine and sine velocities. The unsteady velocity in each case is arranged in the form of transient and post transient parts. It is found that the post transient parts are independent of time. The solutions corresponding to Newtonian fluids are recovered as a special case and comparison between Newtonian fluid and Maxwell fluid is shown graphically.

A scientific report on heat transfer analysis in mixed convection flow of Maxwell fluid over an oscillating vertical plate

PubMed Central

Khan, Ilyas; Shah, Nehad Ali; Dennis, L. C. C.

2017-01-01

This scientific report investigates the heat transfer analysis in mixed convection flow of Maxwell fluid over an oscillating vertical plate with constant wall temperature. The problem is modelled in terms of coupled partial differential equations with initial and boundary conditions. Some suitable non-dimensional variables are introduced in order to transform the governing problem into dimensionless form. The resulting problem is solved via Laplace transform method and exact solutions for velocity, shear stress and temperature are obtained. These solutions are greatly influenced with the variation of embedded parameters which include the Prandtl number and Grashof number for various times. In the absence of free convection, the corresponding solutions representing the mechanical part of velocity reduced to the well known solutions in the literature. The total velocity is presented as a sum of both cosine and sine velocities. The unsteady velocity in each case is arranged in the form of transient and post transient parts. It is found that the post transient parts are independent of time. The solutions corresponding to Newtonian fluids are recovered as a special case and comparison between Newtonian fluid and Maxwell fluid is shown graphically. PMID:28294186

Accretion-driven turbulence in filaments - I. Non-gravitational accretion

NASA Astrophysics Data System (ADS)

Heigl, S.; Burkert, A.; Gritschneder, M.

2018-03-01

We study accretion-driven turbulence for different inflow velocities in star-forming filaments using the code RAMSES. Filaments are rarely isolated objects and their gravitational potential will lead to radially dominated accretion. In the non-gravitational case, accretion by itself can already provoke non-isotropic, radially dominated turbulent motions responsible for the complex structure and non-thermal line widths observed in filaments. We find that there is a direct linear relation between the absolute value of the total density-weighted velocity dispersion and the infall velocity. The turbulent velocity dispersion in the filaments is independent of sound speed or any net flow along the filament. We show that the density-weighted velocity dispersion acts as an additional pressure term, supporting the filament in hydrostatic equilibrium. Comparing to observations, we find that the projected non-thermal line width variation is generally subsonic independent of inflow velocity.

Transient heterogeneity in an aquifer undergoing bioremediation of hydrocarbons.

PubMed

Schillig, P C; Devlin, J F; Roberts, J A; Tsoflias, G P; McGlashan, M A

2011-01-01

Localized, transient heterogeneity was studied in a sand aquifer undergoing benzene, toluene, ethylbenzene, and xylene bioremediation using a novel array of multilevel, in situ point velocity probes (PVPs). The experiment was conducted within a sheet-pile alleyway to maintain a constant average flow direction through time. The PVPs measured changes in groundwater velocity direction and magnitude at the centimeter scale, making them ideal to monitor small-scale changes in hydraulic conductivity (K). Velocities were shown to vary nonuniformly by up to a factor of 3 when a source of oxygen was established down-gradient of the petroleum spill. In spite of these local variations, the average groundwater velocity within the 7 m × 20 m sheet-piled test area only varied within ± 25%. The nonuniform nature of the velocity variations across the gate indicated that the changes were not due solely to seasonal hydraulic gradient fluctuations. At the conclusion of the experiment, microbial biomass levels in the aquifer sediments was approximately 1 order of magnitude higher in the oxygen-amended portion of the aquifer than at the edge of the plume or in locations up-gradient of the source. These data suggest that the transient velocities resulted, at least in part, from enhanced biological activity that caused transient heterogeneities in the porous medium.

A Mechanism for Stratifying Lava Flows

NASA Astrophysics Data System (ADS)

Rice, A.

2005-12-01

Relict lava flows (e.g., komatiites) are often reported to be zoned in the vertical, each zone separated by a sharp contact. Such stratifications in igneous flows, both intrusive and extrusive, can be treated as analogues of suspended loads of sediments in rivers and streams, and hence amenable to quantitative treatment derived for the hydraulic environment as long as dynamic similitude is assured. Situations typically encountered in the hydraulic environment are streams carrying a bed load at the bottom of the stream, the bed load separated by a sharp horizon from a sediment load carried above it. This sediment load may be topped by others of decreasing density as one moves to the surface of the flow, with perhaps the uppermost layer clear of any suspended matter. Rules exist for estimating the thickness D of these loads: one of them is given by D ~ 4.4V3/rgcvs where V is the shear velocity or average velocity of the flow, r = (ρs - ρl)/ρl where ρs is the density of the suspended solid matter, ρl the density of the fluid, g the acceleration of gravity, c the concentration of the particulate content and vs the settling velocity. The settling velocity is secured through Stoke's Law and the velocity of the flow is given by V = R2/3S1/2/n where R is the hydraulic radius, S the gradient along which the fluid flows and n is the Manning Coefficient. In the igneous case, the bed load would be composed of primocrysts, i.e., of the first crystals to come out of solution as the flow cools along its run. This would leave the upper portions of the flow more evolved except perhaps for a quenched crust riding atop the flow. As the viscosity of the flow is dependent not only on temperature but on composition and crystal content, the mean velocity of each layer will be different from the layer above and below it. This requires shear at the interface of adjoining stratifications, which brings into play another mechanism: dispersive pressure (the Bagnold effect). Dispersive pressure will drive primocrysts into boundary layers such as that attending the bottom of the flow and at those separating stratifications. For instance, if the primocrysts were spinals, then a Cr high might be expected at the interfaces separating stratifications. Since the melt throughout is evolving as it moves down stream, compositional variations along strike (as well is in the vertical) might be expected. Application of the above notions falls within the confines of field observation.

Shaded computer graphic techniques for visualizing and interpreting analytic fluid flow models

NASA Technical Reports Server (NTRS)

Parke, F. I.

1981-01-01

Mathematical models which predict the behavior of fluid flow in different experiments are simulated using digital computers. The simulations predict values of parameters of the fluid flow (pressure, temperature and velocity vector) at many points in the fluid. Visualization of the spatial variation in the value of these parameters is important to comprehend and check the data generated, to identify the regions of interest in the flow, and for effectively communicating information about the flow to others. The state of the art imaging techniques developed in the field of three dimensional shaded computer graphics is applied to visualization of fluid flow. Use of an imaging technique known as 'SCAN' for visualizing fluid flow, is studied and the results are presented.

Oscillatory slip flow past a spherical inclusion embedded in a Brinkman medium

NASA Astrophysics Data System (ADS)

Palaniappan, D.

2016-11-01

Non-steady flow past an impermeable sphere embedded in a porous medium is investigated based on Brinkman model with Navier slip conditions. Exact analytic solution for the stream-function - involving modified Bessel function of the second kind - describing the slow oscillatory flow around a rigid spherical inclusion is obtained in the limit of low-Reynolds-number. The key parameters such as the frequency of oscillation λ, the permeability constant δ, and the slip coefficient ξ control the flow fields and physical quantities in the entire flow domain. Local streamlines for fixed times demonstrate the variations in flow patterns. Closed form expressions for the tangential velocity profile, wall shear stress, and the force acting on the sphere are computed and compared with the existing results. It is noted that the slip parameter in the range 0 <= ξ <= 0 . 5 has a significant effect in reducing the stress and force. The steady-state velocity overshoot behavior in the vicinity of the sphere is re-iterated. In the limit of large permeability, Darcy (potential) flow is recovered outside a boundary layer. The results are of some interest in predicting maximum wall stress and pressure drop associated with biological models in fibrous media.

An experimental investigation of the flow past a finite circular cylinder at a low subcritical Reynolds number

NASA Technical Reports Server (NTRS)

Budair, M.; Ayoub, A.; Karamcheti, K.

1981-01-01

Results of hot wire measurements made in the near wake at a Reynolds number of 9955 are reported. The measurements include the mean velocity profiles, root mean square values of the velocity fluctuations, frequency spectra, and velocity cross correlations. The mean velocity profiles were used to determine the wake width, whose variation in the downstream and spanwise directions was examined. It is observed that close to the cylinder, the wake is narrower toward the free end than it is away from it, while further downstream the wake is wider toward the tip than it is away from it. It is found that the flow over the span can be characterized by four regions: a tip region where vortex shedding occurs at a lower frequency than that prevalent for away from the tip; an intermediate region adjacent to the first one where a frequency component of a nonshedding character is present; a third region characterized by a gradually increasing shedding frequency with increasing distance from the tip; and a two dimensional region where the shedding frequency is constant.

Experimental Investigation of Rainfall Impact on Overland Flow Driven Erosion Processes and Flow Hydrodynamics on a Steep Hillslope

NASA Astrophysics Data System (ADS)

Tian, P.; Xu, X.; Pan, C.; Hsu, K. L.; Yang, T.

2016-12-01

Few attempts have been made to investigate the quantitative effects of rainfall on overland flow driven erosion processes and flow hydrodynamics on steep hillslopes under field conditions. Field experiments were performed in flows for six inflow rates (q: 6-36 Lmin-1m-1) with and without rainfall (60 mm h-1) on a steep slope (26°) to investigate: (1) the quantitative effects of rainfall on runoff and sediment yield processes, and flow hydrodynamics; (2) the effect of interaction between rainfall and overland flow on soil loss. Results showed that the rainfall increased runoff coefficients and the fluctuation of temporal variations in runoff. The rainfall significantly increased soil loss (10.6-68.0%), but this increment declined as q increased. When the interrill erosion dominated (q=6 Lmin-1m-1), the increment in the rill erosion was 1.5 times that in the interrill erosion, and the effect of the interaction on soil loss was negative. When the rill erosion dominated (q=6-36 Lmin-1m-1), the increment in the interrill erosion was 1.7-8.8 times that in the rill erosion, and the effect of the interaction on soil loss became positive. The rainfall was conducive to the development of rills especially for low inflow rates. The rainfall always decreased interrill flow velocity, decreased rill flow velocity (q=6-24 Lmin-1m-1), and enhanced the spatial uniformity of the velocity distribution. Under rainfall disturbance, flow depth, Reynolds number (Re) and resistance were increased but Froude number was reduced, and lower Re was needed to transform a laminar flow to turbulent flow. The rainfall significantly increased flow shear stress (τ) and stream power (φ), with the most sensitive parameters to sediment yield being τ (R2=0.994) and φ (R2=0.993), respectively, for non-rainfall and rainfall conditions. Compared to non-rainfall conditions, there was a reduction in the critical hydrodynamic parameters of mean flow velocity, τ, and φ by the rainfall. These findings provide a better understanding on the influence mechanism of rainfall impact on hillslope erosion processes.

Wind flow modulation due to variations of the water surface roughness

NASA Astrophysics Data System (ADS)

Shomina, Olga; Ermakov, Stanislav; Kapustin, Ivan; Lazareva, Tatiana

2016-04-01

Air-ocean interaction is a classical problem in atmosphere and ocean physics, which has important geophysical applications related to calculation of vertical and horizontal humidity, aerosol and gas fluxes, development of global climate models and weather forecasts. The structure of wind flow over fixed underlying surfaces, such as forestry, buildings, mountains, is well described, while the interaction between a rough water surface and turbulent wind is far more complicated because of the presence of wind waves with different wavelength and amplitudes and propagating with different velocities and directions. The aim of this study was to investigate experimentally the variability of the wind profile structure due to variations of wave characteristics. The surface roughness variations were produced using a) surfactant films (oleic acid) spread on the water surface and b) mechanically generated waves superimposed on wind waves. The first case is related to oil slicks on sea surface, the second one - to the sea swell, which propagates into zones with lower wind velocities and interacts with wind flow. Laboratory experiments were conducted in the Oval Wind Wave Tank (OWWT) at the Institute of Applied Physics, cross-section of the wind channel is 30 cm x30 cm. Wave amplitude and the spectrum of surface waves were measured by a wire wave gauge, the wind speed was measured using a hot-wire anemometer DISA and a Pitot tube. In the experiments with surfactants, two frequencies of dripping of the oleic acid were studied, so that low concentration films with the elasticity parameters of about 19 mN/m and the high concentration ("thick") films with the elasticity of 34 mN/m were formed. In the experiments with mechanically generated waves (MGW) different regimes were studied with MGW amplitude of 3.4 mm and of 4.4 mm, and with MGW frequencies of 3.3 Hz and 3.7 Hz. It was shown, that: a) the mean velocity of the wind flow in the presence of surfactant and MGW can be described by a logarithmic profile; b) in the presence of a surfactant film an increase of wind speed was revealed; the more elastic films was deployed on the surface - the stronger wind acceleration was detected; c) MGW result in deceleration of wind flow, the larger MGW amplitude the stronger wind flow reduction is; d) the wind deceleration effect is more pronounced for MGW with higher frequency, i.e. for slower propagating MGW. e) experimental dependencies of the logarithmic wind profile characteristics as functions of the rout mean square (RMS) wave height were obtained demonstrating the growth of the wind friction velocity and the roughness coefficient with RMS. The work has been supported by the Russian Foundation of Basic Research (Projects № 14-05-31535, 14-05-00876, 15-35-20992).

Analysis of Poiseuille Flow Property in Two-Dimensional Mi-cro Channels of Microfluidic Pneumatic Micro-Valve

NASA Astrophysics Data System (ADS)

Yang, Shaohua; Long, Wei; Chen, Yajun

2018-03-01

In this paper, the control mechanism and mathematical description of the microfluidic flow in the microfluidic process of the PDMS membrane type pneumatic micro-valve were studied. The velocity and pressure variation law of the velocity field inside micro valve was analyzed by numerical simulation method. The influence of the two kinds of inlet drive modes on the working effect and the pressure flow characteristics of the pneumatic micro-valve was studied. The structure of the elastic solid valve diaphragm under the dual action of the airway and the liquid channel was analyzed. Deformation and stress distribution. The results show that the gas flow in the gas flow channel under the diaphragm by the vacuum part of the role of the formation of a suction gas vortex, pressure-driven mode was easier under the diaphragm to produce a strong gas vortex, resulting in internal and external pressure to promote diaphragm cut-off liquid channel; In the pressure pneumatic mode, the stress at both ends of the diaphragm was smaller, the membrane was not easy to tear failure.

Oceanic Residual Depth Anomalies Maintained by a Shallow Asthenospheric Channel

NASA Astrophysics Data System (ADS)

Richards, F. D.; Hoggard, M.; White, N.

2016-12-01

Oceanic residual depth anomalies vary on wavelengths of 800-2,000 km and have amplitudesof ±1 km. There is also evidence from glacio-isostatic adjustment, plate motions and seismicanisotropy studies for the existence of a low-viscosity asthenospheric channel immediately beneaththe lithospheric plates. Here, we investigate whether global residual depth anomalies are consistentwith temperature variations within a sub-plate channel. For a given channel thickness, we convertresidual depth anomalies into temperature anomalies, assuming thermal isostasy alone (i.e. no mantle flow). Using aparameterisation that is calibrated against stacked oceanic shear wave velocity profiles, we convertthese temperature anomalies into velocity variations. We then compare the inferred velocity vari-ations with published seismic tomographic models. We find that thermal anomalies of ±100 °Cwithin a 150 ± 50 km thick channel yield a good match to > 95% of global residual depth anoma-lies. These temperature variations are consistent with geochemical evidence from mid-oceanic ridgebasalts and oceanic crustal thicknesses. The apparent success of this simple isostatic approach sup-ports the existence of a low-viscosity asthenospheric channel that plays a key role in controllingresidual depth anomalies. Far from subduction zones and from plume conduits, dynamic topog-raphy in the oceanic realm appears to be primarily controlled by temperature-induced buoyancyvariations within this channel.

Second-sound studies of coflow and counterflow of superfluid {sup 4}He in channels

DOE Office of Scientific and Technical Information (OSTI.GOV)

Varga, Emil; Skrbek, L.; Babuin, Simone, E-mail: babuin@fzu.cz

2015-06-15

We report a comprehensive study of turbulent superfluid {sup 4}He flow through a channel of square cross section. We study for the first time two distinct flow configurations with the same apparatus: coflow (normal and superfluid components move in the same direction), and counterflow (normal and superfluid components move in opposite directions). We realise also a variation of counterflow with the same relative velocity, but where the superfluid component moves while there is no net flow of the normal component through the channel, i.e., pure superflow. We use the second-sound attenuation technique to measure the density of quantised vortex linesmore » in the temperature range 1.2 K ≲ T ≲ T{sub λ} ≈ 2.18 K and for flow velocities from about 1 mm/s up to almost 1 m/s in fully developed turbulence. We find that both the steady-state and temporal decay of the turbulence significantly differ in the three flow configurations, yielding an interesting insight into two-fluid hydrodynamics. In both pure superflow and counterflow, the same scaling of vortex line density with counterflow velocity is observed, L∝V{sub cf}{sup 2}, with a pronounced temperature dependence; in coflow instead, the vortex line density scales with velocity as L ∝ V{sup 3/2} and is temperature independent; we provide theoretical explanations for these observations. Further, we develop a new promising technique to use different second-sound resonant modes to probe the spatial distribution of quantised vortices in the direction perpendicular to the flow. Preliminary measurements indicate that coflow is less homogeneous than counterflow/superflow, with a denser concentration of vortices between the centre of the channel and its walls.« less

Three-dimensional velocity structure of crust and upper mantle in southwestern China and its tectonic implications

USGS Publications Warehouse

Wang, Chun-Yong; Chan, W.W.; Mooney, W.D.

2003-01-01

Using P and S arrival times from 4625 local and regional earthquakes recorded at 174 seismic stations and associated geophysical investigations, this paper presents a three-dimensional crustal and upper mantle velocity structure of southwestern China (21??-34??N, 97??-105??E). Southwestern China lies in the transition zone between the uplifted Tibetan plateau to the west and the Yangtze continental platform to the east. In the upper crust a positive velocity anomaly exists in the Sichuan Basin, whereas a large-scale negative velocity anomaly exists in the western Sichuan Plateau, consistent with the upper crustal structure under the southern Tibetan plateau. The boundary between these two anomaly zones is the Longmen Shan Fault. The negative velocity anomalies at 50-km depth in the Tengchong volcanic area and the Panxi tectonic zone appear to be associated with temperature and composition variations in the upper mantle. The Red River Fault is the boundary between the positive and negative velocity anomalies at 50-km depth. The overall features of the crustal and the upper mantle structures in southwestern China are a low average velocity, large crustal thickness variations, the existence of a high-conductivity layer in the crust or/and upper mantle, and a high heat flow value. All these features are closely related to the collision between the Indian and the Asian plates.

Fluid mechanics of continuous flow electrophoresis

NASA Technical Reports Server (NTRS)

Saville, D. A.; Ostrach, S.

1978-01-01

The following aspects of continuous flow electrophoresis were studied: (1) flow and temperature fields; (2) hydrodynamic stability; (3) separation efficiency, and (4) characteristics of wide gap chambers (the SPAR apparatus). Simplified mathematical models were developed so as to furnish a basis for understanding the phenomena and comparison of different chambers and operating conditions. Studies of the hydrodynamic stability disclosed that a wide gap chamber may be particularly sensitive to axial temperature variations which could be due to uneven heating or cooling. The mathematical model of the separation process includes effects due to the axial velocity, electro-osmotic cross flow and electrophoretic migration, all including the effects of temperature dependent properties.

Experimental studies of laminar-turbulent transition on a body of revolution

NASA Astrophysics Data System (ADS)

Dovgal, A. V.; Zanin, B. Yu; Sorokin, A. M.

2017-10-01

The focus of the present paper is hydrodynamic stability and transition to turbulence on an axisymmetric body. The objective is to trace the evolution of perturbed flow close to the surface of experimental model with increase of the angle of attack starting with zero incidence. In what follows, we briefly summarize our wind-tunnel data on this topic which were obtained at low subsonic velocities through hot-wire measurements and flow visualization. As is found, in conditions of laminar boundary-layer separation and flow instability, even small variations of the body incidence may have a profound effect on the flow pattern.

Hydrodynamic Controls on Muddy Sedimentary Fabric Development on Low-Gradient Shelves: Atchafalaya Chenier Plain Subaqueous Delta

NASA Astrophysics Data System (ADS)

Denommee, K.; Bentley, S. J.; Harazim, D.; Macquaker, J.

2016-02-01

Short sediment cores and geophysical data collected on the Southwest Louisiana Chenier Plain inner shelf have been studied in order to examine the sedimentary products of current-wave-enhanced sediment gravity flows (CWESGFs), a type of sediment gravity flow where the driving energy required to transport sediment across low-gradient settings is augmented by the near-bed orbital velocity of surface gravity wave and near-bed currents. Sedimentary fabrics observed on the SWLA shelf document the following flow evolution: (1) the erosion of the underlying substrate in response to wave-generated shear stresses in the bottom boundary layer, followed by (2) the deposition of ripple a crossbeded unit during wave-mediated oscillatory motions in low-viscosity suspension; (3) the deposition of subtle intercalated laminae during laminar flow at higher suspended sediment concentrations; followed by the deposition of (4) normally graded sediments during the waning phases of the flow. Significantly, the sedimentary fabrics deposited by CWESGFs on SWLA shelf show diagnostic variations from CWESGF-generated sedimentary fabrics observed on the Eel and Amazon shelves. Differences between the observed sedimentary fabrics are hypothesized to result from variations in the relative contribution of near-bed currents, wave orbital velocities, and bed slope (gravity) to the driving energy of the CWESGF, and as such can be catalogued as diagnostic recognition criteria using a prismatic ternary diagram where current-, wave-, and gravity-dominated end members form the vertices of a triangle, and wave period forms the prism axis. In this framework forcing mechanisms can be represented quantitatively, based on wave period and the relative contribution of each of the CWESGF velocity terms. This framework can be used to explore relationships between hydrodynamics and CWESGF fabrics, providing geologists with a tool with which to better recognize the depositional products of CWESGFs in the rock record; allowing for more accurate paleoenvironmental interpretations of extensive muddy successions.

Tables for the Rapid Estimation of Downwash and Sidewash Behind Wings Performing Various Motions at Supersonic Speeds

NASA Technical Reports Server (NTRS)

Bobbitt, Percy J.

1959-01-01

Equations for the downwash and sidewash due to supersonic yawed and unswept horseshoe vortices have been utilized in formulating tables and charts to permit a rapid estimation of the flow velocities behind wings performing various steady motions. Tabulations are presented of the downwash and sidewash in the wing vertical plane of symmetry due to a unit-strength yawed horseshoe vortex located at 20 equally spaced spanwise positions along lifting lines of various sweeps. (The bound portion of the yawed vortex is coincident with the lifting line.) Charts are presented for the purpose of estimating the spanwise variations of the flow-field velocities and give longitudinal variations of the downwash and sidewash at a nuMber of vertical and spanwise locations due to a unit-strength unswept horseshoe vortex. Use of the tables and charts to calculate wing downwash or sidewash requires a knowledge of the wing spanwise distribution of circulation. Sample computations for the rolling sidewash and angle-of-attack downwash behind a typical swept wing are presented to demonstrate the use of the tables and charts.

Suprasternal notch echocardiography: a potential alternative for the measurement of respiratory variation in aortic blood flow peak velocity in mechanically ventilated children.

PubMed

Devauchelle, Pauline; de Queiroz Siqueira, Mathilde; Lilot, Marc; Chassard, Dominique; Desgranges, François-Pierrick

2018-06-01

We conducted a prospective, observational study to investigate the relationship between the respiratory variation in aortic blood flow peak velocity (ΔVPeak) measured by echocardiography in the proximal ascending aorta from the suprasternal notch window and the ΔVPeak measured at the level of the aortic annulus from the classical apical five-chamber view. We studied children aged from 1 to 10 years referred for surgery under general anesthesia with positive pressure ventilation, after induction of general anesthesia. Twenty-two children (mean age = 5 ± 3 years) were recruited. There was a significant relationship between the ΔVPeak recorded via the suprasternal notch view and the ΔVPeak recorded via the apical five-chamber view (r = 0.62 [95% confidence interval 0.25-0.84], P = 0.003). The ΔVPeak measured using the suprasternal notch route could be considered to predict fluid responsiveness in children under mechanical ventilation, notably when the access to the chest wall is limited during surgery.

Combined Effects of Flow Diverting Strategies and Parent Artery Curvature on Aneurysmal Hemodynamics: A CFD Study

PubMed Central

Yu, Ying; Lv, Nan; Wang, Shengzhang; Karmonik, Christof; Liu, Jian-Min; Huang, Qinghai

2015-01-01

Purpose Flow diverters (FD) are increasingly being considered for treating large or giant wide-neck aneurysms. Clinical outcome is highly variable and depends on the type of aneurysm, the flow diverting device and treatment strategies. The objective of this study was to analyze the effect of different flow diverting strategies together with parent artery curvature variations on altering intra-aneurysmal hemodynamics. Methods Four ideal intracranial aneurysm models with different parent artery curvature were constructed. Computational fluid dynamics (CFD) simulations of the hemodynamics before and after applying five types of flow diverting strategies (single FD, single FD with 5% and 10% packing density of coils, two FDs with 25% and 50% overlapping rate) were performed. Changes in pressure, wall shear stress (WSS), relative residence time (RRT), inflow velocity and inflow volume rate were calculated and compared. Results Each flow diverting strategy resulted in enhancement of RRT and reduction of normalized mean WSS, inflow volume rate and inflow velocity in various levels. Among them, 50% overlapped FD induced most effective hemodynamic changes in RRT and inflow volume rate. The mean pressure only slightly decreased after treatment. Regardless of the kind of implantation of FD, the mean pressure, inflow volume rate and inflow velocity increased and the RRT decreased as the curvature of the parent artery increased. Conclusions Of all flow diverting strategies, overlapping FDs induced most favorable hemodynamic changes. Hemodynamics alterations post treatment were substantially influenced by parent artery curvature. Our results indicate the need of an individualized flow diverting strategy that is tailored for a specific aneurysm. PMID:26398847

Development of a subsurface gas flow probe

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cutler, R.P.; Ballard, S.; Barker, G.T.

1997-04-01

This report describes a project to develop a flow probe to monitor gas movement in the vadose zone due to passive venting or active remediation efforts such as soil vapor extraction. 3-D and 1-D probes were designed, fabricated, tested in known flow fields under laboratory conditions, and field tested. The 3-D pores were based on technology developed for ground water flow monitoring. The probes gave excellent agreement with measured air velocities in the laboratory tests. Data processing software developed for ground water flow probes was modified for use with air flow, and to accommodate various probe designs. Modifications were mademore » to decrease the cost of the probes, including developing a downhole multiplexer. Modeling indicated problems with flow channeling due to the mode of deployment. Additional testing was conducted and modifications were made to the probe and to the deployment methods. The probes were deployed at three test sites: a large outdoor test tank, a brief vapor extraction test at the Chemical Waste landfill, and at an active remediation site at a local gas station. The data from the field tests varied markedly from the laboratory test data. All of the major events such as vapor extraction system turn on and turn off, as well as changes in the flow rate, could be seen in the data. However, there were long term trends in the data which were much larger than the velocity signals, which made it difficult to determine accurate air velocities. These long term trends may be due to changes in soil moisture content and seasonal ground temperature variations.« less

The effect of heat generation on mixed convection flow in nano fluids over a horizontal circular cylinder

NASA Astrophysics Data System (ADS)

Juliyanto, Bagus; Widodo, Basuki; Imron, Chairul

2018-04-01

The purpose of this research is to study the effect of heat generation on mixed convection flow on Nano fluids over a horizontal circular cylinder of a heated in two dimension form. A stream of fluids are steady and incompressible, a stream flowing vertically upwards for circular cylinder and the boundary layer at the stagnation point. Three different types of nanoparticles considered are Cu, Al2O3, and TiO2. Mixed convection flow in Nano fluids on the surface of a circular cylinder will cause the boundary layer. The governing boundary layer equations are transformed into a non-dimensional form, and then the non-dimensional forms are transformed into a similar boundary equations by using stream function. Furthermore, an implicit finite-difference scheme known as the Keller-box method is applied to solve numerically the resulting similar boundary layer equations. The result of the research by varying the non-dimensional parameters are mixed convection, Prandtl number, nanoparticle volume fraction, heat generation, and radius of a cylinder are as follows. First, the velocity profile increase and temperature profile decrease when mixed convection parameter increase. Second, the velocity and temperature profiles decrease when Prandtl number parameter increase. Third, the velocity profile with the variation of nanoparticle volume fraction (χ) is increased when the value of χ is 0,1 ≤ χ ≤ 0,15 and the velocity profile decreases when the value of χ is 0,19 ≤ χ ≤ 0,5 while the temperature profile is increasing when the value of χ is 0,1 ≤ χ ≤ 0,5. Fourth, the velocity and temperature profiles increase when heat generation and the radius of the cylinder increase. The last, Cu, Al 2 O 3, and TiO 2 nanoparticles produce the same velocity and temperature profiles, but the three types of nanoparticles are different at the velocity and temperature values.

Quantification of Lacunar-Canalicular Interstitial Fluid Flow Through Computational Modeling of Fluorescence Recovery After Photobleaching.

PubMed

Kwon, Ronald Y; Frangos, John A

2010-09-01

Skeletal adaptation to mechanical loading has been widely hypothesized to involve the stimulation of osteocytes by interstitial fluid flow (IFF). However, direct investigation of this hypothesis has been difficult due in large part to the inability to directly measure IFF velocities within the lacunar-canalicular system. Measurements of fluorescence recovery after photobleaching (FRAP) within individual lacunae could be used to quantify lacunar-canalicular IFF when combined with mathematical modeling. In this study, we used a computational transport model to characterize the relationship between flow frequency (0.5-10 Hz), peak flow velocity (0-300 μm/s), tracer diffusion coefficient (100-300 μm(2)/s), and transport enhancement (i.e., (k/k(0)) - 1, where k and k(0) are the transport rates in the presence/absence of flow) during lacunar FRAP investigations. We show that this relationship is well described by a simple power law with frequency-dependent coefficients, and is relatively insensitive to variations in lacunar geometry. Using this power law relationship, we estimated peak IFF velocities in hindlimb mice subjected to intramedullary pressurization using values of k and k(0) previously obtained from ex vivo lacunar FRAP investigations. Together, our findings suggest that skeletal adaptation in hindlimb suspended mice subjected to dynamic intramedullary pressure occurred in the presence of IFF at levels associated with physiological loading.

Quantification of Lacunar–Canalicular Interstitial Fluid Flow Through Computational Modeling of Fluorescence Recovery After Photobleaching

PubMed Central

Kwon, Ronald Y.; Frangos, John A.

2010-01-01

Skeletal adaptation to mechanical loading has been widely hypothesized to involve the stimulation of osteocytes by interstitial fluid flow (IFF). However, direct investigation of this hypothesis has been difficult due in large part to the inability to directly measure IFF velocities within the lacunar–canalicular system. Measurements of fluorescence recovery after photobleaching (FRAP) within individual lacunae could be used to quantify lacunar–canalicular IFF when combined with mathematical modeling. In this study, we used a computational transport model to characterize the relationship between flow frequency (0.5–10 Hz), peak flow velocity (0–300 μm/s), tracer diffusion coefficient (100–300 μm2/s), and transport enhancement (i.e., (k/k0) − 1, where k and k0 are the transport rates in the presence/absence of flow) during lacunar FRAP investigations. We show that this relationship is well described by a simple power law with frequency-dependent coefficients, and is relatively insensitive to variations in lacunar geometry. Using this power law relationship, we estimated peak IFF velocities in hindlimb mice subjected to intramedullary pressurization using values of k and k0 previously obtained from ex vivo lacunar FRAP investigations. Together, our findings suggest that skeletal adaptation in hindlimb suspended mice subjected to dynamic intramedullary pressure occurred in the presence of IFF at levels associated with physiological loading. PMID:21076644

What is normal nasal airflow? A computational study of 22 healthy adults

PubMed Central

Zhao, Kai; Jiang, Jianbo

2014-01-01

Objective Nasal airflow is essential for functioning of the human nose. Given individual variation in nasal anatomy, there is yet no consensus what constitutes normal nasal airflow patterns. We attempt to obtain such information that is essential to differentiate disease-related variations. Methods Computational fluid dynamics (CFD) simulated nasal airflow in 22 healthy subjects during resting breathing. Streamline patterns, airflow distributions, velocity profiles, pressure, wall stress, turbulence, and vortical flow characteristics under quasi-steady state were analyzed. Patency ratings, acoustically measured minimum cross-sectional area (MCA), and rhinomanometric nasal resistance (NR) were examined for potential correlations with morphological and airflow-related variables. Results Common features across subjects included: >50% total pressure-drop reached near the inferior turbinate head; wall shear stress, NR, turbulence energy, and vorticity were lower in the turbinate than in the nasal valve region. However, location of the major flow path and coronal velocity distributions varied greatly across individuals. Surprisingly, on average, more flow passed through the middle than the inferior meatus and correlated with better patency ratings (r=-0.65, p<0.01). This middle flow percentage combined with peak post-vestibule nasal heat loss and MCA accounted for >70% of the variance in subjective patency ratings and predicted patency categories with 86% success. Nasal index correlated with forming of the anterior dorsal vortex. Expected for resting breathing, the functional impact for local and total turbulence, vorticity, and helicity was limited. As validation, rhinomanometric NR significantly correlated with CFD simulations (r=0.53, p<0.01). Conclusion Significant variations of nasal airflow found among healthy subjects; Key features may have clinically relevant applications. PMID:24664528

Flow Structure and Channel Morphology at a Confluent-Meander Bend

NASA Astrophysics Data System (ADS)

Riley, J. D.; Rhoads, B. L.

2009-12-01

Flow structure and channel morphology in meander bends have been well documented. Channel curvature subjects flow through a bend to centrifugal acceleration, inducing a counterbalancing pressure-gradient force that initiates secondary circulation. Transverse variations in boundary shear stress and bedload transport parallel cross-stream movement of high velocity flow and determine spatial patterns of erosion along the outer bank and deposition along the inner bank. Laboratory experiments and numerical modeling of confluent-meander bends, a junction planform that develops when a tributary joins a meandering river along the outer bank of a bend, suggest that flow and channel morphology in such bends deviate from typical patterns. The purpose of this study is to examine three-dimensional (3-D) flow structure and channel morphology at a natural confluent-meander bend. Field data were collected in southeastern Illinois where Big Muddy Creek joins the Little Wabash River near a local maximum of curvature along an elongated meander loop. Measurements of 3-D velocity components were obtained with an acoustic Doppler current profiler (ADCP) for two flow events with differing momentum ratios. Channel bathymetry was also resolved from the four-beam depths of the ADCP. Analysis of velocity data reveals a distinct shear layer flanked by dual helical cells within the bend immediately downstream of the confluence. Flow from the tributary confines flow from the main channel along the inner part of the channel cross section, displacing the thalweg inward, limiting the downstream extent of the point bar, protecting the outer bank from erosion and enabling bar-building along this bank. Overall, this pattern of flow and channel morphology is quite different from typical patterns in meander bends, but is consistent with a conceptual model derived from laboratory experiments and numerical modeling.

DESIGN ANALYSIS OF RADIAL INFLOW TURBINES

NASA Technical Reports Server (NTRS)

Glassman, A. J.

1994-01-01

This program performs a velocity-diagram analysis required for determining geometry and estimating performance for radial-inflow turbines. Input design requirements are power, mass flow rate, inlet temperature and pressure, and rotative rate. The design variables include stator-exit angle, rotor-exit-tip to rotor-inlet radius ratio, rotor-exit-hub to tip radius ratio, and the magnitude and radial distribution of rotor-exit tangential velocity. The program output includes diameters, total and static efficiences, all absolute and relative temperatures, pressures, and velocities, and flow angles at stator inlet, stator exit, rotor inlet, and rotor exit. Losses accounted for in this program by the internal loss model are three-dimensional (profile plus end wall) viscous losses in the stator and the rotor, the disk-friction loss on the back side of the rotor, the loss due to the clearance between the rotor tip and the outer casing, and the exit velocity loss. The flow analysis is one-dimensional at the stator inlet, stator exit, and rotor inlet, each of these calculation stations being at a constant radius. At the rotor exit where there is a variation in flow-field radius, an axisymmetric two-dimensional analysis is made using constant height sectors. Simple radial equilibrium is used to establish the static pressure gradient at the rotor exit. This program is written in FORTRAN V and has been implemented on a UNIVAC 1100 series computer with a memory requirement of approximately 22K of 36 bit words.

Fluvial sediment of the Mississippi River at St. Louis, Missouri

USGS Publications Warehouse

Jordan, Paul Robert

1965-01-01

An investigation of the fluvial sediment of the Mississippi River at St. Louis, Mo., was begun in 1948. Most data have been obtained only to determine the daily suspended-sediment discharge and the particle-size distribution of suspended sediment and bed material, but a few data have been obtained to study the flow resistance, the vertical distribution of sediment and velocity, and the bed-material discharge. The flow of the Mississippi River at St. Louis is made up of the flows from the Missouri River, which had an average flow of 79,860 cubic feet per second for 1897-1958 at Hermann, Mo., and from the upper Mississippi River, which had an average flow of 91,890 cubic feet per second for 1928-58 at Alton, Il. The Missouri River is partly controlled by reservoirs that had a total capacity of 90,300,000 acre-feet in 1956, and the upper Mississippi River is partly controlled by lakes and reservoirs that had a total capacity of 4,890,000 acre-feet in 1956. The flows of the Missouri and upper Mississippi Rivers have not become mixed at St. Louis; so the river has a lateral gradient of suspended-sediment concentration. The concentration near the west bank has been as much as 2,400 parts per million greater than the concentration near the east bank. Suspended-sediment discharges from April 1948 to September 1958 ranged from 4,250 to 7,010,000 tons per day and averaged 496,000 tons per day. Mean concentrations for water years decreased steadily from 1,690 parts per million in 1949 to 403 parts per million in 1956, but they increased to 756 parts per million in 1958. Effects of new reservoirs in the Missouri River basin on the concentration have been obscured by the close relation of concentration to streamflow. Measured suspended-sediment discharge through September 1958 averaged 47 percent clay, 38 percent silt, and 15 percent sand. Variations of particle size were due mainly to differences in the source areas of the sediment. Most of the bed material in the main flow was between 0.125 and 1.000 millimeter in diameter. The average of median diameters was related to the discharge for periods of 1 year and longer. Geometric quartile deviations of the bed material ranged from 1.1 to 2.5 and averaged 1.5. The mean elevation of the bed had a range of almost 10 feet and was related to the median diameter of bed material by the regression equation hb=363.0 - 7.8 d50 for which the standard error of estimate was 0.91 foot. The resistance to flow as measured by Manning's n ranged from 0.024 to 0.041 and was related to the discharge and mean velocity but not to the shear velocity. Normal dune height is 2-8 feet, and average dune length is about 250 feet. When the resistance to flow was low, much of the bed was fairly fiat; a few dunes were present, but they were much longer than the average. For a given discharge during individual rises in stage, the gage height was lower for increasing discharge than for decreasing discharge even though the bed elevation was higher. The changes in gage height were not caused by changes in energy gradient due to changing discharge, by channel storage between the gage and the measuring section, nor by return of overbank flow; but they were probably caused by a combination of changes in roughness due to changing bed configuration and of changes in turbulence constant due to changing sediment concentration. Turbulence constants (Von Karman's k) computed from velocity measurements at 5-10 points in the vertical and from routine velocity measurements at 2 points in the vertical averaged 0.35 and 0.33, respectively. The exponent z1 of the vertical distribution of concentration for different size ranges varied with about the 0.77 power of the fall velocity. Except for the difference between the theoretical variation and the actual variation of z1 with changing fall velocity, the theoretical equation for the vertical distribution of sediment concentration seems to apply reasonably well for the Miss

Spatial Variation of Pressure in the Lyophilization Product Chamber Part 1: Computational Modeling.

PubMed

Ganguly, Arnab; Varma, Nikhil; Sane, Pooja; Bogner, Robin; Pikal, Michael; Alexeenko, Alina

2017-04-01

The flow physics in the product chamber of a freeze dryer involves coupled heat and mass transfer at different length and time scales. The low-pressure environment and the relatively small flow velocities make it difficult to quantify the flow structure experimentally. The current work presents the three-dimensional computational fluid dynamics (CFD) modeling for vapor flow in a laboratory scale freeze dryer validated with experimental data and theory. The model accounts for the presence of a non-condensable gas such as nitrogen or air using a continuum multi-species model. The flow structure at different sublimation rates, chamber pressures, and shelf-gaps are systematically investigated. Emphasis has been placed on accurately predicting the pressure variation across the subliming front. At a chamber set pressure of 115 mtorr and a sublimation rate of 1.3 kg/h/m 2 , the pressure variation reaches about 9 mtorr. The pressure variation increased linearly with sublimation rate in the range of 0.5 to 1.3 kg/h/m 2 . The dependence of pressure variation on the shelf-gap was also studied both computationally and experimentally. The CFD modeling results are found to agree within 10% with the experimental measurements. The computational model was also compared to analytical solution valid for small shelf-gaps. Thus, the current work presents validation study motivating broader use of CFD in optimizing freeze-drying process and equipment design.

Effect of coolant flow ejection on aerodynamic performance of low-aspect-ratio vanes. 2: Performance with coolant flow ejection at temperature ratios up to 2

NASA Technical Reports Server (NTRS)

Hass, J. E.; Kofskey, M. G.

1977-01-01

The aerodynamic performance of a 0.5 aspect ratio turbine vane configuration with coolant flow ejection was experimentally determined in a full annular cascade. The vanes were tested at a nominal mean section ideal critical velocity ratio of 0.890 over a range of primary to coolant total temperature ratio from 1.0 to 2.08 and a range of coolant to primary total pressure ratio from 1.0 to 1.4 which corresponded to coolant flows from 3.0 to 10.7 percent of the primary flow. The variations in primary and thermodynamic efficiency and exit flow conditions with circumferential and radial position were obtained.

Anisotropic models of the upper mantle

NASA Technical Reports Server (NTRS)

Regan, J.; Anderson, D. L.

1983-01-01

Long period Rayleigh wave and Love wave dispersion data, particularly for oceanic areas, were not simultaneously satisfied by an isotropic structure. Available phase and group velocity data are inverted by a procedure which includes the effects of transverse anisotropy, an elastic dispersion, sphericity, and gravity. The resulting models, for the average Earth, average ocean and oceanic regions divided according to the age of the ocean floor, are quite different from previous results which ignore the above effects. The models show a low velocity zone with age dependent anisotropy and velocities higher than derived in previous surface wave studies. The correspondence between the anisotropy variation with age and a physical model based on flow aligned olivine is suggested.

The three-dimensional compressible flow in a radial inflow turbine scroll

NASA Technical Reports Server (NTRS)

Hamed, A.; Tabakoff, W.; Malak, M.

1984-01-01

This work presents the results of an analytical study and an experimental investigation of the three-dimensional flow in a turbine scroll. The finite element method is used in the iterative numerical solution of the locally linearized governing equations for the three-dimensional velocity potential field. The results of the numerical computations are compared with the experimental measurements in the scroll cross sections, which were obtained using laser Doppler velocimetry and hot wire techniques. The results of the computations show a variation in the flow conditions around the rotor periphery which was found to depend on the scroll geometry.

Numerical calculations of velocity and pressure distribution around oscillating airfoils

NASA Technical Reports Server (NTRS)

Bratanow, T.; Ecer, A.; Kobiske, M.

1974-01-01

An analytical procedure based on the Navier-Stokes equations was developed for analyzing and representing properties of unsteady viscous flow around oscillating obstacles. A variational formulation of the vorticity transport equation was discretized in finite element form and integrated numerically. At each time step of the numerical integration, the velocity field around the obstacle was determined for the instantaneous vorticity distribution from the finite element solution of Poisson's equation. The time-dependent boundary conditions around the oscillating obstacle were introduced as external constraints, using the Lagrangian Multiplier Technique, at each time step of the numerical integration. The procedure was then applied for determining pressures around obstacles oscillating in unsteady flow. The obtained results for a cylinder and an airfoil were illustrated in the form of streamlines and vorticity and pressure distributions.

Nearly steady flows in GONG prototype data

NASA Technical Reports Server (NTRS)

Hathaway, David H.

1993-01-01

Doppler velocity images obtained with the GONG prototype instrument were analyzed to measure the nearly steady photospheric flows. The data consists of 88 images each of velocity, intensity, and modulation obtained at 20:00 UT on 88 days from July 1992 to February 1994. Each velocity image was temporally filtered to remove the p-mode oscillations, masked to exclude active regions, and then analyzed using spherical harmonics and orthogonal functions as described by Hathaway (1992). The spectral coefficients show very consistent results for the entire time interval with some evidence of year-to-year variations. The rotation profile agrees well with previous results and exhibits a north-south asymmetry that reverses sign during the 20 month interval. The residual rotation velocities exhibit structures with amplitudes of approximately 5 m/s that may be related to torsional oscillations. The meridional circulation is directed from the equator toward the poles with a peak velocity in the photosphere of approximately 50 m/s. The higher order components are very weak but indicate a divergent flow from the mid-latitudes (opposite that found for the June 1989 data). The convective limb shift is well fit by a 3rd order polynomial. The convection spectrum has a prominent peak at spherical harmonic degrees of l approximately 150 with very little signal in the low degree modes. Analysis of this signal shows that there is no evidence for giant cell convection at the level of approximately 10 m/s for all modes up to l = 32.

A study of transient flow turbulence generation during flame/wall interactions in explosions

NASA Astrophysics Data System (ADS)

Hargrave, G. K.; Jarvis, S.; Williams, T. C.

2002-07-01

Experimental data are presented for the turbulent velocity field generated during flame/solid wall interactions in explosions. The presence of turbulence in a flammable gas mixture can wrinkle a flame front, increasing the flame surface area and enhancing the burning rate. In congested process plant, any flame propagating through an accidental release of flammable mixture will encounter obstructions in the form of walls, pipe-work or storage vessels. The interaction between the gas movement and the obstacle creates turbulence by vortex shedding and local wake/recirculation, whereby the flame can be wrapped in on itself, increasing the surface area available for combustion. Particle image velocimetry (PIV) was used to characterize the turbulent flow field in the wake of the obstacles placed in the path of propagating flames. This allowed the quantification of the interaction of the propagating flame and the generated turbulent flow field. Due to the accelerating nature of the explosion flow field, the wake flows develop `transient' turbulent fields and PIV provided data to define the spatial and temporal variation of the velocity field ahead of the propagating flame, providing an understanding of the direct interaction between flow and flame.

Non-Newtonian blood flow dynamics in a right internal carotid artery with a saccular aneurysm

NASA Astrophysics Data System (ADS)

Valencia, Alvaro; Zarate, Alvaro; Galvez, Marcelo; Badilla, Lautaro

2006-02-01

Flow dynamics plays an important role in the pathogenesis and treatment of cerebral aneurysms. The temporal and spatial variations of wall shear stress in the aneurysm are hypothesized to be correlated with its growth and rupture. In addition, the assessment of the velocity field in the aneurysm dome and neck is important for the correct placement of endovascular coils. This work describes the flow dynamics in a patient-specific model of carotid artery with a saccular aneurysm under Newtonian and non-Newtonian fluid assumptions. The model was obtained from three-dimensional rotational angiography image data and blood flow dynamics was studied under physiologically representative waveform of inflow. The three-dimensional continuity and momentum equations for incompressible and unsteady laminar flow were solved with a commercial software using non-structured fine grid with 283 115 tetrahedral elements. The intra-aneurysmal flow shows complex vortex structure that change during one pulsatile cycle. The effect of the non-Newtonian properties of blood on the wall shear stress was important only in the arterial regions with high velocity gradients, on the aneurysmal wall the predictions with the Newtonian and non-Newtonian blood models were similar.

Consistency of flow quantifications in tridirectional phase-contrast MRI

NASA Astrophysics Data System (ADS)

Unterhinninghofen, R.; Ley, S.; Dillmann, R.

2009-02-01

Tridirectionally encoded phase-contrast MRI is a technique to non-invasively acquire time-resolved velocity vector fields of blood flow. These may not only be used to analyze pathological flow patterns, but also to quantify flow at arbitrary positions within the acquired volume. In this paper we examine the validity of this approach by analyzing the consistency of related quantifications instead of comparing it with an external reference measurement. Datasets of the thoracic aorta were acquired from 6 pigs, 1 healthy volunteer and 3 patients with artificial aortic valves. Using in-house software an elliptical flow quantification plane was placed manually at 6 positions along the descending aorta where it was rotated to 5 different angles. For each configuration flow was computed based on the original data and data that had been corrected for phase offsets. Results reveal that quantifications are more dependent on changes in position than on changes in angle. Phase offset correction considerably reduces this dependency. Overall consistency is good with a maximum variation coefficient of 9.9% and a mean variation coefficient of 7.2%.

Equilibrium and initial linear stability analysis of liquid metal falling film flows in a varying spanwise magnetic field

NASA Astrophysics Data System (ADS)

Gao, D.; Morley, N. B.

2002-12-01

A 2D model for MHD free surface flow in a spanwise field is developed. The model, designed to simulate film flows of liquid metals in future thermo­nuclear fusion reactors, considers an applied spanwise magnetic field with spatial and temporal variation and an applied streamwise external current. A special case - a thin falling film flow in spanwise magnetic field with constant gradient and constant applied external streamwise current, is here investigated in depth to gain insight into the behavior of the MHD film flow. The fully developed flow solution is derived and initial linear stability analysis is performed for this special case. It is seen that the velocity profile is significantly changed due to the presence of the MHD effect, resulting in the free surface analog of the classic M-shape velocity profile seen in developing pipe flows in a field gradient. The field gradient is also seen to destabilize the film flow under most conditions. The effect of external current depends on the relative direction of the field gradient to the current direction. By controlling the magnitude of an external current, it is possible to obtain a linearly stable falling film under these magnetic field conditions. Tables 1, Figs 12, Refs 20.

Change in Coronary Blood Flow After Percutaneous Coronary Intervention in Relation to Baseline Lesion Physiology Results of the JUSTIFY-PCI Study

PubMed Central

Nijjer, Sukhjinder S.; Petraco, Ricardo; van de Hoef, Tim P.; Sen, Sayan; van Lavieren, Martijn A.; Foale, Rodney A.; Meuwissen, Martijn; Broyd, Christopher; Echavarria-Pinto, Mauro; Al-Lamee, Rasha; Foin, Nicolas; Sethi, Amarjit; Malik, Iqbal S.; Mikhail, Ghada W.; Hughes, Alun D.; Mayet, Jamil; Francis, Darrel P.; Di Mario, Carlo; Escaned, Javier; Piek, Jan J.; Davies, Justin E.

2016-01-01

Background Percutaneous coronary intervention (PCI) aims to increase coronary blood flow by relieving epicardial obstruction. However, no study has objectively confirmed this and assessed changes in flow over different phases of the cardiac cycle. We quantified the change in resting and hyperemic flow velocity after PCI in stenoses defined physiologically by fractional flow reserve and other parameters. Methods and Results Seventy-five stenoses (67 patients) underwent paired flow velocity assessment before and after PCI. Flow velocity was measured over the whole cardiac cycle and the wave-free period. Mean fractional flow reserve was 0.68±0.02. Pre-PCI, hyperemic flow velocity is diminished in stenoses classed as physiologically significant compared with those classed nonsignificant (P<0.001). In significant stenoses, flow velocity over the resting wave-free period and hyperemic flow velocity did not differ statistically. After PCI, resting flow velocity over the wave-free period increased little (5.6±1.6 cm/s) and significantly less than hyperemic flow velocity (21.2±3 cm/s; P<0.01). The greatest increase in hyperemic flow velocity was observed when treating stenoses below physiological cut points; treating stenoses with fractional flow reserve ≤0.80 gained Δ28.5±3.8 cm/s, whereas those fractional flow reserve >0.80 had a significantly smaller gain (Δ4.6±2.3 cm/s; P<0.001). The change in pressure-only physiological indices demonstrated a curvilinear relationship to the change in hyperemic flow velocity but was flat for resting flow velocity. Conclusions Pre-PCI physiology is strongly associated with post-PCI increase in hyperemic coronary flow velocity. Hyperemic flow velocity increases 6-fold more when stenoses classed as physiologically significant undergo PCI than when nonsignificant stenoses are treated. Resting flow velocity measured over the wave-free period changes at least 4-fold less than hyperemic flow velocity after PCI. PMID:26025217

Change in coronary blood flow after percutaneous coronary intervention in relation to baseline lesion physiology: results of the JUSTIFY-PCI study.

PubMed

Nijjer, Sukhjinder S; Petraco, Ricardo; van de Hoef, Tim P; Sen, Sayan; van Lavieren, Martijn A; Foale, Rodney A; Meuwissen, Martijn; Broyd, Christopher; Echavarria-Pinto, Mauro; Al-Lamee, Rasha; Foin, Nicolas; Sethi, Amarjit; Malik, Iqbal S; Mikhail, Ghada W; Hughes, Alun D; Mayet, Jamil; Francis, Darrel P; Di Mario, Carlo; Escaned, Javier; Piek, Jan J; Davies, Justin E

2015-06-01

Percutaneous coronary intervention (PCI) aims to increase coronary blood flow by relieving epicardial obstruction. However, no study has objectively confirmed this and assessed changes in flow over different phases of the cardiac cycle. We quantified the change in resting and hyperemic flow velocity after PCI in stenoses defined physiologically by fractional flow reserve and other parameters. Seventy-five stenoses (67 patients) underwent paired flow velocity assessment before and after PCI. Flow velocity was measured over the whole cardiac cycle and the wave-free period. Mean fractional flow reserve was 0.68±0.02. Pre-PCI, hyperemic flow velocity is diminished in stenoses classed as physiologically significant compared with those classed nonsignificant (P<0.001). In significant stenoses, flow velocity over the resting wave-free period and hyperemic flow velocity did not differ statistically. After PCI, resting flow velocity over the wave-free period increased little (5.6±1.6 cm/s) and significantly less than hyperemic flow velocity (21.2±3 cm/s; P<0.01). The greatest increase in hyperemic flow velocity was observed when treating stenoses below physiological cut points; treating stenoses with fractional flow reserve ≤0.80 gained Δ28.5±3.8 cm/s, whereas those fractional flow reserve >0.80 had a significantly smaller gain (Δ4.6±2.3 cm/s; P<0.001). The change in pressure-only physiological indices demonstrated a curvilinear relationship to the change in hyperemic flow velocity but was flat for resting flow velocity. Pre-PCI physiology is strongly associated with post-PCI increase in hyperemic coronary flow velocity. Hyperemic flow velocity increases 6-fold more when stenoses classed as physiologically significant undergo PCI than when nonsignificant stenoses are treated. Resting flow velocity measured over the wave-free period changes at least 4-fold less than hyperemic flow velocity after PCI. © 2015 American Heart Association, Inc.

Applications of the discrete Enskog-Boltzmann approach

NASA Astrophysics Data System (ADS)

Chu, Kwang-Hua Rainer

1998-08-01

The continuous progress of micromachining technology has led to a growing interest in MicroElectroMechanical System (MEMS) for applications ranging from simple microsensors and microactuators to sophisticated microsystems. The characteristic length scale of these microdevices will be of the order of sub-microns so that the gas flow in this environment is within the rarified gas (RG) regime. In this PhD work, the mass/momentum/energy transport of the monatomic gases along the microchannel and the dispersion/attenuation of 1-D ultrasound propagation (plane wave) of RG are investigated by using the Discrete Enskog-Boltzmann approaches. We applied the 4-velocity coplanar model to plane Poiseuille flow of RG in microchannels. Firstly we reported a steady-state solution for this flow with a final-stage uniform density distribution. Then, we modified the model by introducing a density ratio to accomodate the density variations along the microchannel and to include the grazing-collision effects. We also borrowed thee idea from the Extended Irreversible/Reversible Thermodynamics to derive the pressure-gradient for the dimensional velocity field. Our results show the Knudsen minimum of the non- dimensional volume flow rate for Knudsen number (Kn) around 1.5. Using the macroscopic velocity fields, with Cercignani's comments for the 'Kinetic Temperature', we can calculate the related temperature distribution across the microchannel. We also checked the thermodynamic or equilibrium properties of 4-, 6-, and 8-velocity models, by calculating the dispersion relation of 1-D plane ultrasound wave propagation in the RG regime which has large Kn of O(1). The results (after comparison with the measurements) confirmed that the 4-velocity model is the most suitable model for our applications.

Study of plasma-chemical NO-containing gas flow for treatment of wounds and inflammatory processes.

PubMed

Pekshev, Alexander V; Shekhter, Anatoly B; Vagapov, Andrey B; Sharapov, Nikolay A; Vanin, Anatoly F

2018-02-28

This work is aimed at exhaustive and detailed study of chemical, physical and physico-chemical characteristics of NO-containing gas flow (NO-CGF) generated by a plasma-chemical generator of Plason device, which has been used in medical practice for more than 15 years for effectively healing wound and inflammatory conditions with exogenous nitric oxide (NO-therapy). Data was obtained on spatial structure of the gas flow, and values of its local parameters in axial and radial directions, such as nitric oxide content, velocity, temperature and mass flow density of nitric oxide, providing altogether the effectiveness of treatment by the exogenous NO-therapy method, were determined experimentally and by computations. It was demonstrated that plasma-chemical synthesis of NO from atmospheric air in a low direct current (DC) arc provides a high mass flow of nitric oxide at the level of 1.6-1.8 mg/s, while in the area of impact of NO-CGF on the biological tissue, on its axis, NO content is 400-600 ppm, flow velocity about 5 m/s, nitric oxide mass flow density 0.25-0.40 mg/(s·cm 2 ), temperature 40-60 °C. Tendencies were determined for designing new devices for further experimental biological and medical research in the field of NO-therapy: lowering the temperature of NO-CGF to ambient temperature will enable variation, in experiments, of the affecting flow parameters in a wide range up to their maximum values: NO content up to 2000 ppm, velocity up to 20 m/s, nitric oxide mass flow density up to 2.5 mg/(s·cm 2 ). Copyright © 2017. Published by Elsevier Inc.

Backward propagating branch of surface waves in a semi-bounded streaming plasma system

NASA Astrophysics Data System (ADS)

Lim, Young Kyung; Lee, Myoung-Jae; Seo, Ki Wan; Jung, Young-Dae

2017-06-01

The influence of wake and magnetic field on the surface ion-cyclotron wave is kinetically investigated in a semi-bounded streaming dusty magnetoplasma in the presence of the ion wake-field. The analytic expressions of the frequency and the group velocity are derived by the plasma dielectric function with the spectral reflection condition. The result shows that the ion wake-field enhances the wave frequency and the group velocity of the surface ion-cyclotron wave in a semi-bounded dusty plasma. It is found that the frequency and the group velocity of the surface electrostatic-ion-cyclotron wave increase with an increase of the strength of the magnetic field. It is interesting to find out that the group velocity without the ion flow has the backward propagation mode in a semi-bounded dusty plasma. The variations due to the frequency and the group velocity of the surface ion-cyclotron wave are also discussed.

Study on of Seepage Flow Velocity in Sand Layer Profile as Affected by Water Depth and Slope Gradience

NASA Astrophysics Data System (ADS)

Han, Z.; Chen, X.

2017-12-01

BACKGROUND: The subsurface water flow velocity is of great significance in understanding the hydrodynamic characteristics of soil seepage and the influence of interaction between seepage flow and surface runoff on the soil erosion and sediment transport process. OBJECTIVE: To propose a visualized method and equipment for determining the seepage flow velocity and measuring the actual flow velocity and Darcy velocity as well as the relationship between them.METHOD: A transparent organic glass tank is used as the test soil tank, the white river sand is used as the seepage test material and the fluorescent dye is used as the indicator for tracing water flow, so as to determine the thickness and velocity of water flow in a visualized way. Water is supplied at the same flow rate (0.84 L h-1) to the three parts with an interval of 1m at the bottom of the soil tank and the pore water velocity and the thickness of each water layer are determined under four gradient conditions. The Darcy velocity of each layer is calculated according to the water supply flow and the discharge section area. The effective discharge flow pore is estimated according to the moisture content and porosity and then the relationship between Darcy velocity and the measured velocity is calculated based on the water supply flow and the water layer thickness, and finally the correctness of the calculation results is verified. RESULTS: According to the velocity calculation results, Darcy velocity increases significantly with the increase of gradient; in the sand layer profile, the flow velocity of pore water at different depths increases with the increase of gradient; under the condition of the same gradient, the lower sand layer has the maximum flow velocity of pore water. The air-filled porosity of sand layer determines the proportional relationship between Darcy velocity and pore flow velocity. CONCLUSIONS: The actual flow velocity and Darcy velocity can be measured by a visualized method and the relationship between Darcy velocity and pore velocity can be expressed well by the air-filled porosity of sand layer. The flow velocity measurement and test method adopted in the research is effective and feasible. IMPLICATIONS: The visualized flow velocity measurement method can be applied to simulate and measure the characteristics of subsurface water flow in the soil.

Tidally induced variations in vertical and horizontal motion on Rutford Ice Stream, West Antarctica, inferred from remotely sensed observations

NASA Astrophysics Data System (ADS)

Minchew, B. M.; Simons, M.; Riel, B.; Milillo, P.

2017-01-01

To better understand the influence of stress changes over floating ice shelves on grounded ice streams, we develop a Bayesian method for inferring time-dependent 3-D surface velocity fields from synthetic aperture radar (SAR) and optical remote sensing data. Our specific goal is to observe ocean tide-induced variability in vertical ice shelf position and horizontal ice stream flow. Thus, we consider the special case where observed surface displacement at a given location can be defined by a 3-D secular velocity vector, a family of 3-D sinusoidal functions, and a correction to the digital elevation model used to process the SAR data. Using nearly 9 months of SAR data collected from multiple satellite viewing geometries with the COSMO-SkyMed 4-satellite constellation, we infer the spatiotemporal response of Rutford Ice Stream, West Antarctica, to ocean tidal forcing. Consistent with expected tidal uplift, inferred vertical motion over the ice shelf is dominated by semidiurnal and diurnal tidal constituents. Horizontal ice flow variability, on the other hand, occurs primarily at the fortnightly spring-neap tidal period (Msf). We propose that periodic grounding of the ice shelf is the primary mechanism for translating vertical tidal motion into horizontal flow variability, causing ice flow to accelerate first and most strongly over the ice shelf. Flow variations then propagate through the grounded ice stream at a mean rate of ˜29 km/d and decay quasi-linearly with distance over ˜85 km upstream of the grounding zone.

Assessment of key transport parameters in a karst system under different dynamic conditions based on tracer experiments: the Jeita karst system, Lebanon

NASA Astrophysics Data System (ADS)

Doummar, Joanna; Margane, Armin; Geyer, Tobias; Sauter, Martin

2018-03-01

Artificial tracer experiments were conducted in the mature karst system of Jeita (Lebanon) under various flow conditions using surface and subsurface tracer injection points, to determine the variation of transport parameters (attenuation of peak concentration, velocity, transit times, dispersivity, and proportion of immobile and mobile regions) along fast and slow flow pathways. Tracer breakthrough curves (TBCs) observed at the karst spring were interpreted using a two-region nonequilibrium approach (2RNEM) to account for the skewness in the TBCs' long tailings. The conduit test results revealed a discharge threshold in the system dynamics, beyond which the transport parameters vary significantly. The polynomial relationship between transport velocity and discharge can be related to the variation of the conduit's cross-sectional area. Longitudinal dispersivity in the conduit system is not a constant value (α = 7-10 m) and decreases linearly with increasing flow rate because of dilution effects. Additionally, the proportion of immobile regions (arising from conduit irregularities) increases with decreasing water level in the conduit system. From tracer tests with injection at the surface, longitudinal dispersivity values are found to be large (8-27 m). The tailing observed in some TBCs is generated in the unsaturated zone before the tracer actually arrives at the major subsurface conduit draining the system. This work allows the estimation and prediction of the key transport parameters in karst aquifers. It shows that these parameters vary with time and flow dynamics, and they reflect the geometry of the flow pathway and the origin of infiltrating (potentially contaminated) recharge.

Flow velocity and the hydrologic behavior of streams during baseflow.

Treesearch

Steven M. Wondzell; Michael N. Gooseff; Brian L. McGlynn

2007-01-01

Diel variations in stream discharge have long been recognized, but are relatively little studied. Here we demonstrate that these diel fluctuations can be used to investigate both streamflow generation and network routing. We treat evapo-transpiration (ET) as a distributed impulse function in an advection model and analyze the effect of ET on diel fluctuations in...

Geophysical characteristics of the hydrothermal systems of Kilauea volcano, Hawaii

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kauahikaua, J.

1993-08-01

Clues to the structure of Kilauea volcano can be obtained from spatial studies of gravity, magnetic, and seismic velocity variations. The rift zones and summit are underlain by dense, magnetic, and seismic velocity variations. The rift zones and summit are underlain by dense, magnetic, high P-wave-velocity rocks at depths of about 2 km less. The gravity and seismic velocity studies indicate that the rift structures are broad, extending farther to the north than to the south of the surface features. The magnetic data allow separation into a narrow, highly-magnetized, shallow zone and broad, flanking, magnetic lows. The patterns of gravity,more » magnetic variations, and seismicity document the southward migration of the upper east rift zone. Regional, hydrologic features of Kilauea can be determined from resistivity and self-potential studies. High-level groundwater exists beneath Kilauea summit to elevations of +800 m within a triangular area bounded by the west edge of the upper southwest rift zone, the east edge of the upper east rift zone, and the Koa'e fault system. High-level groundwater is present within the east rift zone beyond the triangular summit area. Self-potential mapping shows that areas of local heat produce local fluid circulation in the unconfined aquifer (water table). Shallow seismicity and surface deformation indicate that magma is intruding and that fractures are forming beneath the rift zones and summit area. Heat flows of 370--820 mW/m[sup 2] are calculated from deep wells within the lower east rift zone. The estimated heat input rate for Kilauea of 9 gigawatts (GW) is at least 25 times higher than the conductive heat loss as estimated from the heat flow in wells extrapolated over the area of the summit caldera and rift zones. 115 refs., 13 figs., 1 tab.« less

Laminar dispersion at low and high Peclet numbers in finite-length patterned microtubes

NASA Astrophysics Data System (ADS)

Adrover, Alessandra; Cerbelli, Stefano

2017-06-01

Laminar dispersion of solutes in finite-length patterned microtubes is investigated at values of the Reynolds number below unity. Dispersion is strongly influenced by axial flow variations caused by patterns of periodic pillars and gaps in the flow direction. We focus on the Cassie-Baxter state, where the gaps are filled with air pockets, therefore enforcing free-slip boundary conditions at the flat liquid-air interface. The analysis of dispersion is approached by considering the temporal moments of solute concentration. Based on this approach, we investigate the dispersion properties in a wide range of values of the Peclet number, thus gaining insight into how the patterned structure of the microtube influences both the Taylor-Aris and the convection-dominated dispersion regimes. Numerical results for the velocity field and for the moment hierarchy are obtained by means of finite element method solution of the corresponding transport equations. We show that for different patterned geometries, in a range of Peclet values spanning up to six decades, the dispersion features in a patterned microtube are equivalent to those of a microtube characterized by a uniform slip velocity equal to the wall-average velocity of the patterned case. This suggests that two patterned micropipes with different geometry yet characterized by the same flow rate and average wall velocity will exhibit the same dispersion features as well as the same macroscopic pressure drop.

The Influence of Waves on the Near-Wake of an Axial-Flow Marine Hydrokinetic Turbine

NASA Astrophysics Data System (ADS)

Lust, Ethan; Luznik, Luksa; Flack, Karen

2017-11-01

Flow field results are presented for the near-wake of an axial-flow hydrokinetic turbine in the presence of surface gravity waves. The turbine is a 1/25 scale, 0.8 m diameter, two bladed turbine based on the U.S. Department of Energy's Reference Model 1 tidal current turbine. Measurements were obtained in the large towing tank facility at the U.S. Naval Academy with the turbine towed at a constant carriage speed and a tip speed ratio selected to provide maximum power. The turbine has been shown to be nearly scale independent for these conditions. Velocity measurements were obtained using an in-house designed and manufactured, submersible, planar particle image velocimetry (PIV) system at streamwise distances of up to two diameters downstream of the rotor plane. Phase averaged results for steady and unsteady conditions are presented for comparison showing further expansion of the wake in the presence of waves as compared to the quiescent case. The impact of waves on turbine tip vortex characteristics is also examined showing variation in core radius, swirl velocity, and circulation with wave phase. Some aspects of the highly coherent wake observed in the steady case are recognized in the unsteady wake, however, the unsteady velocities imposed by the waves, particularly the vertical velocity component, appears to convect tip vortices into the wake, potentially enhancing energy transport and accelerating the re-energization process.

A unified view of energetic efficiency in active drag reduction, thrust generation and self-propulsion through a loss coefficient with some applications

NASA Astrophysics Data System (ADS)

Arakeri, Jaywant H.; Shukla, Ratnesh K.

2013-08-01

An analysis of the energy budget for the general case of a body translating in a stationary fluid under the action of an external force is used to define a power loss coefficient. This universal definition of power loss coefficient gives a measure of the energy lost in the wake of the translating body and, in general, is applicable to a variety of flow configurations including active drag reduction, self-propulsion and thrust generation. The utility of the power loss coefficient is demonstrated on a model bluff body flow problem concerning a two-dimensional elliptical cylinder in a uniform cross-flow. The upper and lower boundaries of the elliptic cylinder undergo continuous motion due to a prescribed reflectionally symmetric constant tangential surface velocity. It is shown that a decrease in drag resulting from an increase in the strength of tangential surface velocity leads to an initial reduction and eventual rise in the power loss coefficient. A maximum in energetic efficiency is attained for a drag reducing tangential surface velocity which minimizes the power loss coefficient. The effect of the tangential surface velocity on drag reduction and self-propulsion of both bluff and streamlined bodies is explored through a variation in the thickness ratio (ratio of the minor and major axes) of the elliptical cylinders.

Measurement and prediction of flow through a replica segment of a mildly atherosclerotic coronary artery of man

NASA Technical Reports Server (NTRS)

Back, L. H.; Radbill, J. R.; Cho, Y. I.; Crawford, D. W.

1986-01-01

Pressure distributions were measured along a hollow vascular axisymmetric replica of a segment of the left circumflex coronary artery of man with mildly atherosclerotic diffuse disease. A large range of physiological Reynolds numbers from about 60 to 500, including hyperemic response, was spanned in the flows investigation using a fluid simulating blood kinematic viscosity. Predicted pressure distributions from the numerical solution of the Navier-Stokes equations were similar in trend and magnitude to the measurements. Large variations in the predicted velocity profiles occurred along the lumen. The influence of the smaller scale multiple flow obstacles along the wall (lesion variations) led to sharp spikes in the predicted wall shear stresses. Reynolds number similarity was discussed, and estimates of what time averaged in vivo pressure drop and shear stress might be were given for a vessel segment.

Surface velocity divergence model of air/water interfacial gas transfer in open-channel flows

NASA Astrophysics Data System (ADS)

Sanjou, M.; Nezu, I.; Okamoto, T.

2017-04-01

Air/water interfacial gas transfer through a free surface plays a significant role in preserving and restoring water quality in creeks and rivers. However, direct measurements of the gas transfer velocity and reaeration coefficient are still difficult, and therefore a reliable prediction model needs to be developed. Varying systematically the bulk-mean velocity and water depth, laboratory flume experiments were conducted and we measured surface velocities and dissolved oxygen (DO) concentrations in open-channel flows to reveal the relationship between DO transfer velocity and surface divergence (SD). Horizontal particle image velocimetry measurements provide the time-variations of surface velocity divergence. Positive and negative regions of surface velocity divergence are transferred downstream in time, as occurs in boil phenomenon on natural river free-surfaces. The result implies that interfacial gas transfer is related to bottom-situated turbulence motion and vertical mass transfer. The original SD model focuses mainly on small-scale viscous motion, and this model strongly depends on the water depth. Therefore, we modify the SD model theoretically to accommodate the effects of the water depth on gas transfer, introducing a non-dimensional parameter that includes contributions of depth-scale large-vortex motion, such as secondary currents, to surface renewal events related to DO transport. The modified SD model proved effective and reasonable without any dependence on the bulk mean velocity and water depth, and has a larger coefficient of determination than the original SD model. Furthermore, modeling of friction velocity with the Reynolds number improves the practicality of a new formula that is expected to be used in studies of natural rivers.

Low-Energy Electron Effects on the Polar Wind Observed by the POLAR Spacecraft

NASA Technical Reports Server (NTRS)

Horwitz, J. L.; Su, Y.-J.; Dors, E. E.; Moore, Thomas E.; Giles, Barbara L.; Chandler, Michael O.; Craven, Paul D.; Chang, S.-W.; Scudder, J.

1998-01-01

Large ion outflow velocity variation at POLAR apogee have been observed. The observed H+ flow velocities were in the range of 23-110 km/s and 0+ flow velocities were in the range of 5-25 km/s. These velocity ranges lie between those predicted by simulations of the photoelectron-driven polar wind and "baseline" polar wind. The electric current contributions of the photoelectrons and polar rain are expected to control the size and altitude of an electric potential drop which accelerates the polar wind at relatively high altitudes. In this presentation, we compare polar wind characteristics observed near 5000 km and 8 RE altitudes by the Thermal Ion Dynamics Experiment (TIDE) with measurements of low-energy electrons sampled by HYDRA, both from the POLAR spacecraft, to examine possible effects of the polar rain and photoelectrons on the polar wind. Both correlations and anti-correlations are found between the polar wind velocities and the polar rain fluxes at POLAR apogee during different polar cap crossings. Also, the low-altitude upward/downward photoelectron spectra are used to estimates the potential drops above the spacecraft. We interpret these observations in terms of the effects that both photoelectrons and polar rain may have on the electric potential and polar wind acceleration along polar cap magnetic field lines.

Core flow inversion tested with numerical dynamo models

NASA Astrophysics Data System (ADS)

Rau, Steffen; Christensen, Ulrich; Jackson, Andrew; Wicht, Johannes

2000-05-01

We test inversion methods of geomagnetic secular variation data for the pattern of fluid flow near the surface of the core with synthetic data. These are taken from self-consistent 3-D models of convection-driven magnetohydrodynamic dynamos in rotating spherical shells, which generate dipole-dominated magnetic fields with an Earth-like morphology. We find that the frozen-flux approximation, which is fundamental to all inversion schemes, is satisfied to a fair degree in the models. In order to alleviate the non-uniqueness of the inversion, usually a priori conditions are imposed on the flow; for example, it is required to be purely toroidal or geostrophic. Either condition is nearly satisfied by our model flows near the outer surface. However, most of the surface velocity field lies in the nullspace of the inversion problem. Nonetheless, the a priori constraints reduce the nullspace, and by inverting the magnetic data with either one of them we recover a significant part of the flow. With the geostrophic condition the correlation coefficient between the inverted and the true velocity field can reach values of up to 0.65, depending on the choice of the damping parameter. The correlation is significant at the 95 per cent level for most spherical harmonic degrees up to l=26. However, it degrades substantially, even at long wavelengths, when we truncate the magnetic data sets to l <= 14, that is, to the resolution of core-field models. In some of the latter inversions prominent zonal currents, similar to those seen in core-flow models derived from geomagnetic data, occur in the equatorial region. However, the true flow does not contain this flow component. The results suggest that some meaningful information on the core-flow pattern can be retrieved from secular variation data, but also that the limited resolution of the magnetic core field could produce serious artefacts.

[The cerebral hemodynamics in cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy].

PubMed

Jin, De-xin; Chen, Xiu-yun; Huang, He; Zhang, Xu

2006-12-01

To investigate the cerebral hemodynamics in cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL). The blood flow velocity of cerebral arteries was measured by using transcranial Doppler ultrasound (TCD) in 6 cases with CADASIL and a quite number of age and sex matched control subjects. All patients (4 were symptomatic and 2 asymptomatic), being an established CADASIL family with the diagnosis confirmed by clinical characteristics, neuroimaging, pathology and molecular genetics, had abnormal mark signals on MR imagining and no history of hypertension, diabetes, heart disease and migraine. A routinely TCD detection, including peak-systolic velocity (Vp), end-diastolic velocity (Vd), mean velocity (Vm) and pulsatility index (PI), was carried out on the bilateral middle cerebral arteries (MCA), anterior cerebral arteries (ACA), posterior cerebral arteries (PCA) and vertebral arteries (VA) as well as the basilar artery (BA). A comparison between the cases and controls was made. Then, the changes of flow velocity in middle cerebral arteries (MCA) of the patients with CADASIL were observed before and after breathholding tests. In addition, brain CT perfusion imaging (CTP) was carried out in all the cases by using 16-slice spiral CT. The appearances of frequency spectrum were nearly normal in all the cases and there was no abnormality between the two sides on velocity (P > 0.05). As compared with the controls, the bilateral Vp, Vd and Vm in ACA and PCA were decreased obviously (P < 0.05). The velocity parameters of MCA with the exception of left Vm and right PI showed changes (P < 0.05) and there were no changes of PI in the bilateral ACA, PCA and Left MCA (P > 0.05). Moreover, there were marked changes in MCA (including Vm, Vd and PI) of all the cases as compared with the controls after breathholding (P < 0.01). Brain perfusion imaging showing the regional cerebral blood flow and regional cerebral blood volume in frontal lobes were obviously decreasing (P < 0.01) and there was no significant variation of mean transit time (MTT). The characteristic hemodynamic changes in our group is the decreasing flow velocity in bilateral ACA, PCA and MCA and the dominating low flow area occurring usually in frontal and temporal lobes. These changes are in conformity with the ischemic area shown in pathology and neuroimaging in CADASIL patients.

Seasonal Variation of Submesoscale Flow Features in a Mesoscale Eddy-dominant Region in the East Sea

NASA Astrophysics Data System (ADS)

Chang, Yeon S.; Choi, Byoung-Ju; Park, Young-Gyu

2018-03-01

Seasonal changes in the distribution of submesoscale (SM) flow features were examined using a fine-resolution numerical simulation. The SM flows are expected to be strong where mesoscale (MS) eddies actively develop and also when the mixed layer depth (MLD) is deep due to enhanced baroclinic instability. In the East Sea (ES), MS eddies more actively develop in summer while the MLD is deeper in winter, which provided the motivation to conduct this study to test the effects of MLD and MS eddies on the SM activity in this region. Finite-scale Liapunov exponents and the vertical velocity components were employed to analyze the SM activities. It was found that the SM intensity was marked by seasonality: it is stronger in winter when the mixed layer is deep but weaker in summer - despite the greater eddy kinetic energy. This is because in summer the mixed layer is so thin that there is not enough available potential energy. When the SM activity was quantified based on parameterization, (MLD × density gradient), it was determined that the seasonal variation of MLD plays a more important role than the lateral density gradient variation on SM flow motion in the ES.

Modeling experiments on the deceleration and reactivation of Kangerlussuup Sermusa, West Greenland

NASA Astrophysics Data System (ADS)

Rezvanbehbahani, S.; Stearns, L. A.; van der Veen, C. J.; Catania, G. A.

2015-12-01

Seasonal variations in outlet glacier velocity due to basal sliding are well-documented and typically involve acceleration early in the melt season due to enhanced sliding as a result of inefficient drainage of surface water reaching the bed. However, velocity observations from Kangerlussuup Sermusa (KS) in West Greenland contradict this pattern. Instead, ice velocity at KS shows no significant change in early spring compared with the previous winter. This sluggish response of the glacier to spring melt is often followed by an extreme, and short-lived, deceleration. For example, in August 2010, the lower 20 km of the trunk decelerated from about 1600 m a-1 to less than 250 m a-1; this event was followed by a rapid reactivation back to the previous velocity in less than 60 days. Available records since 2006 show that the sequence of steady spring velocity, followed by summer deceleration, and rapid fall reactivation occurs annually; however, the magnitudes of deceleration vary. In this regard, the response of KS to regional environmental forcings is unique compared to its neighboring glaciers. In this study, we investigate whether the unique behavior of KS can be explained by the interaction between changes in basal conditions and the local geometry of the glacier. We model the glacier flow by solving full-Stokes equations using the finite element method in the open-source FEniCS framework. Assuming isothermal ice within the lower trunk, we run experiments on the mechanical properties and boundary conditions of the glacier. These experiments include spatio-temporal changes in basal slipperiness, periodic melt-water influx to the bed, and ice viscosity variations due to changes in melt-water supply to the bed. We also conduct sensitivity analyses on the glacier flow with different ice geometries (e.g. thickness and surface slope) to investigate conditions under which we can produce the unique seasonal behavior of KS. Finally, we assess the impact of the combination of these parameters on the ice flow and evaluate the credibility of our hypothetical scenarios based on available measurements.

Improvement in cochlear flow with Pycnogenol® in patients with tinnitus: a pilot evaluation.

PubMed

Grossi, M G; Belcaro, G; Cesarone, M R; Dugall, M; Hosoi, M; Cacchio, M; Ippolito, E; Bavera, P

2010-06-01

The aim of this preliminary evaluation was to study the efficacy of Pycnogenol in improving cochlear flow in patients with mild-to-moderate tinnitus present for at least two weeks (without vertigo or important hearing loss), possibly associated with cochlear hypo-perfusion. Patients with mild-to-moderate, idiopatic, monolateral tinnitus present for at least 2 weeks were included; no vertigo or important hearing loss had been found in a specific examination. The origin of tinnitus had been sudden (hours or days). Fifty-eight patients used Pycnogenol: 24 used 150 mg/day (group A; mean age 43.2+/-4.3) and 34 patients 100 mg/day (group B: mean age 42.4+/-3.8). Controls included 24 patients (mean age 42.3+/-4.5). The groups were comparable for their clinical problem and age and sex. The average duration of treatment was 34.3+/-3.1 days. No side effects were observed and no drop-outs occurred. The variations in cochlear flow velocity (in cm/s at the cochlear artery), at inclusion and after four weeks of treatment indicated that flow velocity at the level of the affected ear was significantly lower (both the diastolic and systolic components; P<0.05) in comparison with the other ear. The treatment favored an improvement in systolic (P<0.05) and diastolic flow velocity (P<0.05) in the two treatment groups A+B. The increase in flow velocity was very limited and not significant in controls. These results suggest that in selected patients with tinnitus and altered perfusion, Pycnogenol is effective in a short period of time in relieving tinnitus symptoms by improving cochlear blood flow. The effect is more pronounced with higher Pycnogenol dosage. More studies should be planned to better evaluate the pathology and potential applications of Pycnogenol in a larger number of patients who are currently without a real therapeutic solution.

Finite-time barriers to front propagation in two-dimensional fluid flows

NASA Astrophysics Data System (ADS)

Mahoney, John R.; Mitchell, Kevin A.

2015-08-01

Recent theoretical and experimental investigations have demonstrated the role of certain invariant manifolds, termed burning invariant manifolds (BIMs), as one-way dynamical barriers to reaction fronts propagating within a flowing fluid. These barriers form one-dimensional curves in a two-dimensional fluid flow. In prior studies, the fluid velocity field was required to be either time-independent or time-periodic. In the present study, we develop an approach to identify prominent one-way barriers based only on fluid velocity data over a finite time interval, which may have arbitrary time-dependence. We call such a barrier a burning Lagrangian coherent structure (bLCS) in analogy to Lagrangian coherent structures (LCSs) commonly used in passive advection. Our approach is based on the variational formulation of LCSs using curves of stationary "Lagrangian shear," introduced by Farazmand et al. [Physica D 278-279, 44 (2014)] in the context of passive advection. We numerically validate our technique by demonstrating that the bLCS closely tracks the BIM for a time-independent, double-vortex channel flow with an opposing "wind."

The effect of magnetohydrodynamic nano fluid flow through porous cylinder

NASA Astrophysics Data System (ADS)

Widodo, Basuki; Arif, Didik Khusnul; Aryany, Deviana; Asiyah, Nur; Widjajati, Farida Agustini; Kamiran

2017-08-01

This paper concerns about the analysis of the effect of magnetohydrodynamic nano fluid flow through horizontal porous cylinder on steady and incompressible condition. Fluid flow is assumed opposite gravity and induced by magnet field. Porous cylinder is assumed had the same depth of porous and was not absorptive. The First thing to do in this research is to build the model of fluid flow to obtain dimentional governing equations. The dimentional governing equations are consist of continuity equation, momentum equation, and energy equation. Furthermore, the dimensional governing equations are converted to non-dimensional governing equation by using non-dimensional parameters and variables. Then, the non-dimensional governing equations are transformed into similarity equations using stream function and solved using Keller-Box method. The result of numerical solution further is obtained by taking variation of magnetic parameter, Prandtl number, porosity parameter, and volume fraction. The numerical results show that velocity profiles increase and temperature profiles decrease when both of the magnetic and the porosity parameter increase. However, the velocity profiles decrease and the temperature profiles increase when both of the magnetic and the porosity parameter increase.

Lateral variation in upper mantle temperature and composition beneath mid-ocean ridges inferred from shear-wave propagation, geoid, and bathymetry. Ph.D. Thesis

NASA Technical Reports Server (NTRS)

Sheehan, Anne Francis

1991-01-01

Resolution of both the extent and mechanism of lateral heterogeneity in the upper mantle constraints the nature and scales of mantle convection. Oceanic regions are of particular interest as they are likely to provide the closest glimpse at the patterns of temperature anomalies and convective flow in the upper mantle because of their young age and simple crustal structure relative to continental regions. Lateral variations were determined in the seismic velocity and attenuation structure of the lithosphere and astenosphere beneath the oceans, and these seismological observations were combined with the data and theory of geoid and bathymetry anomalies in order to test and improve current models for seafloor spreading and mantle convection. Variations were determined in mantle properties on a scale of about 1000 km, comparable to the thickness of the upper mantle. Seismic velocity, geoid, and bathymetry anomalies are all sensitive to variations in upper mantle density, and inversions were formulated to combine quantitatively these different data and to search for a common origin. Variations in mantle density can be either of thermal or compositional origin and are related to mantle convection or differentiation.

Mathematical modeling of pulsatile flow of non-Newtonian fluid in stenosed arteries

NASA Astrophysics Data System (ADS)

Sankar, D. S.; Lee, Usik

2009-07-01

The pulsatile flow of blood through mild stenosed artery is studied. The effects of pulsatility, stenosis and non-Newtonian behavior of blood, treating the blood as Herschel-Bulkley fluid, are simultaneously considered. A perturbation method is used to analyze the flow. The expressions for the shear stress, velocity, flow rate, wall shear stress, longitudinal impedance and the plug core radius have been obtained. The variations of these flow quantities with different parameters of the fluid have been analyzed. It is found that, the plug core radius, pressure drop and wall shear stress increase with the increase of yield stress or the stenosis height. The velocity and the wall shear stress increase considerably with the increase in the amplitude of the pressure drop. It is clear that for a given value of stenosis height and for the increasing values of the stenosis shape parameter from 3 to 6, there is a sharp increase in the impedance of the flow and also the plots are skewed to the right-hand side. It is observed that the estimates of the increase in the longitudinal impedance increase with the increase of the axial distance or with the increase of the stenosis height. The present study also brings out the effects of asymmetric of the stenosis on the flow quantities.

Supersonic flow calculation using a Reynolds-stress and an eddy thermal diffusivity turbulence model

NASA Technical Reports Server (NTRS)

Sommer, T. P.; So, R. M. C.; Zhang, H. S.

1993-01-01

A second-order model for the velocity field and a two-equation model for the temperature field are used to calculate supersonic boundary layers assuming negligible real gas effects. The modeled equations are formulated on the basis of an incompressible assumption and then extended to supersonic flows by invoking Morkovin's hypothesis, which proposes that compressibility effects are completely accounted for by mean density variations alone. In order to calculate the near-wall flow accurately, correction functions are proposed to render the modeled equations asymptotically consistent with the behavior of the exact equations near a wall and, at the same time, display the proper dependence on the molecular Prandtl number. Thus formulated, the near-wall second order turbulence model for heat transfer is applicable to supersonic flows with different Prandtl numbers. The model is validated against flows with different Prandtl numbers and supersonic flows with free-stream Mach numbers as high as 10 and wall temperature ratios as low as 0.3. Among the flow cases considered, the momentum thickness Reynolds number varies from approximately 4,000 to approximately 21,000. Good correlation with measurements of mean velocity, temperature, and its variance is obtained. Discernible improvements in the law-of-the-wall are observed, especially in the range where the big-law applies.

Subsonic Round and Rectangular Twin Jet Flow Effects

NASA Technical Reports Server (NTRS)

Bozak, Rick; Wernet, Mark

2014-01-01

Subsonic and supersonic aircraft concepts proposed by NASAs Fundamental Aeronautics Program have integrated propulsion systems with asymmetric nozzles. The asymmetry in the exhaust of these propulsion systems creates asymmetric flow and acoustic fields. The flow asymmetries investigated in the current study are from two parallel round, 2:1, and 8:1 aspect ratio rectangular jets at the same nozzle conditions. The flow field was measured with streamwise and cross-stream particle image velocimetry (PIV). A large dataset of single and twin jet flow field measurements was acquired at subsonic jet conditions. The effects of twin jet spacing and forward flight were investigated. For round, 2:1, and 8:1 rectangular twin jets at their closest spacings, turbulence levels between the two jets decreased due to enhanced jet mixing at near static conditions. When the flight Mach number was increased to 0.25, the flow around the twin jet model created a velocity deficit between the two nozzles. This velocity deficit diminished the effect of forward flight causing an increase in turbulent kinetic energy relative to a single jet. Both of these twin jet flow field effects decreased with increasing twin jet spacing relative to a single jet. These variations in turbulent kinetic energy correlate with changes in far-field sound pressure level.

The Effect of Uniform Background Flow on Vortex Ring Formation and Pinch-off

NASA Astrophysics Data System (ADS)

Krueger, Paul S.; Dabiri, John O.; Gharib, Morteza

2002-11-01

Experimental investigations of vortex ring formation are extended to include the effects of a uniform background flow, in a manner relevant to the locomotion of aquatic animals utilizing jet propulsion. Gharib et. al. [J. Fluid Mech. 360, 121 (1998)] generated vortex rings using a piston/cylinder apparatus with relatively large discharge times to demonstrate that the vortex ring at the leading edge of the jet attains its maximum circulation at a piston stroke-to-diameter ratio L/D of 4. This "formation number" is robust over a range of piston motions and cylinder boundary conditions, and can be explained in terms of the Kelvin-Benjamin variational principle. To determine the effect of background flow on formation number and pinch-off of the leading vortex ring, uniform co-flow is established in a large annulus surrounding the vortex generator. The ratio of co-flow velocity to piston velocity is varied between 0 and 1. In addition, the co-flow is initiated at times both before and after the start of vortex ring formation. We present results for stroke ratios L/D = 2 and L/D = 8, in order to discern effects of the co-flow on the leading vortex ring in isolation and in the presence of a trailing jet.

Stochastic simulation for the propagation of high-frequency acoustic waves through a random velocity field

NASA Astrophysics Data System (ADS)

Lu, B.; Darmon, M.; Leymarie, N.; Chatillon, S.; Potel, C.

2012-05-01

In-service inspection of Sodium-Cooled Fast Reactors (SFR) requires the development of non-destructive techniques adapted to the harsh environment conditions and the examination complexity. From past experiences, ultrasonic techniques are considered as suitable candidates. The ultrasonic telemetry is a technique used to constantly insure the safe functioning of reactor inner components by determining their exact position: it consists in measuring the time of flight of the ultrasonic response obtained after propagation of a pulse emitted by a transducer and its interaction with the targets. While in-service the sodium flow creates turbulences that lead to temperature inhomogeneities, which translates into ultrasonic velocity inhomogeneities. These velocity variations could directly impact the accuracy of the target locating by introducing time of flight variations. A stochastic simulation model has been developed to calculate the propagation of ultrasonic waves in such an inhomogeneous medium. Using this approach, the travel time is randomly generated by a stochastic process whose inputs are the statistical moments of travel times known analytically. The stochastic model predicts beam deviations due to velocity inhomogeneities, which are similar to those provided by a determinist method, such as the ray method.

Influence of snow temperature on avalanche impact pressure

NASA Astrophysics Data System (ADS)

Sovilla, Betty; Koehler, Anselm; Steinkogler, Walter; Fischer, Jan-Thomas

2015-04-01

The properties of the snow entrained by an avalanche during its motion (density, temperature) significantly affect flow dynamics and can determine whether the flowing material forms granules or maintains its original fine-grained structure. In general, a cold and light snow cover typically fluidizes, while warmer and more cohesive snow may form a granular denser layer in a flowing avalanche. This structural difference has a fundamental influence not only in the mobility of the flow but also on the impact pressure of avalanches. Using measurements of impact pressure, velocity, density and snow temperature performed at the Swiss Vallée de la Sionne full-scale test site, we show that, impact pressure fundamentally changes with snow temperature. A transition threshold of about -2°C is determined, the same temperature at which snow granulation starts. On the one hand warm avalanches, characterized by temperatures larger than -2°C, move as a plug and exert impact pressures linearly proportional to the avalanche depth. For Froude numbers larger than 1, an additional square-velocity dependent contribution cannot be neglected. On the other hand cold avalanches, characterized by a temperature smaller than -2°C, move as dense sheared flows, or completely dilute powder clouds and exert impact pressures, which are mainly proportional to the square of the flow velocity. For these avalanches the impact pressures strongly depend on density variations within the flow. We suggest that the proposed temperature threshold can be used as a criterion to define the transition between the impact pressures exerted by warm and cold avalanches, thus offering a new way to elude the notorious difficulties in defining the differences between wet and dry flow, respectively.

Variational method enabling simplified solutions to the linearized Boltzmann equation for oscillatory gas flows

NASA Astrophysics Data System (ADS)

Ladiges, Daniel R.; Sader, John E.

2018-05-01

Nanomechanical resonators and sensors, operated in ambient conditions, often generate low-Mach-number oscillating rarefied gas flows. Cercignani [C. Cercignani, J. Stat. Phys. 1, 297 (1969), 10.1007/BF01007482] proposed a variational principle for the linearized Boltzmann equation, which can be used to derive approximate analytical solutions of steady (time-independent) flows. Here we extend and generalize this principle to unsteady oscillatory rarefied flows and thus accommodate resonating nanomechanical devices. This includes a mathematical approach that facilitates its general use and allows for systematic improvements in accuracy. This formulation is demonstrated for two canonical flow problems: oscillatory Couette flow and Stokes' second problem. Approximate analytical formulas giving the bulk velocity and shear stress, valid for arbitrary oscillation frequency, are obtained for Couette flow. For Stokes' second problem, a simple system of ordinary differential equations is derived which may be solved to obtain the desired flow fields. Using this framework, a simple and accurate formula is provided for the shear stress at the oscillating boundary, again for arbitrary frequency, which may prove useful in application. These solutions are easily implemented on any symbolic or numerical package, such as Mathematica or matlab, facilitating the characterization of flows produced by nanomechanical devices and providing insight into the underlying flow physics.

[Rainfall effects on the sap flow of Hedysarum scoparium.

PubMed

Yang, Qiang; Zha, Than Shan; Jia, Xin; Qin, Shu Gao; Qian, Duo; Guo, Xiao Nan; Chen, Guo Peng

2016-03-01

In arid and semi-arid areas, plant physiological responses to water availability depend largely on the intensity and frequency of rain events. Knowledge on the responses of xerophytic plants to rain events is important for predicting the structure and functioning of dryland ecosystems under changing climate. The sap flow of Hedysarum scoparium in the Mu Us Sand Land was continuously measured during the growing season of 2012 and 2013. The objectives were to quantify the dynamics of sap flow under different weather conditions, and to examine the responses of sap flow to rain events of different sizes. The results showed that the daily sap flow rates of H. scoparium were lower on rainy days than on clear days. On clear days, the sap flow of H. scoparium showed a midday plateau, and was positively correlated with solar radiation and relative humidity. On rainy days, the sap flow fluctuated at low levels, and was positively correlated with solar radiation and air temperature. Rain events not only affected the sap flow on rainy days through variations in climatic factors (e.g., solar radiation and air temperature), but also affected post-rainfall sap flow velocities though changes in soil moisture. Small rain events (<20 mm) did not change the sap flow, whereas large rain events (>20 mm) significantly increased the sap flow on days following rainfall. Rain-wetted soil conditions not only resulted in higher sap flow velocities, but also enhanced the sensitivity of sap flow to solar radiation, vapor pressure deficit and air temperature.

Hydrodynamic study of an internal airlift reactor for microalgae culture.

PubMed

Rengel, Ana; Zoughaib, Assaad; Dron, Dominique; Clodic, Denis

2012-01-01

Internal airlift reactors are closed systems considered today for microalgae cultivation. Several works have studied their hydrodynamics but based on important solid concentrations, not with biomass concentrations usually found in microalgae cultures. In this study, an internal airlift reactor has been built and tested in order to clarify the hydrodynamics of this system, based on microalgae typical concentrations. A model is proposed taking into account the variation of air bubble velocity according to volumetric air flow rate injected into the system. A relationship between riser and downcomer gas holdups is established, which varied slightly with solids concentrations. The repartition of solids along the reactor resulted to be homogenous for the range of concentrations and volumetric air flow rate studied here. Liquid velocities increase with volumetric air flow rate, and they vary slightly when solids are added to the system. Finally, liquid circulation time found in each section of the reactor is in concordance with those employed in microalgae culture.

Can the starpatch on Xi Bootis A be explained by using tangential flows?

NASA Technical Reports Server (NTRS)

Toner, Clifford G.; Labonte, Barry J.

1991-01-01

It is demonstrated that a modification of the starpatch model of Toner and Gray (1988), using tangential flows instead of an enhanced granulation velocity dispersion within the patch, is very successful at reproducing both the observed line asymmetry and the line broadening variations observed in the G8 dwarf Xi Boo A. Areal coverage of 10 percent + or - 3 percent of the visible disk, latitude 30 deg + or - 4 deg, mean brightness 0.85 + or - 0.05 relative to the 'quiet' photosphere, mean tangential flow velocities of 8.0 + or - 1.5 km/s, and dispersions about the mean of 8/0 + or - 2.0 km/s are inferred for the patch. A feature at a latitude of about 30 deg is inferred which covers about 10 percent of the visible disk and is 10-20 percent fainter than the rest of the photosphere. It is inferred that 70-80 percent of the patch is penumbra.

Spectral Analysis of Pressure, Noise and Vibration Velocity Measurement in Cavitation

NASA Astrophysics Data System (ADS)

Jablonská, Jana; Mahdal, Miroslav; Kozubková, Milada

2017-12-01

The article deals with experimental investigation of water cavitation in the convergent-divergent nozzle of rectangular cross-section. In practice, a quick and simple determination of cavitation is essential, especially if it is basic cavitation or cavitation generated additionally by the air being sucked. Air influences the formation, development and size of the cavity area in hydraulic elements. Removal or reduction of the cavity area is possible by structural changes of the element. In case of the cavitation with the suction air, it is necessary to find the source of the air and seal it. The pressure gradient, the flow, the oxygen content in the tank, and hence the air dissolved in the water, the air flow rate, the noise intensity and the vibration velocity on the nozzle wall were measured on laboratory equipment. From the selected measurements the frequency spectrum of the variation of the water flow of the cavity with cavitation without air saturation and with air saturation was compared and evaluated.

Vortex generation and wave-vortex interaction over a concave plate with roughness and suction

NASA Technical Reports Server (NTRS)

Bertolotti, Fabio

1993-01-01

The generation and amplification of vortices by surface homogeneities, both in the form of surface waviness and of wall-normal velocity, is investigated using the nonlinear parabolic stability equations. Transients and issues of algebraic growth are avoided through the use of a similarity solution as initial condition for the vortex. In the absence of curvature, the vortex decays as the square root of 1/x when flowing over streamwise aligned riblets of constant height, and grows as the square root of x when flowing over a corresponding streamwise aligned variation of blowing/suction transpiration velocity. However, in the presence of wall inhomogeneities having both streamwise and spanwise periodicity, the growth of the vortex can be much larger. In the presence of curvature, the vortex develops into a Gortler vortex. The 'direct' and 'indirect' interaction mechanisms possible in wave-vortex interaction are presented. The 'direct' interaction does not lead to strong resonance with the flow conditions investigated. The 'indirect' interaction leads to K-type transition.

The influence of free-stream turbulence on separation of turbulent boundary layers in incompressible, two-dimensional flow

NASA Technical Reports Server (NTRS)

Potter, J. Leith; Barnett, R. Joel; Fisher, Carl E.; Koukousakis, Costas E.

1986-01-01

Experiments were conducted to determine if free-stream turbulence scale affects separation of turbulent boundary layers. In consideration of possible interrelation between scale and intensity of turbulence, the latter characteristic also was varied and its role was evaluated. Flow over a 2-dimensional airfoil in a subsonic wind tunnel was studied with the aid of hot-wire anemometry, liquid-film flow visualization, a Preston tube, and static pressure measurements. Profiles of velocity, relative turbulence intensity, and integral scale in the boundary layer were measured. Detachment boundary was determined for various angles of attack and free-stream turbulence. The free-stream turbulence intensity and scale were found to spread into the entire turbulent boundary layer, but the effect decreased as the airfoil surface was approached. When the changes in stream turbulence were such that the boundary layer velocity profiles were unchanged, detachment location was not significantly affected by the variations of intensity and scale. Pressure distribution remained the key factor in determining detachment location.

Calibrant-Free Analyte Quantitation via a Variable Velocity Flow Cell.

PubMed

Beck, Jason G; Skuratovsky, Aleksander; Granger, Michael C; Porter, Marc D

2017-01-17

In this paper, we describe a novel method for analyte quantitation that does not rely on calibrants, internal standards, or calibration curves but, rather, leverages the relationship between disparate and predictable surface-directed analyte flux to an array of sensing addresses and a measured resultant signal. To reduce this concept to practice, we fabricated two flow cells such that the mean linear fluid velocity, U, was varied systematically over an array of electrodes positioned along the flow axis. This resulted in a predictable variation of the address-directed flux of a redox analyte, ferrocenedimethanol (FDM). The resultant limiting currents measured at a series of these electrodes, and accurately described by a convective-diffusive transport model, provided a means to calculate an "unknown" concentration without the use of calibrants, internal standards, or a calibration curve. Furthermore, the experiment and concentration calculation only takes minutes to perform. Deviation in calculated FDM concentrations from true values was minimized to less than 0.5% when empirically derived values of U were employed.

Velocity Gradients in the Intracluster Gas of the Perseus Cluster

NASA Astrophysics Data System (ADS)

Dupke, Renato A.; Bregman, Joel N.

2001-02-01

We report the results of spatially resolved X-ray spectroscopy of eight different ASCA pointings distributed symmetrically around the center of the Perseus Cluster. The outer region of the intracluster gas is roughly isothermal, with temperature ~6-7 keV and metal abundance ~0.3 solar. Spectral analysis of the central pointing is consistent with the presence of a cooling flow and a central metal abundance gradient. A significant velocity gradient is found along an axis at a position angle of ~135°, which is ~45° discrepant with the major axis of the X-ray elongation. The radial velocity difference is found to be greater than 1000 km s-1 Mpc-1 at the 90% confidence level. Simultaneous fittings of GIS 2 and 3 indicate that the velocity gradient is significant at the 95% confidence level, and the F-test rules out constant velocities at the 99% level. Intrinsic short- and long-term variations of gain are unlikely (P<0.03) to explain the velocity discrepancies.

Grounding line migration through the calving season at Jakobshavn Isbræ, Greenland, observed with terrestrial radar interferometry

NASA Astrophysics Data System (ADS)

Xie, Surui; Dixon, Timothy H.; Voytenko, Denis; Deng, Fanghui; Holland, David M.

2018-04-01

Ice velocity variations near the terminus of Jakobshavn Isbræ, Greenland, were observed with a terrestrial radar interferometer (TRI) during three summer campaigns in 2012, 2015, and 2016. We estimate a ˜ 1 km wide floating zone near the calving front in early summer of 2015 and 2016, where ice moves in phase with ocean tides. Digital elevation models (DEMs) generated by the TRI show that the glacier front here was much thinner (within 1 km of the glacier front, average ice surface is ˜ 100 and ˜ 110 m above local sea level in 2015 and 2016, respectively) than ice upstream (average ice surface is > 150 m above local sea level at 2-3 km to the glacier front in 2015 and 2016). However, in late summer 2012, there is no evidence of a floating ice tongue in the TRI observations. Average ice surface elevation near the glacier front was also higher, ˜ 125 m above local sea level within 1 km of the glacier front. We hypothesize that during Jakobshavn Isbræ's recent calving seasons the ice front advances ˜ 3 km from winter to spring, forming a > 1 km long floating ice tongue. During the subsequent calving season in mid- and late summer, the glacier retreats by losing its floating portion through a sequence of calving events. By late summer, the entire glacier is likely grounded. In addition to ice velocity variation driven by tides, we also observed a velocity variation in the mélange and floating ice front that is non-parallel to long-term ice flow motion. This cross-flow-line signal is in phase with the first time derivative of tidal height and is likely associated with tidal currents or bed topography.

Erratum: ``Evidence that a Deep Meridional Flow Sets the Sunspot Cycle Period'' (ApJ, 589, 665 [2003])

NASA Astrophysics Data System (ADS)

Hathaway, David H.; Nandy, Dibyendu; Wilson, Robert M.; Reichmann, Edwin J.

2004-02-01

An error was made in entering the data used in Figure 6. This changes the results concerning the length of the time lag between the variations in the meridional flow speed and those in the cycle amplitude. The final paragraph on page 667 should read: ``Finally, we study the relationship between the drift velocities and the amplitudes of the hemisphere/cycles. In Figure 5 we compare the drift velocity at the maximum of the cycle to the amplitude of that cycle for that hemisphere. There is a positive (0.5) and significant (95%) correlation between the two. However, an even stronger relationship is found between the drift velocity and the amplitude of the N+2 cycle. The correlation is stronger (0.7) and more significant (99%), as shown in Figure 6. This relationship is suggestive of a ``memory'' in the solar cycle, again a property of dynamo models that use meridional circulation. Indeed, the two-cycle lag is precisely the relationship found by Charbonneau & Dikpati (ApJ, 589, 665 [2003]). This behavior is, however, more difficult to interpret, and we elaborate on this in the next section. In either case, these correlations only explain part of the variance in cycle amplitude (25% for the current cycle and 50% for the N+2 cycle). Obviously, other mechanisms, such as variations in the gradient in the rotation rate, also contribute to the cycle amplitude variations. Our investigation of possible connections between drift rates and the amplitudes of the N+1 and N+3 cycles gives no significant correlations at these alternative time lags.'' The revised Figure 6 and its caption are given below

Pulmonary Vein Doppler Patterns in Infants with Single Right Ventricle Anomalies After Initial Staged Palliations.

PubMed

Kirkpatrick, Edward C; Steltzer, Jessica; Simpson, Pippa; Pan, Amy; Dragulescu, Andrea; Falkensammer, Christine B; Gelehrter, Sarah; Lai, Wyman W; Levine, Jami; Miller, Stephen; Miller, Thomas A; Pruetz, Jay; Sachdeva, Ritu; Thacker, Deepika; Frommelt, Peter

2017-08-01

The aim of this study was to describe serial changes in echocardiographic Doppler pulmonary vein flow (PVF) patterns in infants with single right ventricle (RV) anomalies enrolled in the Single Ventricle Reconstruction trial. Measurement of PVF peak systolic (S) and diastolic (D) velocities, velocity time integrals (VTI), S/D peak velocity and VTI ratios, and frequency of atrial reversal (Ar) waves were made at three postoperative time points in 261 infants: early post-Norwood, pre-stage II surgery, and 14 months. Indices were compared over time, between initial shunt type [modified Blalock-Taussig shunt (MBTS) and right ventricle-to-pulmonary artery shunt (RVPAS)] and in relation to clinical outcomes. S velocities and VTI increased over time while D wave was stable, resulting in increasing S/D peak velocity and VTI ratios, with a median post-Norwood S/D VTI ratio of 1.14 versus 1.38 at pre-stage II and 1.89 at 14 months (P < 0.0001 between intervals). MBTS subjects had significantly higher S/D peak velocity and VTI ratios compared to RVPAS at the post-Norwood and pre-stage II time points (P < 0.0001) but not by 14 months. PVF patterns did not correlate with survival or hospitalization course at 1 year. PVF patterns after Norwood palliation differ from normal infants by having a dominant systolic pattern throughout infancy. PVF differences based upon shunt type resolve by 14 months and did not correlate with clinical outcomes. This study describes normative values and variations in PVF for infants with a single RV from shunt-dependent pulmonary blood flow to cavopulmonary blood flow.

Remote measurement of river discharge using thermal particle image velocimetry (PIV) and various sources of bathymetric information

USGS Publications Warehouse

Legleiter, Carl; Kinzel, Paul J.; Nelson, Jonathan M.

2017-01-01

Although river discharge is a fundamental hydrologic quantity, conventional methods of streamgaging are impractical, expensive, and potentially dangerous in remote locations. This study evaluated the potential for measuring discharge via various forms of remote sensing, primarily thermal imaging of flow velocities but also spectrally-based depth retrieval from passive optical image data. We acquired thermal image time series from bridges spanning five streams in Alaska and observed strong agreement between velocities measured in situ and those inferred by Particle Image Velocimetry (PIV), which quantified advection of thermal features by the flow. The resulting surface velocities were converted to depth-averaged velocities by applying site-specific, calibrated velocity indices. Field spectra from three clear-flowing streams provided strong relationships between depth and reflectance, suggesting that, under favorable conditions, spectrally-based bathymetric mapping could complement thermal PIV in a hybrid approach to remote sensing of river discharge; this strategy would not be applicable to larger, more turbid rivers, however. A more flexible and efficient alternative might involve inferring depth from thermal data based on relationships between depth and integral length scales of turbulent fluctuations in temperature, captured as variations in image brightness. We observed moderately strong correlations for a site-aggregated data set that reduced station-to-station variability but encompassed a broad range of depths. Discharges calculated using thermal PIV-derived velocities were within 15% of in situ measurements when combined with depths measured directly in the field or estimated from field spectra and within 40% when the depth information also was derived from thermal images. The results of this initial, proof-of-concept investigation suggest that remote sensing techniques could facilitate measurement of river discharge.

Flow over bedforms in a large sand-bed river: A field investigation

USGS Publications Warehouse

Holmes, Robert R.; Garcia, Marcelo H.

2008-01-01

An experimental field study of flows over bedforms was conducted on the Missouri River near St. Charles, Missouri. Detailed velocity data were collected under two different flow conditions along bedforms in this sand-bed river. The large river-scale data reflect flow characteristics similar to those of laboratory-scale flows, with flow separation occurring downstream of the bedform crest and flow reattachment on the stoss side of the next downstream bedform. Wave-like responses of the flow to the bedforms were detected, with the velocity decreasing throughout the flow depth over bedform troughs, and the velocity increasing over bedform crests. Local and spatially averaged velocity distributions were logarithmic for both datasets. The reach-wise spatially averaged vertical-velocity profile from the standard velocity-defect model was evaluated. The vertically averaged mean flow velocities for the velocity-defect model were within 5% of the measured values and estimated spatially averaged point velocities were within 10% for the upper 90% of the flow depth. The velocity-defect model, neglecting the wake function, was evaluated and found to estimate thevertically averaged mean velocity within 1% of the measured values.  

An implicit time-marching method for the three-dimensional Navier-Stokes equations of contravariant velocity components

NASA Astrophysics Data System (ADS)

Daiguji, Hisaaki; Yamamoto, Satoru

1988-12-01

The implicit time-marching finite-difference method for solving the three-dimensional compressible Euler equations developed by the authors is extended to the Navier-Stokes equations. The distinctive features of this method are to make use of momentum equations of contravariant velocities instead of physical boundaries, and to be able to treat the periodic boundary condition for the three-dimensional impeller flow easily. These equations can be solved by using the same techniques as the Euler equations, such as the delta-form approximate factorization, diagonalization and upstreaming. In addition to them, a simplified total variation diminishing scheme by the authors is applied to the present method in order to capture strong shock waves clearly. Finally, the computed results of the three-dimensional flow through a transonic compressor rotor with tip clearance are shown.

Generation of long waves in a fluid flowing over a localized topography at a periodically varying velocity

NASA Astrophysics Data System (ADS)

Ohsugi, Yasuo; Funakoshi, Mitsuaki

2000-05-01

The generation of long waves in a fluid flowing over a localized topography is examined numerically using the forced KdV equation under the assumption that the velocity U of the fluid far from the topography is close to the phase speed of a linear long wave and varies periodically with period T. For T within a few regions, we observe the 1: n entrainment of the wave motion near the topography to period T, in which n upstream-advancing waves are generated in period T. These regions extend and shift to larger T as the average value or amplitude of the variation of U increases. Furthermore, when the entrainment occurs, the spatial region where time-periodic evolution is almost attained extends toward both upstream and downstream directions with increasing time.

Application of turbulence modeling to predict surface heat transfer in stagnation flow region of circular cylinder

NASA Technical Reports Server (NTRS)

Wang, Chi R.; Yeh, Frederick C.

1987-01-01

A theoretical analysis and numerical calculations for the turbulent flow field and for the effect of free-stream turbulence on the surface heat transfer rate of a stagnation flow are presented. The emphasis is on the modeling of turbulence and its augmentation of surface heat transfer rate. The flow field considered is the region near the forward stagnation point of a circular cylinder in a uniform turbulent mean flow. The free stream is steady and incompressible with a Reynolds number of the order of 10 to the 5th power and turbulence intensity of less than 5 percent. For this analysis, the flow field is divided into three regions: (1) a uniform free-stream region where the turbulence is homogeneous and isotropic; (2) an external viscid flow region where the turbulence is distorted by the variation of the mean flow velocity; and, (3) an anisotropic turbulent boundary layer region over the cylinder surface. The turbulence modeling techniques used are the kappa-epsilon two-equation model in the external flow region and the time-averaged turbulence transport equation in the boundary layer region. The turbulence double correlations, the mean velocity, and the mean temperature within the boundary layer are solved numerically from the transport equations. The surface heat transfer rate is calculated as functions of the free-stream turbulence longitudinal microlength scale, the turbulence intensity, and the Reynolds number.

Structure-Preserving Variational Multiscale Modeling of Turbulent Incompressible Flow with Subgrid Vortices

NASA Astrophysics Data System (ADS)

Evans, John; Coley, Christopher; Aronson, Ryan; Nelson, Corey

2017-11-01

In this talk, a large eddy simulation methodology for turbulent incompressible flow will be presented which combines the best features of divergence-conforming discretizations and the residual-based variational multiscale approach to large eddy simulation. In this method, the resolved motion is represented using a divergence-conforming discretization, that is, a discretization that preserves the incompressibility constraint in a pointwise manner, and the unresolved fluid motion is explicitly modeled by subgrid vortices that lie within individual grid cells. The evolution of the subgrid vortices is governed by dynamical model equations driven by the residual of the resolved motion. Consequently, the subgrid vortices appropriately vanish for laminar flow and fully resolved turbulent flow. As the resolved velocity field and subgrid vortices are both divergence-free, the methodology conserves mass in a pointwise sense and admits discrete balance laws for energy, enstrophy, and helicity. Numerical results demonstrate the methodology yields improved results versus state-of-the-art eddy viscosity models in the context of transitional, wall-bounded, and rotational flow when a divergence-conforming B-spline discretization is utilized to represent the resolved motion.

Glossosoma nigrior (Trichoptera: Glossosomatidae) respiration in moving fluid.

PubMed

Morris, Mark W L; Hondzo, Miki

2013-08-15

Laboratory measurements of dissolved oxygen (DO) uptake by Glossosoma nigrior Banks were conducted in a sealed, recirculating flume under variable fluid flow velocities. Measurements were performed in similar water temperatures, DO concentrations and fluid flow velocities to field conditions in the stream where the larvae were obtained. Total oxygen uptake by both cased larvae and corresponding cases without larvae were quantified. An increased fluid flow velocity corresponded to an increased larval DO uptake rate. Oxygen uptake by the larval cases alone was not as sensitive to changes in the Peclet (Pe) number, the dimensionless ratio of advective to diffusive DO transport, as uptake by larvae themselves. The flux of DO to larvae and their cases was up to seven times larger in a moving fluid in comparison to non-moving fluid conditions in the proximity of larvae for 087, larvae typically remained in their cases. This indicates that oxygen delivery to the larvae at low Pe is insufficient to satisfy the respiratory demands of cased larvae.

Heat and mass transfer boundary conditions at the surface of a heated sessile droplet

NASA Astrophysics Data System (ADS)

Ljung, Anna-Lena; Lundström, T. Staffan

2017-12-01

This work numerically investigates how the boundary conditions of a heated sessile water droplet should be defined in order to include effects of both ambient and internal flow. Significance of water vapor, Marangoni convection, separate simulations of the external and internal flow, and influence of contact angle throughout drying is studied. The quasi-steady simulations are carried out with Computational Fluid Dynamics and conduction, natural convection and Marangoni convection are accounted for inside the droplet. For the studied conditions, a noticeable effect of buoyancy due to evaporation is observed. Hence, the inclusion of moisture increases the maximum velocities in the external flow. Marangoni convection will, in its turn, increase the velocity within the droplet with up to three orders of magnitude. Results furthermore show that the internal and ambient flow can be simulated separately for the conditions studied, and the accuracy is improved if the internal temperature gradient is low, e.g. if Marangoni convection is present. Simultaneous simulations of the domains are however preferred at high plate temperatures if both internal and external flows are dominated by buoyancy and natural convection. The importance of a spatially resolved heat and mass transfer boundary condition is, in its turn, increased if the internal velocity is small or if there is a large variation of the transfer coefficients at the surface. Finally, the results indicate that when the internal convective heat transport is small, a rather constant evaporation rate may be obtained throughout the drying at certain conditions.

Turbulence and secondary motions in square duct flow

NASA Astrophysics Data System (ADS)

Pirozzoli, Sergio; Modesti, Davide; Orlandi, Paolo; Grasso, Francesco

2017-11-01

We study turbulent flows in pressure-driven ducts with square cross-section through DNS up to Reτ 1050 . Numerical simulations are carried out over extremely long integration times to get adequate convergence of the flow statistics, and specifically high-fidelity representation of the secondary motions which arise. The intensity of the latter is found to be in the order of 1-2% of the bulk velocity, and unaffected by Reynolds number variations. The smallness of the mean convection terms in the streamwise vorticity equation points to a simple characterization of the secondary flows, which in the asymptotic high-Re regime are found to be approximated with good accuracy by eigenfunctions of the Laplace operator. Despite their effect of redistributing the wall shear stress along the duct perimeter, we find that secondary motions do not have large influence on the mean velocity field, which can be characterized with good accuracy as that resulting from the concurrent effect of four independent flat walls, each controlling a quarter of the flow domain. As a consequence, we find that parametrizations based on the hydraulic diameter concept, and modifications thereof, are successful in predicting the duct friction coefficient. This research was carried out using resources from PRACE EU Grants.

An investigation of the flow characteristics in the blade endwall corner region

NASA Technical Reports Server (NTRS)

Hazarika, Birinchi K.; Raj, Rishi S.

1987-01-01

Studies were undertaken to determine the structure of the flow in the blade end wall corner region simulated by attaching two uncambered airfoils on either side of a flat plate with a semicircular leading edge. Detailed measurements of the corner flow were obtained with conventional pressure probes, hot wire anemometry, and flow visualization. The mean velocity profiles and six components of the Reynolds stress tensor were obtained with an inclined single sensor hot wire probe whereas power spectra were obtained with a single sensor oriented normal to the flow. Three streamwise vortices were identified based on the surface streamlines, distortion of total pressure profiles, and variation of mean velocity components in the corner. A horseshoe vortex formed near the leading edge of the airfoil. Within a short distance downstream, a corner vortex was detected between the horseshoe vortex and the surfaces forming the corner. A third vortex was formed at the rear portion of the corner between the corner vortex and the surface of the flat plate. Turbulent shear stress and production of turbulence are negligibly small. A region of negative turbulent shear stress was also observed near the region of low turbulence intensity from the vicinity of the flat plate.

A Well-Posed, Objective and Dynamic Two-Fluid Model

NASA Astrophysics Data System (ADS)

Chetty, Krishna; Vaidheeswaran, Avinash; Sharma, Subash; Clausse, Alejandro; Lopez de Bertodano, Martin

The transition from dispersed to clustered bubbly flows due to wake entrainment is analyzed with a well-posed and objective one-dimensional (1-D) Two-Fluid Model, derived from variational principles. Modeling the wake entrainment force using the variational technique requires formulation of the inertial coupling coefficient, which defines the kinetic coupling between the phases. The kinetic coupling between a pair of bubbles and the liquid is obtained from potential flow over two-spheres and the results are validated by comparing the virtual mass coefficients with existing literature. The two-body interaction kinetic coupling is then extended to a lumped parameter model for viscous flow over two cylindrical bubbles, to get the Two-Fluid Model for wake entrainment. Linear stability analyses comprising the characteristics and the dispersion relation and non-linear numerical simulations are performed with the 1-D variational Two-Fluid Model to demonstrate the wake entrainment instability leading to clustering of bubbles. Finally, the wavelengths, amplitudes and propagation velocities of the void waves from non-linear simulations are compared with the experimental data.

Time-resolved seismic tomography at the EGS geothermal reservoir of Soultz-Sous-Forêts (France) during hydraulic stimulations. A comparison between different injection tests

NASA Astrophysics Data System (ADS)

Dorbath, C.; Calo, M.; Cornet, F.; Frogneux, M.

2011-12-01

One major goal of monitoring seismicity accompanying hydraulic fracturing of a reservoir is to recover the seismic velocity field in and around the geothermal site. Several studies have shown that the 4D (time dependent) seismic tomographies are very useful to illustrate and study the temporal variation of the seismic velocities conditioned by injected fluids. However, only an appropriate separation of the data in subsets and a reliable tomographic method allow studying representative variations of the seismic velocities during and after the injection periods. We present here new 4D seismic tomographies performed using datasets regarding some stimulation tests performed at the Enhanced Geothermal System (EGS) site of Soultz-sous-Forêts (Alsace, France). The data used were recorded during the stimulation tests occurred in 2000, 2003 and 2004 that involved the wells GPK2, GPK3 and GPK4. For each set of events, the subsetting of the data was performed by taking into account the injection parameters of the stimulation tests (namely the injected flow rate and the wellhead pressure). The velocity models have been obtained using the Double-Difference tomographic method (Zhang and Thurber 2003) and further improved with the post-processing WAM technique (Calo' et al., 2009, 2011). This technique resulted very powerful because combines high resolution and reliablity of the seismic velocity fields calculated even with small datasets. In this work we show the complete sequence of the time-lapse tomographies and their variations in time and between different stimulation tests.

From the speed of sound to the speed of light: Ultrasonic Cherenkov refractometry

NASA Astrophysics Data System (ADS)

Hallewell, G. D.

2017-12-01

Despite its success in the SLD CRID at the SLAC Linear Collider, ultrasonic measurement of Cherenkov radiator refractive index has been less fully exploited in more recent Cherenkov detectors employing gaseous radiators. This is surprising, since it is ideally suited to monitoring hydrostatic variations in refractive index as well as its evolution during the replacement of a light radiator passivation gas (e.g. N2, CO2) with a heavier fluorocarbon (e.g. C4F10[CF4]; mol. wt. 188[88]). The technique exploits the dependence of sound velocity on the molar concentrations of the two components at known temperature and pressure. The SLD barrel CRID used an 87%C5F12/13%N2 blend, mixed before injection into the radiator vessel: blend control based on ultrasonic mixture analysis maintained the β=1 Cherenkov ring angle to a long term variation better than ±0.3%, with refractivity monitored ultrasonically at multiple points within the radiator vessel. Recent advances using microcontroller-based electronics have led to ultrasonic instruments capable of simultaneously measuring gas flow and binary mixture composition in the fluorocarbon evaporative cooling systems of the ATLAS Inner Detector. Sound transit times are measured with multi-MHz transit time clocks in opposite directions in flowing gas for simultaneous measurement of flow rate and sound velocity. Gas composition is evaluated in real-time by comparison with a sound velocity/composition database. Such instruments could be incorporated into new and upgraded gas Cherenkov detectors for radiator gas mixture (and corresponding refractive index) measurement to a precision better than 10-3. They have other applications in binary gas analysis - including in Xenon-based anaesthesia. These possibilities are discussed.

Steady induction effects in geomagnetism. Part 1A: Steady motional induction of geomagnetic chaos

NASA Technical Reports Server (NTRS)

Voorhies, Coerte V.

1992-01-01

Geomagnetic effects of magnetic induction by hypothetically steady fluid motion and steady magnetic flux diffusion near the top of Earth's core are investigated using electromagnetic theory, simple magnetic earth models, and numerical experiments with geomagnetic field models. The problem of estimating a steady fluid velocity field near the top of Earth's core which induces the secular variation indicated by broad-scale models of the observed geomagnetic field is examined and solved. In Part 1, the steady surficial core flow estimation problem is solved in the context of the source-free mantle/frozen-flux core model. In the first paper (IA), the theory underlying such estimates is reviewed and some consequences of various kinematic and dynamic flow hypotheses are derived. For a frozen-flux core, fluid downwelling is required to change the mean square normal magnetic flux density averaged over the core-mantle boundary. For surficially geostrophic flow, downwelling implies poleward flow. The solution of the forward steady motional induction problem at the surface of a frozen-flux core is derived and found to be a fine, easily visualized example of deterministic chaos. Geomagnetic effects of statistically steady core surface flow may well dominate secular variation over several decades. Indeed, effects of persistent, if not steady, surficially geostrophic core flow are described which may help explain certain features of the present broad-scale geomagnetic field and perhaps paleomagnetic secular variation.

Trajectory of a synthetic jet issuing into a high Reynolds number turbulent boundary layer

NASA Astrophysics Data System (ADS)

Berk, Tim; Baidya, Rio; de Silva, Charitha; Marusic, Ivan; Hutchins, Nicholas; Ganapathisubramani, Bharathram

2017-11-01

Synthetic jets are zero-net-mass-flux actuators that can be used in a range of flow control applications. For several pulsed/synthetic jet in cross-flow applications the variation of the jet trajectory in the mean flow with jet and boundary layer parameters is important. This trajectory will provide an indication of the penetration depth of the pulsed/synthetic jet into a boundary layer. Trajectories of a synthetic jet in a turbulent boundary layer are measured for a range of actuation parameters in both low- and high Reynolds numbers (up to Reτ = 13000). The important parameters influencing the trajectory are determined from these measurements. The Reynolds number of the boundary layer is shown to only have a small effect on the trajectory. In fact, the critical parameters are found to be the Strouhal number of the jet based on jet dimensions as well as the velocity ratio of the jet (defined as a ratio between peak jet velocity and the freestream velocity). An expression for the trajectory of the synthetic (or pulsed) jet is derived from the data, which (in the limit) is consistent with known expressions for the trajectory of a steady jet in a cross-flow. T.B. and B.G. are grateful to the support from the ERC (Grant Agreement No. 277472) and the EPSRC (Grant ref. no. EP/L006383/1).

Diatom assemblages as guides to flow conditions during the 2004 Indian Ocean tsunami at Phra Thong Island, Thailand

NASA Astrophysics Data System (ADS)

Sawai, Y.; Jankaew, K.; Martin, M. E.; Choowong, M.; Charoentitirat, T.; Prendergast, A.

2008-12-01

Diatom assemblages in the 2004 tsunami deposits of Phra Thong Island, Thailand represent flow conditions during the tsunami. The tsunami deposit consists of single or multiple graded beds. Diatom assemblages in the lowermost part of the deposit predominantly comprise beach and subtidal species. In the middle part of the deposit, the assemblages are dominated by marine plankton with increasing finer fractions. A mixed assemblage of freshwater, brackish, and marine species occupies the uppermost part of the deposit. Changes in flow conditions during the tsunami can explain these diatom assemblage variations. During fast current velocities, medium sand is deposited; only beach and subtidal diatoms that live attached to the sand can be incorporated into the tsunami deposit under these flow conditions. It is difficult for diatoms in suspension to settle out under fast current velocities. With decreasing current velocities, marine plankton can settle out of the water column .Finally, during the suspension stage (calm currents) between tsunami waves, the entrained freshwater, brackish, and marine species settle out with mud and plant trash. Fewer broken valves in the lowermost part of the deposit is probably a results of rapid entrainment, whilst selective breakage of marine plankton (Thalassionema nitzschioides, and Thalassiosira and Coscinodiscus spp.) in the middle part of the deposit probably results from abrasion by turbulent current before their deposition.

Motion-sensitized SPRITE measurements of hydrodynamic cavitation in fast pipe flow.

PubMed

Adair, Alexander; Mastikhin, Igor V; Newling, Benedict

2018-06-01

The pressure variations experienced by a liquid flowing through a pipe constriction can, in some cases, result in the formation of a bubble cloud (i.e., hydrodynamic cavitation). Due to the nature of the bubble cloud, it is ideally measured through the use of non-optical and non-invasive techniques; therefore, it is well-suited for study by magnetic resonance imaging. This paper demonstrates the use of Conical SPRITE (a 3D, centric-scan, pure phase-encoding pulse sequence) to acquire time-averaged void fraction and velocity information about hydrodynamic cavitation for water flowing through a pipe constriction. Copyright © 2018 Elsevier Inc. All rights reserved.

Effect of reducing rotor blade inlet diameter on the performance of a 11.66-Centimeter radial-inflow turbine

NASA Technical Reports Server (NTRS)

Kofskey, M. G.; Haas, J. E.

1973-01-01

The effect of increased rotor blade loading on turbine performance was investigated by reducing rotor blade inlet diameter. The reduction was made in four stages. Each modification was tested with the same stator using cold air as the working fluid. Results are presented in terms of equivalent mass flow and efficiency at equivalent design rotative speed and over a range of pressure ratios. Internal flow characteristics are shown in terms of stator exit static pressure and the radial variation of local loss and rotor-exit flow angle with radius ratio. Included are velocity diagrams calculated from the experimental results.

Regular flow reversals in Rayleigh-Bénard convection in a horizontal magnetic field.

PubMed

Tasaka, Yuji; Igaki, Kazuto; Yanagisawa, Takatoshi; Vogt, Tobias; Zuerner, Till; Eckert, Sven

2016-04-01

Magnetohydrodynamic Rayleigh-Bénard convection was studied experimentally using a liquid metal inside a box with a square horizontal cross section and aspect ratio of five. Systematic flow measurements were performed by means of ultrasonic velocity profiling that can capture time variations of instantaneous velocity profiles. Applying a horizontal magnetic field organizes the convective motion into a flow pattern of quasi-two-dimensional rolls arranged parallel to the magnetic field. The number of rolls has the tendency to decrease with increasing Rayleigh number Ra and to increase with increasing Chandrasekhar number Q. We explored convection regimes in a parameter range, at 2×10^{3}

An comprehensive time-distance measurement of deep meridional flow and its temporal variation

NASA Astrophysics Data System (ADS)

Chen, Ruizhu; Zhao, Junwei

2016-10-01

We report our latest results on the Sun's deep solar meridional-flow measurements by time-distance helioseismology technique using 6 years of SDO/HMI Doppler-velocity data. Determination of the meridional flow by time-distance helioseismology depends on a precise measurement of the flow-induced travel-time shifts of acoustic waves traveling in the solar interior. To resolve the weak travel-time-shift signals due to deep meridional flow, we need a high signal-to-noise ratio and a robust removal of the center-to-limb (CtoL) effect, which dominates the travel-time shifts. Here we perform an ultimately comprehensive measurement that tracks acoustic waves between any two points on solar surface. The travel-time shifts are composed of CtoL effect, which is a function of disk-centric distances, and contribution from the flow component parallel to wave traveling direction, which is a function of latitude and orientation. Assuming these two effects are independent, we can derive the CtoL effect and meridional-flow contributions by solving a set of linear equations in a least-square sense. We show the solved CtoL effect and the inversion results for the solar meridional flow, and analyze the annual variation of meridional flow from May 2010 to Apr 2016.

Clustering and flow around a sphere moving into a grain cloud.

PubMed

Seguin, A; Lefebvre-Lepot, A; Faure, S; Gondret, P

2016-06-01

A bidimensional simulation of a sphere moving at constant velocity into a cloud of smaller spherical grains far from any boundaries and without gravity is presented with a non-smooth contact dynamics method. A dense granular "cluster" zone builds progressively around the moving sphere until a stationary regime appears with a constant upstream cluster size. The key point is that the upstream cluster size increases with the initial solid fraction [Formula: see text] but the cluster packing fraction takes an about constant value independent of [Formula: see text]. Although the upstream cluster size around the moving sphere diverges when [Formula: see text] approaches a critical value, the drag force exerted by the grains on the sphere does not. The detailed analysis of the local strain rate and local stress fields made in the non-parallel granular flow inside the cluster allows us to extract the local invariants of the two tensors: dilation rate, shear rate, pressure and shear stress. Despite different spatial variations of these invariants, the local friction coefficient μ appears to depend only on the local inertial number I as well as the local solid fraction, which means that a local rheology does exist in the present non-parallel flow. The key point is that the spatial variations of I inside the cluster do not depend on the sphere velocity and explore only a small range around the value one.

A double-gaussian, percentile-based method for estimating maximum blood flow velocity.

PubMed

Marzban, Caren; Illian, Paul R; Morison, David; Mourad, Pierre D

2013-11-01

Transcranial Doppler sonography allows for the estimation of blood flow velocity, whose maximum value, especially at systole, is often of clinical interest. Given that observed values of flow velocity are subject to noise, a useful notion of "maximum" requires a criterion for separating the signal from the noise. All commonly used criteria produce a point estimate (ie, a single value) of maximum flow velocity at any time and therefore convey no information on the distribution or uncertainty of flow velocity. This limitation has clinical consequences especially for patients in vasospasm, whose largest flow velocities can be difficult to measure. Therefore, a method for estimating flow velocity and its uncertainty is desirable. A gaussian mixture model is used to separate the noise from the signal distribution. The time series of a given percentile of the latter, then, provides a flow velocity envelope. This means of estimating the flow velocity envelope naturally allows for displaying several percentiles (e.g., 95th and 99th), thereby conveying uncertainty in the highest flow velocity. Such envelopes were computed for 59 patients and were shown to provide reasonable and useful estimates of the largest flow velocities compared to a standard algorithm. Moreover, we found that the commonly used envelope was generally consistent with the 90th percentile of the signal distribution derived via the gaussian mixture model. Separating the observed distribution of flow velocity into a noise component and a signal component, using a double-gaussian mixture model, allows for the percentiles of the latter to provide meaningful measures of the largest flow velocities and their uncertainty.

Unsteady Convection Flow and Heat Transfer over a Vertical Stretching Surface

PubMed Central

Cai, Wenli; Su, Ning; Liu, Xiangdong

2014-01-01

This paper investigates the effect of thermal radiation on unsteady convection flow and heat transfer over a vertical permeable stretching surface in porous medium, where the effects of temperature dependent viscosity and thermal conductivity are also considered. By using a similarity transformation, the governing time-dependent boundary layer equations for momentum and thermal energy are first transformed into coupled, non-linear ordinary differential equations with variable coefficients. Numerical solutions to these equations subject to appropriate boundary conditions are obtained by the numerical shooting technique with fourth-fifth order Runge-Kutta scheme. Numerical results show that as viscosity variation parameter increases both the absolute value of the surface friction coefficient and the absolute value of the surface temperature gradient increase whereas the temperature decreases slightly. With the increase of viscosity variation parameter, the velocity decreases near the sheet surface but increases far away from the surface of the sheet in the boundary layer. The increase in permeability parameter leads to the decrease in both the temperature and the absolute value of the surface friction coefficient, and the increase in both the velocity and the absolute value of the surface temperature gradient. PMID:25264737

Unsteady convection flow and heat transfer over a vertical stretching surface.

PubMed

Cai, Wenli; Su, Ning; Liu, Xiangdong

2014-01-01

This paper investigates the effect of thermal radiation on unsteady convection flow and heat transfer over a vertical permeable stretching surface in porous medium, where the effects of temperature dependent viscosity and thermal conductivity are also considered. By using a similarity transformation, the governing time-dependent boundary layer equations for momentum and thermal energy are first transformed into coupled, non-linear ordinary differential equations with variable coefficients. Numerical solutions to these equations subject to appropriate boundary conditions are obtained by the numerical shooting technique with fourth-fifth order Runge-Kutta scheme. Numerical results show that as viscosity variation parameter increases both the absolute value of the surface friction coefficient and the absolute value of the surface temperature gradient increase whereas the temperature decreases slightly. With the increase of viscosity variation parameter, the velocity decreases near the sheet surface but increases far away from the surface of the sheet in the boundary layer. The increase in permeability parameter leads to the decrease in both the temperature and the absolute value of the surface friction coefficient, and the increase in both the velocity and the absolute value of the surface temperature gradient.

The prediction of noise and installation effects of high-subsonic dual-stream jets in flight

NASA Astrophysics Data System (ADS)

Saxena, Swati

Both military and civil aircraft in service generate high levels of noise. One of the major contributors to this noise generated from the aircraft is the jet engine exhaust. This makes the study of jet noise and methods to reduce jet noise an active research area with the aim of designing quieter military and commercial aircraft. The current stringent aircraft noise regulations imposed by the Federal Aviation Administration (FAA) and other international agencies, have further raised the need to perform accurate jet noise calculations for more reliable estimation of the jet noise sources. The main aim of the present research is to perform jet noise simulations of single and dual-stream jets with engineering accuracy and assess forward flight effects on the jet noise. Installation effects such as caused by the pylon are also studied using a simplified pylon nozzle configuration. Due to advances in computational power, it has become possible to perform turbulent flow simulations of high speed jets, which leads to more accurate noise predictions. In the present research, a hybrid unsteady RANS-LES parallel multi-block structured grid solver called EAGLEJet is written to perform the nozzle flow calculations. The far-field noise calculation is performed using solutions to the Ffowcs Williams and Hawkings equation. The present calculations use meshes with 5 to 11 million grid points and require about three weeks of computing time with about 100 processors. A baseline single stream convergent nozzle and a dual-stream coaxial convergent nozzle are used for the flow and noise analysis. Calculations for the convergent nozzle are performed at a high subsonic jet Mach number of Mj = 0.9, which is similar to the operating conditions for commercial aircraft engines. A parallel flow gives the flight effect, which is simulated with a co-flow Mach number, Mcf varying from 0.0 to 0.28. The grid resolution effects, statistical properties of the turbulence and the heated jet effects ( TTR = 2.7) are studied and related to the noise characteristics of the jet. Both flow and noise predictions show good agreement with PIV and microphone measurements. The potential core lengths and nozzle wall boundary characteristics are studied to understand the differences between the numerical potential core lengths as compared to experiments. The flight velocity exponent, m is calculated from the noise reduction in overall sound pressure levels (OASPL, dB) and relative velocity (V j -- Vcf) at all jet inlet (angular) angles. The variation of the exponent, m at lower (50° to 90°) and higher aft inlet angles (120° to 150°) is studied and compared with available measurements. Previous studies have shown a different variation of the exponent with inlet angles while the current numerical data match well with recent experiments conducted on the same nozzle geometry. Today, turbofans are the most efficient engines in service used in almost all major commercial aircraft. Turbofans have a dual-stream exhaust nozzle with primary and secondary flow whose flow and noise characteristics are different from that of single stream jets. A Boeing-designed coaxial nozzle, with area ratio of As/Ap = 3.0, is used to study dual-stream jet noise in the present research. In this configuration, the primary nozzle extends beyond the secondary nozzle, which is representative of large turbofan engines in commercial service. The flow calculations are performed at high subsonic Mach numbers in the primary and secondary nozzles (Mpj = 0.85, Msj = 0.95) with heated core flow, TTRp = 2.26 and unheated fan flow, TTRs = 1.0. The co-flow of Mcf = 0.2 is used. The subscript p, s and amb represent the primary (core) nozzle, the secondary (fan) nozzle, and the ambient flow conditions, respectively. The statistical properties in the primary and secondary shear layers are studied and compared with those of the single stream jets. It has been found that the eddy convection velocity is lower in dual-stream jets as compared to the single stream jet operating at a similar jet exit Mach number. The phase velocity is higher in the secondary shear layer as compared to primary shear layer. The noise measurements agree well with the predicted data and noise reduction is observed in the presence of co-flow. The variation of the flight velocity exponent is calculated as a function of nozzle inlet angle. The value of the exponent at higher inlet angles is lower as compared to the single stream jets. This suggests that the noise levels are less affected in the peak noise direction in the presence of co-flow in dual-stream jets as compared to single stream jets. Two reference velocities: primary jet exit velocity Vpj and mixed velocity Vmix are considered which result in different absolute values of the exponents. Scaling of the jet spectra is performed at different inlet angles and good collapse has been obtained between the spectra. The installation effects on jet noise are studied using a simplified pylon structure with a dual-stream nozzle. In the presence of a pylon, the azimuthal symmetry of the nozzle is lost and thus the flow characteristics are different as compared to the baseline nozzle. This will result in different noise characteristics of the installed jet.

Statistical characteristics of falling-film flows: A synergistic approach at the crossroads of direct numerical simulations and experiments

NASA Astrophysics Data System (ADS)

Charogiannis, Alexandros; Denner, Fabian; van Wachem, Berend G. M.; Kalliadasis, Serafim; Markides, Christos N.

2017-12-01

We scrutinize the statistical characteristics of liquid films flowing over an inclined planar surface based on film height and velocity measurements that are recovered simultaneously by application of planar laser-induced fluorescence (PLIF) and particle tracking velocimetry (PTV), respectively. Our experiments are complemented by direct numerical simulations (DNSs) of liquid films simulated for different conditions so as to expand the parameter space of our investigation. Our statistical analysis builds upon a Reynolds-like decomposition of the time-varying flow rate that was presented in our previous research effort on falling films in [Charogiannis et al., Phys. Rev. Fluids 2, 014002 (2017), 10.1103/PhysRevFluids.2.014002], and which reveals that the dimensionless ratio of the unsteady term to the mean flow rate increases linearly with the product of the coefficients of variation of the film height and bulk velocity, as well as with the ratio of the Nusselt height to the mean film height, both at the same upstream PLIF/PTV measurement location. Based on relations that are derived to describe these results, a methodology for predicting the mass-transfer capability (through the mean and standard deviation of the bulk flow speed) of these flows is developed in terms of the mean and standard deviation of the film thickness and the mean flow rate, which are considerably easier to obtain experimentally than velocity profiles. The errors associated with these predictions are estimated at ≈1.5 % and 8% respectively in the experiments and at <1 % and <2 % respectively in the DNSs. Beyond the generation of these relations for the prediction of important film flow characteristics based on simple flow information, the data provided can be used to design improved heat- and mass-transfer equipment reactors or other process operation units which exploit film flows, but also to develop and validate multiphase flow models in other physical and technological settings.

Model for energy transfer in the solar wind: Model results

NASA Technical Reports Server (NTRS)

Barnes, A. A., Jr.; Hartle, R. E.

1972-01-01

A description is given of the results of solar wind flow in which the heating is due to (1) propagation and dissipation of hydromagnetic waves generated near the base of the wind, and (2) thermal conduction. A series of models is generated for fixed values of density, electron and proton temperature, and magnetic field at the base by varying the wave intensity at the base of the model. This series of models predicts the observed correlation between flow speed and proton temperature for a large range of velocities. The wave heating takes place in a shell about the sun greater than or approximately equal to 10 R thick. We conclude that large-scale variations observed in the solar wind are probably due mainly to variation in the hydromagnetic wave flux near the sun.

Upscaling of Solute Transport in Heterogeneous Media with Non-uniform Flow and Dispersion Fields

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xu, Zhijie; Meakin, Paul

2013-10-01

An analytical and computational model for non-reactive solute transport in periodic heterogeneous media with arbitrary non-uniform flow and dispersion fields within the unit cell of length ε is described. The model lumps the effect of non-uniform flow and dispersion into an effective advection velocity Ve and an effective dispersion coefficient De. It is shown that both Ve and De are scale-dependent (dependent on the length scale of the microscopic heterogeneity, ε), dependent on the Péclet number Pe, and on a dimensionless parameter α that represents the effects of microscopic heterogeneity. The parameter α, confined to the range of [-0.5, 0.5]more » for the numerical example presented, depends on the flow direction and non-uniform flow and dispersion fields. Effective advection velocity Ve and dispersion coefficient De can be derived for any given flow and dispersion fields, and . Homogenized solutions describing the macroscopic variations can be obtained from the effective model. Solutions with sub-unit-cell accuracy can be constructed by homogenized solutions and its spatial derivatives. A numerical implementation of the model compared with direct numerical solutions using a fine grid, demonstrated that the new method was in good agreement with direct solutions, but with significant computational savings.« less

Influence of Lorentz force, Cattaneo-Christov heat flux and viscous dissipation on the flow of micropolar fluid past a nonlinear convective stretching vertical surface

NASA Astrophysics Data System (ADS)

Gnaneswara Reddy, Machireddy

2017-12-01

The problem of micropolar fluid flow over a nonlinear stretching convective vertical surface in the presence of Lorentz force and viscous dissipation is investigated. Due to the nature of heat transfer in the flow past vertical surface, Cattaneo-Christov heat flux model effect is properly accommodated in the energy equation. The governing partial differential equations for the flow and heat transfer are converted into a set of ordinary differential equations by employing the acceptable similarity transformations. Runge-Kutta and Newton's methods are utilized to resolve the altered governing nonlinear equations. Obtained numerical results are compared with the available literature and found to be an excellent agreement. The impacts of dimensionless governing flow pertinent parameters on velocity, micropolar velocity and temperature profiles are presented graphically for two cases (linear and nonlinear) and analyzed in detail. Further, the variations of skin friction coefficient and local Nusselt number are reported with the aid of plots for the sundry flow parameters. The temperature and the related boundary enhances enhances with the boosting values of M. It is found that fluid temperature declines for larger thermal relaxation parameter. Also, it is revealed that the Nusselt number declines for the hike values of Bi.

State-to-state modeling of non-equilibrium air nozzle flows

NASA Astrophysics Data System (ADS)

Nagnibeda, E.; Papina, K.; Kunova, O.

2018-05-01

One-dimensional non-equilibrium air flows in nozzles are studied on the basis of the state-to-state description of vibrational-chemical kinetics. Five-component mixture N2/O2/NO/N/O is considered taking into account Zeldovich exchange reactions of NO formation, dissociation, recombination and vibrational energy transitions. The equations for vibrational and chem-ical kinetics in a flow are coupled to the conservation equations of momentum and total energy and solved numerically for different conditions in a nozzle throat. The vibrational distributions of nitrogen and oxygen molecules, number densities of species as well as the gas temperature and flow velocity along a nozzle axis are analysed using the detailed state-to-state flow description and in the frame of the simplified one-temperature thermal equilibrium kinetic model. The comparison of the results showed the influence of non-equilibrium kinetics on macroscopic nozzle flow parameters. In the state-to-state approach, non-Boltzmann vibrational dis-tributions of N2 and O2 molecules with a plateau part at intermediate levels are found. The results are found with the use of the complete and simplified schemes of reactions and the impact of exchange reactions, dissociation and recombination on variation of vibrational level populations, mixture composition, gas velocity and temperature along a nozzle axis is shown.

Flow above and within granular media composed of spherical and non-spherical particles - using a 3D numerical model

NASA Astrophysics Data System (ADS)

Bartzke, Gerhard; Kuhlmann, Jannis; Huhn, Katrin

2016-04-01

The entrainment of single grains and, hence, their erosion characteristics are dependent on fluid forcing, grain size and density, but also shape variations. To quantitatively describe and capture the hydrodynamic conditions around individual grains, researchers commonly use empirical approaches such as laboratory flume tanks. Nonetheless, it is difficult with such physical experiments to measure the flow velocities in the direct vicinity or within the pore spaces of sediments, at a sufficient resolution and in a non-invasive way. As a result, the hydrodynamic conditions in the water column, at the fluid-porous interface and within pore spaces of a granular medium of various grain shapes is not yet fully understood. For that reason, there is a strong need for numerical models, since these are capable of quantifying fluid speeds within a granular medium. A 3D-SPH (Smooth Particle Hydrodynamics) numerical wave tank model was set up to provide quantitative evidence on the flow velocities in the direct vicinity and in the interior of granular beds composed of two shapes as a complementary method to the difficult task of in situ measurement. On the basis of previous successful numerical wave tank models with SPH, the model geometry was chosen in dimensions of X=2.68 [m], Y=0.48 [m], and Z=0.8 [m]. Three suites of experiments were designed with a range of particle shape models: (1) ellipsoids with the long axis oriented in the across-stream direction, (2) ellipsoids with the long axis oriented in the along-stream direction, and (3) spheres. Particle diameters ranged from 0.04 [m] to 0.08 [m]. A wave was introduced by a vertical paddle that accelerated to 0.8 [m/s] perpendicular to the granular bed. Flow measurements showed that the flow velocity values into the beds were highest when the grains were oriented across the stream direction and lowest in case when the grains were oriented parallel to the stream, indicating that the model was capable to simulate simultaneously the flow into and within a granular medium composed of spherical and non-spherical shapes under wave forcing. It is concluded that variations in grain shape orientation within a bed appear to control the amount of flow that can be accumulated by the pores, which was illustrated in a conceptual model.

Experimental and Theoretical Studies of Condensation on a Horizontal Tube Row with Vapour Shear

NASA Astrophysics Data System (ADS)

Aoune, Azzeddine

Available from UMI in association with The British Library. This thesis presents an experimental and theoretical investigation into the effect of vapour shear on the condensation of steam flowing vertically downwards over a single horizontal tube and a horizontal tube in a row. Honda and Fujii's conjugate heat transfer analysis has been adapted and modified to take account of property variation with temperature and release of sensible heat to the condensing film. In industrial condensers, even in the first row, the vapour velocity profile around a tube is affected by the presence of its neighbours. This work extends Honda and Fujii's analysis to investigate the effect of tube spacing on the heat transfer. The finite element method was used to obtain the velocity field around the tube in a row and subsequently the boundary layer equations for the condensate and vapour film along with the heat flow in the tube wall were solved simultaneously. Data have been obtained at absolute pressures of 0.8 and 0.9 bar and for steam superheat up to 40 degC. Approach steam velocities up to 25 m/s were covered. Cooling water velocities and temperatures were in the range 0.68-1.16 m/s and 18-43^circ C, respectively. Honda et al (67), Roshko's flow, theory was found to fit the data for the steam flowing over the isolated tube. The theoretical data for the latter agreed well with the Shekriladze and Gomelauri (2) and Rose (40) correlations and Honda et al (67), potential flow, theory. On | Nu| Re^{-1/2} versus F basis, an average enhancement of 50% in condensate film heat transfer was observed in the case of steam flowing over the tube in a row compared to the isolated tube. This compared with the predicted value of 23% enhancement.

Origin of the inertial deviation from Darcy's law: An investigation from a microscopic flow analysis on two-dimensional model structures

NASA Astrophysics Data System (ADS)

Agnaou, Mehrez; Lasseux, Didier; Ahmadi, Azita

2017-10-01

Inertial flow in porous media occurs in many situations of practical relevance among which one can cite flows in column reactors, in filters, in aquifers, or near wells for hydrocarbon recovery. It is characterized by a deviation from Darcy's law that leads to a nonlinear relationship between the pressure drop and the filtration velocity. In this work, this deviation, also known as the nonlinear, inertial, correction to Darcy's law, which is subject to controversy upon its origin and dependence on the filtration velocity, is studied through numerical simulations. First, the microscopic flow problem was solved computationally for a wide range of Reynolds numbers up to the limit of steady flow within ordered and disordered porous structures. In a second step, the macroscopic characteristics of the porous medium and flow (permeability and inertial correction tensors) that appear in the macroscale model were computed. From these results, different flow regimes were identified: (1) the weak inertia regime where the inertial correction has a cubic dependence on the filtration velocity and (2) the strong inertia (Forchheimer) regime where the inertial correction depends on the square of the filtration velocity. However, the existence and origin of those regimes, which depend also on the microstructure and flow orientation, are still not well understood in terms of their physical interpretations, as many causes have been conjectured in the literature. In the present study, we provide an in-depth analysis of the flow structure to identify the origin of the deviation from Darcy's law. For accuracy and clarity purposes, this is carried out on two-dimensional structures. Unlike the previous studies reported in the literature, where the origin of inertial effects is often identified on a heuristic basis, a theoretical justification is presented in this work. Indeed, a decomposition of the convective inertial term into two components is carried out formally allowing the identification of a correlation between the flow structure and the different inertial regimes. These components correspond to the curvature of the flow streamlines weighted by the local fluid kinetic energy on the one hand and the distribution of the kinetic energy along these lines on the other hand. In addition, the role of the recirculation zones in the occurrence and in the form of the deviation from Darcy's law was thoroughly analyzed. For the porous structures under consideration, it is shown that (1) the kinetic energy lost in the vortices is insignificant even at high filtration velocities and (2) the shape of the flow streamlines induced by the recirculation zones plays an important role in the variation of the flow structure, which is correlated itself to the different flow regimes.

Methodological inaccuracies in clinical aortic valve severity assessment: insights from computational fluid dynamic modeling of CT-derived aortic valve anatomy

NASA Astrophysics Data System (ADS)

Traeger, Brad; Srivatsa, Sanjay S.; Beussman, Kevin M.; Wang, Yechun; Suzen, Yildirim B.; Rybicki, Frank J.; Mazur, Wojciech; Miszalski-Jamka, Tomasz

2016-04-01

Aortic stenosis is the most common valvular heart disease. Assessing the contribution of the valve as a portion to total ventricular load is essential for the aging population. A CT scan for one patient was used to create one in vivo tricuspid aortic valve geometry and assessed with computational fluid dynamics (CFD). CFD simulated the pressure, velocity, and flow rate, which were used to assess the Gorlin formula and continuity equation, current clinical diagnostic standards. The results demonstrate an underestimation of the anatomic orifice area (AOA) by Gorlin formula and overestimation of AOA by the continuity equation, using peak velocities, as would be measured clinically by Doppler echocardiography. As a result, we suggest that the Gorlin formula is unable to achieve the intended estimation of AOA and largely underestimates AOA at the critical low-flow states present in heart failure. The disparity in the use of echocardiography with the continuity equation is due to the variation in velocity profile between the outflow tract and the valve orifice. Comparison of time-averaged orifice areas by Gorlin and continuity with instantaneous orifice areas by planimetry can mask the errors of these methods, which is a result of the assumption that the blood flow is inviscid.

Particle Resolved DNS of Turbulent Oscillatory Flow Over a Layer of Fixed Particles

NASA Astrophysics Data System (ADS)

Ghodke, Chaitanya; Urzay, Javier; Apte, Sourabh

2014-11-01

Particle resolved direct numerical simulations are performed using fictitious domain approach (Apte et al., JCP 2009) to investigate oscillatory turbulent flow over a layer of fixed particles representative of a sediment layer in coastal environments. Five particle Reynolds numbers in the range, ReD = 660 - 4240 are studied and results are compared against available experimental data (Keiller & Sleath, JFM 1976). Flow is characterized in terms of coherent vortex structures, Reynolds stress variation, turbulent cross-correlations and PDF distributions. The nature of the unsteady hydrodynamic forces on particles and their correlation to sweep and burst events is reported. The net lift coefficient remains positive over the cycle and is well correlated with phase averaged near-bed velocity. Maximum in the lift coefficient occurs when the strength of the horseshoe vortices is maximum. At this phase the lift fluctuations are correlated negatively with pressure and positively with velocity fluctuations in the region above the particle bed. Preliminary analysis shows non-Gaussian distribution for velocity fluctuation and follows 4th order Gram-Charlier. These detailed findings could eventually be useful in improving the existing criterion for predicting sediment incipient motion. Supported by NSF Project # 1133363 as well as Center for Turbulence Research Stanford University Summer Program 2014.

On stagnation point flow of a micro polar nanofluid past a circular cylinder with velocity and thermal slip

NASA Astrophysics Data System (ADS)

Abbas, Nadeem; Saleem, S.; Nadeem, S.; Alderremy, A. A.; Khan, A. U.

2018-06-01

The concerned problem is dedicated to study stagnation point flow of MHD micropolar nanomaterial fluid over a circular cylinder having sinusoidal radius variation. Velocity jump slip phenomenon with porous medium is also taken into account. To be more specific, the physical situation of micropolar fluid in the presence of both weak and strong concentration is mathematically modeled in terms of differential equations. Here, three nanoparticles namely Titania (TiO2) , Copper (Cu) and Alumina (Al2O3) compared with water as base fluids are incorporated for analysis. The resulting non-linear system has been solved by Runge-Kutta-Fehlberg scheme. Numerical solutions for velocities and temperature profiles are settled for alumina-water nanofluid and deliberated through graphs and numerical tables. It is seen that the skin friction coefficients and the rate of heat transfer are maximum for copper-water nanofluid related to the alumina-water and titania-water nanofluids. Also, the precision of the present findings is certified by equating them with the previously published work.

Left ventricular diastolic filling with an implantable ventricular assist device: beat to beat variability with overall improvement

NASA Technical Reports Server (NTRS)

Nakatani, S.; Thomas, J. D.; Vandervoort, P. M.; Zhou, J.; Greenberg, N. L.; Savage, R. M.; McCarthy, P. M.

1997-01-01

OBJECTIVES: We studied the effects of left ventricular (LV) unloading by an implantable ventricular assist device on LV diastolic filling. BACKGROUND: Although many investigators have reported reliable systemic and peripheral circulatory support with implantable LV assist devices, little is known about their effect on cardiac performance. METHODS: Peak velocities of early diastolic filling, late diastolic filling, late to early filling ratio, deceleration time of early filling, diastolic filling period and atrial filling fraction were measured by intraoperative transesophageal Doppler echocardiography before and after insertion of an LV assist device in eight patients. A numerical model was developed to simulate this situation. RESULTS: Before device insertion, all patients showed either a restrictive or a monophasic transmitral flow pattern. After device insertion, transmitral flow showed rapid beat to beat variation in each patient, from abnormal relaxation to restrictive patterns. However, when the average values obtained from 10 consecutive beats were considered, overall filling was significantly normalized from baseline, with early filling velocity falling from 87 +/- 31 to 64 +/- 26 cm/s (p < 0.01) and late filling velocity rising from 8 +/- 11 to 32 +/- 23 cm/s (p < 0.05), resulting in an increase in the late to early filling ratio from 0.13 +/- 0.18 to 0.59 +/- 0.38 (p < 0.01) and a rise in the atrial filling fraction from 8 +/- 10% to 26 +/- 17% (p < 0.01). The deceleration time (from 112 +/- 40 to 160 +/- 44 ms, p < 0.05) and the filling period corrected by the RR interval (from 39 +/- 8% to 54 +/- 10%, p < 0.005) were also significantly prolonged. In the computer model, asynchronous LV assistance produced significant beat to beat variation in filling indexes, but overall a normalization of deceleration time as well as other variables. CONCLUSIONS: With LV assistance, transmitral flow showed rapidly varying patterns beat by beat in each patient, but overall diastolic filling tended to normalize with an increase of atrial contribution to the filling. Because of the variable nature of the transmitral flow pattern with the assist device, the timing of the device cycle must be considered when inferring diastolic function from transmitral flow pattern.

Multi-temporal mapping of a large, slow-moving earth flow for kinematic interpretation

USGS Publications Warehouse

Guerriero, Luigi; Coe, Jeffrey A.; Revellino, Paola; Guadagno, Francesco M.

2014-01-01

Periodic movement of large, thick landslides on discrete basal surfaces produces modifications of the topographic surface, creates faults and folds, and influences the locations of springs, ponds, and streams (Baum, et al., 1993; Coe et al., 2009). The geometry of the basal-slip surface, which can be controlled by geological structures (e.g., fold axes, faults, etc.; Revellino et al., 2010; Grelle et al., 2011), and spatial variation in the rate of displacement, are responsible for differential deformation and kinematic segmentation of the landslide body. Thus, large landslides are often composed of several distinct kinematic elements. Each element represents a discrete kinematic domain within the main landslide that is broadly characterized by stretching (extension) of the upper part of the landslide and shortening (compression) near the landslide toe (Baum and Fleming, 1991; Guerriero et al., in review). On the basis of this knowledge, we used photo interpretive and GPS field mapping methods to map structures on the surface of the Montaguto earth flow in the Apennine Mountains of southern Italy at a scale of 1:6,000. (Guerriero et al., 2013a; Fig.1). The earth flow has been periodically active since at least 1954. The most extensive and destructive period of activity began on April 26, 2006, when an estimated 6 million m3 of material mobilized, covering and closing Italian National Road SS90, and damaging residential structures (Guerriero et al., 2013b). Our maps show the distribution and evolution of normal faults, thrust faults, strike-slip faults, flank ridges, and hydrological features at nine different dates (October, 1954; June, 1976; June, 1991; June, 2003; June, 2005; May, 2006; October, 2007; July, 2009; and March , 2010) between 1954 and 2010. Within the earth flow we recognized several kinematic elements and associated structures (Fig.2a). Within each kinematic element (e.g. the earth flow neck; Fig.2b), the flow velocity was highest in the middle, and lowest in the upper and lower parts. As the velocity of movement initiated and increased, stretching of the earth flow body induced the formation of normal faults. Conversely, decreasing velocity and shortening of the earth flow induced the formation of thrust faults. A zone with relatively few structures, bounded by strike-slip faults, was located between stretching and shortening areas. These kinematic elements indicate that the overall earth flow was actually composed of numerous linked internal earth flows, with each internal flow having a distinct pattern of structures representative of stretching and shortening (Guerriero et al., in review). These observations indicated that the spatial variation in movement velocity associated with each internal earth flow, mimicked the pattern of movement for the overall earth flow. That is, the earth flow displayed a self-similar pattern at different scales. Furthermore, the presence of other structures such as back-tilted surfaces, flank-ridges, and hydrological elements provide specific information about the shape of the basal topographic surface. Our multi-temporal maps provided a basis for interpretation of the long-term kinematic evolution of the earth flow and the influence of the basal-slip surface on the earth flow movement. Our maps showed that main faults remained stationary through time, despite extensive mobilization and movement of material. This observation indicated that the slip-surface has remained relatively stationary since at least 1954.

Shear wave velocity variation across the Taupo Volcanic Zone, New Zealand, from receiver function inversion

USGS Publications Warehouse

Bannister, S.; Bryan, C.J.; Bibby, H.M.

2004-01-01

The Taupo Volcanic Zone (TVZ), New Zealand is a region characterized by very high magma eruption rates and extremely high heat flow, which is manifest in high-temperature geothermal waters. The shear wave velocity structure across the region is inferred using non-linear inversion of receiver functions, which were derived from teleseismic earthquake data. Results from the non-linear inversion, and from forward synthetic modelling, indicate low S velocities at ???6- 16 km depth near the Rotorua and Reporoa calderas. We infer these low-velocity layers to represent the presence of high-level bodies of partial melt associated with the volcanism. Receiver functions at other stations are complicated by reverberations associated with near-surface sedimentary layers. The receiver function data also indicate that the Moho lies between 25 and 30 km, deeper than the 15 ?? 2 km depth previously inferred for the crust-mantle boundary beneath the TVZ. ?? 2004 RAS.

Use of a rotating cylinder to induce laminar and turbulent separation over a flat plate

NASA Astrophysics Data System (ADS)

Afroz, F.; Lang, A.; Jones, E.

2017-06-01

An innovative and easy technique using a rotating cylinder system has been implemented in a water tunnel experiment to generate an adverse pressure gradient (APG). The strength of the APG was varied through adjustment in the rotation speed and location of the cylinder. Then the technique was used for inducing a laminar separation bubble (LSB) and turbulent boundary layer (TBL) separation over a flat plate. A theoretical model to predict the pressure variation induced on the plate consists of an inviscid flow over a reverse doublet-like configuration of two counter rotating cylinders. This model quantified the pressure distribution with changes of cylinder speed and location. The dimensionless velocity ratio (VR) of the cylinder rotation rate to the mainstream velocity and gap to diameter ratio \\tfrac{G}{D} were chosen as the two main ways of varying the strength of the APG, which affects the nature and extent of the LSB as well as TBL separation. The experimental parametric study, using time-resolved digital particle image velocimetry, was then conducted in a water tunnel. The variation in height (h), length (l), and the separation point (S) of the LSB was documented due to the variation in the APG. The similar type of experimental parametric study was used to explore the unsteady, turbulent separation bubble in a 2D plane aligned with the flow and perpendicular to the plate. The mean detachment locations of TBL separation are determined by two different definitions: (i) back-flow coefficient (χ) = 50%, and (ii) location of start of negative mean skin friction coefficient (C f). They are in good agreement and separation bubble characteristics agreed well with results obtained using different methods thus proving the validity of the technique.

On the decades-long stability of the interstellar wind through the solar system

NASA Astrophysics Data System (ADS)

Lallement, R.; Bertaux, J. L.

2014-05-01

We have revisited the series of observations recently used to infer a temporal variation in the interstellar helium flow over the past forty years. Concerning the recent IBEX-Lo direct detection of helium neutrals, there are two types of precise and unambiguous measurements that do not rely on the exact response of the instrument: the count rate maxima as a function of the spin angle, which determines the ecliptic latitude of the flow, and the count rate maxima as a function of IBEX longitude, which determines a tight relationship between the ecliptic longitude of the flow and its velocity far from the Sun. These measurements provide parameters (and couples of parameters in the second case) that are remarkably similar to the canonical, old values. In contrast, the preferred choice of a lower velocity and higher longitude reported before from IBEX data is only based on the count rate variation (at each spin phase maximum) as a function of the satellite longitude, when drifting across the region of high fluxes. We have examined the consequences of dead-time counting effects and conclude that including them at a realistic level is sufficient to reconcile the data with the old parameters, calling for further investigations. We discuss the analyses of the STEREO pickup ion data and argue that the statistical method that has been preferred to infer the neutral flow longitude (instead of the more direct method based on the pickup ion maximum flux directions) is not appropriate. Moreover, transport effects may have been significant at the very weak solar activity level of 2007-2009, in which case the longitudes of the pickup ion maxima are only upper limits on the flow longitude. Finally, we found that using some flow longitude determinations based on UV glow data is not adequate. Based on this global study, and at variance with recent conclusions, we find no evidence for a temporal variability of the interstellar helium flow. This has implications for inner and outer heliosphere studies.

Hydrodynamic investigation of USP dissolution test apparatus II.

PubMed

Bai, Ge; Armenante, Piero M; Plank, Russell V; Gentzler, Michael; Ford, Kenneth; Harmon, Paul

2007-09-01

The USP Apparatus II is the device commonly used to conduct dissolution testing in the pharmaceutical industry. Despite its widespread use, dissolution testing remains susceptible to significant error and test failures, and limited information is available on the hydrodynamics of this apparatus. In this work, laser-Doppler velocimetry (LDV) and computational fluid dynamics (CFD) were used, respectively, to experimentally map and computationally predict the velocity distribution inside a standard USP Apparatus II under the typical operating conditions mandated by the dissolution test procedure. The flow in the apparatus is strongly dominated by the tangential component of the velocity. Secondary flows consist of an upper and lower recirculation loop in the vertical plane, above and below the impeller, respectively. A low recirculation zone was observed in the lower part of the hemispherical vessel bottom where the tablet dissolution process takes place. The radial and axial velocities in the region just below the impeller were found to be very small. This is the most critical region of the apparatus since the dissolving tablet will likely be at this location during the dissolution test. The velocities in this region change significantly over short distances along the vessel bottom. This implies that small variations in the location of the tablet on the vessel bottom caused by the randomness of the tablet descent through the liquid are likely to result in significantly different velocities and velocity gradients near the tablet. This is likely to introduce variability in the test. (c) 2007 Wiley-Liss, Inc. and the American Pharmacists Association.

Transport processes and sound velocity in vibrationally non-equilibrium gas of anharmonic oscillators

NASA Astrophysics Data System (ADS)

Rydalevskaya, Maria A.; Voroshilova, Yulia N.

2018-05-01

Vibrationally non-equilibrium flows of chemically homogeneous diatomic gases are considered under the conditions that the distribution of the molecules over vibrational levels differs significantly from the Boltzmann distribution. In such flows, molecular collisions can be divided into two groups: the first group corresponds to "rapid" microscopic processes whereas the second one corresponds to "slow" microscopic processes (their rate is comparable to or larger than that of gasdynamic parameters variation). The collisions of the first group form quasi-stationary vibrationally non-equilibrium distribution functions. The model kinetic equations are used to study the transport processes under these conditions. In these equations, the BGK-type approximation is used to model only the collision operators of the first group. It allows us to simplify derivation of the transport fluxes and calculation of the kinetic coefficients. Special attention is given to the connection between the formulae for the bulk viscosity coefficient and the sound velocity square.

Searching for order in atmospheric pressure plasma jets

NASA Astrophysics Data System (ADS)

Schäfer, Jan; Sigeneger, Florian; Šperka, Jiří; Rodenburg, Cornelia; Foest, Rüdiger

2018-01-01

The self-organized discharge behaviour occurring in a non-thermal radio-frequency plasma jet in rare gases at atmospheric pressure was investigated. The frequency of the azimuthal rotation of filaments in the active plasma volume and their inclination were measured along with the gas temperature under varying discharge conditions. The gas flow and heating were described theoretically by a three-dimensional hydrodynamic model. The rotation frequencies obtained by both methods qualitatively agree. The results demonstrate that the plasma filaments forming an inclination angle α with the axial gas velocity u z are forced to a transversal movement with the velocity {u}φ =\\tan (α )\\cdot {u}z, which is oriented in the inclination direction. Variations of {u}φ in the model reveal that the observed dynamics minimizes the energy loss due to convective heat transfer by the gas flow. The control of the self-organization regime motivates the application of the plasma jet for precise and reproducible material processing.

Seismic velocity anisotropy and heterogeneity beneath the Mantle Electromagnetic and Tomography Experiment (MELT) region of the East Pacific Rise from analysis of P and S body waves

USGS Publications Warehouse

Hammond, W.C.; Toomey, D.R.

2003-01-01

We use teleseismic P and S delay times and shear wave splitting measurements to constrain isotropic and anisotropic heterogeneity in the mantle beneath the southern East Pacific Rise (SEPR). The data comprise 462 P and S delay times and 18 shear wave splitting observations recorded during the Mantle Electromagnetic and Tomography (MELT) Experiment. We estimate the mantle melt content (F) and temperature (T) variation from the isotropic velocity variation. Our results indicate that the maximum variation in F beneath our array is between zero and ???1.2%, and maximum variation in T is between zero and ???100 K. We favor an explanation having partial contributions from both T and F. We approximate the seismic anisotropy of the upper mantle with hexagonal symmetry, consistent with the assumption of two dimensionality of mantle flow. Our new tomographic technique uses a nonlinear inversion of P and slow S polarization delay times to simultaneously solve for coupled VP and VS heterogeneity throughout the model and for the magnitude of anisotropy within discrete domains. The domain dimensions and the dip of the anisotropy are fixed for each inversion but are varied in a grid search, obtaining the misfit of the models to the body wave delay data and to split times of vertically propagating S waves. The data misfit and the isotropic heterogeneity are sensitive to domain dimensions and dip of anisotropy. In a region centered beneath the SEPR the best average dip of the hexagonal symmetry axis is horizontal or dipping shallowly (<30??) west. Given the resolution of our data, a subaxial region characterized by vertically aligned symmetry axes may exist but is limited to be <80 km deep. We infer that the mantle flow beneath the SEPR is consistent with shallow asthenospheric return flow from the direction of the South Pacific superswell.

Inverse problems, non-roundness and flat pieces of the effective burning velocity from an inviscid quadratic Hamilton-Jacobi model

NASA Astrophysics Data System (ADS)

Jing, Wenjia; Tran, Hung V.; Yu, Yifeng

2017-05-01

The main goal of this paper is to understand finer properties of the effective burning velocity from a combustion model introduced by Majda and Souganidis (1994 Nonlinearity 7 1-30). Motivated by results in Bangert (1994 Calculus Variations PDE 2 49-63) and applications in turbulent combustion, we show that when the dimension is two and the flow of the ambient fluid is either weak or very strong, the level set of the effective burning velocity has flat pieces. Due to the lack of an applicable Hopf-type rigidity result, we need to identify the exact location of at least one flat piece. Implications on the effective flame front and other related inverse type problems are also discussed.

A Day in the Life of the Suwannee River: Lagrangian Sampling of Process Rates Along the River Continuum

NASA Astrophysics Data System (ADS)

Cohen, M. J.; Hensley, R. T.; Spangler, M.; Gooseff, M. N.

2017-12-01

A key organizing idea in stream ecology is the river continuum concept (RCC) which makes testable predictions about network-scale variation in metabolic and community attributes. Using high resolution (ca. 0.1 Hz) Lagrangian sampling of a wide suite of solutes - including nitrate, fDOM, dissolved oyxgen and specific conductance, we sampled the river continuum from headwaters to the sea in the Suwannee River (Florida, USA). We specifically sought to test two predictions that follow from the RCC: first, that changes in metabolism and hydraulics lead to progressive reduction in total N retention but greater diel variation with increasing stream order; and second, that variation in metabolic and nutrient processing rates is larger across stream orders than between low order streams. In addition to providing a novel test of theory, these measurements enabled new insights into the evolution of water quality through a complex landscape, in part because main-stem profiles were obtained for both high and historically low flow conditions. We observed strong evidence of metabolism and nutrient retention at low flow. Both the rate of uptake velocity and the mass retention per unit area declined with increasing stream order, and declined dramatically at high flow. Clear evidence for time varying retention (i.e., diel variation) was observed at low flow, but was masked or absent at high flow. In this geologically complex river - with alluvial, spring-fed, and blackwater headwater streams - variation across low-order streams was large, suggesting the presence of many river continuua across the network. This application of longitudinal sampling and inference underscores the utility of changing reference frames to draw new insights, but also highlights some of the challenges that need to be considered and, where possible, controlled.

The Effect of Flow Velocity on Waveform Inversion

NASA Astrophysics Data System (ADS)

Lee, D.; Shin, S.; Chung, W.; Ha, J.; Lim, Y.; Kim, S.

2017-12-01

The waveform inversion is a velocity modeling technique that reconstructs accurate subsurface physical properties. Therefore, using the model in its final, updated version, we generated data identical to modeled data. Flow velocity, like several other factors, affects observed data in seismic exploration. Despite this, there is insufficient research on its relationship with waveform inversion. In this study, the generated synthetic data considering flow velocity was factored in waveform inversion and the influence of flow velocity in waveform inversion was analyzed. Measuring the flow velocity generally requires additional equipment. However, for situations where only seismic data was available, flow velocity was calculated by fixed-point iteration method using direct wave in observed data. Further, a new waveform inversion was proposed, which can be applied to the calculated flow velocity. We used a wave equation, which can work with the flow velocities used in the study by Käser and Dumbser. Further, we enhanced the efficiency of computation by applying the back-propagation method. To verify the proposed algorithm, six different data sets were generated using the Marmousi2 model; each of these data sets used different flow velocities in the range 0-50, i.e., 0, 2, 5, 10, 25, and 50. Thereafter, the inversion results from these data sets along with the results without the use of flow velocity were compared and analyzed. In this study, we analyzed the results of waveform inversion after flow velocity has been factored in. It was demonstrated that the waveform inversion is not affected significantly when the flow velocity is of smaller value. However, when the flow velocity has a large value, factoring it in the waveform inversion produces superior results. This research was supported by the Basic Research Project(17-3312, 17-3313) of the Korea Institute of Geoscience and Mineral Resources(KIGAM) funded by the Ministry of Science, ICT and Future Planning of Korea.

Effect of ship locking on sediment oxygen uptake in impounded rivers

NASA Astrophysics Data System (ADS)

Lorke, A.; McGinnis, D. F.; Maeck, A.; Fischer, H.

2012-12-01

In the majority of large river systems, flow is regulated and/or otherwise affected by operational and management activities, such as ship locking. The effect of lock operation on sediment-water oxygen fluxes was studied within a 12.9 km long impoundment at the Saar River (Germany) using eddy-correlation flux measurements. The continuous observations cover a time period of nearly 5 days and 39 individual locking events. Ship locking is associated with the generation of surges propagating back and forth through the impoundment which causes strong variations of near-bed current velocity and turbulence. These wave-induced flow variations cause variations in sediment-water oxygen fluxes. While the mean flux during time periods without lock operation was 0.5 ± 0.1 g m-2 d-1, it increased by about a factor of 2 to 1.0 ± 0.5 g m-2 d-1within time periods with ship locking. Following the daily schedule of lock operations, fluxes are predominantly enhanced during daytime and follow a pronounced diurnal rhythm. The driving force for the increased flux is the enhancement of diffusive transport across the sediment-water interface by bottom-boundary layer turbulence and perhaps resuspension. Additional means by which the oxygen budget of the impoundment is affected by lock-induced flow variations are discussed.

Influence of bedrock on river hydrodynamics and channel geometry

NASA Astrophysics Data System (ADS)

Rennie, C. D.; Church, M. A.; Venditti, J. G.; Bomhof, J.; Adderley, C.

2013-12-01

We present an acoustic Doppler current profiler (aDcp) survey of a 524 km long reach of Fraser River, British Columbia, Canada, as it passes through the Fraser Canyons. The channel alternates between gravel-bedded reaches that are incised into semi-consolidated glacial deposits and bedrock-bound reaches (7.7% of the reach between the towns of Quesnel and Hope). A continuous centreline aDcp survey was employed to measure longitudinal variation in slope, depth, depth-averaged velocity, and shear velocity. A total of 71 aDcp sectional surveys throughout the reach provided section widths (w), section-averaged depths (d), velocity distributions, and discharge (Q). Finally, air photo analysis using Google imagery provided channel widths at 0.5 km spacing. The survey reach was subdivided into 10 morphological sub-reaches, which ranged from alluvial gravel-bed reaches with relatively moderate slope to steep non-alluvial rock-walled canyons. The resulting data provide a unique opportunity to evaluate the influence of bedrock confinement on river hydrodynamics and channel geometry. Continuous centreline longitudinal aDcp data and the widths from air photo analysis were grouped within each sub-reach based on presence of bedrock confinement on both banks, either bank, or neither bank. The results demonstrate that river widths decreased and water depths, flow velocities, and shear velocities increased from the alluvial sub-reaches to the semi-alluvial reaches to the canyon reaches. Within each sub-reach, locations with bedrock encroachment on both banks were also narrower and deeper, but had lower depth-averaged velocity and shear velocity. Sectional geometry data were homogenized along the river (to compensate increasing flows at tributary junctions) by computing w/Q^{1/2} and d/Q^{1/3}, following commonly observed scaling relations. Alluvial reaches are 2.3x wider than rock-bound reaches (from the more abundant imagery data) and 0.60x as deep (from aDcp sections), implying that mean velocity is accelerated in rock reaches by 38%. There is also variation from reach to reach along the river controlled by variation in rock lithologies, with the narrowest canyons occurring in Fraser Canyon proper (w/Q^{1/2} = 0.083 compared with 1.4 elsewhere). The uppermost (';Marguerite') and lowermost (';Agassiz') alluvial reaches are considerably wider (w/Q^{1/2}= 3.9 and 7.1 respectively) than intervening ones ( 2.35). These reaches have lower gradients and exhibit wandering channels. Because of lithological control, the downstream hydraulic geometry of the river does not, in fact, conform with the common pattern, even when sections are analyzed according to boundary material. However, river gradient is well correlated with scaled width; inversely for gravel reaches and directly, but with little sensitivity, for rock-bound reaches.

Weekly glacier flow estimation from dense satellite time series using adapted optical flow technology

NASA Astrophysics Data System (ADS)

Altena, Bas; Kääb, Andreas

2017-06-01

Contemporary optical remote sensing satellites or constellations of satellites can acquire imagery at sub-weekly or even daily timescales. Thus, these systems facilitate the potential for within-season velocity estimation of glacier surfaces. State-of-the-art techniques for displacement estimation are based on matching image pairs and are thus constrained by the need of significant displacement and/or preservation of the surface over time. Consequently, such approaches cannot benefit entirely from the increasing satellite revisit times. Here, we explore an approach that is fundamentally different from image correlation or similar techniques and exploits the concept of optical flow. Our goal is to assess if this concept could overcome above current limitations of image matching and thus give new insights in glacier flow dynamics. We implement two different methods of optical flow, and test these on the SPOT5 Take5 dataset over Kronebreen, Svalbard and over Kaskawulsh Glacier, Yukon. For Kaskawulsh Glacier we are able to extract seasonal velocity variation, that temporally coincide with events of increased air temperatures. Furthermore, even for the cloudy dataset of Kronebreen, we were able to extract spatio-temporal trajectories which correlate well with measured GPS flow paths. Because the underlying concept is simple and computationally efficient due to data-reduction, our methodology can easily be used for exploratory regional studies of several glaciers or estimation of small and slow flowing glaciers.

Numerical modelling of bedload sediment transport

NASA Astrophysics Data System (ADS)

Langlois, Vincent J.

2010-05-01

We present a numerical study of sediment transport in the bedload regime. Classical bedload transport laws only describe the variation of the vertically integrated flux of grains as a function of the Shields number. However, these relations are only valid if the moving layer of the bed is at equilibrium with the external flow. Besides, they do not contain enough information for many geomorphological applications. For instance, understanding inertial effects in the moving bed requires models that are able to account for the variability of hydrodynamical conditions, and the discrete nature of the sediment material. We developped a numerical modelling of the behaviour of a three-dimensional bed of grains sheared by a unidirectional fluid flow. These simulations are based on a combination of discrete and continuum approaches: sediment particles are modelled by hard spheres interacting through simple contact forces, whereas the fluid flow is described by a 'mean field' model. Both the drag exerted on grains by the fluid and the retroactive effect of the presence of grains on the flow are accounted for, allowing the system to converge to its equilibrium state (no assumption is made on the fluid velocity profile inside the layer of moving grains). Above the motion threshold, the variation of the flux of grains in the steady state is found to vary like the cube of the Shields number (as predicted by Bagnold). Besides, our simulations allow us to obtain new insights into the detailed mechanisms of bedload transport, by giving access to non-integral quantities, such as the trajectories of each individual grains, the detailed velocity and packing fraction profiles inside the granular bed, etc. It is therefore possible to investigate some effects that are not accounted for in usual continuum models, such as the polydispersity of grains, the ageing of the bed, the response to a variation of the flowrate, etc.

Crust and Mantle Deformation Revealed from High-Resolution Radially Anisotropic Velocity Models

NASA Astrophysics Data System (ADS)

Li, A.; Dave, R.; Yao, Y.

2017-12-01

Love wave tomography, which can achieve a similar model resolution as Rayleigh wave, so far has limited applications to the USArray data. Recently, we have developed high-resolution Love wave phase velocity maps in the Wyoming craton and Texas using data at the Transportable Array stations. 3-D, radially anisotropic velocity models are obtained by jointly inverting Love and Rayleigh wave phase velocities. A high-velocity anomaly extending to about 200 km depth beneath central Wyoming correlates with negative radial anisotropy (Vsv>Vsh), suggesting that mantle downwelling develops under the cratonic lithosphere. Surprisingly, the significantly low velocity beneath the Yellowstone hotspot, which has been interpreted as partial melting and asthenospheric upwelling, is associated with the largest radial anisotropy (Vsh>Vsv) in the area. This observation does not support mantle upwelling. Instead, it indicates that the upper mantle beneath the hotspot has experienced strong shear deformation probably by the plate motion and large-scale mantle flow. In Texas, positive radial anisotropy in the lower crust extends from the coast to the Ouachita belt, which is characterized by high velocity and negative radial anisotropy. In the upper mantle, large variations of velocity and anisotropy exit under the coastal plain. A common feature in these anisotropic models is that high-velocity anomalies in the upper mantle often correlate with negative anisotropy (Vsv>Vsh) while low-velocity anomalies are associated with positive anisotropy (Vsh>Vsv). The manifestation of mantle downweling as negative radial anisotropy is largely due to the relatively high viscosity of the high-velocity mantle block, which is less affected by the surrounding large-scale horizontal flow. However, mantle upwelling, which is often associated with low-velocity anomalies, presumably low-viscosity mantle blocks, is invisible in radial anisotropy models. Such upwelling may happen too quickly to make last effects or too slow to alter the dominant shear deformation in the asthenosphere.

The principal factors contributing to the flux of salt in a narrow, partially stratified estuary

NASA Astrophysics Data System (ADS)

Lewis, R. E.; Lewis, J. O.

1983-06-01

Observations of the velocity and salinity structure of the Tees estuary were made at eight stations along the estuary axis between Victoria Bridge and the sea during the summer of 1975. The measurements were made on ten separate tidal periods covering neap and spring tides. The data were collected over a period of relatively low freshwater flows and the residual current was found to have a strong dependence on the Stokes drift. At the upstream stations, the residuals were more than an order of magnitude greater than the currents anticipated from the freshwater discharge. Although the mean stratification decreased as the tidal range increased, the vertical circulation was stronger on spring tides than on neaps. Vertical variations in the amplitude and phase of the tidal current results in a current which strengthens the vertical circulation. However, this effect only made a relatively small contribution to the observed vertical circulation. The relative contribution of the individual salt flux terms to the net upstream transport of salt varies along the estuary. As the estuary narrows, the contribution by the oscillatory terms dominates that from the shear in the steady state flow. Of these oscillatory terms, the correlation of velocity and salinity fluctuations plays a key rôle in the salt transport. The depth mean values make a greater contribution than deviations from the depth mean and the flux due to phase variations over depth is smaller than either of these. Since the Stokes drift is compensated by a down-stream steady state flow, it does not contribute to the tidal mean transport of salt. At the seaward end of the estuary, the salt fluxes due to the steady state vertical shear and the convariance of the tidal fluctuations act in a complementary way to counter the seaward transport of salt by the freshwater flow. With the possible exceptions of the wide or narrow reaches of the Tees, the longitudinal fluxes of salt due to transverse variations in velocity, salinity and depth and turbulent fluctuations are of secondary importance as contributors to the estuary salt budget. On both neap and spring tides, the computed total salt transports at the Newport and Victoria bridges did not match the values required for a salt balance with the corresponding freshwater flows. These fluxes were probably the cause of the observed downstream displacement of the tidal mean salinity distribution between neap and spring tides.

Comparative study of laminar and turbulent flow model with different operating parameters for radio frequency-inductively coupled plasma torch working at 3  MHz frequency at atmospheric pressure

DOE Office of Scientific and Technical Information (OSTI.GOV)

Punjabi, Sangeeta B., E-mail: p.sangeeta@gmail.com; Department of Physics, University of Mumbai, Kalina, Santacruz; Sahasrabudhe, S. N.

2014-01-15

This paper provides 2D comparative study of results obtained using laminar and turbulent flow model for RF (radio frequency) Inductively Coupled Plasma (ICP) torch. The study was done for the RF-ICP torch operating at 50 kW DC power and 3 MHz frequency located at BARC. The numerical modeling for this RF-ICP torch is done using ANSYS software with the developed User Defined Function. A comparative study is done between laminar and turbulent flow model to investigate how temperature and flow fields change when using different operating conditions such as (a) swirl and no swirl velocity for sheath gas flow rate, (b) variationmore » in sheath gas flow rate, and (c) variation in plasma gas flow rate. These studies will be useful for different material processing applications.« less

Flowing gas, non-nuclear experiments on the gas core reactor

NASA Technical Reports Server (NTRS)

Kunze, J. F.; Suckling, D. H.; Copper, C. G.

1972-01-01

Flow tests were conducted on models of the gas core (cavity) reactor. Variations in cavity wall and injection configurations were aimed at establishing flow patterns that give a maximum of the nuclear criticality eigenvalue. Correlation with the nuclear effect was made using multigroup diffusion theory normalized by previous benchmark critical experiments. Air was used to simulate the hydrogen propellant in the flow tests, and smoked air, argon, or freon to simulate the central nuclear fuel gas. All tests were run in the down-firing direction so that gravitational effects simulated the acceleration effect of a rocket. Results show that acceptable flow patterns with high volume fraction for the simulated nuclear fuel gas and high flow rate ratios of propellant to fuel can be obtained. Using a point injector for the fuel, good flow patterns are obtained by directing the outer gas at high velocity along the cavity wall, using louvered or oblique-angle-honeycomb injection schemes.

Schlieren technique in soap film flows

NASA Astrophysics Data System (ADS)

Auliel, M. I.; Hebrero, F. Castro; Sosa, R.; Artana, G.

2017-05-01

We propose the use of the Schlieren technique as a tool to analyse the flows in soap film tunnels. The technique enables to visualize perturbations of the film produced by the interposition of an object in the flow. The variations of intensity of the image are produced as a consequence of the deviations of the light beam traversing the deformed surfaces of the film. The quality of the Schlieren image is compared to images produced by the conventional interferometric technique. The analysis of Schlieren images of a cylinder wake flow indicates that this technique enables an easy visualization of vortex centers. Post-processing of series of two successive images of a grid turbulent flow with a dense motion estimator is used to derive the velocity fields. The results obtained with this self-seeded flow show good agreement with the statistical properties of the 2D turbulent flows reported on the literature.

Mixed Convection Opposing Flow in a Vertical Porous Annulus-Two Temperature Model

NASA Astrophysics Data System (ADS)

Al-Rashed, Abdullah A. AA; J, Salman Ahmed N.; Khaleed, H. M. T.; Yunus Khan, T. M.; NazimAhamed, K. S.

2016-09-01

The opposing flow in a porous medium refers to a condition when the forcing velocity flows in opposite direction to thermal buoyancy obstructing the buoyant force. The present research refers to the effect of opposing flow in a vertical porous annulus embedded with fluid saturated porous medium. The thermal non-equilibrium approach with Darcy modal is considered. The boundary conditions are such that the inner radius is heated with constant temperature Tw the outer radius is maintained at constant temperature Tc. The coupled nonlinear partial differential equations such as momentum equation, energy equation for fluid and energy equation for solid are solved using the finite element method. The opposing flow variation of average Nusselt number with respect to radius ratio Rr, Aspect ratioAr and Radiation parameter Rd for different values of Peclet number Pe are investigated. It is found that the flow behavior is quite different from that of aiding flow.

Blade-to-Blade Variations in Shocks Upstream of Both a Forward-Swept and an Aft-Swept Fan

NASA Technical Reports Server (NTRS)

Podboy, Gary G.; Krupar, Martin J.

2006-01-01

Detailed laser Doppler velocimeter (LDV) flow field measurements were made upstream of two fans, one forward-swept and one aft-swept, in order to learn more about the shocks which propagate upstream of these rotors when they are operated at supersonic tip speeds. The blade-to-blade variations in the flows associated with these shocks are thought to be responsible for generating Multiple Pure Tone (MPT) noise. The measured blade-to-blade variations are documented in this report through a series of slideshows which show relative Mach number contours computed from the velocity measurements. Data are presented for the forward-swept fan operating at three speeds (corresponding to tip relative Mach numbers of 0.817, 1.074, and 1.189), and for the aft-swept fan operating at two (tip relative Mach numbers of 1.074 and 1.189). These LDV data illustrate how the perturbations in the upstream flow field created by the rotating blades vary with axial position, radial position and rotor speed. As expected, at the highest tested speed the forward-swept fan swallowed the shocks which occur in the tip region, whereas the aftswept fan did not. This resulted in a much smaller flow disturbance just upstream of the tip of the forward-swept fan. Nevertheless, further upstream the two fan flows were much more similar.

Extension of the Helmholtz-Smoluchowski velocity to the hydrophobic microchannels with velocity slip.

PubMed

Park, H M; Kim, T W

2009-01-21

Electrokinetic flows through hydrophobic microchannels experience velocity slip at the microchannel wall, which affects volumetric flow rate and solute retention time. The usual method of predicting the volumetric flow rate and velocity profile for hydrophobic microchannels is to solve the Navier-Stokes equation and the Poisson-Boltzmann equation for the electric potential with the boundary condition of velocity slip expressed by the Navier slip coefficient, which is computationally demanding and defies analytic solutions. In the present investigation, we have devised a simple method of predicting the velocity profiles and volumetric flow rates of electrokinetic flows by extending the concept of the Helmholtz-Smoluchowski velocity to microchannels with Navier slip. The extended Helmholtz-Smoluchowski velocity is simple to use and yields accurate results as compared to the exact solutions. Employing the extended Helmholtz-Smoluchowski velocity, the analytical expressions for volumetric flow rate and velocity profile for electrokinetic flows through rectangular microchannels with Navier slip have been obtained at high values of zeta potential. The range of validity of the extended Helmholtz-Smoluchowski velocity is also investigated.

Longitudinal pressure-driven flows between superhydrophobic grooved surfaces: Large effective slip in the narrow-channel limit

NASA Astrophysics Data System (ADS)

Schnitzer, Ory; Yariv, Ehud

2017-07-01

The gross amplification of the fluid velocity in pressure-driven flows due to the introduction of superhydrophobic walls is commonly quantified by an effective slip length. The canonical duct-flow geometry involves a periodic structure of longitudinal shear-free stripes at either one or both of the bounding walls, corresponding to flat-meniscus gas bubbles trapped within a periodic array of grooves. This grating configuration is characterized by two geometric parameters, namely the ratio κ of channel width to microstructure period and the areal fraction Δ of the shear-free stripes. For wide channels, κ ≫1 , this geometry is known to possess an approximate solution where the dimensionless slip length λ , normalized by the duct semiwidth, is small, indicating a weak superhydrophobic effect. We here address the other extreme of narrow channels, κ ≪1 , identifying large O (κ-2) values of λ for the symmetric configuration, where both bounding walls are superhydrophobic. This velocity enhancement is associated with an unconventional Poiseuille-like flow profile where the parabolic velocity variation takes place in a direction parallel (rather than perpendicular) to the boundaries. Use of matched asymptotic expansions and conformal-mapping techniques provides λ up to O (κ-1) , establishing the approximationλ ˜κ-2Δ/33 +κ-1Δ/2π ln4 +⋯, which is in excellent agreement with a semianalytic solution of the dual equations governing the respective coefficients of a Fourier-series representation of the fluid velocity. No similar singularity occurs in the corresponding asymmetric configuration, involving a single superhydrophobic wall; in that geometry, a Hele-Shaw approximation shows that λ =O (1 ) .

Steady-state groundwater recharge in trapezoidal-shaped aquifers: A semi-analytical approach based on variational calculus

NASA Astrophysics Data System (ADS)

Mahdavi, Ali; Seyyedian, Hamid

2014-05-01

This study presents a semi-analytical solution for steady groundwater flow in trapezoidal-shaped aquifers in response to an areal diffusive recharge. The aquifer is homogeneous, anisotropic and interacts with four surrounding streams of constant-head. Flow field in this laterally bounded aquifer-system is efficiently constructed by means of variational calculus. This is accomplished by minimizing a properly defined penalty function for the associated boundary value problem. Simple yet demonstrative scenarios are defined to investigate anisotropy effects on the water table variation. Qualitative examination of the resulting equipotential contour maps and velocity vector field illustrates the validity of the method, especially in the vicinity of boundary lines. Extension to the case of triangular-shaped aquifer with or without an impervious boundary line is also demonstrated through a hypothetical example problem. The present solution benefits from an extremely simple mathematical expression and exhibits strictly close agreement with the numerical results obtained from Modflow. Overall, the solution may be used to conduct sensitivity analysis on various hydrogeological parameters that affect water table variation in aquifers defined in trapezoidal or triangular-shaped domains.

Tidally-driven effluent detected by long-term temperature monitoring at the TAG hydrothermal mound, Mid-Atlantic Ridge

NASA Astrophysics Data System (ADS)

Kinoshita, M.; Von Herzen, R. P.; Matsubayashi, O.; Fujioka, K.

1998-06-01

During Aug. 13-21, 1994, temperatures and current velocity were simultaneously monitored on the TAG hydrothermal mound. Three `Giant Kelps (GKs)', vertical thermistor arrays of 50 m height, were moored on the periphery of the central black smoker complex (CBC). A `Manatee', multi-monitoring system including current velocity, was deployed 50 m east of CBC. Four `Daibutsu' geothermal probes penetrated the sediment south to west of CBC. Compilation of all data revealed semi-diurnal variations in water temperatures and current velocity, and allowed us to discuss the source of these anomalies. Temperature anomalies of GKs correlate well with current velocity, and are interpreted to be caused by the main plume from CBC that was bent over by the tidal current. We identified two types of asymmetric, periodic temperature variations at Daibutsu Probes 2 and 8, located 20 m to the south of CBC. By comparing temperatures and current velocity, they are attributed to non-buoyant effluents laterally advected by the tidal current. The source of one variation is located east to ESE of the probes, and the source of the other is located to the north. On Aug. 31, a new periodic anomaly emerged on Probe 2 with its amplitude up to 0.8°C. The 6-h offset between the new anomaly and the previous one suggests that the source of the new anomaly lies to the west of Probe 2. The heat flux of these non-buoyant effluents is estimated to range from 30 to 100 kW/m 2, which is of the same order as direct estimates of diffuse flow at the TAG mound. It suggests that a significant amount of diffuse effluent is laterally advected by the prevailing current near the seafloor.

Spatial and temporal variation of seismic velocity during earthquakes and volcanic eruptions in western Japan: Insight into mechanism for seismic velocity variation

NASA Astrophysics Data System (ADS)

Tsuji, T.; Ikeda, T.; Nimiya, H.

2017-12-01

We report spatio-temporal variations of seismic velocity around the seismogenic faults in western Japan. We mainly focus on the seismic velocity variation during (1) the 2016 Off-Mie earthquake in the Nankai subduction zone (Mw5.8) and (2) the 2016 Kumamoto earthquake in Kyushu Island (Mw7.0). We applied seismic interferometry and surface wave analysis to the ambient noise data recorded by Hi-net and DONET seismometers of National Research Institute for Earth Science and Disaster Resilience (NIED). Seismic velocity near the rupture faults and volcano decreased during the earthquake. For example, we observed velocity reduction around the seismogenic Futagawa-Hinagu fault system and Mt Aso in the 2016 Kumamoto earthquake. We also identified velocity increase after the eruptions of Mt Aso. During the 2016 Off-Mie earthquake, we observed seismic velocity variation in the Nankai accretionary prism. After the earthquakes, the seismic velocity gradually returned to the pre-earthquake value. The velocity recovering process (healing process) is caused by several mechanisms, such as pore pressure reduction, strain change, and crack sealing. By showing the velocity variations obtained at different geologic settings (volcano, seismogenic fault, unconsolidated sediment), we discuss the mechanism of seismic velocity variation as well as the post-seismic fault healing process.

Experimental studies on flow visualization and velocity field of compression ramp with different incoming boundary layers

NASA Astrophysics Data System (ADS)

Wu, Yu; Yi, Shi-He; He, Lin; Chen, Zhi; Zhu, Yang-Zhu

2014-11-01

Experimental studies which focus on flow visualization and the velocity field of a supersonic laminar/turbulent flow over a compression ramp were carried out in a Mach 3.0 wind tunnel. Fine flow structures and velocity field structures were obtained via NPLS (nanoparticle-tracer planar laser scattering) and PIV (particle image velocimetry) techniques, time-averaged flow structures were researched, and spatiotemporal evolutions of transient flow structures were analyzed. The flow visualization results indicated that when the ramp angles were 25°, a typical separation occurred in the laminar flow, some typical flow structures such as shock induced by the boundary layer, separation shock, reversed flow and reattachment shock were visible clearly. While a certain extent separation occurred in turbulent flow, the separation region was much smaller. When the ramp angles were 28°, laminar flow separated further, and the separation region expanded evidently, flow structures in the separation region were complex. While a typical separation occurred in turbulent flow, reversed flow structures were significant, flow structures in the separation region were relatively simple. The experimental results of velocity field were corresponding to flow visualization, and the velocity field structures of both compression ramp flows agreed with the flow structures well. There were three layered structures in the U component velocity, and the V component velocity appeared like an oblique “v”. Some differences between these two compression ramp flows can be observed in the velocity profiles of the shear layer and the shearing intensity.

Influence of neighboring adherent cells on laminar flow induced shear stress in vitro—A systematic study

PubMed Central

Djukelic, Mario; Westerhausen, Christoph

2017-01-01

Cells experience forces if subjected to laminar flow. These forces, mostly of shear force character, are strongly dependent not only on the applied flow field itself but also on hydrodynamic effects originating from neighboring cells. This particularly becomes important for the interpretation of data from in vitro experiments in flow chambers without confluent cell layers. By employing numerical Finite Element Method simulations of such assemblies of deformable objects under shear flow, we investigate the occurring stress within elastic adherent cells and the influence of neighboring cells on these quantities. For this, we simulate single and multiple adherent cells of different shapes fixed on a solid substrate under laminar flow parallel to the substrate for different velocities. We determine the local stress within the cells close to the cell-substrate-interface and the overall stress of the cells by surface integration over the cell surface. Comparing each measurand in the case of a multiple cell situation with the corresponding one of single cells under identical conditions, we introduce a dimensionless influence factor. The systematic variation of the distance and angle between cells, where the latter is with respect to the flow direction, flow velocity, Young's modulus, cell shape, and cell number, enables us to describe the actual influence on a cell. Overall, we here demonstrate that the cell density is a crucial parameter for all studies on flow induced experiments on adherent cells in vitro. PMID:28798851

Optical technique to study the impact of heavy rain on aircraft performance

NASA Technical Reports Server (NTRS)

Hess, C. F.; Li, F.

1985-01-01

A laser based technique was investigated and shown to have the potential to obtain measurements of the size and velocity of water droplets used in a wind tunnel to simulate rain. A theoretical model was developed which included some simple effects due to droplet nonsphericity. Parametric studies included the variation of collection distance (up to 4 m), angle of collection, effect of beam interference by the spray, and droplet shape. Accurate measurements were obtained under extremely high liquid water content and spray interference. The technique finds applications in the characterization of two phase flows where the size and velocity of particles are needed.

Constrained H1-regularization schemes for diffeomorphic image registration

PubMed Central

Mang, Andreas; Biros, George

2017-01-01

We propose regularization schemes for deformable registration and efficient algorithms for their numerical approximation. We treat image registration as a variational optimal control problem. The deformation map is parametrized by its velocity. Tikhonov regularization ensures well-posedness. Our scheme augments standard smoothness regularization operators based on H1- and H2-seminorms with a constraint on the divergence of the velocity field, which resembles variational formulations for Stokes incompressible flows. In our formulation, we invert for a stationary velocity field and a mass source map. This allows us to explicitly control the compressibility of the deformation map and by that the determinant of the deformation gradient. We also introduce a new regularization scheme that allows us to control shear. We use a globalized, preconditioned, matrix-free, reduced space (Gauss–)Newton–Krylov scheme for numerical optimization. We exploit variable elimination techniques to reduce the number of unknowns of our system; we only iterate on the reduced space of the velocity field. Our current implementation is limited to the two-dimensional case. The numerical experiments demonstrate that we can control the determinant of the deformation gradient without compromising registration quality. This additional control allows us to avoid oversmoothing of the deformation map. We also demonstrate that we can promote or penalize shear whilst controlling the determinant of the deformation gradient. PMID:29075361

Disintegration of liquid sheets

NASA Technical Reports Server (NTRS)

Mansour, Adel; Chigier, Norman

1990-01-01

The development, stability, and disintegration of liquid sheets issuing from a two-dimensional air-assisted nozzle is studied. Detailed measurements of mean drop size and velocity are made using a phase Doppler particle analyzer. Without air flow the liquid sheet converges toward the axis as a result of surface tension forces. With airflow a quasi-two-dimensional expanding spray is formed. The air flow causes small variations in sheet thickness to develop into major disturbances with the result that disruption starts before the formation of the main break-up region. In the two-dimensional variable geometry air-blast atomizer, it is shown that the air flow is responsible for the formation of large, ordered, and small chaotic 'cell' structures.

Characterization of bed load discharge in unsteady flow events in an ephemeral channel

NASA Astrophysics Data System (ADS)

Halfi, Eran

2017-04-01

There are many methods and equations for estimating bedload flux in steady flow conditions. Yet, very little is known about the effect of very unsteady flows, such as flash floods, on bedload flux. The unpredictable nature of the floods together with many logistic difficulties and safety issues in monitoring explain this gap in knowledge. Global climate change may increase flood event occurrence, making their understanding even more crucial. This research focuses on two durations of flash floods where the flow is most rapidly changing: a) flash flood bore arriving on dry river bed and b) flash flood bore arriving on a column of moving water. The methodology of our study is based on the demonstrated ability of the Eshtemoa gauging station to automatically monitor the variation of bedload flux depending on flow and bed characteristics, along with innovative equipment including hydrophones and geophones for capturing acoustic signals of bedload sediments (1 Hz), video cameras for continuous monitoring of water surface velocity (by the LSPIV method to determine its structure and velocity) and 3-D velocimetry for characterizing turbulence (40 Hz). Additional to these, a well-planned deployment was carried out, including alerting sensors and cellular transmission, enabling to be onsite when bores arrive. During the winter of 2015-2016 two flow events were sufficiently large to transport significant amounts of bedload; the magnitude of the larger event occurs once in a few years. Calibration between the acoustic indirect sensor and the direct slot sampler allow determination of bedload flux at a frequency of 1 Hz. Analyses of the two events indicate an increase of the turbulent nature (increase of the turbulent kinetic energy and the instantaneous vertical velocities), shear stress and bedload flux during the rising limb in the first two minutes of bore arrival.

Mixing zone hydrodynamics in a large confluence: a case study of the Snake and Clearwater Rivers confluence

NASA Astrophysics Data System (ADS)

Shehata, M. M.; Petrie, J.

2015-12-01

Confluences are a basic component in all fluvial systems, which are often characterized by complex flow and sediment transport patterns. Addressing confluences, however, started only recently in parallel with new advances of flow measurement tools and computational techniques. A limited number of field studies exist investigating flow hydrodynamics through confluences, particularly for large confluences with central zone widths of 100 m or greater. Previous studies have indicated that the size of the confluent rivers and the post-confluence zone may impact flow and sediment transport processes in the confluence zone, which consequently could impact the biodiversity within the river network. This study presents the results of a field study conducted at the confluence of the Snake and the Clearwater rivers near the towns of Clarkston, WA and Lewiston, ID (average width of 700 m at the confluence center). This confluence supports many different and, sometimes, conflicting purposes including commercial navigation, recreation, and fish and wildlife conservation. The confluence properties are affected by dredging operations carried out periodically to maintain the minimum water depth required for safe flow conveyance and navigation purposes. Also, a levee system was constructed on the confluence banks as an extra flood control measure. In the recent field work, an Acoustic Doppler Current Profiler was used to measure water velocity profiles at cross sections in the confluence region. Fixed and moving vessel measurements were taken at selected locations to evaluate both the spatial and temporal variation in velocity throughout the confluence. The confluence bathymetry was surveyed with a multi-beam sonar to investigate existent bed morphological elements. The results identify the velocity pattern in the mixing zone between the two rivers. The present findings are compared to previous studies on small confluences to demonstrate the influence of scale on flow processes.

Verification on spray simulation of a pintle injector for liquid rocket engine

NASA Astrophysics Data System (ADS)

Son, Min; Yu, Kijeong; Radhakrishnan, Kanmaniraja; Shin, Bongchul; Koo, Jaye

2016-02-01

The pintle injector used for a liquid rocket engine is a newly re-attracted injection system famous for its wide throttle ability with high efficiency. The pintle injector has many variations with complex inner structures due to its moving parts. In order to study the rotating flow near the injector tip, which was observed from the cold flow experiment using water and air, a numerical simulation was adopted and a verification of the numerical model was later conducted. For the verification process, three types of experimental data including velocity distributions of gas flows, spray angles and liquid distribution were all compared using simulated results. The numerical simulation was performed using a commercial simulation program with the Eulerian multiphase model and axisymmetric two dimensional grids. The maximum and minimum velocities of gas were within the acceptable range of agreement, however, the spray angles experienced up to 25% error when the momentum ratios were increased. The spray density distributions were quantitatively measured and had good agreement. As a result of this study, it was concluded that the simulation method was properly constructed to study specific flow characteristics of the pintle injector despite having the limitations of two dimensional and coarse grids.

Experimental and computational investigations on severe slugging in a catenary riser

NASA Astrophysics Data System (ADS)

Duan, Jin-long; Chen, Ke; You, Yun-xiang; Gao, Song

2017-12-01

Severe slugging can occur in a pipeline-riser system at relatively low liquid and gas flow rates during gas-oil transportation, possibly causing unexpected damage to the production facilities. Experiments with air and water are conducted in a horizontal and downward inclined pipeline followed by a catenary riser in order to investigate the mechanism and characteristics of severe slugging. A theoretical model is introduced to compare with the experiments. The results show that the formation mechanism of severe slugging in a catenary riser is different from that in a vertical riser due to the riser geometry and five flow patterns are obtained and analyzed. A gas-liquid mixture slug stage is observed at the beginning of one cycle of severe slugging, which is seldom noticed in previous studies. Based on both experiments and computations, the time period and variation of pressure amplitude of severe slugging are found closely related to the superficial gas velocity, implying that the gas velocity significantly influences the flow patterns in our experiments. Moreover, good agreements between the experimental data and the numerical results are shown in the stability curve and flow regime map, which can be a possible reference for design in an offshore oil-production system.

Comparison of the surface dielectric barrier discharge characteristics under different electrode gaps

NASA Astrophysics Data System (ADS)

Gao, Guoqiang; Dong, Lei; Peng, Kaisheng; Wei, Wenfu; Li, Chunmao; Wu, Guangning

2017-01-01

Currently, great interests are paid to the surface dielectric barrier discharge due to the diverse and interesting application. In this paper, the influences of the electrode gap on the discharge characteristics have been studied. Aspects of the electrical parameters, the optical emission, and the discharge induced gas flow were considered. The electrode gap varied from 0 mm to 21 mm, while the applied AC voltage was studied in the range of 17 kV-27 kV. Results indicate that with the increase of the electrode gap, the variation of discharge voltage exhibits an increasing trend, while the other parameters (i.e., the current, power, and induced flow velocity) increase first, and then decrease once the gap exceeded the critical value. Mechanisms of the electrode gap influencing these key parameters were discussed from the point of equivalent circuit. The experimental results reveal that an optimal discharge gap can be obtained, which is closely related to the applied voltage. Visualization of the induced flow with different electrode gaps was realized by the Schlieren diagnostic technique. Finally, the velocities of induced gas flow determined by the pitot tube were compared with the results of intensity-integral method, and good agreements were found.

Numerical study of a thermally stratified flow of a tangent hyperbolic fluid induced by a stretching cylindrical surface

NASA Astrophysics Data System (ADS)

Ur Rehman, Khali; Ali Khan, Abid; Malik, M. Y.; Hussain, Arif

2017-09-01

The effects of temperature stratification on a tangent hyperbolic fluid flow over a stretching cylindrical surface are studied. The fluid flow is achieved by taking the no-slip condition into account. The mathematical modelling of the physical problem yields a nonlinear set of partial differential equations. These obtained partial differential equations are converted in terms of ordinary differential equations. Numerical investigation is done to identify the effects of the involved physical parameters on the dimensionless velocity and temperature profiles. In the presence of temperature stratification it is noticed that the curvature parameter makes both the fluid velocity and fluid temperature increase. In addition, positive variations in the thermal stratification parameter produce retardation with respect to the fluid flow, as a result the fluid temperature drops. The skin friction coefficient shows a decreasing nature for increasing value of both power law index and Weissenberg number, whereas the local Nusselt number is an increasing function of the Prandtl number, but opposite trends are found with respect to the thermal stratification parameter. The obtained results are validated by making a comparison with the existing literature which brings support to the presently developed model.

On Fully Developed Channel Flows: Some Solutions and Limitations, and Effects of Compressibility, Variable Properties, and Body Forces

NASA Technical Reports Server (NTRS)

Maslen, Stephen H.

1959-01-01

An examination of the effects of compressibility, variable properties, and body forces on fully developed laminar flow has indicated several limitations on such streams. In the absence of a pressure gradient, but presence of a body force (e.g., gravity), an exact fully developed gas flow results. For a liquid this follows also for the case of a constant streamwise pressure gradient. These motions are exact in the sense of a Couette flow. In the liquid case two solutions (not a new result) can occur for the same boundary conditions. An approximate analytic solution was found which agrees closely with machine calculations.In the case of approximately exact flows, it turns out that for large temperature variations across the channel the effects of convection (due to, say, a wall temperature gradient) and frictional heating must be negligible. In such a case the energy and momentum equations are separated, and the solutions are readily obtained. If the temperature variations are small, then both convection effects and frictional heating can consistently be considered. This case becomes the constant-property incompressible case (or quasi-incompressible case for free-convection flows) considered by many authors. Finally there is a brief discussion of cases wherein streamwise variations of all quantities are allowed but only a such form that independent variables are separable. For the case where the streamwise velocity varies inversely as the square root distance along the channel a solution is given.

On Three-dimensional Structures in Relativistic Hydrodynamic Jets

NASA Astrophysics Data System (ADS)

Hardee, Philip E.

2000-04-01

The appearance of wavelike helical structures on steady relativistic jets is studied using a normal mode analysis of the linearized fluid equations. Helical structures produced by the normal modes scale relative to the resonant (most unstable) wavelength and not with the absolute wavelength. The resonant wavelength of the normal modes can be less than the jet radius even on highly relativistic jets. High-pressure regions helically twisted around the jet beam may be confined close to the jet surface, penetrate deeply into the jet interior, or be confined to the jet interior. The high-pressure regions range from thin and ribbon-like to thick and tubelike depending on the mode and wavelength. The wave speeds can be significantly different at different wavelengths but are less than the flow speed. The highest wave speed for the jets studied has a Lorentz factor somewhat more than half that of the underlying flow speed. A maximum pressure fluctuation criterion found through comparison between theory and a set of relativistic axisymmetric jet simulations is applied to estimate the maximum amplitudes of the helical, elliptical, and triangular normal modes. Transverse velocity fluctuations for these asymmetric modes are up to twice the amplitude of those associated with the axisymmetric pinch mode. The maximum amplitude of jet distortions and the accompanying velocity fluctuations at, for example, the resonant wavelength decreases as the Lorentz factor increases. Long-wavelength helical surface mode and shorter wavelength helical first body mode generated structures should be the most significant. Emission from high-pressure regions as they twist around the jet beam can vary significantly as a result of angular variation in the flow direction associated with normal mode structures if they are viewed at about the beaming angle θ=1/γ. Variation in the Doppler boost factor can lead to brightness asymmetries by factors up to 6 as long-wavelength helical structure produced by the helical surface mode winds around the jet. Higher order surface modes and first body modes produce less variation. Angular variation in the flow direction associated with the helical mode appears consistent with precessing jet models that have been proposed to explain the variability in 3C 273 and BL Lac object AO 0235+164. In particular, cyclic angular variation in the flow direction produced by the normal modes could produce the activity seen in BL Lac object OJ 287. Jet precession provides a mechanism for triggering the helical modes on multiple length scales, e.g., the galactic superluminal GRO J1655-40.

PADDLEFISH BUCCAL FLOW VELOCITY DURING RAM SUSPENSION FEEDING AND RAM VENTILATION

PubMed

Cech; Cheer

1994-01-01

A micro-thermistor probe was inserted into the buccal cavity of freely swimming paddlefish to measure flow velocity during ram ventilation, ram suspension feeding and prey processing. Swimming speed was measured from videotapes recorded simultaneously with the buccal flow velocity measurements. Both swimming velocity and buccal flow velocity were significantly higher during suspension feeding than during ram ventilation. As the paddlefish shifted from ventilation to feeding, buccal flow velocity increased to approximately 60 % of the swimming velocity. During prey processing, buccal flow velocity was significantly higher than the swimming velocity, indicating that prey processing involves the generation of suction. The Reynolds number (Re) for flow at the level of the paddlefish gill rakers during feeding is about 30, an order of magnitude lower than the Re calculated previously for pump suspension-feeding blackfish. These data, combined with data available from the literature, indicate that the gill rakers of ram suspension-feeding teleost fishes may operate at a substantially lower Re than the rakers of pump suspension feeders.

Implementing an empirical scalar constitutive relation for ice with flow-induced polycrystalline anisotropy in large-scale ice sheet models

NASA Astrophysics Data System (ADS)

Graham, Felicity S.; Morlighem, Mathieu; Warner, Roland C.; Treverrow, Adam

2018-03-01

The microstructure of polycrystalline ice evolves under prolonged deformation, leading to anisotropic patterns of crystal orientations. The response of this material to applied stresses is not adequately described by the ice flow relation most commonly used in large-scale ice sheet models - the Glen flow relation. We present a preliminary assessment of the implementation in the Ice Sheet System Model (ISSM) of a computationally efficient, empirical, scalar, constitutive relation which addresses the influence of the dynamically steady-state flow-compatible induced anisotropic crystal orientation patterns that develop when ice is subjected to the same stress regime for a prolonged period - sometimes termed tertiary flow. We call this the ESTAR flow relation. The effect on ice flow dynamics is investigated by comparing idealised simulations using ESTAR and Glen flow relations, where we include in the latter an overall flow enhancement factor. For an idealised embayed ice shelf, the Glen flow relation overestimates velocities by up to 17 % when using an enhancement factor equivalent to the maximum value prescribed in the ESTAR relation. Importantly, no single Glen enhancement factor can accurately capture the spatial variations in flow across the ice shelf generated by the ESTAR flow relation. For flow line studies of idealised grounded flow over varying topography or variable basal friction - both scenarios dominated at depth by bed-parallel shear - the differences between simulated velocities using ESTAR and Glen flow relations depend on the value of the enhancement factor used to calibrate the Glen flow relation. These results demonstrate the importance of describing the deformation of anisotropic ice in a physically realistic manner, and have implications for simulations of ice sheet evolution used to reconstruct paleo-ice sheet extent and predict future ice sheet contributions to sea level.

Dynamics of barite growth in porous media quantified by in situ synchrotron X-ray tomography

NASA Astrophysics Data System (ADS)

Godinho, jose; Gerke, kirill

2016-04-01

Current models used to formulate mineral sequestration strategies of dissolved contaminants in the bedrock often neglect the effect of confinement and the variation of reactive surface area with time. In this work, in situ synchrotron X-ray micro-tomography is used to quantify barite growth rates in a micro-porous structure as a function of time during 13.5 hours with a resolution of 1 μm. Additionally, the 3D porous network at different time frames are used to simulate the flow velocities and calculate the permeability evolution during the experiment. The kinetics of barite growth under porous confinement is compared with the kinetics of barite growth on free surfaces in the same fluid composition. Results are discussed in terms of surface area normalization and the evolution of flow velocities as crystals fill the porous structure. During the initial hours the growth rate measured in porous media is similar to the growth rate on free surfaces. However, as the thinner flow paths clog the growth rate progressively decreases, which is correlated to a decrease of local flow velocity. The largest pores remain open, enabling growth to continue throughout the structure. Quantifying the dynamics of mineral precipitation kinetics in situ in 4D, has revealed the importance of using a time dependent reactive surface area and accounting for the local properties of the porous network, when formulating predictive models of mineral precipitation in porous media.

Flow Velocity Computation, from Temperature and Number Density Measurements using Spontaneous Raman Scattering, for Supersonic Chemically Reacting Flows.

NASA Astrophysics Data System (ADS)

Satish Jeyashekar, Nigil; Seiner, John

2006-11-01

The closure problem in chemically reacting turbulent flows would be solved when velocity, temperature and number density (transport variables) are known. The transport variables provide input to momentum, heat and mass transport equations leading to analysis of turbulence-chemistry interaction, providing a pathway to improve combustion efficiency. There are no measurement techniques to determine all three transport variables simultaneously. This paper shows the formulation to compute flow velocity from temperature and number density measurements, made from spontaneous Raman scattering, using kinetic theory of dilute gases coupled with Maxwell-Boltzmann velocity distribution. Temperature and number density measurements are made in a mach 1.5 supersonic air flow with subsonic hydrogen co-flow. Maxwell-Boltzmann distribution can be used to compute the average molecular velocity of each species, which in turn is used to compute the mass-averaged velocity or flow velocity. This formulation was validated by Raman measurements in a laminar adiabatic burner where the computed flow velocities were in good agreement with hot-wire velocity measurements.

A classification scheme for turbulent flows based on their joint velocity-intermittency structure

NASA Astrophysics Data System (ADS)

Keylock, C. J.; Nishimura, K.; Peinke, J.

2011-12-01

Kolmogorov's classic theory for turbulence assumed an independence between velocity increments and the value for the velocity itself. However, this assumption is questionable, particularly in complex geophysical flows. Here we propose a framework for studying velocity-intermittency coupling that is similar in essence to the popular quadrant analysis method for studying near-wall flows. However, we study the dominant (longitudinal) velocity component along with a measure of the roughness of the signal, given mathematically by its series of Hölder exponents. Thus, we permit a possible dependence between velocity and intermittency. We compare boundary layer data obtained in a wind tunnel to turbulent jets and wake flows. These flow classes all have distinct velocity-intermittency characteristics, which cause them to be readily distinguished using our technique. Our method is much simpler and quicker to apply than approaches that condition the velocity increment statistics at some scale, r, on the increment statistics at a neighbouring, larger spatial scale, r+Δ, and the velocity itself. Classification of environmental flows is then possible based on their similarities to the idealised flow classes and we demonstrate this using laboratory data for flow in a parallel-channel confluence where the region of flow recirculation in the lee of the step is discriminated as a flow class distinct from boundary layer, jet and wake flows. Hence, using our method, it is possible to assign a flow classification to complex geophysical, turbulent flows depending upon which idealised flow class they most resemble.

On blockage effects for a marine hydrokinetic turbine in free surface proximity

NASA Astrophysics Data System (ADS)

Banerjee, A.; Kolekar, N.

2016-12-01

Experimental investigation was carried out with a three-bladed, constant chord marine hydrokinetic turbine to understand the influence of free surface proximity on blockage effects and near wake flow field. The turbine was placed at various depths of immersion as rotational speeds and flow speeds were varied; thrust and torque data was acquired through a submerged thrust torque sensor positioned in-line with the turbine axis. Blockage effects were quantified in terms of changes in power coefficient and were found to be dependent on flow velocity, rotational speed and blade-tip clearence (from free-surface). Flow acceleration near turbine rotation plane was attributed to blockage offered by the rotor, wake, and free surface deformation; the resulting performance improvements were calculated based on the measured thrust values. In addition, stereoscopic particle imaging velocimetry was carried out in the near-wake region using time-averaged and phase-averaged techniques to understand the mechanism responsible for variation of torque (and power coefficient) with rotational speed and free-surface proximity. Flow vizualisation revealed slower wake propagation for higher rotational velocities and increased assymetry in the wake with increasing free surface proximity. Improved performance at high rotational speed was attributed to enhanced wake blockage; performance enhancements with free-surface proximity was attributed to additional blockage effects caused by free surface deformation.

Numerical study of the thermo-flow performances of novel finned tubes for air-cooled condensers in power plant

NASA Astrophysics Data System (ADS)

Guo, Yonghong; Du, Xiaoze; Yang, Lijun

2018-02-01

Air-cooled condenser is the main equipment of the direct dry cooling system in a power plant, which rejects heat of the exhaust steam with the finned tube bundles. Therefore, the thermo-flow performances of the finned tubes have an important effect on the optimal operation of the direct dry cooling system. In this paper, the flow and heat transfer characteristics of the single row finned tubes with the conventional flat fins and novel jagged fins are investigated by numerical method. The flow and temperature fields of cooling air for the finned tubes are obtained. Moreover, the variations of the flow resistance and average convection heat transfer coefficient under different frontal velocity of air and jag number are presented. Finally, the correlating equations of the friction factor and Nusselt number versus the Reynolds number are fitted. The results show that with increasing the frontal velocity of air, the heat transfer performances of the finned tubes are enhanced but the pressure drop will increase accordingly, resulting in the average convection heat transfer coefficient and friction factor increasing. Meanwhile, with increasing the number of fin jag, the heat transfer performance is intensified. The present studies provide a reference in optimal designing for the air-cooled condenser of direct air cooling system.

Performance and Near-Wake Flow field of A Marine Hydrokinetic Turbine Operating in Free surface Proximity

NASA Astrophysics Data System (ADS)

Banerjee, Arindam; Kolekar, Nitin

2015-11-01

The current experimental investigation aims at understanding the effect of free surface proximity and associated blockage on near-wake flow-field and performance of a three bladed horizontal axis marine hydrokinetic turbine. Experiments were conducted on a 0.14m radius, three bladed constant chord turbine in a 0.61m ×0.61m test section water channel. The turbine was subjected to various rotational speeds, flow speeds and depths of immersion. Experimental data was acquired through a submerged in-line thrust-torque sensor that was corrected to an unblocked dataset with a blockage correction using measured thrust data. A detailed comparison is presented between blocked and unblocked datasets to identify influence of Reynolds number and free surface proximity on blockage effects. The percent change in Cp was found to be dependent on flow velocity, rotational speed and free surface to blade tip clearance. Further, flow visualization using a stereoscopic particle image velocimetry was carried out in the near-wake region of turbine to understand the mechanism responsible for variation of Cp with rotational speed and free surface proximity. Results revealed presence of slower wake at higher rotational velocities and increased asymmetry in the wake at high free surface proximity.

Ultrasound Thermal Field Imaging of Opaque Fluids

NASA Technical Reports Server (NTRS)

Andereck, C. David

1999-01-01

We have initiated an experimental program to develop an ultrasound system for non-intrusively imaging the thermal field in opaque fluids under an externally imposed temperature gradient. Many industrial processes involve opaque fluids, such as molten metals, semiconductors, and polymers, often in situations in which thermal gradients are important. For example, one may wish to understand semiconductor crystal growth dynamics in a Bridgman apparatus. Destructive testing of the crystal after the process is completed gives only indirect information about the fluid dynamics of the formation process. Knowledge of the coupled thermal and velocity fields during the growth process is then essential. Most techniques for non-intrusive velocity and temperature measurement in fluids are optical in nature, and hence the fluids studied must be transparent. In some cases (for example, LDV (laser Doppler velocimetry) and PIV (particle imaging velocimetry)) the velocities of small neutrally buoyant seed particles suspended in the fluid, are measured. Without particle seeding one can use the variation of the index of refraction of the fluid with temperature to visualize, through interferometric, Schlieren or shadowgraph techniques, the thermal field. The thermal field in turn gives a picture of the pattern existing in the fluid. If the object of study is opaque, non-optical techniques must be used. In this project we focus on the use of ultrasound, which propagates easily through opaque liquids and solids. To date ultrasound measurements have almost exclusively relied on the detection of sound scattered from density discontinuities inside the opaque material of interest. In most cases it has been used to visualize structural properties, but more recently the ultrasound Doppler velocimeter has become available. As in the optical case, it relies on seed particles that scatter Doppler shifted sound back to the detector. Doppler ultrasound techniques are, however, not useful for studying convective fluid flow in crystal growth, because particle seeding is unacceptable and flow velocities are typically too low to be resolved, and may be even lower in microgravity conditions where buoyancy forces are negligible. We will investigate a different use of ultrasound to probe the flows of opaque fluids non-intrusively and without the use of seed particles: our goal is to ultrasonically visualize the thermal field of opaque fluids with relatively high spatial resolution. The proposed technique relies upon the variation of sound speed with temperature of the fluid. A high frequency ultra-sound pulse passing through a fluid-filled chamber will traverse the chamber in a time determined by the relevant chamber dimension and the temperature of the fluid through which the pulse passes. With high time-resolution instrumentation that compares the excitation signal with the received pulse we can detect the influence of the fluid temperature on the pulse travel time. This is effectively an interferometric system, which in its optical form is an extremely sensitive approach to measuring thermal fields in fluids. Moreover, the temperature dependence of sound velocity in liquid metals is comparable to the temperature dependence of the speed of light required for accurate interferometric thermal images in transparent fluids. With an array of transducers scanned electronically a map of the thermal field over the chamber could be produced. An alternative approach would be to use the ultrasound analog of the shadowgraph technique. In the optical version, collimated light passes through the fluid, where it is focused or defocused locally by temperature field induced variations of the index of refraction. The resulting image reveals the thermal field through the spatial pattern of light intensity variations. By analogy, an ultrasound plane wave traversing an opaque fluid sample would be also locally focused or defocused depending on the speed of sound variations, giving rise to spatial variations in sound intensity that will reveal the thermal field pattern. These approaches could be applied to any situation in which temperature differences are expected to occur, and will rapidly provide information about the flow that simply cannot be obtained by any current intrusive or non-intrusive diagnostic technique. As materials processing in microgravity matures it will become increasingly important to have available simple and versatile diagnostic tools, such as we will develop, for studying the flows of opaque fluids under thermal forcing.

"Ladder" structure in tonal noise generated by laminar flow around an airfoil.

PubMed

Chong, Tze Pei; Joseph, Phillip

2012-06-01

The presence of a "ladder" structure in the airfoil tonal noise was discovered in the 1970s, but its mechanism hitherto remains a subject of continual investigation in the research community. Based on the measured noise results and some numerical analysis presented in this letter, the variations of four types of airfoil tonal noise frequencies with the flow velocity were analyzed individually. The ladder structure is proposed to be caused by the acoustic/hydrodynamic frequency lag between the scattering of the boundary layer instability noise and the discrete noise produced by an aeroacoustic feedback loop.

Internal Flow and Burning Characteristics of 16-inch Ram Jet Operating in a Free Jet at Mach Numbers of 1.35 and 1.73

NASA Technical Reports Server (NTRS)

Perchonok, Eugene; Farley, John M

1951-01-01

The effects of mass-flow ratio on the additive drag and normal-shock position of a single oblique-shock diffuser are presented. Also evaluated is the variation with operating condition of the velocity distribution at the combustion-chamber inlet. A comparison with connected-pipe data is included. Burner performance with a corrugated gutter-grid flame holder is discussed. It is shown that the total-pressure drop across the combustion chamber can be predicted with reasonable accuracy from the computed flame holder and combustion momentum pressure losses.

Dynamics of temporal variations in phonatory flow.

PubMed

Krane, Michael H; Barry, Michael; Wei, Timothy

2010-07-01

This paper addresses the dynamic relevance of time variations of phonatory airflow, commonly neglected under the quasisteady phonatory flow assumption. In contrast to previous efforts, which relied on direct measurement of glottal impedance, this work uses spatially and temporally resolved measurements of the velocity field to estimate the unsteady and convective acceleration terms in the unsteady Bernoulli equation. Theoretical considerations suggest that phonatory flow is inherently unsteady when two related conditions apply: (1) that the unsteady and convective accelerations are commensurate, and (2) that the inertia of the glottal jet is non-negligible. Acceleration waveforms, computed from experimental data, show that unsteady and convective accelerations to be the same order of magnitude, throughout the cycle, and that the jet flow contributes significantly to the unsteady acceleration. In the middle of the cycle, however, jet inertia is negligible because the convective and unsteady accelerations nearly offset one another in the jet region. These results, consistent with previous findings treating quasisteady phonatory flow, emphasize that unsteady acceleration cannot be neglected during the final stages of the phonation cycle, during which voice sound power and spectral content are largely determined. Furthermore, glottal jet dynamics must be included in any model of phonatory airflow.

Dynamics of temporal variations in phonatory flow1

PubMed Central

Krane, Michael H.; Barry, Michael; Wei, Timothy

2010-01-01

This paper addresses the dynamic relevance of time variations of phonatory airflow, commonly neglected under the quasisteady phonatory flow assumption. In contrast to previous efforts, which relied on direct measurement of glottal impedance, this work uses spatially and temporally resolved measurements of the velocity field to estimate the unsteady and convective acceleration terms in the unsteady Bernoulli equation. Theoretical considerations suggest that phonatory flow is inherently unsteady when two related conditions apply: (1) that the unsteady and convective accelerations are commensurate, and (2) that the inertia of the glottal jet is non-negligible. Acceleration waveforms, computed from experimental data, show that unsteady and convective accelerations to be the same order of magnitude, throughout the cycle, and that the jet flow contributes significantly to the unsteady acceleration. In the middle of the cycle, however, jet inertia is negligible because the convective and unsteady accelerations nearly offset one another in the jet region. These results, consistent with previous findings treating quasisteady phonatory flow, emphasize that unsteady acceleration cannot be neglected during the final stages of the phonation cycle, during which voice sound power and spectral content are largely determined. Furthermore, glottal jet dynamics must be included in any model of phonatory airflow. PMID:20649231

UHF RiverSonde observations of water surface velocity at Threemile Slough, California

USGS Publications Warehouse

Teague, C.C.; Barrick, D.E.; Lilleboe, P.M.; Cheng, R.T.; Ruhl, C.A.

2005-01-01

A UHF RiverSonde system, operating near 350 MHz, has been in operation at Threemile Slough in central California, USA since September 2004. The water in the slough is dominated by tidal effects, with flow reversals four times a day and a peak velocity of about 0.8 m/s in each direction. Water level and water velocity are continually measured by the U. S. Geological Survey at the experiment site. The velocity is measured every 15 minutes by an ultrasonic velocity meter (UVM) which determines the water velocity from two-way acoustic propagation time-difference measurements made across the channel. The RiverSonde also measures surface velocity every 15 minutes using radar resonant backscatter techniques. Velocity and water level data are retrieved through a radio data link and a wideband internet connection. Over a period of several months, the radar-derived mean surface velocity has been very highly correlated with the UVM index velocity several meters below the surface, with a coefficient of determination R2 of 0.976 and an RMS difference of less than 10 cm/s. The wind has a small but measurable effect on the velocities measured by both instruments. In addition to the mean surface velocity across the channel, the RiverSonde system provides an estimate of the cross-channel variation of the surface velocity. ?? 2005 IEEE.

Consistent modelling of wind turbine noise propagation from source to receiver.

PubMed

Barlas, Emre; Zhu, Wei Jun; Shen, Wen Zhong; Dag, Kaya O; Moriarty, Patrick

2017-11-01

The unsteady nature of wind turbine noise is a major reason for annoyance. The variation of far-field sound pressure levels is not only caused by the continuous change in wind turbine noise source levels but also by the unsteady flow field and the ground characteristics between the turbine and receiver. To take these phenomena into account, a consistent numerical technique that models the sound propagation from the source to receiver is developed. Large eddy simulation with an actuator line technique is employed for the flow modelling and the corresponding flow fields are used to simulate sound generation and propagation. The local blade relative velocity, angle of attack, and turbulence characteristics are input to the sound generation model. Time-dependent blade locations and the velocity between the noise source and receiver are considered within a quasi-3D propagation model. Long-range noise propagation of a 5 MW wind turbine is investigated. Sound pressure level time series evaluated at the source time are studied for varying wind speeds, surface roughness, and ground impedances within a 2000 m radius from the turbine.

Consistent modelling of wind turbine noise propagation from source to receiver

DOE PAGES

Barlas, Emre; Zhu, Wei Jun; Shen, Wen Zhong; ...

2017-11-28

The unsteady nature of wind turbine noise is a major reason for annoyance. The variation of far-field sound pressure levels is not only caused by the continuous change in wind turbine noise source levels but also by the unsteady flow field and the ground characteristics between the turbine and receiver. To take these phenomena into account, a consistent numerical technique that models the sound propagation from the source to receiver is developed. Large eddy simulation with an actuator line technique is employed for the flow modelling and the corresponding flow fields are used to simulate sound generation and propagation. Themore » local blade relative velocity, angle of attack, and turbulence characteristics are input to the sound generation model. Time-dependent blade locations and the velocity between the noise source and receiver are considered within a quasi-3D propagation model. Long-range noise propagation of a 5 MW wind turbine is investigated. Sound pressure level time series evaluated at the source time are studied for varying wind speeds, surface roughness, and ground impedances within a 2000 m radius from the turbine.« less

Consistent modelling of wind turbine noise propagation from source to receiver

DOE Office of Scientific and Technical Information (OSTI.GOV)

Barlas, Emre; Zhu, Wei Jun; Shen, Wen Zhong

The unsteady nature of wind turbine noise is a major reason for annoyance. The variation of far-field sound pressure levels is not only caused by the continuous change in wind turbine noise source levels but also by the unsteady flow field and the ground characteristics between the turbine and receiver. To take these phenomena into account, a consistent numerical technique that models the sound propagation from the source to receiver is developed. Large eddy simulation with an actuator line technique is employed for the flow modelling and the corresponding flow fields are used to simulate sound generation and propagation. Themore » local blade relative velocity, angle of attack, and turbulence characteristics are input to the sound generation model. Time-dependent blade locations and the velocity between the noise source and receiver are considered within a quasi-3D propagation model. Long-range noise propagation of a 5 MW wind turbine is investigated. Sound pressure level time series evaluated at the source time are studied for varying wind speeds, surface roughness, and ground impedances within a 2000 m radius from the turbine.« less

Interfacial Stability of Spherically Converging Plasma Jets for Magnetized Target Fusion

NASA Technical Reports Server (NTRS)

Thio, Y. C. Francis; Cassibry, Jason; Wu, S. T.; Eskridge, Richard; Smith, James; Lee, Michael; Rodgers, Stephen L. (Technical Monitor)

2000-01-01

A fusion propulsion scheme has been proposed that makes use of the merging of a spherical distribution of plasma jets to dynamically form a gaseous liner to implode a magnetized target to produce the fusion reaction. In this paper, a study is made of the interfacial stability of the interaction of these jets. Specifically, the Orr-Sommerfeld equation is integrated to obtain the growth rate of a perturbation to the primary flow at the interface between the colliding jets. The results lead to an estimate on the tolerances on the relative flow velocities of the merging plasma jets to form a stable, imploding liner. The results show that the maximum temporal growth rate of the perturbed flow at the jet interface is very small in comparison with the time to full compression of the liner. These data suggest that, as far as the stability of the interface between the merging jets is concerned, the formation of the gaseous liner can withstand velocity variation of the order of 10% between the neighboring jets over the density and temperature ranges investigated.

Role of medium heterogeneity and viscosity contrast in miscible flow regimes and mixing zone growth: A computational pore-scale approach

NASA Astrophysics Data System (ADS)

Afshari, Saied; Hejazi, S. Hossein; Kantzas, Apostolos

2018-05-01

Miscible displacement of fluids in porous media is often characterized by the scaling of the mixing zone length with displacement time. Depending on the viscosity contrast of fluids, the scaling law varies between the square root relationship, a sign for dispersive transport regime during stable displacement, and the linear relationship, which represents the viscous fingering regime during an unstable displacement. The presence of heterogeneities in a porous medium significantly affects the scaling behavior of the mixing length as it interacts with the viscosity contrast to control the mixing of fluids in the pore space. In this study, the dynamics of the flow and transport during both unit and adverse viscosity ratio miscible displacements are investigated in heterogeneous packings of circular grains using pore-scale numerical simulations. The pore-scale heterogeneity level is characterized by the variations of the grain diameter and velocity field. The growth of mixing length is employed to identify the nature of the miscible transport regime at different viscosity ratios and heterogeneity levels. It is shown that as the viscosity ratio increases to higher adverse values, the scaling law of mixing length gradually shifts from dispersive to fingering nature up to a certain viscosity ratio and remains almost the same afterwards. In heterogeneous media, the mixing length scaling law is observed to be generally governed by the variations of the velocity field rather than the grain size. Furthermore, the normalization of mixing length temporal plots with respect to the governing parameters of viscosity ratio, heterogeneity, medium length, and medium aspect ratio is performed. The results indicate that mixing length scales exponentially with log-viscosity ratio and grain size standard deviation while the impact of aspect ratio is insignificant. For stable flows, mixing length scales with the square root of medium length, whereas it changes linearly with length during unstable flows. This scaling procedure allows us to describe the temporal variation of mixing length using a generalized curve for various combinations of the flow conditions and porous medium properties.

A Study of the Impact of Variations on Aerodynamic Flow in Gas Turbine Engines via Monte-Carlo Simulations

NASA Technical Reports Server (NTRS)

Ngo, Khiem Viet; Tumer, Irem Y.

2003-01-01

The unsteady compressible inviscid flow is characterized by the conservations of mass, momentum, and energy; or simply the Euler equations. In this paper, a study of the subsonic one-dimensional Euler equations with local preconditioning is presented with a modal analysis approach. Specifically, this study investigates the behavior of airflow in a gas turbine engine using the specified conditions at the inflow and outflow boundaries of the compressor, combustion chamber, and turbine, under the impact of variations in pressure, velocity, temperature, and density at low Mach numbers. Two main questions that motivate this research are: 1) Is there any aerodynamic problem with the existing gas turbine engines that could impact aircraft performance? 2) If yes, what aspect of a gas turbine engine could be improved via design to alleviate that impact and to optimize aircraft performance. This paper presents an initial attempt to the flow behavior in terms (perturbation) using simulation outputs from a customer-deck model obtained from Pratt&Whitney, (i.e., pressure, temperature, velocity, density) about their mean states at the inflow and outflow boundaries of the compressor, combustion chamber, and turbine. Flow behavior is analyzed for the high pressure compressor and combustion chamber employing the conditions on their left and right boundaries. In the same fashion, similar analyses are carried out for the high and low-pressure turbines. In each case, the eigenfrequencies that are obtained for different boundary conditions are examined closely based on their probabilistic distributions, a result of a Monte Carlo 10,000-sample simulation. Furthermore, the characteristic waves and eave response are analyzed and contrasted among different cases, with and without preconditioners. The results reveal the existence of flow instabilities due to the combined effect of variations and excessive pressures; which are clearly the case in the combustion chamber and high-pressure turbine. Finally a discussion is presented on potential impacts of the instabilities and what can be improved via design to alleviate them for a better aircraft performance.

Hydrogen And Deuterium In The Local Interstellar Medium.

NASA Astrophysics Data System (ADS)

Murthy, Jayant

2016-03-01

In this work we report on the results of a series of IUE observations of interstellar HI and DI Ly alpha absorption against the chromospheric Lyalpha emission of the nearby late -type stars alpha Cen B(1.3 pc), epsilon Eri (3.3 pc), Procyon (3.5 pc), Altair (5.1 pc), Capella (13.2 pc), and HR 1099 (33 pc). From these observations we have derived the density, velocity dispersion, and bulk velocity of the neutral hydrogen along the line of sight to each of these stars. We have also placed lower limits on the deuterium to hydrogen (D/H) ratio towards the same stars. Our IUE results are generally consistent with previous observations of the same stars with the Copernicus satellite showing that our modelling procedure is independent of stellar variations over a period of several years. The HI absorption profile towards Altair shows a broad saturated core and steep line wings, consistent with a multicomponent interstellar medium in that direction. The bulk velocities towards the other stars are consistent with a bulk flow from the approximate direction of the galactic center but do show local variations from a uniform flow, possibly indicating a complicated velocity structure even in the solar neighbourhood. Interstellar deuterium is detected towards every star except Altair and the derived values for the D/H ratio are consistent with those previously found with Copernicus. In particular, we confirm the strong lower limit of 1.9 times 10^{-5} on the D/H ratio found towards Capella and we also place a lower limit of 1.5 times 10 ^{-5} on the D/H ratio towards alpha Cen B. Although an interstellar D/H ratio of 2 times 10^ {-5} is consistent with all the observations of late-type stars, the lower D/H ratios found towards several hot stars may indicate real variations in the D/H ratio in the local interstellar medium. Finally, we discuss the reality of a step in the cosmic background and of several galactic emission lines found by Auriemma et al. (1984) and show that, in fact, they are both artifacts of the data and of the analysis.

Effect of flow velocity on erosion-corrosion behaviour of QSn6 alloy

NASA Astrophysics Data System (ADS)

Huang, Weijiu; Zhou, Yongtao; Wang, Zhenguo; Li, Zhijun; Zheng, Ziqing

2018-05-01

The erosion-corrosion behaviour of QSn6 alloy used as propellers in marine environment was evaluated by erosion-corrosion experiments with/without cathodic protection, electrochemical tests and scanning electron microscope (SEM) observations. The analysis was focused on the effect of flow velocity. The dynamic polarization curves showed that the corrosion rate of the QSn6 alloy increased as the flow velocity increased, due to the protective surface film removal at higher velocities. The lowest corrosion current densities of 1.26 × 10‑4 A cm‑2 was obtained at the flow velocity of 7 m s‑1. Because of the higher particle kinetic energies at higher flow velocity, the mass loss rate of the QSn6 alloy increased as the flow velocity increased. The mass loss rate with cathodic protection was lower than that without cathodic protection under the same conditions. Also, the lowest mass loss rate of 0.7 g m‑2 · h‑1 was acquired at the flow velocity of 7 m s‑1 with cathodic protection. However, the increase rate of corrosion rate and mass loss were decreased with increasing the flow velocity. Through observation the SEM morphologies of the worn surfaces, the main wear mechanism was ploughing with/without cathodic protection. The removal rates of the QSn6 alloy increased as the flow velocity increased in both pure erosion and erosion-corrosion, whereas the erosion and corrosion intensified each other. At the flow velocity of 7 m s‑1, the synergy rate (ΔW) exceeded by 5 times the erosion rate (Wwear). Through establishment and observation the erosion-corrosion mechanism map, the erosion-corrosion was the dominant regime in the study due to the contribution of erosion on the mass loss rate exceeded the corrosion contribution. The QSn6 alloy with cathodic protection is feasible as propellers, there are higher security at lower flow velocity, such as the flow velocity of 7 m s‑1 in the paper.

Influence of the tilt angle of Percutaneous Aortic Prosthesis on Velocity and Shear Stress Fields

PubMed Central

Gomes, Bruno Alvares de Azevedo; Camargo, Gabriel Cordeiro; dos Santos, Jorge Roberto Lopes; Azevedo, Luis Fernando Alzuguir; Nieckele, Ângela Ourivio; Siqueira-Filho, Aristarco Gonçalves; de Oliveira, Glaucia Maria Moraes

2017-01-01

Background Due to the nature of the percutaneous prosthesis deployment process, a variation in its final position is expected. Prosthetic valve placement will define the spatial location of its effective orifice in relation to the aortic annulus. The blood flow pattern in the ascending aorta is related to the aortic remodeling process, and depends on the spatial location of the effective orifice. The hemodynamic effect of small variations in the angle of inclination of the effective orifice has not been studied in detail. Objective To implement an in vitro simulation to characterize the hydrodynamic blood flow pattern associated with small variations in the effective orifice inclination. Methods A three-dimensional aortic phantom was constructed, reproducing the anatomy of one patient submitted to percutaneous aortic valve implantation. Flow analysis was performed by use of the Particle Image Velocimetry technique. The flow pattern in the ascending aorta was characterized for six flow rate levels. In addition, six angles of inclination of the effective orifice were assessed. Results The effective orifice at the -4º and -2º angles directed the main flow towards the anterior wall of the aortic model, inducing asymmetric and high shear stress in that region. However, the effective orifice at the +3º and +5º angles mimics the physiological pattern, centralizing the main flow and promoting a symmetric distribution of shear stress. Conclusion The measurements performed suggest that small changes in the angle of inclination of the percutaneous prosthesis aid in the generation of a physiological hemodynamic pattern, and can contribute to reduce aortic remodeling. PMID:28793046

Cyclic variation of ultrasonic backscattering from porcine whole blood under pulsatile flow

NASA Astrophysics Data System (ADS)

Lin, Yu-Hong

1997-10-01

The cyclic variation of ultrasonic backscattering from blood under pulsatile flow is believed to be related to the change of aggregation state of red cells and is only observed in whole blood. This study was to investigate the phenomenon by an invasive approach which was performed by inserting a 10 MHz catheter mounted transducer into a vessel. For ultrasonic measurement from blood, the most fundamental scheme is the hematocrit dependence. The backscatter maximum location was changed as the blood was stirred or stationary, as well as under steady laminar or turbulent flows. The same trend was also observed under pulsatile flow with 10% to 50% hematocrits in this study, as the backscattering to hematocrit curves were plotted at different times during a flow cycle. When the cyclic variation at 20 beats per minute (BPM) was interpreted in time domain, the enhanced aggregation at the beginning of shearing was observed. At 20 BPM with 40% hematocrit, the amplitude of cyclic variation was reduced when the shear rate was increased and the threshold of 150 s-1 was estimated. The results showed that there was no cyclic variation at 60 BPM. The backscattering was also plotted against the mean flow velocity, which demonstrated the hysteresis loops. The ultrasonic measurements showed that the relationship between the forward and backward paths of the loops were altered as beat rate, hematocrit, and shear rate were varied. Since the pulsatile flow was very complicated, a computational fluid dynamics package, FIDAPTM, was used to compute the shear rate based on the Power Law Model for non-Newtonian fluid viscosity. The non- Newtonian index and consistency in the model were computed from the viscosity to shear rate curves at 10% to 50% hematocrits measured by a cone-plate viscometer. For in vivo measurements, small pigs were used as models. Ultrasonic backscattering measurements were performed in the arteries and veins. The effect of stenosis was also investigated at the site below the renal branch in the artery. The results show that the cyclic variation from whole blood was mediated by the shear rate, hematocrit, beat rate, and fibrinogen concentration.

A generalized quasi-geostrophic core flow formalism

NASA Astrophysics Data System (ADS)

Amit, H.; Coutelier, M.

2016-12-01

The quasi-geostrophic formalism provides a theoretical coupling between toroidal and poloidal core flows. By enforcing impermeable core-mantle boundary, conservation of mass and a linear variation of the axial flow along an axial column, this coupling can be written as div_h · u_h = c tan θ/R u_θ where u_h is the tangential velocity at the top of the core, θ is co-latitude, R is the core radius and c=2 (Amit and Olson, 2004; Amit and Pais, 2013). We extend this theory and develop this expression for different profiles of the axial flow. Our results show that the same expression holds but the value of c may vary depending on the profile of the axial flow, including c=1 as in the tangential geostrophy formalism. These results may therefore provide new constraints on quasi-geostrophic core flow inversions from geomagnetic SV.

Kinematics and the origin of the internal structures in HL Tauri jet (HH 151)

NASA Astrophysics Data System (ADS)

Movsessian, T. A.; Magakian, T. Yu.; Moiseev, A. V.

2012-05-01

Context. Knotty structures of Herbig-Haro jets are common phenomena, and knowing the origin of these structures is essential for understanding the processes of jet formation. Basically, there are two theoretical approaches: different types of instabilities in stationary flow, and velocity variations in the flow. Aims: We investigate the structures with different radial velocities in the knots of the HL Tau jet as well as its unusual behaviour starting from 20'' from the source. Collation of radial velocity data with proper motion measurements of emission structures in the jet of HL Tau makes it possible to understand the origin of these structures and decide on the mechanism for the formation of the knotty structures in Herbig-Haro flows. Methods: We present observations obtained with a 6 m telescope (Russia) using the SCORPIO camera with scanning Fabry-Perót interferometer. Two epochs of the observations of the HL/XZ Tau region in Hα emission (2001 and 2007) allowed us to measure proper motions for high and low radial velocity structures. Results: The structures with low and high radial velocities in the HL Tau jet show the same proper motion. The point where the HL Tau jet bents to the north (it coincides with the trailing edge of so-called knot A) is stationary, i.e. does not have any perceptible proper motion and is visible in Hα emission only. Conclusions: We conclude that the high- and low-velocity structures in the HL Tau jet represent bow-shocks and Mach disks in the internal working surfaces of episodic outflows. The bend of the jet and the brightness increase starting some distance from the source coincides with the observed stationary deflecting shock. The increase of relative surface brightness of bow-shocks could be the result of the abrupt change of the physical conditions of the ambient medium as well as the interaction of a highly collimated flow and the side wind from XZ Tau. Based on observations collected with the 6 m telescope of the Special Astrophysical Observatory (SAO) of the Russian Academy of Sciences (RAS), operated under the financial support of the Science Department of Russia (registration number 01-43).

Dynamics in the Modern Upper Atmosphere of Venus: Zonal Wind Transition to Subsolar-to-Antisolar Flow

NASA Astrophysics Data System (ADS)

Livengood, T. A.; Kostiuk, T.; Hewagama, T.; Fast, K. E.

2017-12-01

We observed Venus on 19-23 Aug 2010 (UT) to investigate equatorial wind velocities from above the cloud tops through the lower thermosphere. Measurements were made from the NASA Infrared Telescope Facility using the NASA Goddard Space Flight Center Heterodyne Instrument for Planetary Winds and Composition. High-resolution spectra were acquired on a CO2 pressure-broadened absorption feature that probes the lower mesosphere ( 70 km altitude) with a non-LTE core emission of the same transition that probes the lower thermosphere ( 110 km). The resolving power of λ/Δλ≈3×107 determines line-of-sight velocity from Doppler shifts to high precision. The altitude differential between the features enables investigating the transition from zonal wind flow near the cloud tops to subsolar-to-antisolar flow in the thermosphere. The fully-resolved carbon dioxide transition was measured near 952.8808 cm-1 (10.494 µm) rest frequency at the equator with 1 arcsec field-of-view on Venus (24 arcsec diameter) distributed about the central meridian and across the terminator at ±15° intervals in longitude. The non-LTE emission is solar-pumped and appears only on the daylight side, probing subsolar-to-antisolar wind velocity vector flowing radially from the subsolar point through the terminator, which was near the central meridian in these observations and had zero line-of-sight wind projection at the terminator. The velocity of the zonal flow is approximately uniform, with maximum line-of-sight projection at the limb, and can be measured by the frequency of the absorption line on both the daylight and dark side. Variations in Doppler shift between the observable features and the differing angular dependence of the contributing wind phenomena thus provide independent mechanisms to distinguish the dynamical processes at the altitude of each observed spectral feature. Winds up to >100 m/s were determined in previous investigations with uncertainties of order 10 m/s or less.

Comparison of thermal, salt and dye tracing to estimate shallow flow velocities: Novel triple-tracer approach

NASA Astrophysics Data System (ADS)

Abrantes, João R. C. B.; Moruzzi, Rodrigo B.; Silveira, Alexandre; de Lima, João L. M. P.

2018-02-01

The accurate measurement of shallow flow velocities is crucial to understand and model the dynamics of sediment and pollutant transport by overland flow. In this study, a novel triple-tracer approach was used to re-evaluate and compare the traditional and well established dye and salt tracer techniques with the more recent thermal tracer technique in estimating shallow flow velocities. For this purpose a triple tracer (i.e. dyed-salted-heated water) was used. Optical and infrared video cameras and an electrical conductivity sensor were used to detect the tracers in the flow. Leading edge and centroid velocities of the tracers were measured and the correction factors used to determine the actual mean flow velocities from tracer measured velocities were compared and investigated. Experiments were carried out for different flow discharges (32-1813 ml s-1) on smooth acrylic, sand, stones and synthetic grass bed surfaces with 0.8, 4.4 and 13.2% slopes. The results showed that thermal tracers can be used to estimate shallow flow velocities, since the three techniques yielded very similar results without significant differences between them. The main advantages of the thermal tracer were that the movement of the tracer along the measuring section was more easily visible than it was in the real image videos and that it was possible to measure space-averaged flow velocities instead of only one velocity value, with the salt tracer. The correction factors used to determine the actual mean velocity of overland flow varied directly with Reynolds and Froude numbers, flow velocity and slope and inversely with flow depth and bed roughness. In shallow flows, velocity estimation using tracers entails considerable uncertainty and caution must be taken with these measurements, especially in field studies where these variables vary appreciably in space and time.

a Numerical Study of Basic Coastal Upwelling Processes.

NASA Astrophysics Data System (ADS)

Li, Zhihong

Available from UMI in association with The British Library. Two-dimensional (2-D) and three-dimensional (3 -D) numerical models with a second order turbulence closure are developed for the study of coastal upwelling processes. A logarithmic coordinate system is introduced to obtain increased resolution in the regions near the surface and bottom where high velocity shear occurs and in the upwelling zone where its width is confined to the coast. In the experiments performed in the 2-D model an ocean initially at rest is driven by a spatially uniform alongshore wind-stress. There is a development of an offshore flow in the surface layer and an onshore flow below the surface layer. In the wind-stress direction there is a development of a coastal surface jet. The neglect of the alongshore pressure gradient leads to the intensification of the jet, and the concentration of the onshore flow in an over-developed Ekman layer yielding an unrealistic deepening of a bottom mixed layer. When bathymetric variations are introduced, some modifications in the dynamics of upwelling are observed. On the shelf region there is another upwelling zone and isotherms are interested with the bottom topography. When an alongshore pressure gradient is added externally into the model, the strength of the coastal jet decreases and a coastal undercurrent exists at greater depth. In addition the return onshore flow is largely independent of depth and the deepening of the bottom mixed layer disappears. In the experiments performed in the 3-D model a wind-stress with limited domain is used. Coastally trapped waves are generated and propagate along the coastline leading to a development of an alongshore pressure gradient, which has a significant effect on upwelling. The evolution of the alongshore flow, vertical velocity and the temperature is determined by both remote and local wind due to the propagation of waves. As the integration proceeds, the flow pattern becomes remarkably 3-dimensional. Finally the influence of bathymetric variations on upwelling processes is examined.

Andreas Acrivos Dissertation Prize Lecture: Stability of inviscid flows from bifurcation diagrams exploiting a variational argument

NASA Astrophysics Data System (ADS)

Luzzatto-Fegiz, Paolo

2011-11-01

Steady fluid solutions play a special role in the dynamics of a flow: stable states may be realized in practice, while unstable ones may act as attractors. Unfortunately, determining stability is often a process far more laborious than finding steady states; indeed, even for simple vortex or wave flows, stability properties have often been the subject of debate. We consider here a stability idea originating with Lord Kelvin (1876), which involves using the second variation of the energy, δ2 E , to establish bounds on a perturbation. However, for numerically obtained flows, computing δ2 E explicitly is often not feasible. To circumvent this issue, Saffman & Szeto (1980) proposed an argument linking changes in δ2 E to turning points in a bifurcation diagram, for families of steady flows. Later work has shown that this argument is unreliable; the two key issues are associated with the absence of a formal turning-point theory, and with the inability to detect bifurcations (Dritschel 1995, and references therein). In this work, we build on ideas from bifurcation theory, and link turning points in a velocity-impulse diagram to changes in δ2 E ; in addition, this diagram delivers the direction of the change of δ2 E , thereby providing information as to whether stability is gained or lost. To detect hidden solution branches, we introduce to these fluid problems concepts from imperfection theory. The resulting approach, involving ``imperfect velocity-impulse'' diagrams, leads us to new and surprising results for a wide range of fundamental vortex and wave flows; we mention here the calculation of the first steady vortices without any symmetry, and the uncovering of the complete solution structure for vortex pairs. In addition, we find precise agreement with available results from linear stability analysis. Doctoral work advised by C.H.K. Williamson at Cornell University.

Computing 3-D wavefields in mantle circulations models to test hypotheses on the origin of lower mantle heterogeneity under Africa directly against seismic observations

NASA Astrophysics Data System (ADS)

Schuberth, Bernhard; Zaroli, Christophe; Nolet, Guust

2015-04-01

Of particular interest for the tectonic evolution of the Atlantic region is the influence of lower mantle structure under Africa on flow in the upper mantle beneath the ocean basin. Along with its Pacific counterpart, the large African anomaly in the lowermost mantle with strongly reduced seismic velocities has received considerable attention in seismological and geodynamic studies. Several seismological observations are typically taken as an indication that these two anomalies are being caused by large-scale compositional variations and that they are piles of material with higher density than normal mantle rock. This would imply negative buoyancy in the lowermost mantle under Africa, which has important implications for the flow at shallower depth and inferences on the processes that led to the formation of the Atlantic Ocean basin. However, a large number of recent studies argue for a strong thermal gradient across the core-mantle boundary that might provide an alternative explanation for the lower mantle anomaly through the resulting large lateral temperature variations. Recently, we developed a new joint forward modeling approach to test such geodynamic hypotheses directly against the seismic observations: Seismic heterogeneity is predicted by converting the temperature field of a high-resolution 3-D mantle circulation model into seismic velocities using thermodynamic models of mantle mineralogy. 3-D global wave propagation in the synthetic elastic structures is then simulated using a spectral element method. Being based on forward modelling only, this approach allows us to generate synthetic wavefields and seismograms independently of seismic observations. The statistics of observed long-period body wave traveltime variations show a markedly different behaviour for P- and S-waves: the standard deviation of P-wave delay times stays almost constant with ray turning depth, while that of the S-wave delay times increases strongly throughout the mantle. In an earlier study, we showed that synthetic traveltime variations computed for an isochemical mantle circulation model with strong core heating can reproduce these different trends. This was taken as a strong indication that seismic heterogeneity in the lower mantle is likely dominated by thermal variations on large length-scales (i.e., relevant for long-period body waves). We will discuss the robustness of this earlier conclusion by exploring the uncertainties in the mineralogical models used to convert temperatures to seismic velocities. In particular, we investigate the influence of anelasticity on the standard deviation of our synthetic traveltime variations. Owing to the differences in seismic frequency content between laboratory measurements (MHz to GHz) and the Earth (mHz to Hz), the seismic velocities given in the mineralogical model need to be adjusted; that is, corrected for dispersion due to anelastic effects.

Effects of Lewis number on the statistics of the invariants of the velocity gradient tensor and local flow topologies in turbulent premixed flames

NASA Astrophysics Data System (ADS)

Wacks, Daniel; Konstantinou, Ilias; Chakraborty, Nilanjan

2018-04-01

The behaviours of the three invariants of the velocity gradient tensor and the resultant local flow topologies in turbulent premixed flames have been analysed using three-dimensional direct numerical simulation data for different values of the characteristic Lewis number ranging from 0.34 to 1.2. The results have been analysed to reveal the statistical behaviours of the invariants and the flow topologies conditional upon the reaction progress variable. The behaviours of the invariants have been explained in terms of the relative strengths of the thermal and mass diffusions, embodied by the influence of the Lewis number on turbulent premixed combustion. Similarly, the behaviours of the flow topologies have been explained in terms not only of the Lewis number but also of the likelihood of the occurrence of individual flow topologies in the different flame regions. Furthermore, the sensitivity of the joint probability density function of the second and third invariants and the joint probability density functions of the mean and Gaussian curvatures to the variation in Lewis number have similarly been examined. Finally, the dependences of the scalar-turbulence interaction term on augmented heat release and of the vortex-stretching term on flame-induced turbulence have been explained in terms of the Lewis number, flow topology and reaction progress variable.

Effects of Lewis number on the statistics of the invariants of the velocity gradient tensor and local flow topologies in turbulent premixed flames

PubMed Central

Konstantinou, Ilias; Chakraborty, Nilanjan

2018-01-01

The behaviours of the three invariants of the velocity gradient tensor and the resultant local flow topologies in turbulent premixed flames have been analysed using three-dimensional direct numerical simulation data for different values of the characteristic Lewis number ranging from 0.34 to 1.2. The results have been analysed to reveal the statistical behaviours of the invariants and the flow topologies conditional upon the reaction progress variable. The behaviours of the invariants have been explained in terms of the relative strengths of the thermal and mass diffusions, embodied by the influence of the Lewis number on turbulent premixed combustion. Similarly, the behaviours of the flow topologies have been explained in terms not only of the Lewis number but also of the likelihood of the occurrence of individual flow topologies in the different flame regions. Furthermore, the sensitivity of the joint probability density function of the second and third invariants and the joint probability density functions of the mean and Gaussian curvatures to the variation in Lewis number have similarly been examined. Finally, the dependences of the scalar--turbulence interaction term on augmented heat release and of the vortex-stretching term on flame-induced turbulence have been explained in terms of the Lewis number, flow topology and reaction progress variable. PMID:29740257

Sublithospheric flows in the mantle

NASA Astrophysics Data System (ADS)

Trifonov, V. G.; Sokolov, S. Yu.

2017-11-01

The estimated rates of upper mantle sublithospheric flows in the Hawaii-Emperor Range and Ethiopia-Arabia-Caucasus systems are reported. In the Hawaii-Emperor Range system, calculation is based on motion of the asthenospheric flow and the plate moved by it over the branch of the Central Pacific plume. The travel rate has been determined based on the position of variably aged volcanoes (up to 76 Ma) with respect to the active Kilauea Volcano. As for the Ethiopia-Arabia-Caucasus system, the age of volcanic eruptions (55-2.8 Ma) has been used to estimate the asthenospheric flow from the Ethiopian-Afar superplume in the northern bearing lines. Both systems are characterized by variations in a rate of the upper mantle flows in different epochs from 4 to 12 cm/yr, about 8 cm/yr on average. Analysis of the global seismic tomographic data has made it possible to reveal rock volumes with higher seismic wave velocities under ancient cratons; rocks reach a depth of more than 2000 km and are interpreted as detached fragments of the thickened continental lithosphere. Such volumes on both sides of the Atlantic Ocean were submerged at an average velocity of 0.9-1.0 cm/yr along with its opening. The estimated rates of the mantle flows clarify the deformation properties of the mantle and regulate the numerical models of mantle convection.

Challenges in the determination of the interstellar flow longitude from the pickup ion cutoff

NASA Astrophysics Data System (ADS)

Taut, A.; Berger, L.; Möbius, E.; Drews, C.; Heidrich-Meisner, V.; Keilbach, D.; Lee, M. A.; Wimmer-Schweingruber, R. F.

2018-03-01

Context. The interstellar flow longitude corresponds to the Sun's direction of movement relative to the local interstellar medium. Thus, it constitutes a fundamental parameter for our understanding of the heliosphere and, in particular, its interaction with its surroundings, which is currently investigated by the Interstellar Boundary EXplorer (IBEX). One possibility to derive this parameter is based on pickup ions (PUIs) that are former neutral ions that have been ionized in the inner heliosphere. The neutrals enter the heliosphere as an interstellar wind from the direction of the Sun's movement against the partially ionized interstellar medium. PUIs carry information about the spatial variation of their neutral parent population (density and flow vector field) in their velocity distribution function. From the symmetry of the longitudinal flow velocity distribution, the interstellar flow longitude can be derived. Aim. The aim of this paper is to identify and eliminate systematic errors that are connected to this approach of measuring the interstellar flow longitude; we want to minimize any systematic influences on the result of this analysis and give a reasonable estimate for the uncertainty. Methods: We use He+ data measured by the PLAsma and SupraThermal Ion Composition (PLASTIC) sensor on the Solar TErrestrial RElations Observatory Ahead (STEREO A) spacecraft. We analyze a recent approach, identify sources of systematic errors, and propose solutions to eliminate them. Furthermore, a method is introduced to estimate the error associated with this approach. Additionally, we investigate how the selection of interplanetary magnetic field angles, which is closely connected to the pickup ion velocity distribution function, affects the result for the interstellar flow longitude. Results: We find that the revised analysis used to address part of the expected systematic effects obtains significantly different results than presented in the previous study. In particular, the derived uncertainties are considerably larger. Furthermore, an unexpected systematic trend of the resulting interstellar flow longitude with the selection of interplanetary magnetic field orientation is uncovered.

Experimental study of heat and mass transfer in a buoyant countercurrent exchange flow

NASA Astrophysics Data System (ADS)

Conover, Timothy Allan

Buoyant Countercurrent Exchange Flow occurs in a vertical vent through which two miscible fluids communicate, the higher-density fluid, residing above the lower-density fluid, separated by the vented partition. The buoyancy- driven zero net volumetric flow through the vent transports any passive scalars, such as heat and toxic fumes, between the two compartments as the fluids seek thermodynamic and gravitational equilibrium. The plume rising from the vent into the top compartment resembles a pool fire plume. In some circumstances both countercurrent flows and pool fires can ``puff'' periodically, with distinct frequencies. One experimental test section containing fresh water in the top compartment and brine (NaCl solution) in the bottom compartment provided a convenient, idealized flow for study. This brine flow decayed in time as the concentrations approached equilibrium. A second test section contained fresh water that was cooled by heat exchangers above and heated by electrical elements below and operated steadily, allowing more time for data acquisition. Brine transport was reduced to a buoyancy- scaled flow coefficient, Q*, and heat transfer was reduced to an analogous coefficient, H*. Results for vent diameter D = 5.08 cm were consistent between test sections and with the literature. Some results for D = 2.54 cm were inconsistent, suggesting viscosity and/or molecular diffusion of heat become important at smaller scales. Laser Doppler Velocimetry was used to measure velocity fields in both test sections, and in thermal flow a small thermocouple measured temperature simultaneously with velocity. Measurement fields were restricted to the plume base region, above the vent proper. In baseline periodic flow, instantaneous velocity and temperature were ensemble averaged, producing a movie of the average variation of each measure during a puffing flow cycle. The temperature movie revealed the previously unknown cold core of the puff during its early development. The renewal-length model for puffing frequency of pool fire plumes was extended to puffing countercurrent flows by estimating inflow dilution. Puffing frequencies at several conditions were reduced to Strouhal number based on dilute plume density. Results for D = 5.08 cm compared favorably to published measurements of puffing pool fires, suggesting that the two different flows obey the same periodic dynamic process.

An entropy-based method for determining the flow depth distribution in natural channels

NASA Astrophysics Data System (ADS)

Moramarco, Tommaso; Corato, Giovanni; Melone, Florisa; Singh, Vijay P.

2013-08-01

A methodology for determining the bathymetry of river cross-sections during floods by the sampling of surface flow velocity and existing low flow hydraulic data is developed . Similar to Chiu (1988) who proposed an entropy-based velocity distribution, the flow depth distribution in a cross-section of a natural channel is derived by entropy maximization. The depth distribution depends on one parameter, whose estimate is straightforward, and on the maximum flow depth. Applying to a velocity data set of five river gage sites, the method modeled the flow area observed during flow measurements and accurately assessed the corresponding discharge by coupling the flow depth distribution and the entropic relation between mean velocity and maximum velocity. The methodology unfolds a new perspective for flow monitoring by remote sensing, considering that the two main quantities on which the methodology is based, i.e., surface flow velocity and flow depth, might be potentially sensed by new sensors operating aboard an aircraft or satellite.

Airlift Cargo Hub Port Hold Times: Controlling Variations in Defense Supply Chain Delivery

DTIC Science & Technology

2010-06-01

AIR UNIVERSITY AIR FORCE INSTITUTE OF TECHNOLOGY Wright-Patterson Air Force Base, Ohio APPROVED FOR PUBLIC RELEASE; DISTRIBUTION UNLIMITED...Department of Operational Sciences Graduate School of Engineering and Management Air Force Institute of Technology Air University Air...process for a seamless flow of cargo onto the aircraft segment (AMC and DDC , 24 Sep 08). Figure 6 AMC Velocity Efforts (Anderson D. , 2009) While

Detection of memory loss of symmetry in the blockage of a turbulent flow within a duct

NASA Astrophysics Data System (ADS)

Santos, F. Rodrigues; da Silva Costa, G.; da Cunha Lima, A. T.; de Almeida, M. P.; da Cunha Lima, I. C.

This paper aims to detect memory loss of the symmetry of blockades in ducts and how far the information on the asymmetry of the obstacles travels in the turbulent flow from computational simulations with OpenFOAM. From a practical point of view, it seeks alternatives to detect the formation of obstructions in pipelines. The numerical solutions of the Navier-Stokes equations were obtained through the solver PisoFOAM of the OpenFOAM library, using the large Eddy simulation (LES) for the turbulent model. Obstructions were placed near the duct inlet and, keeping the blockade ratio fixed, five combinations for the obstacles sizes were adopted. The results show that the information about the symmetry is preserved for a larger distance near the ducts wall than in mid-channel. For an inlet velocity of 5m/s near the walls the memory is kept up to distance 40 times the duct width, while in mid-channel this distance is reduced almost by half. The maximum distance in which the symmetry breaking memory is preserved shows sensitivity to Reynolds number variations in regions near the duct walls, while in the mid channel that variations do not cause relevant effects to the velocity distribution.

Clustering and relative velocity of heavy particles under gravitational settling in isotropic turbulent flows

NASA Astrophysics Data System (ADS)

Jin, Guodong; He, Guo-Wei

2015-11-01

Clustering and intermittency in radial relative velocity (RRV) of heavy particles of same size settling in turbulent flows can be remarkably changed due to gravity. Clustering is monotonically reduced at Stokes number less than 1 under gravity due to the disability of the centrifugal mechanism, however it is non-monotonically enhanced at Stokes number greater than 1 due to the multiplicative amplification in the case that the proposed effective Kubo number is less than 1. Although gravity causes monotonical reduction in the rms of RRV of particles at a given Stokes number with decreasing Froude number, the variation tendency in the tails of standardized PDF of RRV versus Froude number is obviously different: the tails become narrower at a small Stokes number, while they become broader at a large Stokes number. The mechanism of this variation stems from the compromise between the following two competing factors. The mitigation of correlation of particle positions and the regions of high strain rate which are more intermittent reduces the intermittency in RRV at small Stokes numbers, while the significant reduction in the backward-in-time relative separations will make particle pairs see small-scale structures, leading to a higher intermittency in RRV at large Stokes numbers. NSAF of China (grant number U1230126); NSFC (grant numbers 11072247 and 11232011).

A study of methods to estimate debris flow velocity

USGS Publications Warehouse

Prochaska, A.B.; Santi, P.M.; Higgins, J.D.; Cannon, S.H.

2008-01-01

Debris flow velocities are commonly back-calculated from superelevation events which require subjective estimates of radii of curvature of bends in the debris flow channel or predicted using flow equations that require the selection of appropriate rheological models and material property inputs. This research investigated difficulties associated with the use of these conventional velocity estimation methods. Radii of curvature estimates were found to vary with the extent of the channel investigated and with the scale of the media used, and back-calculated velocities varied among different investigated locations along a channel. Distinct populations of Bingham properties were found to exist between those measured by laboratory tests and those back-calculated from field data; thus, laboratory-obtained values would not be representative of field-scale debris flow behavior. To avoid these difficulties with conventional methods, a new preliminary velocity estimation method is presented that statistically relates flow velocity to the channel slope and the flow depth. This method presents ranges of reasonable velocity predictions based on 30 previously measured velocities. ?? 2008 Springer-Verlag.

Flow behaviour and structure of heterogeneous particles-water mixture in horizontal and inclined pipes

NASA Astrophysics Data System (ADS)

Vlasák, Pavel; Chára, Zdeněk; Konfršt, Jiří

2018-06-01

The effect of slurry velocity and mean concentration of heterogeneous particle-water mixture on flow behaviour and structure in the turbulent regime was studied in horizontal and inclined pipe sections of inner diameter D = 100 mm. The stratified flow pattern of heterogeneous particle-water mixture in the inclined pipe sections was revealed. The particles moved mostly near to the pipe invert. Concentration distribution in ascending and descending vertical pipe sections confirmed the effect of fall velocity on particle-carrier liquid slip velocity and increase of in situ concentration in the ascending pipe section. Slip velocity in two-phase flow, which is defined as the velocity difference between the solid and liquid phase, is one of mechanism of particle movement in two-phase flow. Due to the slip velocity, there is difference between transport and in situ concentrations, and the slip velocity can be determined from comparison of the in situ and transport concentration. For heterogeneous particle-water mixture flow the slip velocity depends on the flow structure.

Echocardiographic nomograms for upper abdominal aorta Doppler systolic wave values and systo-diastolic diameters variations in children.

PubMed

Cantinotti, Massimiliano; Giordano, Raffaele; Corsini, Iuri; Dani, Carlo; Scalese, Marco; Murzi, Bruno; Assanta, Nadia; Spadoni, Isabella; Molinaro, Sabrina; Kutty, Shelby; Iervasi, Giorgio; Franchi, Eliana

2018-04-01

Abdominal aorta pulsatility and blood flow patterns are important diagnostic indicators in congenital heart disease. Reference values for these indexes are lacking. We prospectively studied abdominal aorta pulsed-wave Doppler systolic peak velocity, deceleration time, and wave duration, and two-dimensional vessel diameters in systole and diastole in healthy Caucasian children. Heteroscedasticity was accounted for by White or Breusch-Pagan test. Age, weight, height, heart rate (HR), and body surface area (BSA) were used as independent variables in different analyses to predict the mean values of each measurement. Structured Z-scores were then computed. In all, 853 subjects (age 0 days to 17 years; 45% females; BSA 0.12-2.12m 2 ) were studied. The predicted values and Z-score boundaries are presented. Data are also presented as mean±2 SDs for a given BSA. We report paediatric echocardiographic nomograms for multiple proximal abdominal aorta parameters including pulsed-wave Doppler systolic velocities, deceleration time, wave duration, and two-dimensional vessel diameter variations. Significant variations in these functional indexes with age were found that should be taken into account in clinical practice. At lower ages, steeper and shorter pulsed-wave Doppler peak velocity and limited pulsatility should be expected as physiologic findings. Copyright © 2017 Japanese College of Cardiology. Published by Elsevier Ltd. All rights reserved.

Visualization of flow by vector analysis of multidirectional cine MR velocity mapping.

PubMed

Mohiaddin, R H; Yang, G Z; Kilner, P J

1994-01-01

We describe a noninvasive method for visualization of flow and demonstrate its application in a flow phantom and in the great vessels of healthy volunteers and patients with aortic and pulmonary arterial disease. The technique uses multidirectional MR velocity mapping acquired in selected planes. Maps of orthogonal velocity components were then processed into a graphic form immediately recognizable as flow. Cine MR velocity maps of orthogonal velocity components in selected planes were acquired in a flow phantom, 10 healthy volunteers, and 13 patients with dilated great vessels. Velocities were presented by multiple computer-generated streaks whose orientation, length, and movement corresponded to velocity vectors in the chosen plane. The velocity vector maps allowed visualization of complex patterns of primary and secondary flow in the thoracic aorta and pulmonary arteries. The technique revealed coherent, helical forward blood movements in the normal thoracic aorta during midsystole and a reverse flow during early diastole. Abnormal flow patterns with secondary vortices were seen in patients with dilated arteries. The potential of MR velocity vector mapping for in vitro and in vivo visualization of flow patterns is demonstrated. Although this study was limited to two-directional flow in a single anatomical plane, the method provides information that might advance our understanding of the human vascular system in health and disease. Further developments to reduce the acquisition time and the handling and presenting of three-directional velocity data are required to enhance the capability of this method.

Impact of laminar flow velocity of different acids on enamel calcium loss.

PubMed

Attin, T; Becker, K; Wiegand, A; Tauböck, T T; Wegehaupt, F J

2013-03-01

The aim of the study was to evaluate the impact of flow velocity under laminar flow conditions of different acidic solutions on enamel erosion. A total of 240 bovine enamel specimens were prepared and allocated to 30 groups (n = 8 each). Samples of 18 groups were superfused in a flow chamber system with laminar flow behavior using 1 ml of citric acid or hydrochloric acid (HCl) of pH 2.0, 2.6 or 3.0. Flow rates in the sample chamber were adjusted to 10, 60 or 100 μl/min. To simulate turbulent flow behavior, samples of six groups were immersed in 1 ml of the respective solution, which was vortexed (15 min, 600 rpm). For simulating non-agitated conditions, specimens of the remaining six groups were immersed in 1 ml of the respective solution without stirring. Calcium in the solutions, released from the enamel samples, was determined using Arsenazo III method. For acidic solutions of pH 2.6 and 3.0, erosive potential of citric acid was equivalent to that of HCl at a flow of 100 μl/min. The same observation was made for the samples subjected to turbulent conditions at pH 3. At all other conditions, citric acid induced a significantly higher calcium loss than HCl. It is concluded that under slow laminar flow conditions, flow rate variations lead to higher erosive impact of citric acid compared to hydrochloric acid at pH 2.0, but not at pH ≥ 2.6 and increasing laminar flow or turbulent conditions. Erosive enamel dissolution under laminar flow conditions is a complex issue influenced by flow rate and acidic substrate.

Fish habitat selection in a large hydropeaking river: Strong individual and temporal variations revealed by telemetry.

PubMed

Capra, Hervé; Plichard, Laura; Bergé, Julien; Pella, Hervé; Ovidio, Michaël; McNeil, Eric; Lamouroux, Nicolas

2017-02-01

Modeling individual fish habitat selection in highly variable environments such as hydropeaking rivers is required for guiding efficient management decisions. We analyzed fish microhabitat selection in the heterogeneous hydraulic and thermal conditions (modeled in two-dimensions) of a reach of the large hydropeaking Rhône River locally warmed by the cooling system of a nuclear power plant. We used modern fixed acoustic telemetry techniques to survey 18 fish individuals (five barbels, six catfishes, seven chubs) signaling their position every 3s over a three-month period. Fish habitat selection depended on combinations of current microhabitat hydraulics (e.g. velocity, depth), past microhabitat hydraulics (e.g. dewatering risk or maximum velocities during the past 15days) and to a lesser extent substrate and temperature. Mixed-effects habitat selection models indicated that individual effects were often stronger than specific effects. In the Rhône, fish individuals appear to memorize spatial and temporal environmental changes and to adopt a "least constraining" habitat selection. Avoiding fast-flowing midstream habitats, fish generally live along the banks in areas where the dewatering risk is high. When discharge decreases, however, they select higher velocities but avoid both dewatering areas and very fast-flowing midstream habitats. Although consistent with the available knowledge on static fish habitat selection, our quantitative results demonstrate temporal variations in habitat selection, depending on individual behavior and environmental history. Their generality could be further tested using comparative experiments in different environmental configurations. Copyright © 2016 Elsevier B.V. All rights reserved.

Effects of particle-fluid density ratio on the interactions between the turbulent channel flow and finite-size particles

NASA Astrophysics Data System (ADS)

Yu, Zhaosheng; Lin, Zhaowu; Shao, Xueming; Wang, Lian-Ping

2017-09-01

A parallel direct-forcing fictitious domain method is employed to perform fully resolved numerical simulations of turbulent channel flow laden with finite-size particles. The effects of the particle-fluid density ratio on the turbulence modulation in the channel flow are investigated at the friction Reynolds number of 180, the particle volume fraction of 0.84 % , and the particle-fluid density ratio ranging from 1 to 104.2. The results show that the variation of the flow drag with the particle-fluid density ratio is not monotonic, with a larger flow drag for the density ratio of 10.42, compared to those of unity and 104.2. A significant drag reduction by the particles is observed for large particle-fluid density ratios during the transient stage, but not at the statistically stationary stage. The intensity of particle velocity fluctuations generally decreases with increasing particle inertia, except that the particle streamwise root-mean-square velocity and streamwise-transverse velocity correlation in the near-wall region are largest at the density ratio of the order of 10. The averaged momentum equations are derived with the spatial averaging theorem and are used to analyze the mechanisms for the effects of the particles on the flow drag. The results indicate that the drag-reduction effect due to the decrease in the fluid Reynolds shear stress is counteracted by the drag-enhancement effect due to the increase in the total particle stress or the interphase drag force for the large particle-inertia case. The sum of the total Reynolds stress and particle inner stress contributions to the flow drag is largest at the density ratio of the order of 10, which is the reason for the largest flow drag at this density ratio. The interphase drag force obtained from the averaged momentum equation (the balance theory) is significantly smaller than (but agrees qualitatively with) that from the empirical drag formula based on the phase-averaged slip velocity for large density ratios. For the neutrally buoyant case, the balance theory predicts a positive interphase force on the particles arising from the negative gradient of the particle inner stress, which cannot be predicted by the drag formula based on the phase-averaged slip velocity. In addition, our results show that both particle collision and particle-turbulence interaction play roles in the formation of the inhomogeneous distribution of the particles at the density ratio of the order of 10.

Effects of particle-fluid density ratio on the interactions between the turbulent channel flow and finite-size particles.

PubMed

Yu, Zhaosheng; Lin, Zhaowu; Shao, Xueming; Wang, Lian-Ping

2017-09-01

A parallel direct-forcing fictitious domain method is employed to perform fully resolved numerical simulations of turbulent channel flow laden with finite-size particles. The effects of the particle-fluid density ratio on the turbulence modulation in the channel flow are investigated at the friction Reynolds number of 180, the particle volume fraction of 0.84%, and the particle-fluid density ratio ranging from 1 to 104.2. The results show that the variation of the flow drag with the particle-fluid density ratio is not monotonic, with a larger flow drag for the density ratio of 10.42, compared to those of unity and 104.2. A significant drag reduction by the particles is observed for large particle-fluid density ratios during the transient stage, but not at the statistically stationary stage. The intensity of particle velocity fluctuations generally decreases with increasing particle inertia, except that the particle streamwise root-mean-square velocity and streamwise-transverse velocity correlation in the near-wall region are largest at the density ratio of the order of 10. The averaged momentum equations are derived with the spatial averaging theorem and are used to analyze the mechanisms for the effects of the particles on the flow drag. The results indicate that the drag-reduction effect due to the decrease in the fluid Reynolds shear stress is counteracted by the drag-enhancement effect due to the increase in the total particle stress or the interphase drag force for the large particle-inertia case. The sum of the total Reynolds stress and particle inner stress contributions to the flow drag is largest at the density ratio of the order of 10, which is the reason for the largest flow drag at this density ratio. The interphase drag force obtained from the averaged momentum equation (the balance theory) is significantly smaller than (but agrees qualitatively with) that from the empirical drag formula based on the phase-averaged slip velocity for large density ratios. For the neutrally buoyant case, the balance theory predicts a positive interphase force on the particles arising from the negative gradient of the particle inner stress, which cannot be predicted by the drag formula based on the phase-averaged slip velocity. In addition, our results show that both particle collision and particle-turbulence interaction play roles in the formation of the inhomogeneous distribution of the particles at the density ratio of the order of 10.

LOW-VELOCITY COMPRESSIBLE FLOW THEORY

EPA Science Inventory

The widespread application of incompressible flow theory dominates low-velocity fluid dynamics, virtually preventing research into compressible low-velocity flow dynamics. Yet, compressible solutions to simple and well-defined flow problems and a series of contradictions in incom...

Delayed Neutrons Effect on Power Reactor with Variation of Fluid Fuel Velocity at MSR Fuji-12

NASA Astrophysics Data System (ADS)

Kuncoro Aji, Indarta; Pramuditya, Syeilendra; Novitrian; Irwanto, Dwi; Waris, Abdul

2017-01-01

As the nuclear reactor operate with liquid fuel, controlling velocity of the fuel flow on the Molten salt reactor very influence on the neutron kinetics in that reactor system. The effect of the pace fuel changes to the populations number of neutrons and power density on vertical direction (1 dimension) from the first until fifth year reactor operating had been analyzed on this research. This research had been conducted on MSR Fuji-12 with a two meters core high, and LiF-BeF2-ThF4-233UF4 as fuel composition respectively 71.78%-16%-11.86%-0.36%. Data of reactivity, neutron flux, and the macroscopic fission cross section obtained from ouput of SRAC (neutronic calculation code has been developed by JAEA, with JENDL-4.0 as data library on the SRAC calculation) was being used for the calculation process of this research. The calculation process of this research had been performed numerically by SOR (successive over relaxation) and finite difference methode, as well as using C programing language. From the calculation, regarding to the value of power density resulting from delayed neutrons, concluded that 20 m/s is the optimum fuel flow velocity in all the years reactor had operated. Where the increases number of power are inversely proportional with the fuel flow speed.

Influence of the shape factor on the flow and heat transfer of a water-based nanofluid in a rotating system

NASA Astrophysics Data System (ADS)

Khan, Umar; Adnan; Ahmed, Naveed; Mohyud-Din, Syed Tauseef

2017-04-01

The flow of a nanofluid between two parallel plates (horizontally placed) has been investigated. Different shapes of nanoparticles (suspended in a base fluid) have been considered and the effect of the shape factor has been analyzed. The lower plate is being stretched in opposite directions with forces of the same magnitude. The plates and nanofluid rotate together with angular velocity Ω. The dimensionless form of the flow model, in the form of a system of ordinary differential equations, is obtained by employing some viable similarity transformations. A well-knows analytical method i.e. Variation of Parameters Method (VPM), has been used to solve the problem. Besides, the same system of equations has also been solved numerically by using the forth order Runge-Kutta method, combined with shooting technique. The graphs highlight the influence of ingrained dimensionless physical parameters on the skin friction coefficient, velocity and temperature profiles, and local rate of heat transfer. It is observed that the velocity increases by varying suction/injection parameter and the temperature seems to drop for higher values of the Reynolds number. A decrement in skin friction is observed for increasing nanoparticles volume fraction. On the other hand, the local rate of heat transfer increases for increasing suction/injection parameter, Reynolds number and nanoparticles volume fraction.

Ion flow measurements during the MHD relaxation processes in the HIST spherical torus device

NASA Astrophysics Data System (ADS)

Nishioka, T.; Hashimoto, S.; Ando, K.; Kikuchi, Y.; Fukumoto, N.; Nagata, M.

2008-11-01

Plasma flow is one of the key roles in self-organization and magnetic reconnection processes of helicity-driven spherical torus (ST) and spheromak. The HIST spherical torus can form the standard ST and the flipped ST plasmas by utilizing the variation of the external toroidal field coil current. The flipped ST plasma can be generated by changing the polarity of the toroidal magnetic field during the standard ST discharge [1]. We have developed an ion Doppler spectrometer (IDS) system using a compact 16 channel photomultiplier tube (PMT) in order to measure the spatial profile of ion temperature and rotation velocity in the HIST device. The IDS system consists of a light collection system including optical fibers, 1 m-spectrometer and the PMT detector. As the results, it was observed that ion velocity was about 10 km/s in the same direction as the toroidal current and ExB direction in the standard ST discharge. The observed ion velocity agrees with Mach probe measurements. During the transition from the standard ST to the flipped ST state, the ion temperature was fluctuated and increased. The result implies an ion heating during magnetic reconnections. In addition, the toroidal direction of the ion flow was reversed. The detail physics of the observed phenomenon will be shown. [1] M. Nagata et al., Phys Rev. Lett. 90, pp. 225001-225004 (2003).

Characterization of the startup transient electrokinetic flow in rectangular channels of arbitrary dimensions, zeta potential distribution, and time-varying pressure gradient.

PubMed

Miller, Andrew; Villegas, Arturo; Diez, F Javier

2015-03-01

The solution to the startup transient EOF in an arbitrary rectangular microchannel is derived analytically and validated experimentally. This full 2D transient solution describes the evolution of the flow through five distinct periods until reaching a final steady state. The derived analytical velocity solution is validated experimentally for different channel sizes and aspect ratios under time-varying pressure gradients. The experiments used a time resolved micro particle image velocimetry technique to calculate the startup transient velocity profiles. The measurements captured the effect of time-varying pressure gradient fields derived in the analytical solutions. This is tested by using small reservoirs at both ends of the channel which allowed a time-varying pressure gradient to develop with a time scale on the order of the transient EOF. Results showed that under these common conditions, the effect of the pressure build up in the reservoirs on the temporal development of the transient startup EOF in the channels cannot be neglected. The measurements also captured the analytical predictions for channel walls made of different materials (i.e., zeta potentials). This was tested in channels that had three PDMS and one quartz wall, resulting in a flow with an asymmetric velocity profile due to variations in the zeta potential between the walls. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Vertebral Artery Diameter and Flow: Nature or Nurture.

PubMed

Tarnoki, Adam Domonkos; Fejer, Bence; Tarnoki, David Laszlo; Littvay, Levente; Lucatelli, Pierleone; Cirelli, Carlo; Fanelli, Fabrizio; Sacconi, Beatrice; Fagnani, Corrado; Medda, Emanuela; Farina, Filippo; Meneghetti, Giorgio; Horvath, Tamas; Pucci, Giacomo; Schillaci, Giuseppe; Stazi, Maria Antonietta; Baracchini, Claudio

2017-09-01

In contrast with the carotid arteries, the vertebral arteries (VAs) show considerable variation in length, caliber, and vessel course. This study investigated whether the variation in diameter and flow characteristics of the VAs might be inherited. A total of 172 Italian twins from Padua, Perugia, and Terni (54 monozygotic, 32 dizygotic) recruited from the Italian Twin Registry underwent B-mode and pulsed-wave Doppler ultrasound assessment of their VAs. VA diameters, peak systolic velocity (PSV) and end diastolic velocity (EDV) were assessed at the level of a horizontal V2 segment. Univariate quantitative genetic modeling was performed. Fourteen percent of the sample had VA hypoplasia. Within pair correlation in monozygotic twins was higher than in dizygotics (.552 vs. .229) for VA diameter. Age- and sex-adjusted genetic effect, under the most parsimonious model, accounted for 54.7% (95% CI: 42.2-69.1%) of the variance of VA diameter, and unshared environmental effect for 45.3% (95% CI: 30.9-57.8%). No heritability was found for the PSV of VA, but shared (34.1%; 95% CI: 16.7-53.7%) and unshared (65.9%; 95% CI: 45.9-83.1%) environmental factors determined the variance. EDV of VA is moderately genetically influenced (42.4%; 95% CI: 16.1-64.9%) and also determined by the unshared environment (57.6%; 95% CI: 34.7-83.7%). The diameter of the VAs is moderately genetically determined. Different factors influence the PSV and EDV of VAs, which may highlight the complex hemodynamic background of VA flow and help to understand the vertebral flow anomalies found by ultrasound. Copyright © 2017 by the American Society of Neuroimaging.

Detection of rip current using camera monitoring techniques

NASA Astrophysics Data System (ADS)

Kim, T.

2016-02-01

Rip currents are approximately shore normal seaward flows which are strong, localized and rather narrow. They are known that stacked water by longshore currents suddenly flow back out to sea as rip currents. They are transient phenomena and their generation time and location are unpredictable. They are also doing significant roles for offshore sediment transport and beach erosion. Rip currents can be very hazardous to swimmers or floaters because of their strong seaward flows and sudden depth changes by narrow and strong flows. Because of its importance in terms of safety, shoreline evolution and pollutant transport, a number of studies have been attempted to find out their mechanisms. However, understanding of rip currents is still not enough to make warning to people in the water by predicting their location and time. This paper investigates the development of rip currents using camera images. Since rip currents are developed by longshore currents, the observed longshore current variations in space and time can be used to detect rip current generation. Most of the time convergence of two longshore currents in the opposite direction is the outbreak of rip current. In order to observe longshore currents, an optical current meter(OCM) technique proposed by Chickadel et al.(2003) is used. The relationship between rip current generation time and longshore current velocity variation observed by OCM is analyzed from the images taken on the shore. The direct measurement of rip current velocity is also tested using image analysis techniques. Quantitative estimation of rip current strength is also conducted by using average and variance image of rip current area. These efforts will contribute to reduce the hazards of swimmers by prediction and warning of rip current generation.

Experimental and mathematical modeling of flow in headboxes

NASA Astrophysics Data System (ADS)

Shariati, Mohammad Reza

The fluid flow patterns in a paper-machine headbox have a strong influence on the quality of the paper produced by the machine. Due to increasing demand for high quality paper there is a need to investigate the details of the fluid flow in the paper machine headbox. The objective of this thesis is to use experimental and computational methods of modeling the flow inside a typical headbox in order to evaluate and understand the mean flow patterns and turbulence created there. In particular, spatial variations of the mean flow and of the turbulence quantities and the turbulence generated secondary flows are studied. In addition to the flow inside the headbox, the flow leaving the slice is also modeled both experimentally and computationally. Comparison of the experimental and numerical results indicated that streamwise mean components of the velocities in the headbox are predicted well by all the turbulence models considered in this study. However, the standard k-epsilon model and the algebraic turbulence models fail to predict the turbulence quantities accurately. Standard k-epsilon-model also fails to predict the direction and magnitude of the secondary flows. Significant improvements in the k-epsilon model predictions were achieved when the turbulence production term was artificially set to zero. This is justified by observations of the turbulent velocities from the experiments and by a consideration of the form of the kinetic energy equation. A better estimation of the Reynolds normal stress distribution and the degree of anisotropy of turbulence was achieved using the Reynolds stress turbulence model. Careful examination of the measured turbulence velocity results shows that after the initial decay of the turbulence in the headbox, there is a short region close to the exit, but inside the headbox, where the turbulent kinetic energy actually increases as a result of the distortion imposed by the contraction. The turbulence energy quickly resumes its decay in the free jet after the headbox. The overall conclusion from this thesis, obtained by comparison of experimental and computational simulations of the flow in a headbox, is that numerical simulations show great promise for predictions of headbox flows. Mean velocities and turbulence characteristics can now be predicted with fair accuracy by careful use of specialized turbulence models. Standard engineering turbulence models, such as the k-epsilon model and its immediate relatives, should not be used to estimate the turbulence quantities essential for predicting pulp fiber dispersion within the contracting region and free jet of a headbox, particularly when the overall contraction ratio is greater than about five. (Abstract shortened by UMI.)

How can we Optimize Global Satellite Observations of Glacier Velocity and Elevation Changes?

NASA Astrophysics Data System (ADS)

Willis, M. J.; Pritchard, M. E.; Zheng, W.

2015-12-01

We have started a global compilation of glacier surface elevation change rates measured by altimeters and differencing of Digital Elevation Models and glacier velocities measured by Synthetic Aperture Radar (SAR) and optical feature tracking as well as from Interferometric SAR (InSAR). Our goal is to compile statistics on recent ice flow velocities and surface elevation change rates near the fronts of all available glaciers using literature and our own data sets of the Russian Arctic, Patagonia, Alaska, Greenland and Antarctica, the Himalayas, and other locations. We quantify the percentage of the glaciers on the planet that can be regarded as fast flowing glaciers, with surface velocities of more than 50 meters per year, while also recording glaciers that have elevation change rates of more than 2 meters per year. We examine whether glaciers have significant interannual variations in velocities, or have accelerated or stagnated where time series of ice motions are available. We use glacier boundaries and identifiers from the Randolph Glacier Inventory. Our survey highlights glaciers that are likely to react quickly to changes in their mass accumulation rates. The study also identifies geographical areas where our knowledge of glacier dynamics remains poor. Our survey helps guide how frequently observations must be made in order to provide quality satellite-derived velocity and ice elevation observations at a variety of glacier thermal regimes, speeds and widths. Our objectives are to determine to what extent the joint NASA and Indian Space Research Organization Synthetic Aperture Radar mission (NISAR) will be able to provide global precision coverage of ice speed changes and to determine how to optimize observations from the global constellation of satellite missions to record important changes to glacier elevations and velocities worldwide.

Imaging water velocity and volume fraction distributions in water continuous multiphase flows using inductive flow tomography and electrical resistance tomography

NASA Astrophysics Data System (ADS)

Meng, Yiqing; Lucas, Gary P.

2017-05-01

This paper presents the design and implementation of an inductive flow tomography (IFT) system, employing a multi-electrode electromagnetic flow meter (EMFM) and novel reconstruction techniques, for measuring the local water velocity distribution in water continuous single and multiphase flows. A series of experiments were carried out in vertical-upward and upward-inclined single phase water flows and ‘water continuous’ gas-water and oil-gas-water flows in which the velocity profiles ranged from axisymmetric (single phase and vertical-upward multiphase flows) to highly asymmetric (upward-inclined multiphase flows). Using potential difference measurements obtained from the electrode array of the EMFM, local axial velocity distributions of the continuous water phase were reconstructed using two different IFT reconstruction algorithms denoted RT#1, which assumes that the overall water velocity profile comprises the sum of a series of polynomial velocity components, and RT#2, which is similar to RT#1 but which assumes that the zero’th order velocity component may be replaced by an axisymmetric ‘power law’ velocity distribution. During each experiment, measurement of the local water volume fraction distribution was also made using the well-established technique of electrical resistance tomography (ERT). By integrating the product of the local axial water velocity and the local water volume fraction in the cross section an estimate of the water volumetric flow rate was made which was compared with a reference measurement of the water volumetric flow rate. In vertical upward flows RT#2 was found to give rise to water velocity profiles which are consistent with the previous literature although the profiles obtained in the multiphase flows had relatively higher central velocity peaks than was observed for the single phase profiles. This observation was almost certainly a result of the transfer of axial momentum from the less dense dispersed phases to the water, which occurred preferentially at the pipe centre. For upward inclined multiphase flows RT#1 was found to give rise to water velocity profiles which are more consistent with results in the previous literature than was the case for RT#2—which leads to the tentative conclusion that the upward inclined multiphase flows investigated in the present study did not contain significant axisymmetric velocity components.

Super-Cavitating Flow Around Two-Dimensional Conical, Spherical, Disc and Stepped Disc Cavitators

NASA Astrophysics Data System (ADS)

Sooraj, S.; Chandrasekharan, Vaishakh; Robson, Rony S.; Bhanu Prakash, S.

2017-08-01

A super-cavitating object is a high speed submerged object that is designed to initiate a cavitation bubble at the nose which extends past the aft end of the object, substantially reducing the skin friction drag that would be present if the sides of the object were in contact with the liquid in which the object is submerged. By reducing the drag force the thermal energy consumption to move faster can also be minimised. The super-cavitation behavioural changes with respect to Cavitators of various geometries have been studied by varying the inlet velocity. Two-dimensional computational fluid dynamics analysis has been carried out by applying k-ε turbulence model. The variation of drag coefficient, cavity length with respect to cavitation number and inlet velocity are analyzed. Results showed conical Cavitator with wedge angle of 30° has lesser drag coefficient and cavity length when compared to conical Cavitators with wedge angles 45° and 60°, spherical, disc and stepped disc Cavitators. Conical cavitator 60° and disc cavitator have the maximum cavity length but with higher drag coefficient. Also there is significant variation of supercavitation effect observed between inlet velocities of 32 m/s to 40 m/s.

Implementation and validation of a wake model for vortex-surface interactions in low speed forward flight

NASA Technical Reports Server (NTRS)

Komerath, Narayanan M.; Schreiber, Olivier A.

1987-01-01

The wake model was implemented using a VAX 750 and a Microvax II workstation. Online graphics capability using a DISSPLA graphics package. The rotor model used by Beddoes was significantly extended to include azimuthal variations due to forward flight and a simplified scheme for locating critical points where vortex elements are placed. A test case was obtained for validation of the predictions of induced velocity. Comparison of the results indicates that the code requires some more features before satisfactory predictions can be made over the whole rotor disk. Specifically, shed vorticity due to the azimuthal variation of blade loading must be incorporated into the model. Interactions between vortices shed from the four blades of the model rotor must be included. The Scully code for calculating the velocity field is being modified in parallel with these efforts to enable comparison with experimental data. To date, some comparisons with flow visualization data obtained at Georgia Tech were performed and show good agreement for the isolated rotor case. Comparison of time-resolved velocity data obtained at Georgia Tech also shows good agreement. Modifications are being implemented to enable generation of time-averaged results for comparison with NASA data.

g-Jitter Mixed Convective Slip Flow of Nanofluid past a Permeable Stretching Sheet Embedded in a Darcian Porous Media with Variable Viscosity

PubMed Central

Uddin, Mohammed J.; Khan, Waqar A.; Amin, Norsarahaida S.

2014-01-01

The unsteady two-dimensional laminar g-Jitter mixed convective boundary layer flow of Cu-water and Al2O3-water nanofluids past a permeable stretching sheet in a Darcian porous is studied by using an implicit finite difference numerical method with quasi-linearization technique. It is assumed that the plate is subjected to velocity and thermal slip boundary conditions. We have considered temperature dependent viscosity. The governing boundary layer equations are converted into non-similar equations using suitable transformations, before being solved numerically. The transport equations have been shown to be controlled by a number of parameters including viscosity parameter, Darcy number, nanoparticle volume fraction, Prandtl number, velocity slip, thermal slip, suction/injection and mixed convection parameters. The dimensionless velocity and temperature profiles as well as friction factor and heat transfer rates are presented graphically and discussed. It is found that the velocity reduces with velocity slip parameter for both nanofluids for fluid with both constant and variable properties. It is further found that the skin friction decreases with both Darcy number and momentum slip parameter while it increases with viscosity variation parameter. The surface temperature increases as the dimensionless time increases for both nanofluids. Nusselt numbers increase with mixed convection parameter and Darcy numbers and decreases with the momentum slip. Excellent agreement is found between the numerical results of the present paper with published results. PMID:24927277

Flow of colloid particle solution past macroscopic bodies and drag crisis

DOE Office of Scientific and Technical Information (OSTI.GOV)

Iordanskii, S. V., E-mail: iordansk@itp.ac.ru

2013-11-15

The motion of colloid particles in a viscous fluid flow is considered. Small sizes of colloid particles as compared to the characteristic scale of the flow make it possible to calculate their velocity relative to the liquid. If the density of a colloid particle is higher than the density of the liquid, the flow splits into regions in which the velocity of colloid particles coincides with the velocity of the liquid and regions of flow stagnation in which the colloid velocity is higher than the velocity of the fluid. This effect is used to explain qualitatively the decrease in themore » drag to the flows past macroscopic bodies and flows in pipes.« less

Near Continuum Velocity and Temperature Coupled Compressible Boundary Layer Flow over a Flat Plate

NASA Astrophysics Data System (ADS)

He, Xin; Cai, Chunpei

2017-04-01

The problem of a compressible gas flows over a flat plate with the velocity-slip and temperature-jump boundary conditions are being studied. The standard single- shooting method is applied to obtain the exact solutions for velocity and temperature profiles when the momentum and energy equations are weakly coupled. A double-shooting method is applied if these two equations are closely coupled. If the temperature affects the velocity directly, more significant velocity slip happens at locations closer to the plate's leading edge, and inflections on the velocity profiles appear, indicating flows may become unstable. As a consequence, the temperature-jump and velocity-slip boundary conditions may trigger earlier flow transitions from a laminar to a turbulent flow state.

The imperative for controlled mechanical stresses in unraveling cellular mechanisms of mechanotransduction

PubMed Central

Anderson, Eric J; Falls, Thomas D; Sorkin, Adam M; Tate, Melissa L Knothe

2006-01-01

Background In vitro mechanotransduction studies are designed to elucidate cell behavior in response to a well-defined mechanical signal that is imparted to cultured cells, e.g. through fluid flow. Typically, flow rates are calculated based on a parallel plate flow assumption, to achieve a targeted cellular shear stress. This study evaluates the performance of specific flow/perfusion chambers in imparting the targeted stress at the cellular level. Methods To evaluate how well actual flow chambers meet their target stresses (set for 1 and 10 dyn/cm2 for this study) at a cellular level, computational models were developed to calculate flow velocity components and imparted shear stresses for a given pressure gradient. Computational predictions were validated with micro-particle image velocimetry (μPIV) experiments. Results Based on these computational and experimental studies, as few as 66% of cells seeded along the midplane of commonly implemented flow/perfusion chambers are subjected to stresses within ±10% of the target stress. In addition, flow velocities and shear stresses imparted through fluid drag vary as a function of location within each chamber. Hence, not only a limited number of cells are exposed to target stress levels within each chamber, but also neighboring cells may experience different flow regimes. Finally, flow regimes are highly dependent on flow chamber geometry, resulting in significant variation in magnitudes and spatial distributions of stress between chambers. Conclusion The results of this study challenge the basic premise of in vitro mechanotransduction studies, i.e. that a controlled flow regime is applied to impart a defined mechanical stimulus to cells. These results also underscore the fact that data from studies in which different chambers are utilized can not be compared, even if the target stress regimes are comparable. PMID:16672051

Dynamic three-dimensional phase-contrast technique in MRI: application to complex flow analysis around the artificial heart valve

NASA Astrophysics Data System (ADS)

Kim, Soo Jeong; Lee, Dong Hyuk; Song, Inchang; Kim, Nam Gook; Park, Jae-Hyeung; Kim, JongHyo; Han, Man Chung; Min, Byong Goo

1998-07-01

Phase-contrast (PC) method of magnetic resonance imaging (MRI) has bee used for quantitative measurements of flow velocity and volume flow rate. It is a noninvasive technique which provides an accurate two-dimensional velocity image. Moreover, Phase Contrast Cine magnetic resonance imaging combines the flow dependent contrast of PC-MRI with the ability of cardiac cine imaging to produce images throughout the cardiac cycle. However, the accuracy of the data acquired from the single through-plane velocity encoding can be reduced by the effect of flow direction, because in many practical cases flow directions are not uniform throughout the whole region of interest. In this study, we present dynamic three-dimensional velocity vector mapping method using PC-MRI which can visualize the complex flow pattern through 3D volume rendered images displayed dynamically. The direction of velocity mapping can be selected along any three orthogonal axes. By vector summation, the three maps can be combined to form a velocity vector map that determines the velocity regardless of the flow direction. At the same time, Cine method is used to observe the dynamic change of flow. We performed a phantom study to evaluate the accuracy of the suggested PC-MRI in continuous and pulsatile flow measurement. Pulsatile flow wave form is generated by the ventricular assistant device (VAD), HEMO-PULSA (Biomedlab, Seoul, Korea). We varied flow velocity, pulsatile flow wave form, and pulsing rate. The PC-MRI-derived velocities were compared with Doppler-derived results. The velocities of the two measurements showed a significant linear correlation. Dynamic three-dimensional velocity vector mapping was carried out for two cases. First, we applied to the flow analysis around the artificial heart valve in a flat phantom. We could observe the flow pattern around the valve through the 3-dimensional cine image. Next, it is applied to the complex flow inside the polymer sac that is used as ventricle in totally implantable artificial heart (TAH). As a result we could observe the flow pattern around the valves of the sac, though complex flow can not be detected correctly in the conventional phase contrast method. In addition, we could calculate the cardiac output from TAH sac by quantitative measurement of the volume of flow across the outlet valve.

Neutron Resonance Spectrometry Shock Temperatures in Molybdenum

NASA Astrophysics Data System (ADS)

Swift, Damian; Seifter, Achim; Holtkamp, David; Yuan, Vincent; Clark, David; Buttler, William

2007-06-01

Neutron resonance spectrometry (NRS) has been used to measure the temperature in Mo during shock loading, giving temperatures higher than expected. The effect of plastic flow and non-ideal projectile behavior were assessed. Plastic flow was estimated to contribute a temperature rise of 55K compared with hydrodynamic flow, and 100-150K on release, consistent with pyrometry measurements. Simulations were performed of the HE flyer system used to induce the shock in the Mo sample. The simulations predicted that the flyer was slightly curved on impact. The resulting spatial variations in load, including radial components of velocity, were predicted to increase the apparent NRS temperature by 160K. These corrections are sufficient to reconcile the apparent temperatures deduced using NRS with the accepted properties of Mo.

Dual Solutions for Nonlinear Flow Using Lie Group Analysis

PubMed Central

Awais, Muhammad; Hayat, Tasawar; Irum, Sania; Saleem, Salman

2015-01-01

`The aim of this analysis is to investigate the existence of the dual solutions for magnetohydrodynamic (MHD) flow of an upper-convected Maxwell (UCM) fluid over a porous shrinking wall. We have employed the Lie group analysis for the simplification of the nonlinear differential system and computed the absolute invariants explicitly. An efficient numerical technique namely the shooting method has been employed for the constructions of solutions. Dual solutions are computed for velocity profile of an upper-convected Maxwell (UCM) fluid flow. Plots reflecting the impact of dual solutions for the variations of Deborah number, Hartman number, wall mass transfer are presented and analyzed. Streamlines are also plotted for the wall mass transfer effects when suction and blowing situations are considered. PMID:26575996

Wall-wake velocity profile for compressible non-adiabatic flows

NASA Technical Reports Server (NTRS)

Sun, C. C.; Childs, M. E.

1975-01-01

A form of the wall-wake profile, which is applicable to flows with heat transfer, and for which a variation in y = O at y = delta, was suggested. The modified profile, which takes into account the effect of turbulent Prandtl number, was found to provide a good representation of experimental data for a wide range numbers and heat transfer. The Cf values which are determined by a least squares fit of the profile to the data agree well with values which were measured by the floating element technique. In addition, the values of delta determined by the fit correspond more closely to the outer edge of the viscous flow region than those obtained with earlier versions of the wall-wake profile.

Experimental investigation on the effect of liquid injection by multiple orifices in the formation of droplets in a Venturi scrubber.

PubMed

Guerra, V G; Gonçalves, J A S; Coury, J R

2009-01-15

Venturi scrubbers are widely utilized in gas cleaning. The cleansing elements in these scrubbers are droplets formed from the atomization of a liquid into a dust-laden gas. In industrial scrubbers, this liquid is injected through several orifices so that the cloud of droplets can be evenly distributed throughout the duct. The interaction between droplets when injected through many orifices, where opposite clouds of atomized liquid can reach each other, is to be expected. This work presents experimental measurements of droplet size measured in situ and the evidence of cloud interaction within a Venturi scrubber operating with multi-orifice jet injection. The influence of gas velocity, liquid flow rate and droplet size variation in the axial position after the point of the injection of the liquid were also evaluated for the different injection configurations. The experimental results showed that an increase in the liquid flow rate generated greater interaction between jets. The number of orifices had a significant influence on droplet size. In general, the increase in the velocity of the liquid jet and in the gas velocity favored the atomization process by reducing the size of the droplets.

Quantification of mitral and tricuspid regurgitation by the proximal flow convergence method using two-dimensional colour Doppler and colour Doppler M-mode: influence of the mechanism of regurgitation.

PubMed

Grossmann, G; Giesler, M; Stein, M; Kochs, M; Höher, M; Hombach, V

1998-10-30

In patients with mitral (n=77: organic=49, functional=28) and tricuspid regurgitation (n=55: functional=54) quantified by angiography, the temporal variation of the proximal flow convergence region throughout systole was assessed by colour Doppler M-Mode, and peak and mean radius of the proximal isovelocity surface area for 28 cm/s blood flow velocity were measured. Additionally, the peak radius derived from two-dimensional colour Doppler was obtained. About 50% of the patients with mitral and tricuspid regurgitation showed a typical temporal variation of the flow convergence region related to the mechanism of regurgitation. The different proximal isovelocity surface area radii were similarly correlated to the angiographic grade in mitral and tricuspid regurgitation (rank correlation coefficients 0.55-0.89) and they differentiated mild to moderate (grade < or =II) from severe (grade > or =III) mitral and tricuspid regurgitation with comparable accuracy (82-96%). However, moderate mitral regurgitation due to leaflet prolapse in two patients was correctly classified by the mean M-mode radius and overestimated by both peak radii. Only half of the patients showed a typical variation of the flow convergence region related to the mechanism of regurgitation. The different proximal isovelocity surface area radii were suitable to quantify mitral and tricuspid regurgitation in most patients. However, in mitral regurgitation due to leaflet prolapse the use of the mean M-mode radius may avoid overestimation.

Helmholtz-Smoluchowski velocity for viscoelastic electroosmotic flows.

PubMed

Park, H M; Lee, W M

2008-01-15

Many biofluids such as blood and DNA solutions are viscoelastic and exhibit extraordinary flow behaviors, not existing in Newtonian fluids. Adopting appropriate constitutive equations these exotic flow behaviors can be modeled and predicted reasonably using various numerical methods. However, the governing equations for viscoelastic flows are not easily solvable, especially for electroosmotic flows where the streamwise velocity varies rapidly from zero at the wall to a nearly uniform velocity at the outside of the very thin electric double layer. In the present investigation, we have devised a simple method to find the volumetric flow rate of viscoelastic electroosmotic flows through microchannels. It is based on the concept of the Helmholtz-Smoluchowski velocity which is widely adopted in the electroosmotic flows of Newtonian fluids. It is shown that the Helmholtz-Smoluchowski velocity for viscoelastic fluids can be found by solving a simple cubic algebraic equation. The volumetric flow rate obtained using this Helmholtz-Smoluchowski velocity is found to be almost the same as that obtained by solving the governing partial differential equations for various viscoelastic fluids.

Some predictions of the attached eddy model for a high Reynolds number boundary layer.

PubMed

Nickels, T B; Marusic, I; Hafez, S; Hutchins, N; Chong, M S

2007-03-15

Many flows of practical interest occur at high Reynolds number, at which the flow in most of the boundary layer is turbulent, showing apparently random fluctuations in velocity across a wide range of scales. The range of scales over which these fluctuations occur increases with the Reynolds number and hence high Reynolds number flows are difficult to compute or predict. In this paper, we discuss the structure of these flows and describe a physical model, based on the attached eddy hypothesis, which makes predictions for the statistical properties of these flows and their variation with Reynolds number. The predictions are shown to compare well with the results from recent experiments in a new purpose-built high Reynolds number facility. The model is also shown to provide a clear physical explanation for the trends in the data. The limits of applicability of the model are also discussed.

Bending the law: tidal bending and its effects on ice viscosity and flow

NASA Astrophysics Data System (ADS)

Rosier, S.; Gudmundsson, G. H.

2017-12-01

Many ice shelves are subject to strong ocean tides and, in order to accommodate this vertical motion, the ice must bend within the grounding zone. This tidal bending generates large stresses within the ice, changing its effective viscosity. For a confined ice shelf, this is particularly relevant because the tidal bending stresses occur along the sidewalls, which play an important role in the overall flow regime of the ice shelf. Hence, tidal bending stresses will affect both the mean and time-varying components of ice shelf flow. GPS measurements reveal strong variations in horizontal ice shelf velocities at a variety of tidal frequencies. We show, using full-Stokes viscoelastic modelling, that inclusion of tidal bending within the model accounts for much of the observed tidal modulation of horizontal ice shelf flow. Furthermore, our model shows that in the absence of a vertical tidal forcing, the mean flow of the ice shelf is reduced considerably.

Measuring Taylor Slough boundary and internal flows, Everglades National Park, Florida

USGS Publications Warehouse

Tillis, G.M.

2001-01-01

Four intensive data-collection efforts, intended to represent the spectrum of precipitation events and associated flow conditions, were conducted during 1997 and 1998 in the Taylor Slough Basin, Everglades National Park. Flow velocities were measured by newly developed, portable Acoustic Doppler Velocity meters along three transects bisecting the Taylor Slough Basin from east to west, roughly perpendicular to the centerline axis of the slough as well as a fourth transect along the slough's axis. These meters provided the required levels of accuracy in flow-velocity measurements while enabling the rapid collection of multiple time series of flow data at remote sites. Concurrently, flow measurements were made along bordering road culverts and under L-31W and Taylor Slough bridges. Flows across the study area's boundaries provided net flow of water into the system and transect measurements provided flow data within the basin. Collected data are available through the World Wide Web (http://sofia.usgs.gov/projects/flow_velocity/). The high-water and low-water events corresponded with the highest and lowest flow velocities, respectively. The July 1998 data had lower than expected flow velocities and, in some cases, strong winds reversed flow direction.

Modeling Food Delivery Dynamics For Juvenile Salmonids Under Variable Flow Regimes

NASA Astrophysics Data System (ADS)

Harrison, L.; Utz, R.; Anderson, K.; Nisbet, R.

2010-12-01

Traditional approaches for assessing instream flow needs for salmonids have typically focused on the importance of physical habitat in determining fish habitat selection. This somewhat simplistic approach does not account for differences in food delivery rates to salmonids that arise due to spatial variability in river morphology, hydraulics and temporal variations in the flow regime. Explicitly linking how changes in the flow regime influences food delivery dynamics is an important step in advancing process-based bioenergetic models that seek to predict growth rates of salmonids across various life-stages. Here we investigate how food delivery rates for juvenile salmonids vary both spatially and with flow magnitude in a meandering reach of the Merced River, CA. We utilize a two-dimensional (2D) hydrodynamic model and discrete particle tracking algorithm to simulate invertebrate drift transport rates at baseflow and a near-bankfull discharge. Modeling results indicate that at baseflow, the maximum drift density occurs in the channel thalweg, while drift densities decrease towards the channel margins due to the process of organisms settling out of the drift. During high-flow events, typical of spring dam-releases, the invertebrate drift transport pathway follows a similar trajectory along the high velocity core and the drift concentrations are greatest in the channel centerline, though the zone of invertebrate transport occupies a greater fraction of the channel width. Based on invertebrate supply rates alone, feeding juvenile salmonids would be expected to be distributed down the channel centerline where the maximum predicted food delivery rates are located in this reach. However, flow velocities in these channel sections are beyond maximum sustainable swimming speeds for most juvenile salmonids. Our preliminary findings suggest that a lack of low velocity refuge may prevent juvenile salmonids from deriving energy from the areas with maximum drift density in this reach. Future efforts will focus on integration of food delivery and bioenergetic models to account for conflicting demands of maximizing food intake while minimizing the energetic costs of swimming.

Improving H-Q rating curves in temprorary streams by using Acoustic Doppler Current meters

NASA Astrophysics Data System (ADS)

Marchand, P.; Salles, C.; Rodier, C.; Hernandez, F.; Gayrard, E.; Tournoud, M.-G.

2012-04-01

Intermittent rivers pose different challenges to stream rating due to high spatial and temporal gradients. Long dry periods, cut by short duration flush flood events explain the difficulty to obtain reliable discharge data, for low flows as well as for floods: problems occur with standard gauging, zero flow period, etc. Our study aims to test the use of an acoustic Doppler currentmeter (ADC) for improving stream rating curves in small catchments subject to large variations of discharge, solid transport and high eutrophication levels. The study is conducted at the outlet of the river Vène, a small coastal river (67 km2) located close to the city of Montpellier (France). The low flow period lasts for more than 6 month; during this period the river flow is sustained by effluents from urban sewage systems, which allows development of algae and macrophytes in the riverbed. The ADC device (Sontek ®Argonaut SW) is a pulsed Doppler current profiling system designed for measuring water velocity profiles and levels that are used to compute volumetric flow rates. It is designed for shallow waters (less than 4 meter depth). Its main advantages are its low cost and high accuracy (±1% of the measured velocity or ±0.05 m/sec, as reported by the manufacturer). The study will evaluate the improvement in rating curves in an intermittent flow context and the effect of differences in sensitivity between low and high water level, by comparing mean flow velocity obtained by ADC to direct discharges measurements. The study will also report long-term use of ADC device, by considering effects of biofilms, algae and macrophytes, as well as solid transport on the accuracy of the measurements. In conclusion, we show the possibility to improve stream rating and continuous data collection of an intermittent river by using a ADC with some precautions.

Effect of external jet-flow deflector geometry on OTW aero-acoustic characteristics

NASA Technical Reports Server (NTRS)

Vonglahn, U.; Groesbeck, D.

1976-01-01

The effect of geometry variations in the design of external deflectors for use with over-the-wing (OTW) configurations was studied at model scale and subsonic jet velocities. Included in the variations were deflector size and angle as well as wing size and flap setting. A conical nozzle (5.2-cm diameter) mounted at 0.1 chord above and downstream of the wing leading edges was used. The data indicate that external deflectors provide satisfactory takeoff and approach aerodynamic performance and acoustic characteristics for OTW configurations. These characteristics together with expected good cruise aerodynamics, since external deflectors are storable, may provide optimum OTW design configurations.

Green's formula and variational principles for cosmic-ray transport with application to rotating and shearing flows

NASA Technical Reports Server (NTRS)

Webb, G. M.; Jokipii, J. R.; Morfill, G. E.

1994-01-01

Green's theorem and Green's formula for the diffusive cosmic-ray transport equation in relativistic flows are derived. Green's formula gives the solution of the transport equation in terms of the Green's function of the adjoint transport equation, and in terms of distributed sources throughout the region R of interest, plus terms involving the particle intensity and streaming on the boundary. The adjoint transport equation describes the time-reversed particle transport. An Euler-Lagrange variational principle is then obtained for both the mean scattering frame distribution function f, and its adjoint f(dagger). Variations of the variational functional with respect to f(dagger) yield the transport equation, whereas variations of f yield the adjoint transport equation. The variational principle, when combined with Noether's theorem, yields the conservation law associated with Green's theorem. An investigation of the transport equation for steady, azimuthal, rotating flows suggests the introduction of a new independent variable H to replace the comoving frame momentum variable p'. For the case of rigid rotating flows, H is conserved and is shown to be analogous to the Hamiltonian for a bead on a rigidly rotating wire. The variable H corresponds to a balance between the centrifugal force and the particle inertia in the rotating frame. The physical interpretation of H includes a discussion of nonrelativistic and special relativistic rotating flows as well as the cases of aziuthal, differentially rotating flows about Schwarzs-child and Kerr black holes. Green's formula is then applied to the problem of the acceleration of ultra-high-energy cosmic rays by galactic rotation. The model for galactic rotation assumes an angular velocity law Omega = Omega(sub 0)(omega(sub 0)/omega), where omega denotes radial distance from the axis of rotation. Green's functions for the galactic rotation problem are used to investigate the spectrum of accelerated particles arising from monoenergetic and truncated power-law sources. We conclude that it is possible to accelerate particles beyond the knee by galactic rotation, but not in sufficient number to adequately explain the observed spectrum.

Effect of flow velocity on the process of air-steam condensation in a vertical tube condenser

NASA Astrophysics Data System (ADS)

Havlík, Jan; Dlouhý, Tomáš

2018-06-01

This article describes the influence of flow velocity on the condensation process in a vertical tube. For the case of condensation in a vertical tube condenser, both the pure steam condensation process and the air-steam mixture condensation process were theoretically and experimentally analyzed. The influence of steam flow velocity on the value of the heat transfer coefficient during the condensation process was evaluated. For the condensation of pure steam, the influence of flow velocity on the value of the heat transfer coefficient begins to be seen at higher speeds, conversely, this effect is negligible at low values of steam velocity. On the other hand, for the air-steam mixture condensation, the influence of flow velocity must always be taken into account. The flow velocity affects the water vapor diffusion process through non-condensing air. The presence of air significantly reduces the value of the heat transfer coefficient. This drop in the heat transfer coefficient is significant at low velocities; on the contrary, the decrease is relatively small at high values of the velocity.

On the wake flow of asymmetrically beveled trailing edges

NASA Astrophysics Data System (ADS)

Guan, Yaoyi; Pröbsting, Stefan; Stephens, David; Gupta, Abhineet; Morris, Scott C.

2016-05-01

Trailing edge and wake flows are of interest for a wide range of applications. Small changes in the design of asymmetrically beveled or semi-rounded trailing edges can result in significant difference in flow features which are relevant for the aerodynamic performance, flow-induced structural vibration and aerodynamically generated sound. The present study describes in detail the flow field characteristics around a family of asymmetrically beveled trailing edges with an enclosed trailing-edge angle of 25° and variable radius of curvature R. The flow fields over the beveled trailing edges are described using data obtained by particle image velocimetry (PIV) experiments. The flow topology for different trailing edges was found to be strongly dependent on the radius of curvature R, with flow separation occurring further downstream as R increases. This variation in the location of flow separation influences the aerodynamic force coefficients, which were evaluated from the PIV data using a control volume approach. Two-point correlations of the in-plane velocity components are considered to assess the structure in the flow field. The analysis shows large-scale coherent motions in the far wake, which are associated with vortex shedding. The wake thickness parameter yf is confirmed as an appropriate length scale to characterize this large-scale roll-up motion in the wake. The development in the very near wake was found to be critically dependent on R. In addition, high-speed PIV measurements provide insight into the spectral characteristics of the turbulent fluctuations. Based on the time-resolved flow field data, the frequency range associated with the shedding of coherent vortex pairs in the wake is identified. By means of time-correlation of the velocity components, turbulent structures are found to convect from the attached or separated shear layers without distinct separation point into the wake.

Discussion of "Evaluating vertical velocities between the stream and the hyporheic zone from temperature data" by Seydell, I., Wawra, B.E., and Zanke, U.C.E. [Chapter 5].

Treesearch

John M. Buffington; Daniele Tonina

2008-01-01

Hyporheic exchange is principally driven by spatial variations of near-bed pressure, which can be sensitive to seasonal changes in discharge, flow depth, and watersurface profile (Tonina and Buffington, 2003, 2007). Simulations of hyporheic exchange across two-dimensional pool-riffle topography show that the strength and spatial extent of the hyporheic exchange vary...

Space-time correlations of fluctuating velocities in turbulent shear flows

NASA Astrophysics Data System (ADS)

Zhao, Xin; He, Guo-Wei

2009-04-01

Space-time correlations or Eulerian two-point two-time correlations of fluctuating velocities are analytically and numerically investigated in turbulent shear flows. An elliptic model for the space-time correlations in the inertial range is developed from the similarity assumptions on the isocorrelation contours: they share a uniform preference direction and a constant aspect ratio. The similarity assumptions are justified using the Kolmogorov similarity hypotheses and verified using the direct numerical simulation (DNS) of turbulent channel flows. The model relates the space-time correlations to the space correlations via the convection and sweeping characteristic velocities. The analytical expressions for the convection and sweeping velocities are derived from the Navier-Stokes equations for homogeneous turbulent shear flows, where the convection velocity is represented by the mean velocity and the sweeping velocity is the sum of the random sweeping velocity and the shear-induced velocity. This suggests that unlike Taylor’s model where the convection velocity is dominating and Kraichnan and Tennekes’ model where the random sweeping velocity is dominating, the decorrelation time scales of the space-time correlations in turbulent shear flows are determined by the convection velocity, the random sweeping velocity, and the shear-induced velocity. This model predicts a universal form of the space-time correlations with the two characteristic velocities. The DNS of turbulent channel flows supports the prediction: the correlation functions exhibit a fair good collapse, when plotted against the normalized space and time separations defined by the elliptic model.

Measurement of viscous flow velocity and flow visualization using two magnetic resonance imagers

NASA Astrophysics Data System (ADS)

Boiko, A. V.; Akulov, A. E.; Chupakhin, A. P.; Cherevko, A. A.; Denisenko, N. S.; Savelov, A. A.; Stankevich, Yu. A.; Khe, A. K.; Yanchenko, A. A.; Tulupov, A. A.

2017-03-01

The accuracies of measuring the velocity field using clinical and research magnetic resonance imagers are compared. The flow velocity of a fluid simulating blood in a carotid artery model connected to a programmable pump was measured. Using phase-contrast magnetic resonance tomography, the velocity distributions in the carotid artery model were obtained and compared with the analytical solution for viscous liquid flow in a cylindrical tube (Poiseuille flow). It is found that the accuracy of the velocity measurement does not depend on the field induction and spatial resolution of the imagers.

Asymptotic Spreading Rate of Initially Compressible Jets-Experiment and Analysis

NASA Technical Reports Server (NTRS)

Zaman, K. B. M. Q.

1998-01-01

Experimental results for the spreading and centerline velocity decay rates for round, compressible jets, from a convergent and a convergent-divergent nozzle, are presented. The spreading rate is determined from the variation of streamwise mass flux obtained from Pitot probe surveys. Results for the far asymptotic region show that both spreading and centerline velocity decay rates, when nondimensionalized by parameters at the nozzle exit, decrease with increasing "jet Mach number" M(sub j). Dimensional analysis with the assumption of momentum conservation, together with compressible flow calculations for the conditions at the nozzle exit, predict this Mach number dependence well. The analysis also demonstrates that an increase in the "potential core length" of the jet occurring with increasing M(sub j), a commonly observed trend, is largely accounted for simply by the variations in the density and static pressure at the nozzle exit. The effect of decreasing mixing efficiency with increasing compressibility is inferred to contribute only partially to the latter trend.