Science.gov

Sample records for study flow structure

  1. Basic flow structure in saccular aneurysms: a flow visualization study.

    PubMed

    Steiger, H J; Poll, A; Liepsch, D; Reulen, H J

    1987-01-01

    Basic flow patterns were investigated in a set of glass aneurysm models by means of flow visualization methods. Dye injection and streaming double refraction were used to visualize flow. The circulation inside lateral aneurysms arising at a 90 degree angle from a straight parent conduit could not be visualized by the dye-injection technique but could be demonstrated by streaming double refraction. The inflow was seen to arise from the downstream lip of the orifice and to project to the dome of the aneurysm. Backflow to the parent conduit took place along the walls of the aneurysm. In aneurysms located at bifurcations, flow characteristics depended on the geometry of the bifurcation and the flow ratio between the branches. Relatively little intra-aneurysmal flow was demonstrated in side branch-related aneurysms arising distal to an asymmetric 90 degrees bifurcation of the type encountered at the junction of the internal carotid and posterior communicating arteries. Stagnation of flow at the neck and little intra-aneurysmal circulation were found with terminal aneurysms of the basilar bifurcation type if the outflow through the branches was symmetric. With asymmetric outflow, however, or if the axis of the aneurysm did not coincide with that of the afferent vessel, an active rotation developed in these aneurysms. The size of the aneurysm had no influence on the basic pattern of intra-aneurysmal circulation. The use of pulsatile perfusion did not significantly alter the basic flow patterns observed with steady flow. Locally disturbed laminar flow was observed in certain models at physiological Reynold's numbers, but there were no signs of fully developed turbulence.

  2. Flow Structures and Efficiency of Swimming Fish school: Numerical Study

    NASA Astrophysics Data System (ADS)

    Yatagai, Yuzuru; Hattori, Yuji

    2013-11-01

    The flow structure and energy-saving mechanism in fish school is numerically investigated by using the volume penalization method. We calculate the various patterns of configuration of fishes and investigate the relation between spatial arrangement and the performance of fish. It is found that the down-stream fish gains a hydrodynamic advantage from the upstream wake shed by the upstream fish. The most efficient configuration is that the downstream fish is placed in the wake. It reduces the drag force of the downstream fish in comparison with that in solo swimming.

  3. A water tunnel flow visualization study of the vortex flow structures on the F/A-18 aircraft

    NASA Technical Reports Server (NTRS)

    Sandlin, Doral R.; Ramirez, Edgar J.

    1991-01-01

    The vortex flow structures occurring on the F/A-18 aircraft at high angles of attack were studied. A water tunnel was used to gather flow visualization data on the forebody vortex and the wing leading edge extension vortex. The longitudinal location of breakdown of the leading edge vortex was found to be consistently dependent on the angle of attack. Other parameters such as Reynolds number, model scale, and model fidelity had little influence on the overall behavior of the flow structures studied. The lateral location of the forebody vortex system was greatly influenced by changes in the angle of sideslip. Strong interactions can occur between the leading edge extension vortex and the forebody vortex. Close attention was paid to vortex induced flows on various airframe components of the F/A-18. Reynolds number and angle of attack greatly affected the swirling intensity, and therefore the strength of the studied vortices. Water tunnel results on the F/A-18 correlated well with those obtained in similar studies at both full and sub scale levels. The water tunnel can provide, under certain conditions, good simulations of realistic flows in full scale configurations.

  4. Study of Interfacial Structures: Bubbly Flow in 1.27 cm Diameter Pipe

    SciTech Connect

    Paranjape, S.; Kim, S.; Ishii, M.; Uhle, J.

    2002-07-01

    The objective of the present research is to study the flow regime map, the detailed interfacial structures, and the bubble transport in an adiabatic air-water two-phase flow mixture, flowing upward through a vertical round pipe having 1.27 cm. inner diameter. The flow regime map is obtained by processing the characteristic signals acquired from an impedance void meter, using a self-organized neural network. The local two-phase flow parameters are measured by the state-of-the-art four-sensor conductivity probe at three axial locations in the pipe. The measured local parameters include void fraction ({alpha}), interfacial area concentration (a{sub i}), bubble frequency (f{sub b}), bubble velocity (U{sub b}) and bubble Sauter mean diameter (D{sub sm}). The radial profiles of these parameters and their development along the axial direction reveals the structure of the two phase mixture and the bubble interaction mechanisms. (authors)

  5. Influence of laminar flow on preorientation of coal tar pitch structural units: Raman microspectroscopic study

    NASA Astrophysics Data System (ADS)

    Urban, O.; Jehlička, J.; Pokorný, J.; Rouzaud, J. N.

    2003-08-01

    In order to estimate the role of laminar flow of viscous, aromatic matter of carbonaceous precursor on microtextural preorientation in pregraphitization stage, we performed experiments with coal tar pitch (CTP). The principal hypothesis of preorientation of basic structural units (BSUs) in the case of laminar flow (pressure impregnation of CTP into porous matrix) and secondary release of volatiles during carbonization were studied. Glass microplates, planar porous medium with average distance between single microplates 5 μm were used as suitable porous matrix. Samples of CTP were carbonized up to 2500 °C. Optical microscopy reveals large flow domains in the sample of cokes carbonized between glass microplates. Raman microspectroscopy and high resolution transmission electron microscopy (HRTEM) show that at nanometric scale, the samples do not support the proposed hypotheses. With increasing temperature of pyrolysis, the graphitization of CTP impregnated into porous matrix proceeds to lower degree of structural ordering in comparison with single pyrolyzed CTP. This is explained by the release of volatile matter during carbonization in geometrically restricted spaces. More evident structural changes were discovered with the sample of single coke, where parts of fine grain mosaics, relicts of 'so called QI parts', reveal higher structural organization, in comparison with large and prolonged flow domains, similar to flow domains of cokes from microplates.

  6. Numerical study of vortical structures around a wall-mounted cubic obstacle in channel flow

    NASA Astrophysics Data System (ADS)

    Hwang, Jong-Yeon; Yang, Kyung-Soo

    2004-07-01

    Vortical structures around a wall-mounted cubic obstacle in channel flow are studied using numerical simulation. Flows of low-to-moderate Reynolds numbers up to Re=3500 are considered. The objective of this work is to elucidate characteristics of coherent vortical structures produced by the presence of the wall-mounted cubic obstacle, including horseshoe vortex systems upstream of the obstacle, lateral vortices in the vicinity of the two lateral faces of the cube, and hairpin vortices in the near-wake region. As the flow approaches the cube, the adverse pressure gradient produces three-dimensional boundary-layer separation, resulting in the formation of laminar horseshoe vortices. As the Reynolds number increases, the structure of the horseshoe vortex system becomes complex and the number of vortices increases in pairs. The distribution of skin friction on the cube-mounted wall reflects the effect of the horseshoe vortices. Unsteady horseshoe vortex systems are hardly found as long as the upstream flow is fully viscous; they are obtained when the cube is placed in the entrance region of a developing channel flow. The unsteady horseshoe vortex systems are characterized by a repeated process of generation, translation, and mutual merging of the vortices. The laminar wake is characterized by a pair of spiral vortices behind the obstacle; distinct singular points are identified leading to consistent flow topology. In the case of a turbulent wake, however, it is observed that the flow becomes less coherent in the near-wall region downstream of the obstacle. Instead, coherent structures such as lateral vortices and hairpin vortices are found in the vicinity of the two lateral faces of the cube and in the turbulent near-wake region, respectively. Quasiperiodic behaviors of those vortices are noticed and their frequencies are computed. The translating speed of the head portion of a hairpin vortex is lower than the streamwise mean velocity at that location. In the vicinity

  7. Flow visualization study of role of coherent structures in a tab wake

    NASA Astrophysics Data System (ADS)

    Elavarasan, R.; Meng, Hui

    2000-09-01

    A simple surface-mounted tapered tab has recently attracted fluids research both for its ability to enhance mixing and heat transfer (for which it is known as high-efficiency vortab mixer) and for its generation of coherent structures that are topologically similar to those found in natural turbulent boundary layers. Two types of structures, namely pressure-driven counter-rotating vortex pair (CVP) and hairpin vortices were previously identified in the tab wake, but the contribution of individual structures to the mixing enhancement process and how they interact are not known. In the present study, flow visualization using a planar laser-induced fluorescence (PLIF) technique is carried out to probe into the flow dynamics in the wake of the mixing tab. By injecting dye at an appropriate location and illuminating the flow in various planes, the structures are visualized clearly. The results show, in contrary to earlier observations, that the two types of structures dominate different regions. At the Reynolds number of 700 based on tab height ( h), the CVP has more influence in the region 0< x/ h<1.5. The counter-rotating action of the vortex pair induces a pumping action along the symmetry by which the low-speed fluid from the boundary layer is transported to the high-speed outer shear layer. The displaced fluid is entrained by the recirculating counter-rotating vortices and is mixed well while convecting downstream. Beyond this region, fully developed hairpin structures contribute more to mixing in a similar way as in a turbulent boundary layer. It is observed that the shedding frequency of hairpin vortices is slightly higher than the pumping frequency of the counter-rotating vortex pair. It is also observed that the hairpin structures loses their identity beyond x/ h>15, and there is no large-scale cross-stream mixing visible in this region.

  8. A field study of coherent flow structures over low angle dunes: Fraser Estuary, British Columbia

    NASA Astrophysics Data System (ADS)

    Bradley, R. W.; Hendershot, M. L.; Venditti, J. G.; Kostaschuk, R. A.; Allison, M. A.; Church, M. A.

    2011-12-01

    Aqueous dunes are present in nearly all sand bedded alluvial channels and can significantly influence flow resistance and sediment transport and deposition. The geometry of these bedforms can take on a high angle asymmetrical or low angle symmetrical shape. While advances have been made in understanding the mean and turbulent flow over high angle dunes, far less progress has been made in detailing flow over low angle dunes, commonly observed in large rivers, due to difficulties measuring near the bed and quantifying the turbulence over these bedforms. This field study documents the flow over low angle dunes in the Fraser Estuary, British Columbia, using an acoustic Doppler profiler (aDcp) to measure 3-D flow characteristics and a multi-beam echo sounder (MBES) to provide high-resolution bed topography. Measurements were made over a dune field (~1 km long and ~0.5 wide) through two semi-diurnal tidal cycles during the 2010 freshet. We examine the coupling between the bedform morphology and the generation of coherent flow structures. Bedforms in the dune field range from low-angle symmetric to higher angle asymmetric and vary over tidal cycles; however, none display the classic angle of repose geometry. Mean flow velocity increases on falling tide while it decreases the rising tide. At lower tides, large scale motions caused by topographic forcing emerge on stoss slopes and rise up over the crest producing variations in suspended sediment over the bedforms. Our analysis is intended to contribute insight into what controls the occurrence of low angle bedforms in rivers.

  9. Structural power flow measurement

    SciTech Connect

    Falter, K.J.; Keltie, R.F.

    1988-12-01

    Previous investigations of structural power flow through beam-like structures resulted in some unexplained anomalies in the calculated data. In order to develop structural power flow measurement as a viable technique for machine tool design, the causes of these anomalies needed to be found. Once found, techniques for eliminating the errors could be developed. Error sources were found in the experimental apparatus itself as well as in the instrumentation. Although flexural waves are the carriers of power in the experimental apparatus, at some frequencies longitudinal waves were excited which were picked up by the accelerometers and altered power measurements. Errors were found in the phase and gain response of the sensors and amplifiers used for measurement. A transfer function correction technique was employed to compensate for these instrumentation errors.

  10. Noninvasive imaging methods in a study of preferential flow in structured soil

    NASA Astrophysics Data System (ADS)

    Votrubová, J.; Císlerová, M.; Amin, M. G.; Hall, L. D.

    2003-04-01

    Two non-invasive imaging methods were combined to study hydraulic phenomena in structured heterogeneous soil. Two undisturbed samples (5.4-cm diameter and 9-cm height) of coarse sandy loam from Korkusova Hut, CR, were examined. The internal structure of the samples was visualized by means of X-ray computed tomography (CT). The distribution of water within the samples during a recurrent ponded infiltration (RPI) was monitored using magnetic resonance imaging (MRI). Hydraulic behaviour of the soil type studied is characterized by fast preferential flow and a decrease of the effective hydraulic conductivity as observed during the two infiltration runs of RPI. Present research is aimed at identifying the source of these phenomena. Regarding the two samples studied, the behaviour of interest was fully pronounced only in one of them. This difference was related to the difference of the internal structure of the samples as determined by CT. Moreover, it was clearly reflected in the MRI results, providing base for linking the specific features of the MRI results to the specific hydraulic phenomena. Use of the MRI technique in studies water in natural soils is complicated by the properties of the soil material, primarily by the high content of paramagnetic particles. Although the image intensity is related to the amount of water in the respective volume, it is also influenced by the geometry of the water-filled space and thus a quantitative analysis of the relationship becomes unfeasible. Joint analysis of the water distribution information obtained by MRI and the internal structure information produced by CT is prevented due to MRI image distortion originating in the heterogeneity of the magnetic properties of the soil-water-air system studied. Nevertheless, the qualitative analysis of the results is instructive. Specifically, it is demonstrated that MRI detects only water in regions of low local density. As these can be assumed to represent potential preferential pathways

  11. Edge Flow and Canopy Structure: A Large-Eddy Simulation Study

    NASA Astrophysics Data System (ADS)

    Dupont, Sylvain; Brunet, Yves

    2008-01-01

    Sharp heterogeneities in forest structure, such as edges, are often responsible for wind damage. In order to better understand the behaviour of turbulent flow through canopy edges, large-eddy simulations (LES) have been performed at very fine scale (2 m) within and above heterogeneous vegetation canopies. A modified version of the Advanced Regional Prediction System (ARPS), previously validated in homogeneous conditions against field and wind-tunnel measurements, has been used for this purpose. Here it is validated in a simple forest-clearing-forest configuration. The model is shown to be able to reproduce accurately the main features observed in turbulent edge flow, especially the “enhanced gust zone” (EGZ) present around the canopy top at a few canopy heights downwind from the edge, and the turbulent region that develops further downstream. The EGZ is characterized by a peak in streamwise velocity skewness, which reflects the presence of intense intermittent wind gusts. A sensitivity study of the edge flow to the forest morphology shows that with increasing canopy density the flow adjusts faster and turbulent features such as the EGZ become more marked. When the canopy is characterized by a sparse trunk space the length of the adjustment region increases significantly due to the formation of a sub-canopy wind jet from the leading edge. It is shown that the position and magnitude of the EGZ are related to the mean upward motion formed around canopy top behind the leading edge, caused by the deceleration in the sub-canopy. Indeed, this mean upward motion advects low turbulence levels from the bottom of the canopy; this emphasises the passage of sudden strong wind gusts from the clearing, thereby increasing the skewness in streamwise velocity as compared with locations further downstream where ambient turbulence is stronger.

  12. Computational extended magneto-hydrodynamical study of shock structure generated by flows past an obstacle

    SciTech Connect

    Zhao, Xuan; Seyler, C. E.

    2015-07-15

    The magnetized shock problem is studied in the context where supersonic plasma flows past a solid obstacle. This problem exhibits interesting and important phenomena such as a bow shock, magnetotail formation, reconnection, and plasmoid formation. This study is carried out using a discontinuous Galerkin method to solve an extended magneto-hydrodynamic model (XMHD). The main goals of this paper are to present a reasonably complete picture of the properties of this interaction using the MHD model and then to compare the results to the XMHD model. The inflow parameters, such as the magnetosonic Mach number M{sub f} and the ratio of thermal pressure to magnetic pressure β, can significantly affect the physical structures of the flow-obstacle interaction. The Hall effect can also significantly influence the results in the regime in which the ion inertial length is numerically resolved. Most of the results presented are for the two-dimensional case; however, two three-dimensional simulations are presented to make a connection to the important case in which the solar wind interacts with a solid body and to explore the possibility of performing scaled laboratory experiments.

  13. Flow structure in continuous flow electrophoresis chambers

    NASA Technical Reports Server (NTRS)

    Deiber, J. A.; Saville, D. A.

    1982-01-01

    There are at least two ways that hydrodynamic processes can limit continiuous flow electrophoresis. One arises from the sensitivity of the flow to small temerature gradients, especially at low flow rates and power levels. This sensitivity can be suppressed, at least in principle, by providing a carefully tailored, stabilizing temperature gradient in the cooling system that surrounds the flow channel. At higher power levels another limitation arises due to a restructuring of the main flow. This restructuring is caused by buoyancy, which is in turn affected by the electro-osmotic crossflow. Approximate solutions to appropriate partial differential equations have been computed by finite difference methods. One set of results is described here to illustrate the strong coupling between the structure of the main (axial) flow and the electro-osmotic flow.

  14. A wind tunnel study of flow structure adjustment on deformable sand beds containing a surface-mounted obstacle

    NASA Astrophysics Data System (ADS)

    McKenna Neuman, Cheryl; Bédard, OttO

    2015-09-01

    Roughness elements of varied scale and geometry commonly appear on the surfaces of sedimentary deposits in a wide range of planetary environments. They perturb the local fluid flow so that the entrainment, transport, and deposition of particles surrounding each element are fundamentally altered. Fluid dynamists have expended much effort in examining the flow structures surrounding idealized elements mounted on fixed, planar walls. However self-regulation occurs in sedimentary systems as a result of the bed surface undergoing rapid topographic modification with sediment transport, until it reaches a stable form that enhances the net physical roughness. The present wind tunnel study examines how the flow pattern surrounding an isolated cylinder, a problem extensively studied in classical fluid mechanics, is altered through morphodynamic development of a deep well that envelopes the windward face and sidewalls of the roughness element. Spatial patterns in the fluid velocity, turbulence intensity, and Reynolds stress obtained from laser Doppler anemometer measurements suggest that the flow structures surrounding such a cylinder are fundamentally altered through self-regulation of the bed topography as it reaches steady state. For example, flow stagnation and the turbulent dissipation of momentum are substantially increased at selected points surrounding the upwind face and sidewalls of the cylinder, respectively. Along the center line of the wake flow to the rear of the cylinder, several structures arising from flow separation are annihilated by strong upwelling of the airflow exhausted from the terminus of the well. Feedback plays a complex, time-dependent role in this system.

  15. Experimental study of the effect of spacer grid on the flow structure in fuel assemblies of the AES 2006 reactor

    NASA Astrophysics Data System (ADS)

    Kashinskii, O. N.; Lobanov, P. D.; Pribaturin, N. A.; Kurdyumov, A. S.; Volkov, S. E.

    2013-01-01

    Results from an experimental study of the local hydrodynamic structure of liquid flow in a 37-cell model simulating a fuel assembly used in the AES-2006 reactor are presented. Special attention is paid to the effect of spacer grid on flow hydrodynamics. Data on variations of the local and integral values of the liquid axial velocity and friction stress on the fuel rod simulator's wall with distance from the grid are given.

  16. The applicability of the flow cytometric sperm chromatin structure assay in epidemiological studies. Asclepios.

    PubMed

    Spanò, M; Kolstad, A H; Larsen, S B; Cordelli, E; Leter, G; Giwercman, A; Bonde, J P

    1998-09-01

    The impact of demographic, lifestyle, and seminal factors on the sperm chromatin structure assay (SCSA) parameters was evaluated in a population of 277 healthy Danish men. This cohort was established within the framework of a European Concerted Action on occupational hazards to male reproductive capability in order to examine the possible reproductive effects of exposure to styrene or pesticides. The SCSA measures the susceptibility of sperm DNA to in-situ acid-induced denaturation, by multiparameter flow cytometric analysis after staining with the DNA-specific fluorescent dye acridine orange. The green versus red bivariate cytogram patterns were quite variable among donors, showing a wide heterogeneity of sperm DNA denaturability. Nevertheless, in those cases where we had the possibility to measure two semen samples from the same donor, the cytogram pattern remained stable over time (0.64 < r < 0.78). Analysis of variance demonstrated that the SCSA results can be influenced by the age of the donor (P < 0.0001), smoking habits (P < 0.05), the presence of leukocytes and immature germ forms in the ejaculate (P < 0.0001), and the duration of sexual abstinence (P < 0.0001). Furthermore, the relationship between the SCSA data and sperm concentration, morphology, and vitality was weak (-0.22 < r < -0.46). Therefore, the SCSA provides independent and complementary measurements of semen quality and is thus a useful tool for epidemiological studies, but the effects of some confounders should be accounted for in the survey design and analysis.

  17. Structural resistance of reinforced concrete buildings under pyroclastic flows: a study of the Vesuvian area

    NASA Astrophysics Data System (ADS)

    Petrazzuoli, S. M.; Zuccaro, G.

    2004-05-01

    The analysis of the effects of pyroclastic flows on humans and on buildings represents the main tool to define the boundary of the most hazardous area around an active volcano such as Somma-Vesuvius. Estimation of the lateral pressure on buildings derived from analogies with the damages observed after a nuclear explosion [Valentine (1998) J. Volcanol. Geotherm. Res. 87, 117-140] lead to pressure values and/or structural resistance which are not realistic (too high). Recent evidence [Baxter (2000) Human and Structural Vulnerability Assessment for Emergency Planning in a Future Eruption of Vesuvius. Final Report EC Project ENV4-CT98-0699; Young et al. (1997) EOS, Trans. Am. Geophys. Union, 78, 401] have shown that beyond 2-3 km from the vent, even after a great eruption, resistance to collapse of buildings affected by a pyroclastic flow is still possible. Neri et al. [(2000) Numerical simulation of pyroclastic flows. In: Human and Human and Structural Vulnerability Assessment for Emergency Planning in a Future Eruption of Vesuvius. Final Report EC Project ENV4-CT98-0699], by means of a numerical model of a collapsing column, show that the peak overpressures of the pyroclastic flows range from 1 to 2 kPa at a distance from the vent of about 4-5 km, where important historical centres of the Vesuvian area are located. A detailed analysis of urban settlement of the area [Cherubini et al. (2001) Vulnerabilita' Sismica dell'Area Vesuviana. Gruppo Nazionale per la Difesa dai Terremoti, CNR, Roma] has shown that most of the people live in reinforced concrete (r.c.) structures, not designed to resist horizontal seismic actions. The present work is aimed at analyzing the collapse limit load of r.c. structures to horizontal pressure for different structural design typologies (strong aseismic, weak aseismic, strong non-aseismic, weak non-aseismic). The simulations performed have also taken into account the specific features of the r.c. structures of the area (local building

  18. Field and numerical studies of flow structure in Lake Shira (Khakassia) in summer

    NASA Astrophysics Data System (ADS)

    Yakubaylik, Tatyana; Kompaniets, Lidia

    2014-05-01

    Investigations of Lake Shira are conducted within a multidisciplinary approach that includes the study of biodiversity, biochemistry, geology of lake sediments, as well as its hydrophysics. Our report focuses on field measurements in the lake during the 2009 - 2013 and numerical modeling of flow structure. The flow velocity, temperature and salinity distribution and fluctuations of the thermocline (density) were measured in summer. An analysis of spatial and temporal variability of the major hydrophysical characteristics leads us to conclusion that certain meteorological conditions may cause internal waves in this lake. Digital terrain model is constructed from measurements of Lake bathymetry allowing us to carry out numerical simulation. Three-dimensional primitive equation numerical model GETM is applied to simulate hydrophysical processes in Lake Shira. The model is hydrostatic and Boussinesq. An algorithm of high order approximation is opted for calculating the equations of heat and salt transfer. Temperature and salinity distributions resulting from field observations are taken as initial data for numerical simulations. Model calculations as well as calculations with appropriate real wind pattern being observed on Lake Shira have been carried out. In the model calculations we follow (1). Significant differences are observed between model calculations with constant wind and calculations with real wind pattern. Unsteady wind pattern leads to the appearance of horizontal vortexes and a significant increase of vertical fluctuations in temperature (density, impurities). It causes lifting of the sediments to the upper layers at the areas where the thermocline contacts the bottom. It is important for understanding the overall picture of the processes occurring in the lake in summer. Comparison of the results of numerical experiments with the field data shows the possibility of such a phenomena in Lake Shira. The work was supported by the Russian Foundation for

  19. Motivation, Instructional Design, Flow, and Academic Achievement at a Korean Online University: A Structural Equation Modeling Study

    ERIC Educational Resources Information Center

    Joo, Young Ju; Oh, Eunjung; Kim, Su Mi

    2015-01-01

    The purpose of this study is to examine the structural relationships among self-efficacy, intrinsic value, test anxiety, instructional design, flow, and achievement among students at a Korean online university. To address research questions, the researchers administered online surveys to 963 college students at an online university in Korea…

  20. Numerical study on the 3-D complex characteristics of flow around the hull structure of TLP

    NASA Astrophysics Data System (ADS)

    Gu, Jia-yang; Zhu, Xin-yao; Yang, Jian-min; Lu, Yan-xiang; Xiao, Long-fei

    2015-06-01

    Vortex-induced motion is based on the complex characteristics of the flow around the tension leg platform (TLP) hull. By considering the flow field of the South China Sea and the configuration of the platform, three typical flow velocities and three flow directions are chosen to study the numerical simulation of the flow field characteristics around the TLP hull. Reynolds-averaged Navier-Stokes equations combined with the detached eddy simulation turbulence model are employed in the numerical study. The hydrodynamic coefficients of columns and pontoons, the total drag and lift coefficients of the TLP, the formation and development of the wake, and the vorticity iso-surfaces for different inlet velocities and current directions are discussed in this paper. The average value of the drag coefficient of the upstream columns is considerably larger than that of the downstream columns in the inlet direction of 0°. Although the time history of the lift coefficient demonstrates a "beating" behavior, the plot shows regularity in general. The Strouhal number decreases as the inlet velocity increases from the power spectral density plot at different flow velocities. The mean root values of the lift and drag coefficients of the front column decrease as the current direction increases. Under the symmetrical configuration of 45°, the streamwise force on C4 is the smallest, whereas the transverse force is the largest. The broken vortex conditions in current directions of 22.5° and 45° are more serious than that in the current direction of 0°. In addition, turbulence at the bottom of the TLP becomes stronger when the current direction changes from 0° to 45°. However, a high inlet velocity indicates a large region influenced by the broken vortex and shows the emergence of the wake behind the TLP under the same current angle.

  1. Flow structure inside and above a variable wind farm: A wind tunnel study.

    NASA Astrophysics Data System (ADS)

    Chamorro, Leonardo; Porte-Agel, Fernando

    2010-05-01

    Wind turbine wakes are known to have important effects on both power generation and fatigue loads in wind farms. Wake characteristics are expected to depend on the incoming atmospheric boundary layer flow statistics (e.g., mean velocity, turbulence intensity and turbulent fluxes), and vertical transport, which is affected by the relative position of the turbines in the wind farm. In this study, wind-tunnel experiments were carried out at the St. Anthony Falls Laboratory atmospheric boundary layer wind tunnel using a 10 by 3 model wind turbine array placed inside a neutrally stratified boundary layer developed over a smooth surface. Different turbine layouts (aligned and staggered farm with different inter-turbine spacing) were considered. Cross-wire anemometry and Particle Image Velocimetry (PIV) were used to characterize the mean velocity, turbulence intensity and turbulent stress at different locations in the wind farm. Results suggest that the turbulent flow can be divided into two main regions. The first, located below the turbine top tip height, has a direct effect on the performance of the turbines. Here the mean flow statistics appear to reach equilibrium as close as 3-4 turbines downwind from the edge of the wind farm. In the second region, located immediately above the first region, the flow adjustment is slower. Here, two distinct layers were found: and internal boundary layer where the flow starts to adjust to the new farm conditions but is still affected by the upwind condition; and an equilibrium layer, where the flow statistics are fully adjusted to the wind farm conditions. The high-resolution spatial and temporal information obtained in the laboratory experiments is being used to test and guide the development of improved parameterizations of wind turbines in high-resolution numerical models, such as large-eddy simulations (LES).

  2. Flow structure inside and above a variable wind farm: A wind tunnel study.

    NASA Astrophysics Data System (ADS)

    Chamorro, L.; Porte-Agel, F.

    2010-09-01

    Wind turbine wakes are known to have important effects on both power generation and fatigue loads in wind farms. Wake characteristics are expected to depend on the incoming atmospheric boundary layer flow statistics (e.g., mean velocity, turbulence intensity and turbulent fluxes), and vertical transport, which is affected by the relative position of the turbines in the wind farm. In this study, wind-tunnel experiments were carried out at the St. Anthony Falls Laboratory atmospheric boundary layer wind tunnel using a 10 by 3 model wind turbine array placed inside a neutrally stratified boundary layer developed over a smooth surface. Different turbine layouts of aligned wind turbines were considered. Cross-wire anemometry was used to characterize the mean velocity, turbulence intensity and turbulent stress at different locations in the wind farm. Results suggest that the turbulent flow can be divided into two main regions. The first, located below the turbine top tip height, has a direct effect on the performance of the turbines. Here the mean flow statistics appear to reach equilibrium as close as 3-4 turbines downwind from the edge of the wind farm. In the second region, located immediately above the first region, the flow adjustment is slower. Here, two distinct layers were found: and internal boundary layer where the flow starts to adjust to the new farm conditions and an equilibrium layer, where the flow statistics are fully adjusted. The high-resolution spatial and temporal information obtained in the laboratory experiments is being used to test and guide the development of improved parameterizations of wind turbines in high-resolution numerical models, such as large-eddy simulations (LES).

  3. Experimental study on the signs of particulate structures formation in annular geometry of rapid granular shear flows

    NASA Astrophysics Data System (ADS)

    Ritvanen, J.; Jalali, P.

    2009-06-01

    Rapid granular shear flow is a classical example in granular materials which exhibits both fluid-like and solid-like behaviors. Another interesting feature of rapid granular shear flows is the formation of ordered structures upon shearing. Certain amount of granular material, with uniform size distribution, is required to be loaded in the container in order to shear it under stable conditions. This work concerns the experimental study of rapid granular shear flows in annular Couette geometry. The flow is induced by continuous rotation of the plate over the top of the granular bed in an annulus. The compressive pressure, driving torque, instantaneous bed height from three symmetric locations and rotational speed of the shearing plate are measured. The annulus has a capacity of up to 15 kg of spherical steel balls of 3 mm in diameter. Rapid shear flow experiments are performed in one compressive force and rotation rate. The sensitivity of fluctuations is then investigated by different means through monodisperse packing. In this work, we present the results of the experiments showing how the flow properties depend on the amount of loaded granular material which is varied by small amounts between different experiments. The flow can exist in stable (fixed behavior) and unstable (time-dependent behavior) regimes as a function of the loaded material. We present the characteristics of flow to detect the formation of any additional structured layer in the annulus. As a result, an evolution graph for the bed height has been obtained as material is gradually added. This graph shows how the bed height grows when material increases. Using these results, the structure inside the medium can be estimated at extreme stable and unstable conditions.

  4. Coherent structures in reacting flows

    NASA Astrophysics Data System (ADS)

    Mahoney, John; Mitchell, Kevin

    2013-11-01

    Our goal is to characterize the nature of reacting flows by identifying important ``coherent'' structures. We follow the recent work by Haller, Beron-Vera, and Farazmand which formalized the the notion of lagrangian coherent structures (LCSs) in fluid flows. In this theory, LCSs were derived from the Cauchy-Green strain tensor. We adapt this perspective to analogously define coherent structures in reacting flows. By this we mean a fluid flow with a reaction front propagating through it such that the propagation does not affect the underlying flow. A reaction front might be chemical (Belousov-Zhabotinsky, flame front, etc.) or some other type of front (electromagnetic, acoustic, etc.). While the recently developed theory of burning invariant manifolds (BIMs) describes barriers to front propagation in time-periodic flows, this current work provides an important complement by extending to the aperiodic setting. The present work was supported by the US National Science Foundation under grants PHY- 0748828 and CMMI-1201236.

  5. Micromodel foam flow study

    SciTech Connect

    Chambers, K.T.; Radke, C.J.

    1990-10-01

    Foams are often utilized as part of enhanced oil recovery techniques. This report presents the results of a micromodel foam flow study. Micromodels are valuable tools in uncovering capillary phenomena responsible for lamellae generation and coalescence during foam flow in porous media. Among the mechanisms observed are snap-off, weeping-flow breakup, and lamella division and leave behind. Coalescence mechanisms include dynamic capillary-pressure-induced lamella drainage and gas diffusion. These phenomena are sensitive to the mode of injection, the local capillary environment, and the geometry of the pore structure. An important consideration in presenting a tractable model of foam flow behavior is the ability to identify the pore-level mechanisms having the greatest impact on foam texture. The predominant mechanisms will vary depending upon the application for foam as an enhanced oil recovery (EOR) fluid. Both simultaneous gas and surfactant injection and surfactant alternating with gas injection (SAG) have been used to create foam for mobility control in EOR projects. The model developed is based on simultaneous gas and surfactant injection during steady-state conditions into a Berea sandstone core. The lamellae generation and coalescence mechanisms included in this model are snap-off, lamella division, and dynamic capillary-pressure-induced lamella drainage. This simplified steady-state model serves as a foundation for developing more complete rate expressions and for extending the population balance to handle transient foam flow behavior. 70 refs., 30 figs.

  6. Studying the structure of a zone in which the single-phase flow moving in an annular channel with partially blocked cross section becomes spatially disturbed

    NASA Astrophysics Data System (ADS)

    Kashinskii, O. N.; Lobanov, P. D.; Kurdyumov, A. S.; Pribaturin, N. A.

    2013-05-01

    The flow of liquid in an annular channel with a partially shaded flow section is experimentally studied using the electrodiffusion method. The effect on the flow structure produced by a shutter closing one-quarter of the channel cross section is shown. An obstacle installed in the channel causes the flow to attain a 3D structure. The flow pattern in such channel differs significantly from that observed in undisturbed flow moving in an annular channel. It is revealed that the friction stress values measured on the channel's inner wall depend essentially on the azimuth angle over the channel height. With distance away from the obstacle, the influence it has on the hydrodynamic flow structure tends to decrease, but the disturbance produced by it does not die out completely even at a distance of more than 600 mm from the obstacle. Data quantitatively characterizing the disturbance of flow structure in the studied channel are presented.

  7. Fluid/structure interactions. Internal flows

    NASA Astrophysics Data System (ADS)

    Weaver, D. S.

    1991-05-01

    Flow-induced vibrations are found wherever structures are exposed to high velocity fluid flows. Internal flows are usually characterized by the close proximity of solid boundaries. There are surfaces against which separated flows may reattach, or from which pressure disturbances may be reflected resulting in acoustic resonance. When the fluid is a liquid, the close proximity of solid boundaries to a vibrating component can produce very high added mass effects. This paper presents three different experimental studies of flow-induced vibration problems associated with internal flows. The emphasis was on experimental techniques developed for understanding excitation mechanisms. In difficult flow-induced vibration problems, a useful experimental technique is flow visualization using a large scale model and strobe light triggered by the phenomenon being observed. This should be supported by point measurements of velocity and frequency spectra. When the flow excitation is associated with acoustic resonance, the sound can be fed back to enhance or eliminate the instability. This is potentially a very useful tool for studying and controlling fluid-structure interaction problems. Some flow-induced vibration problems involve a number of different excitation mechanisms and care must be taken to ensure that the mechanisms are properly identified. Artificially imposing structural vibrations or acoustic fields may induce flow structures not naturally present in the system.

  8. Structural isomers of C2N(+) - A selected-ion flow tube study

    NASA Technical Reports Server (NTRS)

    Knight, J. S.; Petrie, S. A. H.; Freeman, C. G.; Mcewan, M. J.; Mclean, A. D.

    1988-01-01

    Reactivities of the structural isomers CCN(+) and CNC(+) were examined in a selected-ion flow tube at 300 + or - 5 K. The less reactive CNC(+) isomer was identified as the product of the reactions of C(+) + HCN and C(+) + C2N2; in these reactions only CNC(+) can be produced because of energy constraints. Rate coefficients and branching ratios are reported for the reactions of each isomer with H2, CH4, NH3, H2O, C2H2, HCN, N2, O2, N2O, and CO2. Ab initio calculations are presented for CCN(+) and CNC(+); a saddle point for the reaction CCN(+) yielding CNC(+) is calculated to be 195 kJ/mol above CNC(+). The results provide evidence that the more reactive CCN(+) isomer is unlikely to be present in measurable densities in interstellar clouds.

  9. Structural isomers of C2N+: a selected-ion flow tube study.

    PubMed

    Knight, J S; Petrie, S A; Freeman, C G; McEwan, M J; McLean, A D; DeFrees, D J

    1988-01-01

    Reactivities of the structural isomers CCN+ and CNC+ were examined in a selected-ion flow tube at 300 +/- 5 K. The less reactive CNC+ isomer was identified as the product of the reactions of C(+) + HCN and C(+) + C2N2; in these reactions only CNC+ can be produced because of energy constraints. Rate coefficients and branching ratios are reported for the reactions of each isomer with H2, CH4, NH3, H2O, C2H2, HCN, N2, O2, N2O, and CO2. Ab initio calculations are presented for CCN+ and CNC+; a saddle point for the reaction CCN+ --> CNC+ is calculated to be 195 kJ mol-1 above the CNC+. The results provide evidence that the more reactive CCN+ isomer is unlikely to be present in measurable densities in interstellar clouds.

  10. Integrated flow field (IFF) structure

    NASA Technical Reports Server (NTRS)

    Pien, Shyhing M. (Inventor); Warshay, Marvin (Inventor)

    2012-01-01

    The present disclosure relates in part to a flow field structure comprising a hydrophilic part and a hydrophobic part communicably attached to each other via a connecting interface. The present disclosure further relates to electrochemical cells comprising the aforementioned flow fields.

  11. Comparative study of microbial community structure in integrated vertical-flow constructed wetlands for treatment of domestic and nitrified wastewaters.

    PubMed

    Chang, Jun-Jun; Wu, Su-Qing; Liang, Kang; Wu, Zhenbin; Liang, Wei

    2015-03-01

    Microbial processes play a vital important role in the removal of contaminants in constructed wetland (CW). However, the microbial physiology and community structure can be influenced by environmental conditions. In this study, four pilot-scale integrated vertical-flow constructed wetlands (IVCWs) were employed to treat domestic and nitrified wastewaters. The microbial properties, along with their response to wastewater quality characteristics and seasonal variation, were determined. The results showed higher Shannon-Weiner diversity (H) and evenness (E) index of fatty acids (FAs), and relative abundances of signature FAs in down-flow cells and in the systems fed with domestic wastewater (DW). The relative abundances of fungi and gram-negative and aerobic bacteria were greater in up-flow cells. The dominant anaerobic bacteria found in most cells might be accounted for the prevailing anaerobic environment within the wetland beds, which could mean that the system fed with nitrified wastewater (NW) should perform better in nitrogen removal. The redundancy analysis (RDA) showed that pollutant concentrations, especially organic matter, influence the FA compositions greatly, and the most significant difference of microbial community structures was detected in down-flow cells fed with DW and up-flow ones with NW. The branched FAs, which could be used to represent anaerobic bacteria, were observed in down-flow cells treating DW and had a significant positive correlation with chemical oxygen demand (COD) concentration, probably suggesting the important role of anaerobic bacteria in organic matter degradation in the IVCWs. Seasonal variation, however, did not greatly influence the microbial community structure in the IVCWs.

  12. Study of the structure of turbulent shear flows at supersonic speeds and high Reynolds number

    NASA Technical Reports Server (NTRS)

    Smits, A. J.; Bogdonoff, S. M.

    1984-01-01

    A major effort to improve the accuracies of turbulence measurement techniques is described including the development and testing of constant temperature hot-wire anemometers which automatically compensate for frequency responses. Calibration and data acquisition techniques for normal and inclined wires operated in the constant temperature mode, flow geometries, and physical models to explain the observed behavior of flows are discussed, as well as cooperation with computational groups in the calculation of compression corner flows.

  13. X-ray photon correlation spectroscopy studies of structural irreversibility in a colloidal gel subjected to oscillatory shear flow

    NASA Astrophysics Data System (ADS)

    Kweon, Mu Sung; Burghardt, Wesley; Ramakrishnan, Subramanian; Louis, Golda; Thomas, Danica; Narayanan, Suresh

    2015-03-01

    X-ray photon correlation spectroscopy (XPCS) is used to probe the microscopic structural reversibility in a colloidal gel subjected to oscillatory shear flow. Silicon dioxide particles in decalin aggregate into a gel structure as a result of depletion interactions associated with dissolved polystyrene molecules. XPCS studies on aged quiescent gels show negligible structural dynamics on time scales of tens of seconds. Such samples were subjected to oscillatory shear with varying stain amplitude using a rheometer installed in the XPCS beam line and x-ray capable polycarbonate fixtures; this enable simultaneous rheological measurements during the XPCS experiment. In the presence of unidirectional shear flow, the decay of the XPCS autocorrelation function is dominated by the convective motion induced by the applied deformation. In oscillatory shearing of samples in the absence of significant structural relaxation, the autocorrelation function becomes periodic, returning to its initial value once every oscillation period. At higher strains, irreversible motions at the microscopic level lead to decay in the 'echos' of the autocorrelation function. Interestingly, structural irreversibility is detected by XPCS only at strains that are significantly higher than those at which nonlinearity

  14. Beyond lognormal inequality: The Lorenz Flow Structure

    NASA Astrophysics Data System (ADS)

    Eliazar, Iddo

    2016-11-01

    Observed from a socioeconomic perspective, the intrinsic inequality of the lognormal law happens to manifest a flow generated by an underlying ordinary differential equation. In this paper we extend this feature of the lognormal law to a general "Lorenz Flow Structure" of Lorenz curves-objects that quantify socioeconomic inequality. The Lorenz Flow Structure establishes a general framework of size distributions that span continuous spectra of socioeconomic states ranging from the pure-communism extreme to the absolute-monarchy extreme. This study introduces and explores the Lorenz Flow Structure, analyzes its statistical properties and its inequality properties, unveils the unique role of the lognormal law within this general structure, and presents various examples of this general structure. Beyond the lognormal law, the examples include the inverse-Pareto and Pareto laws-which often govern the tails of composite size distributions.

  15. Network structure of inter-industry flows

    NASA Astrophysics Data System (ADS)

    McNerney, James; Fath, Brian D.; Silverberg, Gerald

    2013-12-01

    We study the structure of inter-industry relationships using networks of money flows between industries in 45 national economies. We find these networks vary around a typical structure characterized by a Weibull link weight distribution, exponential industry size distribution, and a common community structure. The community structure is hierarchical, with the top level of the hierarchy comprising five industry communities: food industries, chemical industries, manufacturing industries, service industries, and extraction industries.

  16. Characteristic flow patterns generated by macrozoobenthic structures

    NASA Astrophysics Data System (ADS)

    Friedrichs, M.; Graf, G.

    2009-02-01

    food particle capture due to altered particle pathways and residence times, but also for the exchange of gases, solutes and spawn. The present results confirm previous studies on flow interaction effects of various biogenic structures, and they add a deeper level of detail for a better understanding of the fine-scale effects.

  17. Structure of Hot Flow Anomaly

    NASA Astrophysics Data System (ADS)

    Shestakov, A.; Vaisberg, O. L.

    2012-12-01

    Hot Flow Anomalies (HFAs) were first discovered in 1980s. These are active processes of hot plasma bulks formation that usually occur at planetary bow shocks. Though HFA were studied for long time it is still not clear if they are reforming structures and what defines particular internal structure of HFA. Our study is based on the Interball Tail Probe data. We used 10-sec measurements of complex plasma analyzer SCA-1 and 1-second magnetic field measurements, and ELECTRON spectrometer 2-dimensional measurements with 3,75-sec temporal resolution. Five anomalies that were observed on the basis of well resolved structure for which we obtained displacement velocity along bow shock, flow velocities within HFA, and estimated the size. We checked if main criteria of HFA formation were fulfilled for each case. The following criteria were satisfied: motional electric field direction was directed toward current sheet at least at one side of it, bow shock was quasi-perpendicular at least at one side of HFA, and angle between current sheet normal and solar wind velocity was large. Convection velocities of plasma within HFA were calculated by subtracting average velocity from measured ion convection velocities along spacecraft trajectory through anomaly. These convection velocities viewed in coordinate system of shock normal and calculated IMF current sheet normal clearly show separation of HFA region in 3 parts: leading part, narrow central part, and trailing part. Ion velocity distributions confirm this triple structure of HFA. Thomsen et al. [1986] identified the region within HFA that they called "internal recovery". It looks like central region that we call narrow central part. Vaisberg et al. [1999] discussed separation of HFA into 2 distinct parts that correspond to leading and trailing parts. Judging from plasma convection pattern within HFAs we assumed that "internal recovery" region is the source of energy and momentum around interplanetary current sheet crossing. HFA

  18. Numerical and experimental study of expiratory flow in the case of major upper airway obstructions with fluid structure interaction

    NASA Astrophysics Data System (ADS)

    Chouly, F.; van Hirtum, A.; Lagrée, P.-Y.; Pelorson, X.; Payan, Y.

    2008-02-01

    This study deals with the numerical prediction and experimental description of the flow-induced deformation in a rapidly convergent divergent geometry which stands for a simplified tongue, in interaction with an expiratory airflow. An original in vitro experimental model is proposed, which allows measurement of the deformation of the artificial tongue, in condition of major initial airway obstruction. The experimental model accounts for asymmetries in geometry and tissue properties which are two major physiological upper airway characteristics. The numerical method for prediction of the fluid structure interaction is described. The theory of linear elasticity in small deformations has been chosen to compute the mechanical behaviour of the tongue. The main features of the flow are taken into account using a boundary layer theory. The overall numerical method entails finite element solving of the solid problem and finite differences solving of the fluid problem. First, the numerical method predicts the deformation of the tongue with an overall error of the order of 20%, which can be seen as a preliminary successful validation of the theory and simulations. Moreover, expiratory flow limitation is predicted in this configuration. As a result, both the physical and numerical models could be useful to understand this phenomenon reported in heavy snorers and apneic patients during sleep.

  19. Sensitivity of flow evolution on turbulence structure

    NASA Astrophysics Data System (ADS)

    Mishra, Aashwin A.; Iaccarino, Gianluca; Duraisamy, Karthik

    2016-09-01

    Reynolds averaged Navier-Stokes models represent the workhorse for studying turbulent flows in academia and in industry. Such single-point turbulence models have limitations in accounting for the influence of the nonlocal physics and flow history on turbulence evolution. In this context, we investigate the sensitivity inherent in such single-point models due to their characterization of the internal structure of homogeneous turbulent flows solely by the means of the Reynolds stresses. For a wide variety of mean flows under diverse conditions, we study the prediction intervals engendered due to this coarse-grained description. The nature of this variability and its dependence on parameters such as the mean flow topology, the initial Reynolds stress tensor, and the relative influence of linear contra nonlinear physics is identified, analyzed, and explicated.

  20. Flow Interaction With Highly Flexible Structures

    NASA Astrophysics Data System (ADS)

    Shoele, Kourosh

    Studying the interaction between fluid and structure is an essential step towards the understanding of many engineering and physical problems, from the flow instability of structures to the biolocomotion of insects, birds and fishes. The simulation of such problems is computationally challenging. This justifies the attempts to develop more sophisticated and more efficient numerical models of fluid-solid interactions. In this dissertation, we proposed numerical models both in potential flow and fully viscous flow for the interaction of immersed structure with a strongly unsteady flow. In particular we have developed efficient approaches to study two groups of problems, the flow interaction with skeleton-reinforced fish fins and flow interaction with highly flexible bluff bodies. Fins of bony fishes are characterized by a skeleton-reinforced membrane structure consisting of a soft collagen membrane strengthened by embedded flexible rays. Morphologically, each ray is connected to a group of muscles so that the fish can control the rotational motion of each ray individually, enabling multi-degree of freedom control over the fin motion and deformation. We have developed fluid-structure interaction models to simulate the kinematics and dynamic performance of a structurally idealized fin. The first method includes a boundary-element model of the fluid motion and a fully-nonlinear Euler-Bernoulli beam model of the embedded rays. In the second method, we use an improved immersed boundary approach. Using these models, we study thrust generation and propulsion efficiency of the fin at different combinations of parameters at both high-Re and intermediate-Re flow. Effects of kinematic as well as structural properties are examined. It has been illustrated that the fish's capacity to control the motion of each individual ray, as well as the anisotropic deformability of the fin determined by distribution of the rays (especially the detailed distribution of ray stiffness), is

  1. Flow structure and channel morphodynamics of meander bend chute cutoffs: A case study of the Wabash River, USA

    NASA Astrophysics Data System (ADS)

    Zinger, Jessica A.; Rhoads, Bruce L.; Best, James L.; Johnson, Kevin K.

    2013-12-01

    paper documents the three-dimensional structure of flow and bed morphology of two developing chute cutoffs on a single meander bend on the lower Wabash River, USA, and relates the flow structure to patterns of morphologic change in the evolving cutoff channels. The upstream end of the cutoff channels is characterized by: (1) a zone of flow velocity reduction/stagnation and bar development in the main channel across from the cutoff entrance, (2) flow separation and bar development along the inner (left) bank of the cutoff channel immediately downstream from the cutoff entrance, and (3) helical motion and outward advection of flow momentum entering the cutoff channel, leading to erosion of the outer (right) bank of the cutoff channel. At the downstream end of the cutoff channels, the major hydrodynamic and morphologic features are: (1) flow stagnation along the bank of the main channel immediately upstream of the cutoff channel mouth, (2) convergence of flows from the cutoff and main channels, (3) helical motion of flow from the cutoff, (4) a zone of reduced velocity along the bank of the main channel immediately downstream from the cutoff channel mouth, and (5) development of a prominent bar complex that penetrates into the main channel and extends from the stagnation zone upstream to downstream of the cutoff mouth. These results provide the basis for a conceptual model of chute-cutoff dynamics in which the upstream and downstream ends of a cutoff channel are treated as a bifurcation and confluence, respectively.

  2. Bypass Flow Study

    SciTech Connect

    Richard Schultz

    2011-09-01

    The purpose of the fluid dynamics experiments in the MIR (Matched Index of-Refraction) flow system at Idaho National Laboratory (INL) is to develop benchmark databases for the assessment of Computational Fluid Dynamics (CFD) solutions of the momentum equations, scalar mixing, and turbulence models for the flow ratios between coolant channels and bypass gaps in the interstitial regions of typical prismatic standard fuel element (SFE) or upper reflector block geometries of typical Modular High-temperature Gas-cooled Reactors (MHTGR) in the limiting case of negligible buoyancy and constant fluid properties. The experiments use Particle Image Velocimetry (PIV) to measure the velocity fields that will populate the bypass flow study database.

  3. Arterial stiffness, pressure and flow pulsatility and brain structure and function: the Age, Gene/Environment Susceptibility--Reykjavik study.

    PubMed

    Mitchell, Gary F; van Buchem, Mark A; Sigurdsson, Sigurdur; Gotal, John D; Jonsdottir, Maria K; Kjartansson, Ólafur; Garcia, Melissa; Aspelund, Thor; Harris, Tamara B; Gudnason, Vilmundur; Launer, Lenore J

    2011-11-01

    Aortic stiffness increases with age and vascular risk factor exposure and is associated with increased risk for structural and functional abnormalities in the brain. High ambient flow and low impedance are thought to sensitize the cerebral microcirculation to harmful effects of excessive pressure and flow pulsatility. However, haemodynamic mechanisms contributing to structural brain lesions and cognitive impairment in the presence of high aortic stiffness remain unclear. We hypothesized that disproportionate stiffening of the proximal aorta as compared with the carotid arteries reduces wave reflection at this important interface and thereby facilitates transmission of excessive pulsatile energy into the cerebral microcirculation, leading to microvascular damage and impaired function. To assess this hypothesis, we evaluated carotid pressure and flow, carotid-femoral pulse wave velocity, brain magnetic resonance images and cognitive scores in participants in the community-based Age, Gene/Environment Susceptibility--Reykjavik study who had no history of stroke, transient ischaemic attack or dementia (n = 668, 378 females, 69-93 years of age). Aortic characteristic impedance was assessed in a random subset (n = 422) and the reflection coefficient at the aorta-carotid interface was computed. Carotid flow pulsatility index was negatively related to the aorta-carotid reflection coefficient (R = -0.66, P<0.001). Carotid pulse pressure, pulsatility index and carotid-femoral pulse wave velocity were each associated with increased risk for silent subcortical infarcts (hazard ratios of 1.62-1.71 per standard deviation, P<0.002). Carotid-femoral pulse wave velocity was associated with higher white matter hyperintensity volume (0.108 ± 0.045 SD/SD, P = 0.018). Pulsatility index was associated with lower whole brain (-0.127 ± 0.037 SD/SD, P<0.001), grey matter (-0.079 ± 0.038 SD/SD, P = 0.038) and white matter (-0.128 ± 0.039 SD/SD, P<0.001) volumes. Carotid-femoral pulse

  4. Lagrangian Coherent Structures in Blood Flow

    NASA Astrophysics Data System (ADS)

    Shadden, Shawn

    2008-11-01

    Knowledge of fluid transport is particularly compelling in understanding the function of cardiovascular processes. Transport of chemicals, cells, and compounds in the vascular system is influenced by local flow structures in large vessels. Local flow features can also induce cell-signaling pathways and biologic response critical to maintaining health or disease progression. Complex vessel geometry, the pulsatile pumping of blood, and low Reynolds number turbulence leads to complex flow features in large vessels. However, we are gaining the ability to study transport in large vessels with unprecedented detail, which is in part allowing us to broaden the ``shear-centric'' view of hemodynamics. In this talk we will describe the application of computational fluid mechanics and the computation of Lagrangian coherent structures (LCS) to study transport in various cardiovascular applications. We will discuss some of the challenges of this work and some results of computing LCS in several regions of the vascular system. In collaboration with Charles Taylor, Stanford University.

  5. Studies on reactive flows

    SciTech Connect

    Sheu, Wenjenn.

    1989-01-01

    Theoretical, numerical and experimental studies are presented on the upstream interactions between premixed flamelets in turbulent combustions, the effect of centrifugal acceleration due to the rotation on Bunsen flames, extinction of counterflow diffusion flames in a counter-rotating finite jet, and nonplanar flame configurations in stagnation point flow. The processes during the upstream flame interactions are numerically investigated using two ozone decomposition planar flames propagating towards each other. The flame temperature and speed during the whole interaction process are also analyzed. One basic kind of rotational effects on the shape and stability of the premixed flames stabilized in Bunsen burner is theoretically and experimentally studied. The relation between the flame stabilization by the burner rim and rotation across the flame is examined. In addition the stable and unstable flame configuration are identified. In the study of the extinction characteristics of diffusion flames in opposed-jet flows with angular velocities which are equal in magnitude but opposite in directions, the extinction characteristics with vorticity in the flow were explored. The general configurations of premixed flame fronts in a stagnation point flow is pursued. Some flame shapes other than planar flames were verified. A simple mathematical model is given to provide the explicit expressions of flame fronts. The implications of these studies to the modeling of turbulent combustion are discussed.

  6. A numerical study on the evolution and structure of a stress-driven free-surface turbulent shear flow

    NASA Astrophysics Data System (ADS)

    Tsai, Wu-Ting; Chen, Shi-Ming; Moeng, Chin-Hoh

    2005-12-01

    implications for the formation of the flow structures are discussed.

  7. Experimental study on dynamics of coherent structures formed by inertial solid particles in three-dimensional periodic flows

    NASA Astrophysics Data System (ADS)

    Gotoda, Masakazu; Melnikov, Denis E.; Ueno, Ichiro; Shevtsova, Valentina

    2016-07-01

    We present experimental results obtained under normal gravity on the dynamics of solid particles in periodic oscillatory thermocapillary-driven flows in a non-isothermal liquid bridge made of decane. Inertial particles of different densities and in the size range approximately 0.75 - 75 μm are able to form stable coherent structures (particle accumulation structures, or PASs). Two image processing techniques were developed and successfully applied to compute time required for an ensemble of particles to form a structure. It is shown that the formation time grows with the decrease of the Stokes number. The observations indicate the probable irrelevance of the memory term for these experiments. Two types of PAS were observed—single (SL-I) and double-loop (SL-II)—which sometimes co-existed. Only large or very dense particles may form an SL-II type structure. A number of novel features of the system were perceived. In some cases, intermittently stable structures emerged (their dynamics is characterized by alternating time intervals during which a structure exists and is destroyed). Whereas in most experiments we observed a conventional symmetric and centered PAS, there were cases when a long-term stable asymmetric structure appeared. Experiments wherein two different types of PAS-forming particles were used simultaneously revealed the destructive role of collisions between the particles on formation of structures.

  8. Experimental study on dynamics of coherent structures formed by inertial solid particles in three-dimensional periodic flows.

    PubMed

    Gotoda, Masakazu; Melnikov, Denis E; Ueno, Ichiro; Shevtsova, Valentina

    2016-07-01

    We present experimental results obtained under normal gravity on the dynamics of solid particles in periodic oscillatory thermocapillary-driven flows in a non-isothermal liquid bridge made of decane. Inertial particles of different densities and in the size range approximately 0.75-75 μm are able to form stable coherent structures (particle accumulation structures, or PASs). Two image processing techniques were developed and successfully applied to compute time required for an ensemble of particles to form a structure. It is shown that the formation time grows with the decrease of the Stokes number. The observations indicate the probable irrelevance of the memory term for these experiments. Two types of PAS were observed-single (SL-I) and double-loop (SL-II)-which sometimes co-existed. Only large or very dense particles may form an SL-II type structure. A number of novel features of the system were perceived. In some cases, intermittently stable structures emerged (their dynamics is characterized by alternating time intervals during which a structure exists and is destroyed). Whereas in most experiments we observed a conventional symmetric and centered PAS, there were cases when a long-term stable asymmetric structure appeared. Experiments wherein two different types of PAS-forming particles were used simultaneously revealed the destructive role of collisions between the particles on formation of structures. PMID:27475066

  9. SAXS studies of the structure of a BCC-ordered block copolymer melt subjected to uniaxial extensional flow

    NASA Astrophysics Data System (ADS)

    Burghardt, Wesley; McCready, Erica

    We report in situ small-angle x-ray scattering (SAXS) investigations of a spherically-ordered block copolymer melt with a low styrene content (13%) resulting in spherical polystyrene microdomains ordered in BCC lattice. Melt annealing after clearing above the ODT produces ordered samples that have a macroscopically random orientation distribution of BCC 'grains'. Melt samples are subjected to uniaxial extensional flow in a counter-rotating drum extensional flow fixture housed in an oven with synchrotron x-ray access. During flow, initially isotropic diffraction rings in SAXS patterns become deformed, reflecting distortion of the BCC lattice. Diffracted intensity also concentrates azimuthally, indicating macroscopic alignment of the BCC lattice. There is evidence that extensional flow leads to progressive disordering of the BCC structure, with loss of higher order peaks and the emergence of a diffuse 'halo' of scattering. While the primary diffraction peak is visible in directions parallel and perpendicular to the stretching direction, the deformation of the lattice d-spacing follows affine deformation. Indications of ordering persist to higher strains in samples stretched at higher extension rates, and evidence of affine lattice deformation persists to very high strains (Hencky

  10. Structure of a reattaching supersonic shear flow

    NASA Technical Reports Server (NTRS)

    Samimy, M.; Abu-Hijleh, B. A. K.

    1988-01-01

    A Mach 1.83 fully developed turbulent boundary layer with boundary layer thickness, free stream velocity, and Reynolds number of 7.5 mm, 476 m/s, and 6.2 x 10 to the 7th/m, respectively, was separated at a 25.4-mm backward step and formed a shear layer. Fast-response pressure transducers, schlieren photography, and LDV were used to study the structure of this reattaching shear flow. The preliminary results show that large-scale relatively organized structures with limited spanwise extent form in the free shear layer. Some of these structures appear to survive the recompression and reattachment processes, while others break down into smaller scales and the flow becomes increasingly three-dimensional. The survived large-scale structures lose their organization through recompression/reattachment, but regain it after reattachment. The structures after reattachment form a 40-45-degree angle relative to the free stream and deteriorate gradually as they move downstream.

  11. Nuclear magnetic resonance studies of the solvation structures of a high-performance nonaqueous redox flow electrolyte

    NASA Astrophysics Data System (ADS)

    Deng, Xuchu; Hu, Mary; Wei, Xiaoliang; Wang, Wei; Mueller, Karl T.; Chen, Zhong; Hu, Jian Zhi

    2016-03-01

    Understanding the solvation structures of electrolytes is important for developing nonaqueous redox flow batteries that hold considerable potential for future large scale energy storage systems. The utilization of an emerging ionic-derivatived ferrocene compound, ferrocenylmethyl dimethyl ethyl ammonium bis(trifluoromethanesulfonyl)imide (Fc1N112-TFSI), has recently overcome the issue of solubility in the supporting electrolyte. In this work, 13C, 1H and 17O NMR investigations were carried out using electrolyte solutions consisting of Fc1N112-TFSI as the solute and the mixed alkyl carbonate as the solvent. It was observed that the spectra of 13C experience changes of chemical shifts while those of 17O undergo linewidth broadening, indicating interactions between solute and solvent molecules. Quantum chemistry calculations of both molecular structures and chemical shifts (13C, 1H and 17O) are performed for interpreting experimental results and for understanding the detailed solvation structures. The results indicate that Fc1N112-TFSI is dissociated at varying degrees in mixed solvent depending on concentrations. At dilute solute concentrations, most Fc1N112+ and TFSI- are fully disassociated with their own solvation shells formed by solvent molecules. At saturated concentration, Fc1N112+-TFSI- contact ion pairs are formed and the solvent molecules are preferentially interacting with the Fc rings rather than interacting with the ionic pendant arm of Fc1N112-TFSI.

  12. Studies of shear flows

    NASA Astrophysics Data System (ADS)

    Kline, S. J.; Johnston, J. P.; Moffat, R. J.

    1986-03-01

    The objective of the work reported is construction of zonal models for accurate prediction of turbulent flows in rapid-running computer programs. The work follows the ideas set down in the discussion of zonal modeling by S. J. Kline in Vol. 2 of the Proceedings of the 1980-81 AFOSR-Stanford Conference on Complex Turbulent Flows. This discussion noted that the fast-running models available lack sufficient span to predict all classes of turbulent flows of engineering importance in a standard, invariant form. It therefore suggested that the models be treated as zonal. In the zonal approach, the constants in th models are adjusted for each important zone of the flow, where the word zone implies a region with a particular type of flow physics. In the proposal for the work, it was also noted that the parametrization of the flows and the selection of appropriate constants would ultimately need to be guided by the domain over which accurate results could be obtained, and that might well be different from pre-conceptions embodied in conventional taxonomies of the flows.

  13. Resistive interchange modes and plasma flow structures

    NASA Astrophysics Data System (ADS)

    Paccagnella, Roberto

    2011-10-01

    Interchange modes are ubiquitous in magnetic confinement systems and are likely to determine or influence their transport properties. For example a good agreement between theory predictions for linear interchange modes and experimental results has been found recently in a Reverse Field Pinch device. In this work a set of magneto-hydro-dynamic (MHD) equations that describe the dynamical evolution for the pressure driven interchange modes in a magnetic confinement system are studied. Global and local solutions relevant for tokamaks and Reversed Field Pinches (RFPs) configurations are considered. The emphasis is especially in the characterization of the plasma flow structures associated with the dominant modes.

  14. Coherent structures in transitional pipe flow

    NASA Astrophysics Data System (ADS)

    Hellström, Leo H. O.; Ganapathisubramani, Bharathram; Smits, Alexander J.

    2016-06-01

    Transition to turbulence in pipe flow is investigated experimentally using a temporally resolved dual-plane particle image velocimetry approach, at a Reynolds number of 3440. The flow is analyzed using proper orthogonal decomposition and it is shown that the flow can be divided into two regions: a pseudolaminar region governed by the presence of azimuthally steady traveling waves, and turbulent slugs. The evolution of the structures within the slugs is identified by using the temporally resolved data along with the dual-plane velocity field. These structures are shown to be remarkably similar to the large-scale motions found in fully turbulent flows, with a streamwise and spatiotemporal extent about four pipe radii. The transition between structures is characterized by the detachment and decay of an old structure and the initiation of a new structure at the wall.

  15. Study on the effect of punched holes on flow structure and heat transfer of the plain fin with multi-row delta winglets

    NASA Astrophysics Data System (ADS)

    Tian, Liting; Liu, Bin; Min, Chunhua; Wang, Jin; He, Yaling

    2015-11-01

    Three dimensional numerical simulations are performed to investigate the flow and heat transfer characteristics of the plain fin with multi-row delta winglets punched out from the fin. The Reynolds number based on the tube outside diameter varies from 360 to 1440. The effects of punched holes and their orientations on flow structure and heat transfer are numerically studied. Results show that a down-wash flow is formed through the hole punched at the windward side, which has little influence on the longitudinal vortices in the main flow, and a longitudinal main vortex is formed behind each delta winglet. An up-wash flow is formed through the hole punched at the leeward side, the up-wash flow impinges the longitudinal vortices generated by the delta winglet, and then a counter-rotating pair of main vortices is generated behind each delta winglet. The windward punched holes have little effect on the flow friction and heat transfer of the plain fin with delta winglets, while the leeward punched holes deteriorate the heat transfer and decrease the flow friction of the fin channel, the Nusselt number decreases by 3.5-5.0 % with a corresponding decrease of 3.9-4.8 % in the friction factor. The effect of the punched holes on the heat transfer of the fin can be well explained by the field synergy principle. The overall analysis of the thermal performance is performed for all fin configurations, including the slit fins and the wavy fins with one-row delta winglets, the plain fin with the windward punched delta winglets shows the better thermal performance than one with the leeward punched delta winglets.

  16. A field study of the effects of soil structure and irrigation method on preferential flow of pesticides in unsaturated soil

    NASA Astrophysics Data System (ADS)

    Ghodrati, Masoud; Jury, William A.

    1992-10-01

    A large number of field plot experiments were performed to characterize the downward flow of three pesticides (atrazine, napropamide and prometryn) and a water tracer (chloride) under various soil water regimes and soil surface conditions. Each experiment consisted of the uniform application of a 0.4-cm pulse of a solution containing a mixture of the four chemicals to the surface of a 1.5 × 1.5-m plot. The plot was then irrigated with 12 cm of water and soil samples were collected and analyzed to a depth of 150 cm. In all, 64 different plots were employed to study individual as well as interactive effects of such variables as irrigation method (continuous or intermittent sprinkling or ponding), pesticide formulation method (technical grade dissolved in water, wettable powder, or emulsifiable concentrate), and tillage (undisturbed or tilled and repacked surface layer) on pesticide transport. While all three pesticides were expected to be retained in the top 10-20 cm, there was considerable movement below this zone. When averaged over all the treatments, 18.8% of the recovered mass of atrazine, 9.4% of the prometryn and 16.4% of the napropamide were found between 30- and 150cm depth. Moreover, all pesticides were highly mobile in the surface 30 cm regardless of their adsorption coefficient. There were occureences of extreme mobility or "preferential flow" of pesticide under every experimental condition except where the pesticides were applied in wettable powder form to plots which had their surface tilled and repacked. This finding implies that there may be fine preferential flow pathways through which solution may move but particulates may not.

  17. Rheological and structural studies of liquid decane, hexadecane, and tetracosane under planar elongational flow using nonequilibrium molecular-dynamics simulations

    NASA Astrophysics Data System (ADS)

    Baig, C.; Edwards, B. J.; Keffer, D. J.; Cochran, H. D.

    2005-05-01

    We report for the first time rheological and structural properties of liquid decane, hexadecane, and tetracosane using nonequilibrium molecular-dynamics (NEMD) simulations under planar elongational flow (PEF). The underlying NEMD algorithm employed is the so-called p-SLLOD algorithm [C. Baig, B. J. Edwards, D. J. Keffer, and H. D. Cochran, J. Chem. Phys. 122, 114103 (2005)]. Two elongational viscosities are measured, and they are shown not to be equal to each other, indicating two independent viscometric functions in PEF. With an appropriate definition, it is observed that the two elongational viscosities converge to each other at very low elongation rates, i.e., in the Newtonian regime. For all three alkanes, tension-thinning behavior is observed. At high elongation rates, chains appear to be fully stretched. This is supported by the result of the mean-square end-to-end distance of chains ⟨Rete2⟩ and the mean-square radius of gyration of chains ⟨Rg2⟩, and further supported by the result of the intramolecular Lennard-Jones (LJ) potential energy. It is also observed that ⟨Rete2⟩ and ⟨Rg2⟩ show a different trend as a function of strain rate from those in shear flow: after reaching a plateau value, ⟨Rete2⟩ and ⟨Rg2⟩ are found to increase further as elongation rate increases. A minimum in the hydrostatic pressure is observed for hexadecane and tetracosane at about ɛ˙(mσ2/ɛ)1/2=0.02. This phenomenon is shown to be associated with the intermolecular LJ potential energy. The bond-bending and torsional energies display similar trends, but a different behavior is observed for the bond-stretching energy. An important observation common in these three bonded-intramolecular interactions is that all three modes are suppressed to a small value at high elongation rates. We conjecture that a liquid-crystal-like, nematic structure is present in these systems at high elongation rates, which is characterized by a strong chain alignment with a fully

  18. Coherent Flow Structures in Basaltic Lava Flows - Flow Dynamics and Rheology

    NASA Astrophysics Data System (ADS)

    Cashman, K. V.; Grant, G. E.

    2011-12-01

    Basaltic lavas form multiphase flows with variable proportions of liquid (silicate melt), solid (silicate crystals) and gas bubbles. The hydraulics of these flows is poorly understood, in large part because of the difficulties involved in making direct measurements on large hot lava streams. For example, although surface flow velocity and width can be measured given sufficient logistical support in the field, even as simple a parameter as flow depth must be estimated, and thus generates large uncertainties in instantaneous effusion rate, the lava flow analog for stream discharge. Additionally, there is a dramatic down-flow change in rheology caused by gas loss and solidification that is difficult to characterize without extensive along-flow sampling and analysis. For these reasons, the dynamics of basaltic lava flows are poorly understood. However, distinctive flow features such as standing waves and lateral shocks have been observed in some basaltic lava flows; we suggest that these structures offer a novel approach for calculating key flow parameters and effusion rates. Specifically, we argue that such structures suggest that lava flows can attain transcritical flow regimes (Froude Number [Fr] ≈ 1), similar to high gradient streamflows. This hypothesis is supported by measurements of Hawaiian lava flows from Mauna Loa during the 1984 eruption, where surface flow velocities (measured by timing the advance of surface fragments) and flow depths (estimated by assuming neutral buoyancy for solidified lava "boats") show diminishing velocities and Fr with distance from the vent. Near-vent Fr are supercritical but approach 1.0 at a distance of 3-4 km. Corresponding photographic observations of standing waves, hydraulic jumps and shocks in these flows confirm the correspondence between flow structures and measured hydraulics. In contrast to stream flows, however, these coherent flow structures occur under laminar flow conditions that reflect the moderate Reynolds

  19. Flow Structure in a Bedrock Canyon (Invited)

    NASA Astrophysics Data System (ADS)

    Venditti, J. G.; Rennie, C. D.; Church, M. A.; Bomhof, J.; Lin, M.

    2013-12-01

    Bedrock canyon incision is widely recognized as setting the pace of landscape evolution. A variety of models link flow and sediment transport processes to the bedrock canyon incision rate. The model components that represent sediment transport processes are quite well developed in some models. In contrast, the model components that represent fluid flow remain rudimentary. Part of the reason is that there have been relatively few observations of flow structure in a bedrock canyon. Here, we present observations of flow obtained using an array of three acoustic Doppler current profilers during a 524 km long continuous centerline traverse of the Fraser River, British Columbia, Canada as it passes through a series of bedrock canyons. Through this portion of the river, the channel alternates between gravel-bedded reaches that are deeply incised into semi-consolidated glacial deposits and solid bedrock-bound reaches. We present observations of flow through 41 bedrock bound reaches of the river, derived from our centerline traverses and more detailed three-dimensional mapping of the flow structure in 2 canyons. Our observations suggest that flow in the most well-defined canyons (deep, laterally constrained, completely bedrock bound) is far more complex than that in a simple prismatic channel. As flow enters the canyon, a high velocity core plunges from the surface to the bed, causing a velocity inversion (high velocities at the bed and low velocities at the surface). This plunging flow then upwells along the canyon wall, resulting in a three-dimensional flow with counter-rotating, along-stream eddies that diverge near the bed. We observe centerline ridges along the canyon floors that result from the divergence and large-scale surface boils caused by the upwelling. This flow structure causes deep scour in the bedrock channel floor, and ensures the base of the canyon walls are swept of debris that otherwise may be deposited due to lower shear stresses abutting the walls. The

  20. Structure of Flow in a Bedrock Canyon

    NASA Astrophysics Data System (ADS)

    Venditti, J. G.; Rennie, C. D.; Church, M. A.; Bomhof, J.; Lin, M.

    2012-12-01

    Bedrock canyon incision is widely recognized as setting the pace of landscape evolution. A variety of models link flow and sediment transport processes to the bedrock canyon incision rate. The model components that represent sediment transport processes are quite well developed in some models. In contrast, the model components that represent fluid flow remain rudimentary. Part of the reason is that there have been relatively few observations of flow structure in a bedrock canyon. Here, we present observations of flow obtained using an array of three acoustic Doppler current profilers during a 524 km long continuous centerline traverse of the Fraser River, British Columbia, Canada as it passes through a series of bedrock canyons. Through this portion of the river, the channel alternates between gravel-bedded reaches that are deeply incised into semi-consolidated glacial deposits and solid bedrock-bound reaches. We present observations of flow through 41 bedrock bound reaches of the river, derived from our centerline traverses and more detailed three-dimensional mapping of the flow structure in 2 canyons. Our observations suggest that flow in the most well-defined canyons (deep, laterally constrained, completely bedrock bound) is far more complex than that in a simple prismatic channel. As flow enters the canyon, a high velocity core plunges from the surface to the bed, causing a velocity inversion (high velocities at the bed and low velocities at the surface). This plunging flow then upwells along the canyon wall, resulting in a three-dimensional flow with counter-rotating, along-stream eddies that diverge near the bed. We observe centerline ridges along the canyon floors that result from the divergence and large-scale surface boils caused by the upwelling. This flow structure causes deep scour in the bedrock channel floor, and ensures the base of the canyon walls are swept of debris that otherwise may be deposited due to lower shear stresses abutting the walls. The

  1. Comparison of cerebral blood flow and structural penumbras in relation to white matter hyperintensities: A multi-modal magnetic resonance imaging study

    PubMed Central

    Lahna, David L; Kaye, Jeffrey A; Dodge, Hiroko H; Erten-Lyons, Deniz; Rooney, William D; Silbert, Lisa C

    2016-01-01

    Normal-appearing white matter (NAWM) surrounding WMHs is associated with decreased structural integrity and perfusion, increased risk of WMH growth, and is referred to as the WMH penumbra. Studies comparing structural and cerebral blood flow (CBF) penumbras within the same individuals are lacking, however, and would facilitate our understanding of mechanisms resulting in WM damage. This study aimed to compare both CBF and structural WMH penumbras in non-demented aging. Eighty-two elderly volunteers underwent 3T-MRI including fluid attenuated inversion recovery (FLAIR), pulsed arterial spin labeling and diffusion tensor imaging (DTI). A NAWM layer mask was generated for periventricular and deep WMHs. Mean CBF, DTI-fractional anisotropy (DTI-FA), DTI-mean diffusivity (DTI-MD) and FLAIR intensity for WMHs and its corresponding NAWM layer masks were computed and compared against its mean within total brain NAWM using mixed effects models. For both periventricular and deep WMHs, DTI-FA, DTI-MD and FLAIR intensity changes extended 2-9 mm surrounding WMHs (p ≤ 0.05), while CBF changes extended 13-14 mm (p ≤ 0.05). The CBF penumbra is more extensive than structural penumbras in relation to WMHs and includes WM tissue both with and without microstructural changes. Findings implicate CBF as a potential target for the prevention of both micro and macro structural WM damage. PMID:27270266

  2. Inverted annular flow experimental study

    SciTech Connect

    De Jarlais, G.; Ishii, M.

    1985-04-01

    Steady-state inverted annular flow of Freon 113 in up flow was established in a transparent test section. Using a special inlet configuration consisting of long aspect-ratio liquid nozzles coaxially centered within a heated quartz tube, idealized inverted annular flow initial geometry (cylindrical liquid core surrounded by coaxial annulus of gas) could be established. Inlet liquid and gas flowrates, liquid subcooling, and gas density (using various gas species) were measured and varied systematically. The hydrodynamic behavior of the liquid core, and the subsequent downstream break-up of this core into slugs, ligaments and/or droplets of various sizes, was observed. In general, for low inlet liquid velocities it was observed that after the initial formation of roll waves on the liquid core surface, an agitated region of high surface area, with attendant high momentum and energy transfers, occurs. This agitated region appears to propagate downsteam in a quasi-periodic pattern. Increased inlet liquid flow rates, and high gas annulus flow rates tend to diminish the significance of this agitated region. Observed inverted annular flow (and subsequent downstream flow pattern) hydrodynamic behavior is reported, and comparisons are drawn to data generated by previous experimenters studying post-CHF flow.

  3. Experimental studies of influence of the turbulent flow structure on temperature distribution in a compact heat exchanger

    NASA Astrophysics Data System (ADS)

    Perepelitsa, B. V.

    2008-12-01

    Results of experimental investigation of temperature distribution over the surface of a complex heat exchanger (the Frenkel packing type) are presented. Measurements were carried out in the air flow between two sheets with triangular corrugations directed at 90° to each other. Measurements were carried out by the microthermocouples glued on the heated outer surface. The effect of Reynolds numbers, a gap between corrugated sheets, and substitution of one corrugated sheet by the smooth one on temperature distribution over the heat exchanger surface in the turbulent air flow is analysed. According to the performed experiments, there is a significant effect of a gap and applied perturbations on the type of temperature distribution over the perimeter of a heated cell.

  4. Internal wave structures in abyssal cataract flows

    NASA Astrophysics Data System (ADS)

    Makarenko, Nikolay; Liapidevskii, Valery; Morozov, Eugene; Tarakanov, Roman

    2014-05-01

    We discuss some theoretical approaches, experimental results and field data concerning wave phenomena in ocean near-bottom stratified flows. Such strong flows of cold water form everywhere in the Atlantic abyssal channels, and these currents play significant role in the global water exchange. Most interesting wave structures arise in a powerful cataract flows near orographic obstacles which disturb gravity currents by forced lee waves, attached hydraulic jumps, mixing layers etc. All these effects were observed by the authors in the Romanche and Chain fracture zones of Atlantic Ocean during recent cruises of the R/V Akademik Ioffe and R/V Akademik Sergei Vavilov (Morozov et al., Dokl. Earth Sci., 2012, 446(2)). In a general way, deep-water cataract flows down the slope are similar to the stratified flows examined in laboratory experiments. Strong mixing in the sill region leads to the splitting of the gravity current into the layers having the fluids with different densities. Another peculiarity is the presence of critical layers in shear flows sustained over the sill. In the case under consideration, this critical level separates the flow of near-bottom cold water from opposite overflow. In accordance with known theoretical models and laboratory measurements, the critical layer can absorb and reflect internal waves generated by the topography, so the upward propagation of these perturbations is blocked from above. High velocity gradients were registered downstream in the vicinity of cataract and it indicates the existence of developed wave structures beyond the sill formed by intense internal waves. This work was supported by RFBR (grants No 12-01-00671-a, 12-08-10001-k and 13-08-10001-k).

  5. Energy structure of MHD flow coupling with outer resistance circuit

    NASA Astrophysics Data System (ADS)

    Huang, Z. Y.; Liu, Y. J.; Chen, Y. Q.; Peng, Z. L.

    2015-08-01

    Energy structure of MHD flow coupling with outer resistance circuit is studied to illuminate qualitatively and quantitatively the energy relation of this basic MHD flow system with energy input and output. Energy structure are analytically derived based on the Navier-Stocks equations for two-dimensional fully-developed flow and generalized Ohm's Law. The influences of applied magnetic field, Hall parameter and conductivity on energy structure are discussed based on the analytical results. Associated energies in MHD flow are deduced and validated by energy conservation. These results reveal that energy structure consists of two sub structures: electrical energy structure and internal energy structure. Energy structure and its sub structures provide an integrated theoretical energy path of the MHD system. Applied magnetic field and conductivity decrease the input energy, dissipation by fluid viscosity and internal energy but increase the ratio of electrical energy to input energy, while Hall parameter has the opposite effects. These are caused by their different effects on Bulk velocity, velocity profiles, voltage and current in outer circuit. Understanding energy structure helps MHD application designers to actively adjust the allocation of different parts of energy so that it is more reasonable and desirable.

  6. Flow structure in submarine meandering channels, a continuous discussion on secondary flow

    NASA Astrophysics Data System (ADS)

    Abad, J. D.; Parker, G.; Sequeiros, O.; Spinewine, B.; Garcia, M. H.; Pirmez, C.

    2011-12-01

    The understanding of the flow structure in deep-sea turbidity currents is important for the formation of submarine meandering channels. Similarly to the case of subaerial channels, several types of secondary flows include turbulence-, curvature- and bed morphodynamic-driven flow structures that modulate sediment transport and channel bed morphodynamics. This study focuses on [1] a review of long-time research effort (Abad et al., 2011) that tackles the description of the secondary flow associated with a subaqueous bottom current (saline) in a high-curvature meandering channel and [2] ongoing numerical simulations of similar settings as the experiments to describe the entire flow structure. In the case of subaerial channels, the classical Rozovskiian paradigm is often invoked which indicates that the near-bottom secondary flow in a bend is directed inward. It has recently been suggested based on experimental and theoretical considerations, however, that this pattern is reversed (near-bottom secondary flow is directed outward) in the case of submarine meandering channels. Experimental results presented here, on the other hand, indicate near-bottom secondary flows that have the same direction as observed in a river (normal secondary flow). The implication is an apparent contradiction between experimental results. This study combines theory, experiments, reconstructions of field flows and ongoing simulations to resolve this apparent contradiction based on the flow densimetric Froude number. Three ranges of densimetric Froude number are found, such that a) in an upper regime, secondary flow is reversed, b) in a middle regime, it is normal and c) in a lower regime, it is reversed. These results are applied to field scale channel-forming turbidity currents in the Amazon submarine canyon-fan system (Amazon Channel) and the Monterey canyon and a saline underflow in the Black Sea flowing from the Bosphorus. Our analysis indicates that secondary flow should be normal

  7. Does stream flow structure woody riparian vegetation in subtropical catchments?

    PubMed

    James, Cassandra S; Mackay, Stephen J; Arthington, Angela H; Capon, Samantha J; Barnes, Anna; Pearson, Ben

    2016-08-01

    The primary objective of this study was to test the relevance of hydrological classification and class differences to the characteristics of woody riparian vegetation in a subtropical landscape in Queensland, Australia. We followed classification procedures of the environmental flow framework ELOHA - Ecological Limits of Hydrologic Alteration. Riparian surveys at 44 sites distributed across five flow classes recorded 191 woody riparian species and 15, 500 individuals. There were differences among flow classes for riparian species richness, total abundance, and abundance of regenerating native trees and shrubs. There were also significant class differences in the occurrence of three common tree species, and 21 indicator species (mostly native taxa) further distinguished the vegetation characteristics of each flow class. We investigated the influence of key drivers of riparian vegetation structure (climate, depth to water table, stream-specific power, substrate type, degree of hydrologic alteration, and land use) on riparian vegetation. Patterns were explained largely by climate, particularly annual rainfall and temperature. Strong covarying drivers (hydrology and climate) prevented us from isolating the independent influences of these drivers on riparian assemblage structure. The prevalence of species considered typically rheophytic in some flow classes implies a more substantial role for flow in these classes but needs further testing. No relationships were found between land use and riparian vegetation composition and structure. This study demonstrates the relevance of flow classification to the structure of riparian vegetation in a subtropical landscape, and the influence of covarying drivers on riparian patterns. Management of environmental flows to influence riparian vegetation assemblages would likely have most potential in sites dominated by rheophytic species where hydrological influences override other controls. In contrast, where vegetation assemblages are

  8. Does stream flow structure woody riparian vegetation in subtropical catchments?

    PubMed

    James, Cassandra S; Mackay, Stephen J; Arthington, Angela H; Capon, Samantha J; Barnes, Anna; Pearson, Ben

    2016-08-01

    The primary objective of this study was to test the relevance of hydrological classification and class differences to the characteristics of woody riparian vegetation in a subtropical landscape in Queensland, Australia. We followed classification procedures of the environmental flow framework ELOHA - Ecological Limits of Hydrologic Alteration. Riparian surveys at 44 sites distributed across five flow classes recorded 191 woody riparian species and 15, 500 individuals. There were differences among flow classes for riparian species richness, total abundance, and abundance of regenerating native trees and shrubs. There were also significant class differences in the occurrence of three common tree species, and 21 indicator species (mostly native taxa) further distinguished the vegetation characteristics of each flow class. We investigated the influence of key drivers of riparian vegetation structure (climate, depth to water table, stream-specific power, substrate type, degree of hydrologic alteration, and land use) on riparian vegetation. Patterns were explained largely by climate, particularly annual rainfall and temperature. Strong covarying drivers (hydrology and climate) prevented us from isolating the independent influences of these drivers on riparian assemblage structure. The prevalence of species considered typically rheophytic in some flow classes implies a more substantial role for flow in these classes but needs further testing. No relationships were found between land use and riparian vegetation composition and structure. This study demonstrates the relevance of flow classification to the structure of riparian vegetation in a subtropical landscape, and the influence of covarying drivers on riparian patterns. Management of environmental flows to influence riparian vegetation assemblages would likely have most potential in sites dominated by rheophytic species where hydrological influences override other controls. In contrast, where vegetation assemblages are

  9. Secondary flow structures in large rivers

    NASA Astrophysics Data System (ADS)

    Chauvet, H.; Devauchelle, O.; Metivier, F.; Limare, A.; Lajeunesse, E.

    2012-04-01

    Measuring the velocity field in large rivers remains a challenge, even with recent measurement techniques such as Acoustic Doppler Current Profiler (ADCP). Indeed, due to the diverging angle between its ultrasonic beams, an ADCP cannot detect small-scale flow structures. However, when the measurements are limited to a single location for a sufficient period of time, averaging can reveal large, stationary flow structures. Here we present velocity measurements in a straight reach of the Seine river in Paris, France, where the cross-section is close to rectangular. The transverse modulation of the streamwise velocity indicates secondary flow cells, which seem to occupy the entire width of the river. This observation is reminiscent of the longitudinal vortices observed in laboratory experiments (e.g. Blanckaert et al., Advances in Water Resources, 2010, 33, 1062-1074). Although the physical origin of these secondary structures remains unclear, their measured velocity is sufficient to significantly impact the distribution of streamwise momentum. We propose a model for the transverse profile of the depth-averaged velocity based on a crude representation of the longitudinal vortices, with a single free parameter. Preliminary results are in good agreement with field measurements. This model also provides an estimate for the bank shear stress, which controls bank erosion.

  10. Flow-structure vibration and sloshing--1990

    SciTech Connect

    Ma, D.C.; Chen, S.S. ); Tani, J. )

    1990-01-01

    This book is covered under some of the following topics: Advances and trends in seismic design of cylindrical liquid storage tanks; Study of the influence of imperfection on the dynamic stability of tanks; Parametric study on parallel flow-induced damping of PWR fuel assembly; Nonlinear dynamic analysis of spent fuel storage racks.

  11. Blood flow structure in patients with coronary heart disease

    NASA Astrophysics Data System (ADS)

    Malinova, Lidia I.; Simonenko, Georgy V.; Denisova, Tatyana P.; Tuchin, Valery V.

    2007-05-01

    Blood flow structure was studied by PC integrated video camera with following slide by slide analysis. Volumetric blood flow velocity was supporting on constant level (1 ml/h). Silicone tube of diameter comparable with coronary arteries diameter was used as vessel model. Cell-cell interactions were studied under glucose and anticoagulants influence. Increased adhesiveness of blood cells to tube walls was revealed in patient with coronary heart disease (CHD) compare to practically healthy persons (PHP). In patients with stable angina pectoris of high functional class and patients with AMI shear stress resistant erythrocyte aggregates were predominating in blood flow structure up to microclots formation. Clotting and erythrocytes aggregation increase as response to glucose solution injection, sharply defined in patients with CHD. Heparin injection (10 000 ED) increased linear blood flow velocity both in patients with CHD and PHP. After compare our results with other author's data we can consider that method used in our study is sensible enough to investigate blood flow structure violations in patients with CHD and PHP. Several differences of cell-cell interaction in flow under glucose and anticoagulant influence were found out in patients with CHD and PHP.

  12. Application of the ultrasonic technique and high-speed filming for the study of the structure of air-water bubbly flows

    SciTech Connect

    Carvalho, R.D.M.; Venturini, O.J.; Tanahashi, E.I.; Neves, F. Jr.; Franca, F.A.

    2009-10-15

    Multiphase flows are very common in industry, oftentimes involving very harsh environments and fluids. Accordingly, there is a need to determine the dispersed phase holdup using noninvasive fast responding techniques; besides, knowledge of the flow structure is essential for the assessment of the transport processes involved. The ultrasonic technique fulfills these requirements and could have the capability to provide the information required. In this paper, the potential of the ultrasonic technique for application to two-phase flows was investigated by checking acoustic attenuation data against experimental data on the void fraction and flow topology of vertical, upward, air-water bubbly flows in the zero to 15% void fraction range. The ultrasonic apparatus consisted of one emitter/receiver transducer and three other receivers at different positions along the pipe circumference; simultaneous high-speed motion pictures of the flow patterns were made at 250 and 1000 fps. The attenuation data for all sensors exhibited a systematic interrelated behavior with void fraction, thereby testifying to the capability of the ultrasonic technique to measure the dispersed phase holdup. From the motion pictures, basic gas phase structures and different flows patterns were identified that corroborated several features of the acoustic attenuation data. Finally, the acoustic wave transit time was also investigated as a function of void fraction. (author)

  13. Flow Structure Associated with Hemodialysis Catheters

    NASA Astrophysics Data System (ADS)

    Foust, Jason

    2005-11-01

    Insertion of a hemodialysis catheter into the superior vena cava (SVC) gives rise to complex flow patterns, which arise from the simultaneous injection and extraction of blood through different holes (ports) of the catheter. Techniques of high-image-density particle image velocimetry are employed in a scaled-up water facility. This approach allows characterization of both the instantaneous and time-averaged flow structure due to generic classes of side hole geometries. The trajectory of the injection jet is related to the ratio of the initial jet velocity to the mainstream velocity through the SVC, and to the type of distortion of the jet cross-section. Furthermore, the mean and fluctuating velocity and vorticity fields are determined. Significant turbulent stresses develop rapidly in the injection jet, which can impinge upon the wall of the simulated SVC. Immediately downstream of the injection hole, a recirculation cell of low velocity exists adjacent to the catheter surface. These and other representations of the flow structure are first evaluated for a steady throughflow, then for the case of a pulsatile waveform in the SVC, which matches that of a normal adult.

  14. Flowing crystals: nonequilibrium structure of foam.

    PubMed

    Garstecki, Piotr; Whitesides, George M

    2006-07-14

    Bubbles pushed through a quasi-two-dimensional channel self-organize into a variety of periodic lattices. The structures of these lattices correspond to local minima of the interfacial energy. The "flowing crystals" are long-lived metastable states, a small subset of possible local minima of confined quasi-two-dimensional foams [P. Garstecki and G. M. Whitesides, Phys. Rev. E 73, 031603 (2006)10.1103/PhysRevE.73.031603]. Experimental results suggest that the choice of the structures that we observe is dictated by the dynamic stability of the cyclic processes of their formation. Thus, the dynamic system that we report provides a unique example of nonequilibrium self-organization that results in structures that correspond to local minima of the relevant energy functional. PMID:16907453

  15. Formation of coherent structures in 3D laminar mixing flows

    NASA Astrophysics Data System (ADS)

    Speetjens, Michel; Clercx, Herman

    2009-11-01

    Mixing under laminar flow conditions is key to a wide variety of industrial systems of size extending from microns to meters. Examples range from the traditional (and still very relevant) mixing of viscous fluids via compact processing equipment down to emerging micro-fluidics applications. Profound insight into laminar mixing mechanisms is imperative for further advancement of mixing technology (particularly for complex micro-fluidics systems) yet remains limited to date. The present study concentrates on a fundamental transport phenomenon of potential relevance to laminar mixing: the formation of coherent structures in the web of 3D fluid trajectories due to fluid inertia. Such coherent structures geometrically determine the transport properties of the flow and better understanding of their formation and characteristics may offer ways to control and manipulate the mixing properties of laminar flows. The formation of coherent structures and its impact upon 3D transport properties is demonstrated by way of examples.

  16. Condensation of Coherent Structures in Turbulent Flows.

    PubMed

    Chong, Kai Leong; Huang, Shi-Di; Kaczorowski, Matthias; Xia, Ke-Qing

    2015-12-31

    Coherent structures are ubiquitous in turbulent flows and play a key role in transport. The most important coherent structures in thermal turbulence are plumes. Despite being the primary heat carriers, the potential of manipulating thermal plumes to transport more heat has been overlooked so far. Unlike some other forms of energy transport, such as electromagnetic or sound waves, heat flow in fluids is generally difficult to manipulate, as it is associated with the random motion of molecules and atoms. Here we report how a simple geometrical confinement can lead to the condensation of elementary plumes. The result is the formation of highly coherent system-sized plumes and the emergence of a new regime of convective thermal turbulence characterized by universal temperature profiles and significantly enhanced heat transfer. It is also found that the universality of the temperature profiles and heat transport originate from the geometrical properties of the coherent structures, i.e., the thermal plumes. Therefore, in contrast to the classical regime, boundary layers in this plume-controlled regime are being controlled, rather than controlling. PMID:26764994

  17. Characterization of large-scale structures in a forced ducted flow with dump

    NASA Astrophysics Data System (ADS)

    Schadow, K. C.; Wilson, K. J.; Gutmark, E.

    1985-01-01

    A forced, subsonic ducted flow with dump was studied using hot-wire anemometry. Forcing to the flow was applied by exciting the duct resonant acoustics. Flow structures (vortices) with high azimuthal coherence and high spatial and temporal periodicity were generated in the shear flow at the dump when the forcing frequency matched the first subharmonic of the initial vortex shedding frequency or the preferred mode frequency. By forcing the flow at the preferred mode frequency, mixing was enhanced in the shear-flow and pipe-flow regimes. A visual description of the coherent structures was obtained in water flow tests.

  18. Viscous Flow Structures Downstream of a Model Tracheoesophageal Prosthesis

    NASA Astrophysics Data System (ADS)

    Hemsing, Frank; Erath, Byron

    2013-11-01

    In tracheoesophageal speech (TES), the glottis is replaced by the tissue of the pharyngeoesophageal segment (PES) as the vibrating element of speech production. During TES air is forced from the lungs into the esophagus via a prosthetic tube that connects the trachea with the esophagus. Air moving up the esophagus incites self-sustained oscillations of the surgically created PES, generating sound analogous to voiced speech. Despite the ubiquity with which TES is employed as a method for restoring speech to laryngectomees, the effect of viscous flow structures on voice production in TES is not well understood. Of particular interest is the flow exiting the prosthetic connection between the trachea and esophagus, because of its influence on the total pressure loss (i.e. effort required to produce speech), and the fluid-structure energy exchange that drives the PES. Understanding this flow behavior can inform prosthesis design to enhance beneficial flow structures and mitigate the need for adjustment of prosthesis placement. This study employs a physical model of the tracheoesophageal geometry to investigate the flow structures that arise in TES. The geometry of this region is modeled at three times physiological scale using water as the working fluid to obtain nondimensional numbers matching flow in TES. Modulation of the flow is achieved with a computer controlled gate valve at a scaled frequency of 0.22 Hz to mimic the oscillations of the PES. Particle image velocimetry is used to resolve flow characteristics at the tracheoesophageal prosthesis. Data are acquired for three cases of prosthesis insertion angle.

  19. Flow dynamics of bank-attached instream structures

    NASA Astrophysics Data System (ADS)

    Kang, Seokkoo

    2016-04-01

    Numerical simulations and experiments for flow past a bank-attached vane, a widely-used instream structure for stream restoration, are carried out to study the turbulent flow dynamics occurring around the structure. In the numerical simulation, the details of the natural rocks that constitute the vane are directly resolved by employing the recently developed computational fluid dynamics model of Kang et al. (2011). The time-averaged flowfield is shown to be in good agreement with the results of laboratory measurements. Analysis of the simulated flow shows that there exist two counter-rotating secondary flows cells downstream of the vane, one of which is located near the center of the channel and the other is located near the corner between the channel bed and the sidewall to which the vane is attached. The formation of the two counter-rotating secondary flow cells is shown to be linked to the plunging of the mean three-dimensional streamlines originating upstream of the vane onto a point downstream of the vane positioned on the lower part of the sidewall. The laboratory experiment also reveals the existence of such flow structures.

  20. Flow Structures in a Healthy and Plaqued Artificial Artery using Fully Index Matched Vascular Flow Facility

    NASA Astrophysics Data System (ADS)

    Mehdi, Faraz; Jain, Akash; Sheng, Jian

    2014-11-01

    Particle Image Velocimetry measurements are made in a closed loop fully index matched flow facility to study the flow structures and flow wall interactions in healthy and diseased model arteries. The test section is 0.63 m long and the facility is capable of emulating both steady and pulsatile flows under physiologically relevant conditions. The model arteries are in-house developed compliant polymer (PDMS) tubes with 1 cm diameter and 1 mm wall thickness. The Reynolds numbers of flows vary up to 20,000. The plaque is simulated by introducing a radially asymmetric bump that can be varied in shape, size and compliancy. The overall compliancy of the model can be also controlled by varying ratio between the elastomer and the curing agent. The tubes are doped with particles allowing the simultaneous measurements of wall deformation and flows over it. The working fluid in the facility is NaI and is refractive index matched to the PDMS model. This allows flow measurement very close to the wall and measurement of wall shear stress. The aim of this study is to characterize the changes in flow as the compliancy and geometry of blood vessels change due to age or disease. These differences can be used to develop a diagnostic tool to detect early onset of vascular diseases.

  1. Debris flow study in Malaysia

    NASA Astrophysics Data System (ADS)

    Bahrin Jaafar, Kamal

    2016-04-01

    The phenomenon of debris flow occurs in Malaysia occasionally. The topography of Peningsular Malysia is characterized by the central mountain ranges running from south to north. Several parts of hilly areas with steep slopes, combined with high saturation of soil strata that deliberately increase the pore water pressure underneath the hill slope. As a tropical country Malaysia has very high intensity rainfall which is triggered the landslide. In the study area where the debris flow are bound to occur, there are a few factors that contribute to this phenomenon such as high rainfall intensity, very steep slope which an inclination more than 35 degree and sandy clay soil type which is easily change to liquidity soil. This paper will discuss the study of rainfall, mechanism, modeling and design of mitigation measure to avoid repeated failure in future in same area.

  2. A beam-membrane structure micromachined differential pressure flow sensor.

    PubMed

    Chen, P; Zhao, Y L; Tian, B; Li, C; Li, Y Y

    2015-04-01

    A beam-membrane structure micromachined flow sensor is designed, depending on the principle of differential pressure caused by the mass flow, which is directly proportional to the square flow rate. The FSI (fluid structure interaction) characteristics of the differential pressure flow sensor are investigated via numerical analysis and analog simulation. The working mechanism of the flow sensor is analyzed depending on the FSI results. Then, the flow sensor is fabricated and calibrated. The calibration results show that the beam-membrane structure differential pressure flow sensor achieves ideal static characteristics and works well in the practical applications.

  3. A beam-membrane structure micromachined differential pressure flow sensor

    SciTech Connect

    Chen, P.; Zhao, Y. L.; Tian, B. Li, C.; Li, Y. Y.

    2015-04-15

    A beam-membrane structure micromachined flow sensor is designed, depending on the principle of differential pressure caused by the mass flow, which is directly proportional to the square flow rate. The FSI (fluid structure interaction) characteristics of the differential pressure flow sensor are investigated via numerical analysis and analog simulation. The working mechanism of the flow sensor is analyzed depending on the FSI results. Then, the flow sensor is fabricated and calibrated. The calibration results show that the beam-membrane structure differential pressure flow sensor achieves ideal static characteristics and works well in the practical applications.

  4. Coherent structures in compressible free-shear-layer flows

    SciTech Connect

    Aeschliman, D.P.; Baty, R.S.; Kennedy, C.A.; Chen, J.H.

    1997-08-01

    Large scale coherent structures are intrinsic fluid mechanical characteristics of all free-shear flows, from incompressible to compressible, and laminar to fully turbulent. These quasi-periodic fluid structures, eddies of size comparable to the thickness of the shear layer, dominate the mixing process at the free-shear interface. As a result, large scale coherent structures greatly influence the operation and efficiency of many important commercial and defense technologies. Large scale coherent structures have been studied here in a research program that combines a synergistic blend of experiment, direct numerical simulation, and analysis. This report summarizes the work completed for this Sandia Laboratory-Directed Research and Development (LDRD) project.

  5. Swan falls instream flow study

    SciTech Connect

    Anglin, D.R.; Cummings, T.R.; Ecklund, A.E.

    1992-10-01

    The purpose of the Swan Falls Instream Flow Study was to define the relationship between streamflows and instream habitat for resident fish species and to assess the relative impact of several different hydrographs on resident fish habitat. Specific objectives included the following: (1) Conduct a literature search to compile life history, distribution, and habitat requirements for species of interest. Physical and hydrologic characteristics of the Snake River were also compiled. (2) Determine physical habitat versus discharge relationships and conduct habitat time series analysis for each species/lifestage using the Instream Flow Incremental Methodology (IFIM) developed by the U.S. Fish and Wildlife Service. (3) Examine the impacts on resident fish habitat of proposed hydrographs, including Swan Falls Agreement flows, relative to current conditions. (4) Characterize water quality conditions, including water temperature and dissolved oxygen, in the vicinity of the study area and determine the implications of those conditions for the resident species of interest. (5) Determine streamflows necessary to protect and maintain resident fish habitat in the study area.

  6. Studies of fluid instabilities in flows of lava and debris

    NASA Technical Reports Server (NTRS)

    Fink, Jonathan H.

    1987-01-01

    At least two instabilities have been identified and utilized in lava flow studies: surface folding and gravity instability. Both lead to the development of regularly spaced structures on the surfaces of lava flows. The geometry of surface folds have been used to estimate the rheology of lava flows on other planets. One investigation's analysis assumed that lava flows have a temperature-dependent Newtonian rheology, and that the lava's viscosity decreased exponentially inward from the upper surface. The author reviews studies by other investigators on the analysis of surface folding, the analysis of Taylor instability in lava flows, and the effect of surface folding on debris flows.

  7. Identification of Coherent Structures in Premixed Reacting Flows

    NASA Astrophysics Data System (ADS)

    Haffner, Eileen; Green, Melissa; Oran, Elaine; Syracuse University Team; University of Maryland Team

    2014-11-01

    Many studies have been conducted on the best ways to quantitatively characterize the turbulence-flame interaction in reacting flows. It has been observed that increased turbulence intensity both wrinkles and broadens the flame front throughout the preheat zone and reaction zone. A Lagrangian coherent structures analysis is used to identify the individual coherent turbulent structures as the maximizing ridges of the Finite-Time Lyapunov exponent scalar field (FTLE). This method provides different information than Eulerian criteria which have predominantly been used in previous reacting flow studies. Preliminary results show that LCS ridges exhibit a clear qualitative correlation to the contour of the fuel mass-fraction of the flame. A quantitative characterization of how the LCS results correlate to observed flame geometries will allow for a better understanding of how these structures affect the flame brush, and could lead to improved efficiency in particular engines.

  8. Fluid-Structure Interaction in Internal Physiological Flows

    NASA Astrophysics Data System (ADS)

    Heil, Matthias; Hazel, Andrew L.

    2011-01-01

    We provide a selective review of recent progress in the analysis of several physiological and physiologically inspired fluid-structure interaction problems, our aim being to explain the underlying physical mechanisms that cause the observed behaviors. Specifically, we discuss recent studies of self-excited oscillations in collapsible tubes, focusing primarily on studies of an idealized model system, the Starling resistor -- a device used in most laboratory experiments. We next review studies of a particular physiological, flow-induced oscillation: vocal-fold oscillations during phonation. Finally, we discuss the closure and reopening of pulmonary airways, physiological fluid-structure interaction problems that also involve the airways' liquid lining.

  9. Transient studies of capillary-induced flow

    NASA Technical Reports Server (NTRS)

    Reagan, M. K.; Bowman, W. J.

    1993-01-01

    This paper presents the numerical and experimental results of a study performed on the transient rise of fluid in a capillary tube. The capillary tube problem provides an excellent mechanism from which to launch an investigation into the transient flow of a fluid in a porous wick structure where capillary forces must balance both adverse gravitational effects and frictional losses. For the study, a capillary tube, initially charged with a small volume of water, was lowered into a pool of water. The behavior of the column of fluid during the transient that followed as more water entered the tube from the pool was both numerically and experimentally studied.

  10. Unsteadiness of Flow Structure on Low Swept Delta Wing

    NASA Astrophysics Data System (ADS)

    Zharfa, Mohammadreza; Ozturk, Ilhan; Yavuz, Mehmet Metin

    2013-11-01

    The flow structure of low-sweep 35 degree delta wing has been analyzed experimentally using flow visualization and flow measurement techniques. Laser illuminated smoke visualization, Laser Doppler Anemometry (LDA), and surface pressure measurements are performed to understand the steady and unsteady behavior of the flow regimes. Reynolds number varying from 10,000 to 100,000 and attack angles varying from 3 to 10 are tested. For the corresponding Reynolds Numbers and attack angles, prestall and poststall regimes are identified. The amplitude and frequency of the pressure and velocity fluctuations at different locations are compared with the regions of reattachment, vortex breakdown, and stall. Using statistics and spectral analysis, the unsteadiness of flow is studied in detail. Both the lift performance of the wing and the regions possibly exposed to surface buffeting are tried to be interpreted. Using the results of the study, an effective active flow control strategy to delay stall and to reduce surface buffeting is going to be determined next. The project was supported by the Turkish Scientific and Technological Research Council of Turkey (3501 - 111M732).

  11. Structure of turbulent flow in a slab mold

    NASA Astrophysics Data System (ADS)

    Ramírez-López, Pável; Demedices, L. G.; Dávila, O.; Sánchez-Pérez, R.; Morales, R. D.

    2005-12-01

    The structure of the turbulent flow in a slab mold is studied using a water model, various experimental techniques, and mathematical simulations. The meniscus stability depends on the turbulence structure of the flow in the mold; mathematical simulations using the k-ɛ model and the Reynolds-stress model (RSM) indicate that the latter is better at predicting the meniscus profile for a given casting speed. Reynolds stresses and flow vorticity measured through the particle-image velocimetry (PIV) technique are very close to those predicted by the RSM model, and maximum and minimum values across the jet diameter are reported. The backflow in the upper side of the submerged entry nozzle (SEN) port (for a fixed SEN design) depends on the casting speed and disappears, increasing this process parameter. At low casting speeds, the jet does not report enough dissipation of energy, so the upper flow roll is able to reach the SEN port. At high casting speeds, the jet energy is strongly dissipated inside the SEN port, the narrow wall, and in the mold corner, weakening the momentum transfer of the upper flow roll, which is unable to reach the SEN port. At low casting speeds, meniscus instability is observed very close to the SEN, while at high casting speeds, this instability is observed in the mold corner. An optimum casting speed is reported where complete meniscus stability was observed. The flow structure at the free surface indicates a composite structure of islands with large gradients of velocity at high casting speeds. These velocity gradients are responsible for the meniscus instability.

  12. A Structured-Grid Quality Measure for Simulated Hypersonic Flows

    NASA Technical Reports Server (NTRS)

    Alter, Stephen J.

    2004-01-01

    A structured-grid quality measure is proposed, combining three traditional measurements: intersection angles, stretching, and curvature. Quality assesses whether the grid generated provides the best possible tradeoffs in grid stretching and skewness that enable accurate flow predictions, whereas the grid density is assumed to be a constraint imposed by the available computational resources and the desired resolution of the flow field. The usefulness of this quality measure is assessed by comparing heat transfer predictions from grid convergence studies for grids of varying quality in the range of [0.6-0.8] on an 8'half-angle sphere-cone, at laminar, perfect gas, Mach 10 wind tunnel conditions.

  13. Turbulent kinetic energy production and flow structures in compressible homogeneous shear flow

    NASA Astrophysics Data System (ADS)

    Ma, Zongqiang; Xiao, Zuoli

    2016-09-01

    The production of turbulent kinetic energy (TKE) and flow structures in compressible homogeneous turbulent shear flow (HTSF) are investigated by using direct numerical simulation. A theoretical analysis suggests that the vertical turbulent transport process should be responsible for the production of TKE in HTSF. It is manifested based on a conditional average method that the pure TKE production becomes increasingly larger in strain regions than in vortex regions of the flow. The velocity-derivative correlation in the shear plane is employed to identify the streaky structures in HTSF, which also tend to occur predominantly in strain regions of turbulence. Localized analyses of conditional averages reveal that the streaky structures in compressible HTSF are closely related to the negative productions of TKE. A comparative study implies that flow compressibility has a considerable effect on the spatial distributions and patterns of the strain- and vortex-dominated fields, which in turn cause the discrepancies in distribution of the TKE production and streaky structures between incompressible and compressible HTSFs.

  14. Footprints of Lagrangian flow structures in Eulerian concentration distributions in periodic mixing flows

    NASA Astrophysics Data System (ADS)

    Speetjens, M. F. M.; Lauret, M.; Nijmeijer, H.; Anderson, P. D.

    2013-05-01

    Transport of passive tracers may be described through the spatio-temporal evolution of Eulerian concentration distributions or via the geometrical composition of the Lagrangian flow structure. The present study seeks to deepen insight into the connection between the Eulerian and Lagrangian perspectives by investigating the role of Lagrangian coherent structures (LCSs) in the Eulerian concentration distributions in time-periodic and spatially-periodic mixing flows. Representation of the Eulerian transport by the mapping method, describing realistic transport problems by distribution matrices, admits a generic analysis based on matrix and graph theory. This reveals that LCSs-and the transport barriers that separate them-leave a distinct “footprint” in the eigenmode spectrum of the distribution matrix and, by proxy, of the underlying Eulerian transport operator. Transport barriers impart a block-diagonal structure upon the mapping matrix, where each block matrix A corresponds with a given LCS. Its kind is reflected in the spectrum of A; higher-order periodicity yields a distinct permutation within A. The composition of the distribution matrix versus the Lagrangian flow structure thus predicted is demonstrated by way of examples. These findings increase fundamental understanding of transport phenomena and have great practical potential for e.g. flow and mixing control.

  15. Measurements of flow structure interaction in a plaqued artificial artery using an index matched flow facility

    NASA Astrophysics Data System (ADS)

    Jain, Akash; Brock, Larry; Sheng, Jian

    2015-11-01

    The aim of the experiment is to study the flow structure interaction in an arterial model with a simulated plaque inside a closed loop index matched pulsatile flow facility. The test section is 24.5 inches long 6 inches wide. The experimental models are compliant polymer (PDMS) tubes having an outer diameter of 9 mm and a wall thickness of 1 mm. The plaque on the models are simulated by means of a radially asymmetric bump. Both flow and polymeric structures are doped with different particles and imaged with Particle Image Velocimetry (PIV) method. To minimize the optical distortion near liquid solid interface, the facility is fully index matched with NaI at 40% by weight. A suite of analysis procedures quantifying complex interactions including solid-fluid phase separation, near wall flow analysis, and wall shear stress approximation as well as wall deformation quantification, have been developed and applied to study the healthy and plaqued artificial arteries in steady and pulsatile flow conditions. 3D ensemble velocity fields, wall shear stress distributions and corresponding strain deformations will be presented.

  16. Analysis and representation of complex structures in separated flows

    NASA Technical Reports Server (NTRS)

    Helman, James; Hesselink, Lambertus

    1991-01-01

    We discuss our recent work on extraction and visualization of topological information in separated fluid flow data sets. As with scene analysis, an abstract representation of a large data set can greatly facilitate the understanding of complex, high-level structures. When studying flow topology, such a representation can be produced by locating and characterizing critical points in the velocity field and generating the associated stream surfaces. In 3D flows, the surface topology serves as the starting point. The 2D tangential velocity field near the surface of the body is examined for critical points. The tangential velocity field is integrated out along the principal directions of certain classes of critical points to produce curves depicting the topology of the flow near the body. The points and curves are linked to form a skeleton representing the 2D vector field topology. This skeleton provides a basis for analyzing the 3D structures associated with the flow separation. The points along the separation curves in the skeleton are used to start tangent curve integrations. Integration origins are successively refined to produce stream surfaces. The map of the global topology is completed by generating those stream surfaces associated with 3D critical points.

  17. Dynamical structure of magnetized dissipative accretion flow around black holes

    NASA Astrophysics Data System (ADS)

    Sarkar, Biplob; Das, Santabrata

    2016-09-01

    We study the global structure of optically thin, advection dominated, magnetized accretion flow around black holes. We consider the magnetic field to be turbulent in nature and dominated by the toroidal component. With this, we obtain the complete set of accretion solutions for dissipative flows where bremsstrahlung process is regarded as the dominant cooling mechanism. We show that rotating magnetized accretion flow experiences virtual barrier around black hole due to centrifugal repulsion that can trigger the discontinuous transition of the flow variables in the form of shock waves. We examine the properties of the shock waves and find that the dynamics of the post-shock corona (PSC) is controlled by the flow parameters, namely viscosity, cooling rate and strength of the magnetic field, respectively. We separate the effective region of the parameter space for standing shock and observe that shock can form for wide range of flow parameters. We obtain the critical viscosity parameter that allows global accretion solutions including shocks. We estimate the energy dissipation at the PSC from where a part of the accreting matter can deflect as outflows and jets. We compare the maximum energy that could be extracted from the PSC and the observed radio luminosity values for several supermassive black hole sources and the observational implications of our present analysis are discussed.

  18. Vortex-dominated flow with viscous core structure

    NASA Technical Reports Server (NTRS)

    Liu, C. H.; Krause, E.; Ting, L.

    1985-01-01

    Recent theoretical studies of vortex-dominated flows are reviewed with special emphasis on those for which the viscous core structures play an important role. The problems to be described are: The interaction and merging of two-dimensional vortices and of curved vortex filaments, the roll-up and decay of trailing far wakes, and the initiation of vortex breakdown. The analysis utilizes finite-difference solutions of the Navier-Stokes equations complemented by asymptotic expansion techniques.

  19. Structure of unsteady flows at leading- and trailing-edges: Flow visualization and its interpretation

    NASA Technical Reports Server (NTRS)

    Rockwell, D.; Atta, R.; Kramer, L.; Lawson, R.; Lusseyran, D.; Magness, C.; Sohn, D.; Staubli, T.

    1987-01-01

    Unsteady two- and three-dimensional flow structure at leading and trailing edges of bodies can be characterized effectively using recently developed techniques for acquisition and interpretation of flow visualization. The techniques addressed here include: flow image/surface pressure correlations; 3-D reconstruction of flow structure from flow images; and interactive interpretation of flow images with theoretical simulations. These techniques can be employed in conjunction with: visual correlation and ensemble-averaging, both within a given image and between images; recognition of patterns from images; and estimates of velocity eigenfunctions from images.

  20. Flow visualization of turbulent boundary layer structure

    NASA Astrophysics Data System (ADS)

    Head, M. R.; Bandyopadhyay, P.

    1980-01-01

    The results from flow visualization experiments performed using an argon-ion laser to illuminate longitudinal and transverse sections of the smoke filled boundary layer in zero pressure gradient are discussed. Most of the experiments were confined to the range 600 Re sub theta 10,000. Results indicate that the boundary layer consists almost exclusively of vortex loops or hairpins, some of which may extend through the complete boundary layer thickness and all of which are inclined at a more or less constant characteristic angle of approximately 45 deg to the wall. Since the cross-stream dimensions of the hairpins appear to scale roughly with the wall variables U sub tau and nu, while their length is limited only by the boundary layer thickness, there are very large scale effects on the turbulence structure. At high Reynolds numbers (Re sub theta = 10,000) there is little evidence of large-scale coherent motions, other than a slow overturning of random agglomerations of the hairpins just mentioned.

  1. Structural evolution of Colloidal Gels under Flow

    NASA Astrophysics Data System (ADS)

    Boromand, Arman; Maia, Joao; Jamali, Safa

    Colloidal suspensions are ubiquitous in different industrial applications ranging from cosmetic and food industries to soft robotics and aerospace. Owing to the fact that mechanical properties of colloidal gels are controlled by its microstructure and network topology, we trace the particles in the networks formed under different attraction potentials and try to find a universal behavior in yielding of colloidal gels. Many authors have implemented different simulation techniques such as molecular dynamics (MD) and Brownian dynamics (BD) to capture better picture during phase separation and yielding mechanism in colloidal system with short-ranged attractive force. However, BD neglects multi-body hydrodynamic interactions (HI) which are believed to be responsible for the second yielding of colloidal gels. We envision using dissipative particle dynamics (DPD) with modified depletion potential and hydrodynamic interactions, as a coarse-grain model, can provide a robust simulation package to address the gel formation process and yielding in short ranged-attractive colloidal systems. The behavior of colloidal gels with different attraction potentials under flow is examined and structural fingerprints of yielding in these systems will be discussed.

  2. Optimal structure of tree-like branching networks for fluid flow

    NASA Astrophysics Data System (ADS)

    Kou, Jianlong; Chen, Yanyan; Zhou, Xiaoyan; Lu, Hangjun; Wu, Fengmin; Fan, Jintu

    2014-01-01

    Tree-like branching networks are very common flow or transportation systems from natural evolution. In this study, the optimal structures of tree-like branching networks for minimum flow resistance are analyzed for both laminar and turbulent flow in both smooth and rough pipes. It is found that the dimensionless effective flow resistance under the volume constraint for different flows is sensitive to the geometrical parameters of the structure. The flow resistance of the tree-like branching networks reaches a minimum when the diameter ratio β∗ satisfies β∗=Nk, where, N is the bifurcation number N=2,3,4,… and k is a constant. For laminar flow, k=-1/3, which is in agreement with the existing Murray’s law; for turbulent flow in smooth pipes, k=-3/7; for turbulent flow in rough pipes, k=-7/17. These results serve as design guidelines of efficient transport and flow systems.

  3. Characterization of large-scale structures in a forced ducted flow with dump

    NASA Astrophysics Data System (ADS)

    Schadow, K. C.; Wilson, K. J.; Gutmark, E.

    1987-09-01

    A forced, subsonic ducted airflow with a dump was studied using hot-wire anemometry. The flow was forced by exciting the duct resonant acoustics. Flow structures (vortices) with high azimuthal coherence and high spatial and temporal periodicity were generated in the shear flow at the dump when the forcing frequency matched the first subharmonic of the initial vortex shedding frequency or the preferred mode frequency. By forcing the flow at the preferred mode frequency, mixing was enhanced in the shear and pipe flow regimes. A visual description of the coherent structures was obtained in water flow tests.

  4. Feasibility study of laminar flow bodies in fully turbulent flow

    SciTech Connect

    Sarkar, T.; Sayer, P.G.; Fraser, S.M.

    1994-12-31

    One of the most important design requirements of long range autonomous underwater vehicles (AUVs) is to minimize propulsive power. An important and relatively easy way of achieving this is by careful selection of hull shape. Two main schools of thought in this respect are: if laminar flow can be maintained for a long length of the body, the effective drag can be reduced; it is not possible to maintain laminar flow for a significant length of the body and hull design should be based on turbulent flow conditions. In this paper, a feasibility study of laminar flow designs is undertaken under the assumption that flow will be turbulent over the entire length. For comparison two laminar flow designs X-35 and F-57 are selected and results are compared with those of two typical torpedo shaped bodies, namely AFTERBODY1 and AFTERBODY2 of DTNSRDC. It has been shown that laminar flow bodies have 10--15% higher drag when flow is turbulent over the entire length. Hence there is some hydrodynamic risk involved in adopting such laminar bodies without further consideration.

  5. FLOWS AND WAVES IN BRAIDED SOLAR CORONAL MAGNETIC STRUCTURES

    SciTech Connect

    Pant, V.; Datta, A.; Banerjee, D.

    2015-03-01

    We study the high frequency dynamics in the braided magnetic structure of an active region (AR 11520) moss as observed by the High-Resolution Coronal Imager (Hi-C). We detect quasi-periodic flows and waves in these structures. We search for high frequency dynamics while looking at power maps of the observed region. We find that shorter periodicities (30–60 s) are associated with small spatial scales which can be resolved by Hi-C only. We detect quasi-periodic flows with a wide range of velocities, from 13–185 km s{sup −1}, associated with braided regions. This can be interpreted as plasma outflows from reconnection sites. We also find short period and large amplitude transverse oscillations associated with the braided magnetic region. Such oscillations could be triggered by reconnection or such oscillations may trigger reconnection.

  6. Development of laminar flow control wing surface porous structure

    NASA Technical Reports Server (NTRS)

    Klotzsche, M.; Pearce, W.; Anderson, C.; Thelander, J.; Boronow, W.; Gallimore, F.; Brown, W.; Matsuo, T.; Christensen, J.; Primavera, G.

    1984-01-01

    It was concluded that the chordwise air collection method, which actually combines chordwise and spanwise air collection, is the best of the designs conceived up to this time for full chord laminar flow control (LFC). Its shallower ducting improved structural efficiency of the main wing box resulting in a reduction in wing weight, and it provided continuous support of the chordwise panel joints, better matching of suction and clearing airflow requirements, and simplified duct to suction source minifolding. Laminar flow control on both the upper and lower surfaces was previously reduced to LFC suction on the upper surface only, back to 85 percent chord. The study concludes that, in addition to reduced wing area and other practical advantages, this system would be lighter because of the increase in effective structural wing thickness.

  7. Optical Flow Structure Effects in Children’s Postural Control

    PubMed Central

    Barela, José A.

    2016-01-01

    The aim of this study was to investigate the effect of distance and optic flow structure on visual information and body sway coupling in children and young adults. Thirty children (from 4 to 12 years of age) and 10 young adults stood upright inside of a moving room oscillating at 0.2 Hz, at 0.25 and 1.5 m from the front wall, and under three optical flow conditions (global, central, and peripheral). Effect of distance and optic flow structure on the coupling of visual information and body sway is age-dependent, with 4-year-olds being more affected at 0.25 m distance than older children and adults are. No such difference was observed at 1.5 m from the front wall. Moreover, 4-year-olds’ sway was larger and displayed higher variability. These results suggest that despite being able to accommodate change resulting from varying optic flow conditions, young children have difficulty in dodging stronger visual stimuli. Lastly, difference in sway performance may be due to immature inter-modality sensory reweighting. PMID:27352305

  8. Optical Flow Structure Effects in Children's Postural Control.

    PubMed

    Godoi, Daniela; Barela, José A

    2016-01-01

    The aim of this study was to investigate the effect of distance and optic flow structure on visual information and body sway coupling in children and young adults. Thirty children (from 4 to 12 years of age) and 10 young adults stood upright inside of a moving room oscillating at 0.2 Hz, at 0.25 and 1.5 m from the front wall, and under three optical flow conditions (global, central, and peripheral). Effect of distance and optic flow structure on the coupling of visual information and body sway is age-dependent, with 4-year-olds being more affected at 0.25 m distance than older children and adults are. No such difference was observed at 1.5 m from the front wall. Moreover, 4-year-olds' sway was larger and displayed higher variability. These results suggest that despite being able to accommodate change resulting from varying optic flow conditions, young children have difficulty in dodging stronger visual stimuli. Lastly, difference in sway performance may be due to immature inter-modality sensory reweighting. PMID:27352305

  9. Embrittlement and Flow Localization in Reactor Structural Materials

    SciTech Connect

    Xianglin Wu; Xiao Pan; James Stubbins

    2006-10-06

    Many reactor components and structural members are made from metal alloys due, in large part, to their strength and ability to resist brittle fracture by plastic deformation. However, brittle fracture can occur when structural material cannot undergo extensive, or even limited, plastic deformation due to irradiation exposure. Certain irradiation conditions lead to the development of a damage microstructure where plastic flow is limited to very small volumes or regions of material, as opposed to the general plastic flow in unexposed materials. This process is referred to as flow localization or plastic instability. The true stress at the onset of necking is a constant regardless of the irradiation level. It is called 'critical stress' and this critical stress has strong temperature dependence. Interrupted tensile testes of 316L SS have been performed to investigate the microstructure evolution and competing mechanism between mechanic twinning and planar slip which are believed to be the controlling mechanism for flow localization. Deformation twinning is the major contribution of strain hardening and good ductility for low temperatures, and the activation of twinning system is determined by the critical twinning stress. Phases transform and texture analyses are also discussed in this study. Finite element analysis is carried out to complement the microstructural analysis and for the prediction of materaials performance with and without stress concentration and irradiation.

  10. Characterization of flow-induced structures in carbon nanotube suspensions

    NASA Astrophysics Data System (ADS)

    Khalkhal, Fatemeh

    Carbon nanotubes (CNTs) are fibre-like nano-particles with many different applications. Due to their high specific surface area, high electric current density, thermal stability and excellent mechanical properties, they are used to reinforce physical properties of polymer matrices. The macroscopic properties of suspensions are inherited from their properties at micron and sub-micron scales. The suspensions structure can be easily influenced by many parameters such as the extent of external shear forces, the suspension concentration, temperature, the particles specifications, etc. This makes the study of the suspension structure a very challenging task and has been the subject of interest to many researchers. In this thesis, the structure of a model carbon nanotube suspension dispersed in an epoxy is studied by employing a set of rheological methods, scaling and fractal theories and a structural thixotropic model. The effect of flow history on linear viscoelastic properties of suspensions and the evolution of structure upon cessation of shear flow has been studied over a wide range of pre-shearing rates, concentration and temperature. The results of these analyses are as follows. The effect of flow history is more pronounced on the suspensions structure in dilute and semi-dilute concentration regimes. By pre-shearing at low rates, more inter-particle entanglements were induced, which resulted in reduction of rheological percolation thresholds. After cessation of shear flow, for dilute and semi-dilute suspensions, the formed metastable structures were distinguishable by different storage moduli, which were inversely related to the rate of pre-shearing. However, for the concentrated suspensions, the formed metastable structures had an approximately equal storage modulus regardless of the rate of the applied pre-shearing. It was shown that the rate of formation of these metastable structures was enhanced by increasing concentration. Furthermore, the rate of structure

  11. Local Interfacial Structure in Downward Two-Phase Bubbly Flow

    SciTech Connect

    Hiroshi Goda; Seungjin Kim; Paranjape, Sidharth S.; Finch, Joshua P.; Mamoru Ishii; Uhle, Jennifer

    2002-07-01

    The local interfacial structure for vertical air-water co-current downward two-phase flow was investigated under adiabatic conditions. A multi-sensor conductivity probe was utilized in order to acquire the local two-phase flow parameters. The present experimental loop consisted of 25.4 mm and 50.8 mm ID round tubes as test sections. The measurement was performed at three axial locations: L/D = 13, 68 and 133 for the 25.4 mm ID loop and L/D 7, 34, 67 for the 50.8 mm ID loop, in order to study the axial development of the flow. A total of 7 and 10 local measurement points along the tube radius were chosen for the 25.4 mm ID loop and the 50.8 mm ID loop, respectively. The experimental flow conditions were determined within bubbly flow regime. The acquired local parameters included the void fraction, interfacial area concentration, bubble interface frequency, bubble Sauter mean diameter, and interfacial velocity. (authors)

  12. Vascular structure determines pulmonary blood flow distribution.

    PubMed

    Hlastala, M P; Glenny, R W

    1999-10-01

    Scientific knowledge develops through the evolution of new concepts. This process is usually driven by new methodologies that provide observations not previously available. Understanding of pulmonary blood flow determinants advanced significantly in the 1960s and is now changing rapidly again, because of increased spatial resolution of regional pulmonary blood flow measurements.

  13. Studies of two phase flow

    NASA Technical Reports Server (NTRS)

    Witte, Larry C.

    1994-01-01

    The development of instrumentation for the support of research in two-phase flow in simulated microgravity conditions was performed. The funds were expended in the development of a technique for characterizing the motion and size distribution of small liquid droplets dispersed in a flowing gas. Phenomena like this occur in both microgravity and normal earth gravity situations inside of conduits that are carrying liquid-vapor mixtures at high flow rates. Some effort to develop a conductance probe for the measurement of liquid film thickness was also expended.

  14. Proteins at flowing interfaces: From understanding structure to treating disease

    NASA Astrophysics Data System (ADS)

    Posada, David; Young, James; Hirsa, Amir

    2012-11-01

    The field of soft matter offers vast opportunities for scientific and technological developments, with many challenges that need to be addressed by various disciplines. Fluid dynamics has a tremendous potential for greater impact, from broadening fundamental understanding to treating disease. Here we demonstrate the use of fluid dynamics in two biotechnology problems involving proteins at the air/water interface: a) 2-Dimensional protein crystallization and b) amyloid fibril formation. Protein crystallization is usually the most challenging step in X-ray diffraction analysis of protein structure. Recently it was demonstrated that flow can induce 2-D protein crystallization at conditions under which quiescent systems do not form crystals. A different form of protein structuring, namely amyloid fibrillization, is also of interest due to its association with several neurodegenerative diseases such as Alzheimer's and Parkinson's disease. Protein denaturation, which is the root of the fibrillization process, is also a significant concern in biotherapeutics production. Both problems are studied by using shearing free-surface flows in simple geometries. The common finding is that flow can significantly enhance the growth of protein structures.

  15. Analysis of high speed flow, thermal and structural interactions

    NASA Technical Reports Server (NTRS)

    Thornton, Earl A.

    1994-01-01

    Research for this grant focused on the following tasks: (1) the prediction of severe, localized aerodynamic heating for complex, high speed flows; (2) finite element adaptive refinement methodology for multi-disciplinary analyses; (3) the prediction of thermoviscoplastic structural response with rate-dependent effects and large deformations; (4) thermoviscoplastic constitutive models for metals; and (5) coolant flow/structural heat transfer analyses.

  16. Origin of Permeability and Structure of Flows in Fractured Media

    NASA Astrophysics Data System (ADS)

    De Dreuzy, J.; Darcel, C.; Davy, P.; Erhel, J.; Le Goc, R.; Maillot, J.; Meheust, Y.; Pichot, G.; Poirriez, B.

    2013-12-01

    After more than three decades of research, flows in fractured media have been shown to result from multi-scale geological structures. Flows result non-exclusively from the damage zone of the large faults, from the percolation within denser networks of smaller fractures, from the aperture heterogeneity within the fracture planes and from some remaining permeability within the matrix. While the effect of each of these causes has been studied independently, global assessments of the main determinisms is still needed. We propose a general approach to determine the geological structures responsible for flows, their permeability and their organization based on field data and numerical modeling [de Dreuzy et al., 2012b]. Multi-scale synthetic networks are reconstructed from field data and simplified mechanical modeling [Davy et al., 2010]. High-performance numerical methods are developed to comply with the specificities of the geometry and physical properties of the fractured media [Pichot et al., 2010; Pichot et al., 2012]. And, based on a large Monte-Carlo sampling, we determine the key determinisms of fractured permeability and flows (Figure). We illustrate our approach on the respective influence of fracture apertures and fracture correlation patterns at large scale. We show the potential role of fracture intersections, so far overlooked between the fracture and the network scales. We also demonstrate how fracture correlations reduce the bulk fracture permeability. Using this analysis, we highlight the need for more specific in-situ characterization of fracture flow structures. Fracture modeling and characterization are necessary to meet the new requirements of a growing number of applications where fractures appear both as potential advantages to enhance permeability and drawbacks for safety, e.g. in energy storage, stimulated geothermal energy and non-conventional gas productions. References Davy, P., et al. (2010), A likely universal model of fracture scaling and

  17. Structure of leading-edge vortex flows including vortex breakdown

    SciTech Connect

    Payne, F.M.

    1987-01-01

    An experimental investigation of the structure of leading-edge vortex flows on thin sharp-edged delta wings was carried out at low Reynolds numbers. Flow-visualization techniques were used to study the topology of the vortex and the phenomenon of vortex breakdown. Seven-hole probe-wake surveys and laser-doppler-anemometer measurements were obtained and compared. Delta wings with sweep angles of 70, 75, 80, and 85/sup 0/ were tested at angles of attack of 10, 20, 30, and 40/sup 0/. The test were conducted in a Reynolds number range of 8.5 x 10/sup 4/ to 6.4 x 10/sup 5/. Smoke-flow visualization revealed the presence of small Kelvin-Helmholtz type vortical structures in the shear layer of a leading-edge vortex. These shear-layer vortices follow a helical path and grow in the streamwise direction as they wind into the vortex core where the individual shear layers merge. The phenomenon of vortex breakdown was studied using high-speed cinema photography. The bubble and spiral types of breakdown were observed and appear to represent the extremes in a continuum of breakdown forms.

  18. Method for controlling coolant flow in airfoil, flow control structure and airfoil incorporating the same

    SciTech Connect

    Itzel, Gary Michael; Devine, II, Robert Henry; Chopra, Sanjay; Toornman, Thomas Nelson

    2003-07-08

    A coolant flow control structure is provided to channel cooling media flow to the fillet region defined at the transition between the wall of a nozzle vane and a wall of a nozzle segment, for cooling the fillet region. In an exemplary embodiment, the flow control structure defines a gap with the fillet region to achieve the required heat transfer coefficients in this region to meet part life requirements.

  19. Hybrid laminar flow control study

    NASA Technical Reports Server (NTRS)

    1982-01-01

    Hybrid laminar flow control (HLFC) in which leading edge suction is used in conjunction with wing pressure distribution tailoring to postpone boundary layer transition and reduce friction drag was examined. Airfoil design characteristics required for laminar flow control (LFC) were determined. The aerodynamic design of the HLFC wing for a 178 passenger commercial turbofan transport was developed, and a drag was estimated. Systems changes required to install HLFC were defined, and weights and fuel economy were estimated. The potential for 9% fuel reduction for a 3926-km (2120-nmi) mission is identified.

  20. Large eddy simulation study of spanwise spacing effects on secondary flows in turbulent channel flow

    NASA Astrophysics Data System (ADS)

    Aliakbarimiyanmahaleh, Mohammad; Anderson, William

    2015-11-01

    The structure of turbulent flow over a complex topography composed of streamwise-aligned rows of cones with varying spanwise spacing, s is studied with large-eddy simulation (LES). Similar to the experimental study of Vanderwel and Ganapathisubramani, 2015: J. Fluid Mech., we investigate the relationship between secondary flow and s, for 0 . 25 <= s / δ <= 5 . For cases with s / δ > 2 , domain-scale rollers freely exist. These had previously been called ``turbulent secondary flows'' (Willingham et al., 2014: Phys. Fluids; Barros and Christensen, 2014: J. Fluid Mech.; Anderson et al., 2015: J. Fluid Mech.), but closer inspection of the statistics indicates these are a turbulent tertiary flow: they only remain ``anchored'' to the conical roughness elements for s / δ > 2 . For s / δ < 2 , turbulent tertiary flows are prevented from occupying the domain by virtue of proximity to adjacent, counter-rotating tertiary flows. Turbulent secondary flows are associated with the conical roughness elements. These turbulent secondary flows emanate from individual conical topographic elements and set the roughness sublayer depth. The turbulent secondary flows remain intact for large and small spacing. For s / δ < 1 , a mean tertiary flow is not present. This work was supported by the Air Force Office of Sci. Research, Young Inv. Program (PM: Dr. R. Ponnoppan and Ms. E. Montomery) under Grant # FA9550-14-1-0394. Computational resources were provided by the Texas Adv. Comp. Center at the Univ. of Texas.

  1. Recent Advances in Hot Flow Anomaly Studies

    NASA Astrophysics Data System (ADS)

    Zhang, H.

    2015-12-01

    Hot flow anomalies (HFAs) are events observed near planetary bow shocks that are characterized by greatly heated solar wind plasmas and substantial flow deflection. HFAs are universal phenomena that have been observed near the bow shock of Earth, Venus, Mars, and Saturn. HFAs are not stable structures and they evolve with time. Statistical study shows that both ion and electron spectra can be used to classify young and mature HFAs. HFAs were also classified into four categories ("-+", "+-", "M", and "W") according their dynamic pressure profile. Most "W" type HFAs are mature HFAs (according to ion spectra) and most "-+" and "+-" type HFAs are young HFAs. Half of the "M" type HFAs are mature HFAs. Superposed epoch analysis result shows that variations of plasma parameters and magnetic field of mature HFAs are more dramatic than those of young HFAs, except for temperature. "M" and "W" type HFAs may be the later evolution stages of "-+" and "+-" type HFAs; on the other hand, four categories of HFAs may be due to the fact that the spacecraft crossed an HFA structure along different paths.

  2. Mean flow and Reynolds stress structure over aeolian ripples

    NASA Astrophysics Data System (ADS)

    Li, Bailiang; McKenna Neuman, Cheryl; Bédard, Otto; O'Brien, Patrick

    2015-04-01

    Mean flow and turbulence structure on transverse ripples have been well documented in hydrodynamic literature. However, very few studies have described the flow characteristics over aeolian ripples. This study adopted laser Doppler anemometry (LDA) to measure the wind field above granular ripples with different bimodal particle size distributions in a wind tunnel. Multiple runs were conducted to examine the vertical profiles of time-averaged horizontal and vertical velocities and Reynolds stress above four different locations: crest, lee slope, trough, and stoss slope. The rippled sand bed has a fine beige fraction with grain size smaller than 0.542 mm concentrated in the troughs and a coarse fraction dyed in red with grain size greater than 0.542 mm concentrated in the crests. The magnitude of the ripples at equilibrium is controlled by both wind velocity and the ratio of beige sand to red sand. Freestream velocity has a range between 8-11 m/s (above the saltation threshold of beige sand and below the threshold of red sand) and the percentage coarse by mass varies from 5.2% to 27.5% with median grain size from 0.289 mm to 0.399 mm. Experimental results indicate that the ripples have the wave length ranged between 20 mm and 140 mm with a characteristic ripple index (wave length/wave height) of 15. Flow streamlines are generally parallel to the bed surface, which is inconsistent with previous hydrodynamic observations that a return flow is usually found at the lee side of the ripples. Reynolds stress has demonstrated a strong spatial differentiation near the sand surface: greatest at crests and smallest at the troughs, however, this difference diminishes with elevation. This is an exploratory study on the turbulence characteristics of air flow above aeolian ripples, and we believe the finding of this research will enhance the understanding the interaction mechanisms between the air and bed morphology.

  3. Mixing layers and coherent structures in vegetated aquatic flows

    NASA Astrophysics Data System (ADS)

    Ghisalberti, Marco; Nepf, Heidi M.

    2002-02-01

    To date, flow through submerged aquatic vegetation has largely been viewed as perturbed boundary layer flow, with vegetative drag treated as an extension of bed drag. However, recent studies of terrestrial canopies demonstrate that the flow structure within and just above an unconfined canopy more strongly resembles a mixing layer than a boundary layer. This paper presents laboratory measurements, obtained from a scaled seagrass model, that demonstrate the applicability of the mixing layer analogy to aquatic systems. Specifically, all vertical profiles of mean velocity contained an inflection point, which makes the flow susceptible to Kelvin-Helmholtz instability. This instability leads to the generation of large, coherent vortices within the mixing layer (observed in the model at frequencies between 0.01 and 0.11 Hz), which dominate the vertical transport of momentum through the layer. The downstream advection of these vortices is shown to cause the progressive, coherent waving of aquatic vegetation, known as the monami. When the monami is present, the turbulent vertical transport of momentum is enhanced, with turbulent stresses penetrating an additional 30% of the plant height into the canopy.

  4. Flow structure of knuckling effect in footballs

    NASA Astrophysics Data System (ADS)

    Asai, Takeshi; Kamemoto, Kyoji

    2011-07-01

    The flight trajectory of a non-spinning or slow-spinning soccer ball might fluctuate in unpredictable ways, as for example, in the many free kicks of C. Ronaldo. Such anomalous horizontal shaking or rapid falling is termed the ‘knuckling effect’. However, the aerodynamic properties and boundary-layer dynamics affecting a ball during the knuckling effect are not well understood. In this study, we analyse the characteristics of the vortex structure of a soccer ball subject to the knuckling effect (knuckleball), using high-speed video images and smoke-generating agents. Two high-speed video cameras were set at one side and in front of the ball trajectory between the ball position and the goal; further, photographs were taken at 1000 fps and a resolution of 1024×512 pixels. Although in a previous study (Taneda, 1978), shedding of horseshoe vortices was observed for smooth spheres in the Reynolds number (Re) range of 3.8×105structure, which consisted of distorted loop vortices, appeared in the wake behind the ball in the supercritical Re number region. Moreover, after the knuckleballs were airborne, large-scale undulations were observed in the vortex trail visualised with a smoke technique. On the other hand, aerodynamic forces acting on the ball were estimated from the data of the ball’s flight trajectory, and a statistically high correlation (r=0.94, p<0.01) between the fluctuation frequency of the lift and side forces and the undulation frequency of the vortex trail was shown to exist. This fact suggests that the phenomenon of large-scale undulations of the vortex trail is closely related to the cause of the unsteady aerodynamic forces acting on the knuckle ball.

  5. Coherent structures - Reality and myth. [in turbulent shear flow

    NASA Technical Reports Server (NTRS)

    Hussain, A. K. M. F.

    1983-01-01

    Large-scale coherent structures (CS) in turbulent shear flows are characterized, reviewing recent theoretical and experimental investigations. The use of computers as a research tool and the flow-visualization experimental technique are introduced, CS are defined, the history of their discovery is traced, and their main characteristics are listed. Topics discussed and illustrated include the initial condition of the free shear layer, triple and double decomposition, topological features of CS, detection and eduction of CS, phase alignment via cross correlation, induced versus natural structures, the bursting phenomenon, turbulent spot, streaks, bursting frequency, the axisymmetric mixing layer, vortex pairing in an axisymmetric jet, CS and jet noise, broadband noise amplification via pure-tone excitation, CS interaction in a plane-jet near field, the Taylor hypothesis applied to CS, negative production, and the validity of the Reynolds-number similarity hypothesis. It is found that the coherent Reynolds stress, vorticity, and production are not much greater than the time-averaged values for fully developed flows with significant incoherent turbulence, suggesting that the importance of CS may have been exaggerated in some recent studies.

  6. Correlating Lagrangian structures with forcing in two-dimensional flow

    NASA Astrophysics Data System (ADS)

    Ouellette, Nicholas T.; Hogg, Charlie A. R.; Liao, Yang

    2016-01-01

    Lagrangian coherent structures (LCSs) are the dominant transport barriers in unsteady, aperiodic flows, and their role in organizing mixing and transport has been well documented. However, nearly all that is known about LCSs has been gleaned from passive observations: they are computed in a post-processing step after a flow has been observed and used to understand why the mixing and transport proceeded as it did. In many applications, the ability instead to control the presence or location of LCSs via imposed forcing would be valuable. With this goal in mind, we study the relationship between LCSs and external forcing in an experimental quasi-two-dimensional weakly turbulent flow. We find that the likelihood of finding a repelling LCS at a given location is positively correlated with the mean strain rate injected at that point and negatively correlated with the mean speed, and that it is not correlated with the vorticity. We also find that mean time between successive LCSs appearing at a fixed location is related to the structure of the forcing field. Finally, we demonstrate a surprising difference in our results between LCSs computed forward and backward in time, with forward-time (repelling) LCSs showing much more correlation with the forcing than backwards-time (attracting) LCSs.

  7. Turbulent rotating plane Couette flow: Reynolds and rotation number dependency of flow structure and momentum transport

    NASA Astrophysics Data System (ADS)

    Kawata, Takuya; Alfredsson, P. Henrik

    2016-07-01

    Plane Couette flow under spanwise, anticyclonic system rotation [rotating plane Couette flow (RPCF)] is studied experimentally using stereoscopic particle image velocimetry for different Reynolds and rotation numbers in the fully turbulent regime. Similar to the laminar regime, the turbulent flow in RPCF is characterized by roll cells, however both instantaneous snapshots of the velocity field and space correlations show that the roll cell structure varies with the rotation number. All three velocity components are measured and both the mean flow and all four nonzero Reynolds stresses are obtained across the central parts of the channel. This also allows us to determine the wall shear stress from the viscous stress and the Reynolds stress in the center of the channel, and for low rotation rates the wall shear stress increases with increasing rotation rate as expected. The results show that zero absolute vorticity is established in the central parts of the channel of turbulent RPCF for high enough rotation rates, but also that the mean velocity profile for certain parameter ranges shows an S shape giving rise to a negative velocity gradient in the center of the channel. We find that from an analysis of the Reynolds stress transport equation using the present data there is a transport of the Reynolds shear stress towards the center of the channel, which may then result in a negative mean velocity gradient there.

  8. Flow structure and mixing in obstructed and confined jets

    NASA Astrophysics Data System (ADS)

    Bryce, S. G.; Fryer-Taylor, R. E. J.

    A comprehensive series of smoke flow visualization and laser induced fluorescence experiments was performed in a study of the dispersion processes of obstructed and confined incompressible gas jets. It was found that large-scale vortical structures dominated the entrainment of ambient air into a free jet. The presence of obstacles within the flowfield generated additional vorticity which locally enhanced the concentration decay within the release. However, the creation of recirculatory regions in the wake of certain obstacles reduced enntrainment into these areas. For hazardous releases, this could give rise to a steady flammable or toxic mixture within the wake.

  9. Solitary waves on inclined films: Flow structure and binary interactions

    NASA Astrophysics Data System (ADS)

    Malamataris, N. A.; Vlachogiannis, M.; Bontozoglou, V.

    2002-03-01

    The downstream evolution of disturbances, introduced at the inlet of a liquid film flowing along an inclined plane wall, is studied numerically by solving the full, time-dependent Navier-Stokes equation. Computational results are validated against the predictions of spatial linear stability analysis and against detailed data of the entire evolution process. The structure of the flow field below the waves is analyzed, and the results are used to test assumptions frequently invoked in the theoretical study of film flow by long-wave equations. An interesting prediction is that solitary waves exhibit strongly nonparabolic velocity profiles in front of the main hump, including a slim region of backflow. The computational scheme is subsequently used to study solitary wave interactions. It is predicted that coalescence (the inelastic collision of two humps) is not inevitable but occurs only when the waves differ appreciably in height. Waves of similar size repel monotonically, whereas for intermediate differences in height a strong oscillatory interaction between the two humps is predicted. Encouraging qualitative agreement with the limited experimental information available is noted.

  10. Large scale structures in transitional pipe flow

    NASA Astrophysics Data System (ADS)

    Hellström, Leo; Ganapathisubramani, Bharathram; Smits, Alexander

    2015-11-01

    We present a dual-plane snapshot POD analysis of transitional pipe flow at a Reynolds number of 3440, based on the pipe diameter. The time-resolved high-speed PIV data were simultaneously acquired in two planes, a cross-stream plane (2D-3C) and a streamwise plane (2D-2C) on the pipe centerline. The two light sheets were orthogonally polarized, allowing particles situated in each plane to be viewed independently. In the snapshot POD analysis, the modal energy is based on the cross-stream plane, while the POD modes are calculated using the dual-plane data. We present results on the emergence and decay of the energetic large scale motions during transition to turbulence, and compare these motions to those observed in fully developed turbulent flow. Supported under ONR Grant N00014-13-1-0174 and ERC Grant No. 277472.

  11. Structural support bracket for gas flow path

    DOEpatents

    None

    2016-08-02

    A structural support system is provided in a can annular gas turbine engine having an arrangement including a plurality of integrated exit pieces (IEPs) forming an annular chamber for delivering gases from a plurality of combustors to a first row of turbine blades. A bracket structure is connected between an IEP and an inner support structure on the engine. The bracket structure includes an axial bracket member attached to an IEP and extending axially in a forward direction. A transverse bracket member has an end attached to the inner support structure and extends circumferentially to a connection with a forward end of the axial bracket member. The transverse bracket member provides a fixed radial position for the forward end of the axial bracket member and is flexible in the axial direction to permit axial movement of the axial bracket member.

  12. Online recognition of the multiphase flow regime and study of slug flow in pipeline

    NASA Astrophysics Data System (ADS)

    Liejin, Guo; Bofeng, Bai; Liang, Zhao; Xin, Wang; Hanyang, Gu

    2009-02-01

    Multiphase flow is the phenomenon existing widely in nature, daily life, as well as petroleum and chemical engineering industrial fields. The interface structure among multiphase and their movement are complicated, which distribute random and heterogeneously in the spatial and temporal scales and have multivalue of the flow structure and state[1]. Flow regime is defined as the macro feature about the multiphase interface structure and its distribution, which is an important feature to describe multiphase flow. The energy and mass transport mechanism differ much for each flow regimes. It is necessary to solve the flow regime recognition to get a clear understanding of the physical phenomena and their mechanism of multiphase flow. And the flow regime is one of the main factors affecting the online measurement accuracy of phase fraction, flow rate and other phase parameters. Therefore, it is of great scientific and technological importance to develop new principles and methods of multiphase flow regime online recognition, and of great industrial background. In this paper, the key reasons that the present method cannot be used to solve the industrial multiphase flow pattern recognition are clarified firstly. Then the prerequisite to realize the online recognition of multiphase flow regime is analyzed, and the recognition rules for partial flow pattern are obtained based on the massive experimental data. The standard templates for every flow regime feature are calculated with self-organization cluster algorithm. The multi-sensor data fusion method is proposed to realize the online recognition of multiphase flow regime with the pressure and differential pressure signals, which overcomes the severe influence of fluid flow velocity and the oil fraction on the recognition. The online recognition method is tested in the practice, which has less than 10 percent measurement error. The method takes advantages of high confidence, good fault tolerance and less requirement of

  13. Investigating Flow-Structure Interactions in Cerebral Aneurysms

    SciTech Connect

    2014-10-13

    Visualization of blood flow in a cerebral aneurysm. Streamlines (colored by fluid velocity magnitude) reveal the complexity of the flow, isocontours of vorticity show blood vortex structures (colored by pressure), and the flexible arterial wall is colored by the stress magnitude, where regions in red indicate areas of high stress.

  14. Velocity dependence of biphasic flow structuration: steady-state and oscillating flow effects

    NASA Astrophysics Data System (ADS)

    Tore Tallakstad, Ken; Jankov, Mihailo; Løvoll, Grunde; Toussaint, Renaud; Jørgen Mâløy, Knut; Grude Flekkøy, Eirik; Schmittbuhl, Jean; Schäfer, Gerhard; Méheust, Yves; Arendt Knudsen, Henning

    2010-05-01

    We study various types of biphasic flows in quasi-two-dimensional transparent porous models. These flows imply a viscous wetting fluid, and a lowly viscous one. The models are transparent, allowing the displacement process and structure to be monitored in space and time. Three different aspects will be presented: 1. In stationary biphasic flows, we study the relationship between the macroscopic pressure drop (related to relative permeability) and the average flow rate, and how this arises from the cluster size distribution of the lowly viscous fluid [1]. 2. In drainage situations, we study how the geometry of the invader can be explained, and how it gives rise to apparent dynamic capillary effects. We show how these can be explained by viscous effects on evolving geometries of invading fluid [2]. 3. We study the impact of oscillating pressure fields superimposed to a background flow over the flow regimes patterns [3]. Steady-State Two-Phase Flow in Porous Media: Statistics and Transport Properties. First, in stationary flow with a control of the flux of both fluids, we show how the pressure drop depends on the flow rate. We will show that the dynamics is dominated by the interplay between a viscous pressure field from the wetting fluid and bubble transport of a less viscous, nonwetting phase. In contrast with more studied displacement front systems, steady-state flow is in equilibrium, statistically speaking. The corresponding theoretical simplicity allows us to explain a data collapse in the cluster size distribution of lowly viscous fluid in the system, as well as the relation |?P|∞√Ca--. This allows to explain so called relative permeability effects by the morphological changes of the cluster size distribution. Influence of viscous fingering on dynamic saturation-pressure curves in porous media. Next, we study drainage in such models, and investigate the relationship between the pressure field and the morphology of the invading fluid. This allows to model

  15. 8. Inverted siphon structure carrying ditch flow under Willow Creek, ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    8. Inverted siphon structure carrying ditch flow under Willow Creek, looking southwest - Natomas Ditch System, Blue Ravine Segment, Juncture of Blue Ravine & Green Valley Roads, Folsom, Sacramento County, CA

  16. 7. Inverted siphon structure carrying ditch flow under Willow Creek, ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    7. Inverted siphon structure carrying ditch flow under Willow Creek, looking east - Natomas Ditch System, Blue Ravine Segment, Juncture of Blue Ravine & Green Valley Roads, Folsom, Sacramento County, CA

  17. Massively Parallel Combined Monte Carlo and Molecular Dynamics Methods to Study the Long-Time-Scale Evolution of Particulate Matter and Molecular Structures Under Reactive Flow Conditions

    SciTech Connect

    Kubota, A; Mundy, C J; Pitz, W J; Melius, C; Westbrook, C K; Caturla, M

    2003-12-19

    An important challenge in computational modeling is the development of new computational methods and capabilities for studying molecular-scale structures over very large time-scales. In particular, there is great interest in understanding the nucleation and growth of carbon soot particles as well as their fate in the atmosphere. We have recently developed and implemented a new computational tool to time-integrate the detailed structure of atomistically resolved surfaces and nanostructures driven by chemical and physical kinetic rule-based rate expressions. Fundamental chemical and physical processes such as chemical reactions, surface adsorption and surface diffusion are performed using a non-lattice real-space kinetic Monte Carlo scheme and driven by user-defined rule-based kinetic rate expressions, while atomic structure relaxation is approached using molecular dynamics. We demonstrate the sensitivity of particle evolution to chemical and physical kinetic mechanism using a parallel implementation of the combined Monte Carlo and molecular dynamics code.

  18. Flow Structure on a Rotating Wing: Effect of Rossby Number

    NASA Astrophysics Data System (ADS)

    Wolfinger, Maxwell; Rockwell, Donald

    2013-11-01

    The flow structure on a rotating wing is determined via stereoscopic particle image velocimetry. Sectional and three-dimensional, volumetric reconstructions define the flow patterns as a function of Rossby number Ro. An aspect ratio AR = 1 rectangular, flat plate is rotated at a geometric angle of attack α = 45°. The flow structure is determined at various angles of rotation, in order to characterize both the initial development and the fully evolved state of the flow structure. The Rossby number Ro =rg / C is varied via alteration of the radius of gyration rg of the wing, to give values from Ro = 1.2 to Ro = 5.1. Large changes of the flow structure are represented by images of of spanwise vorticity, Q-criterion; spanwise velocity; and downwash velocity. At the lowest Rossby number Ro = 1.2, a vortex is attached to the leading edge of the wing; it is present along most of the span. At higher Rossby numbers Ro = 2.1 and Ro = 5.1, this leading-edge vortex becomes less organized and deflects away from the surface of the wing. At a Rossby number Ro = 5.1 the structure of the flow in the vicinity of the leading edge resembles a separated shear layer. The nature of other elements of the three-dimensional flow, such as the root and tip vortices and the downwash velocity, are closely related to the degree of coherence of the leading-edge vortex.

  19. Effects of seagrass structure on a wave dominated flow

    NASA Astrophysics Data System (ADS)

    Pujol, D.; Serra, T.; Colomer, J.; Casamitjana, X.

    2012-04-01

    Shallow coastal areas are characterized by the presence of seagrass which occupy ~ 10% of the zone. In natural systems flows are a combination of steady, oscillatory and turbulent flows. Turbulence significantly affects the bottom boundary, therefore the interaction between turbulence and plant canopies is particularly important. In an effort to understand the dynamics of these complex flows we isolated each physical process in a laboratory study. We studied the progressive waves generated by a wavemaker situated at the beginning of the tank impinging on a simulated seagrass meadow. Our experiment is aimed at studying the relationship between flow structure and canopies in terms of a wide variety of parameters. We quantified the vertical distribution of mean current (uc), oscillatory velocity (uw), turbulent kinetic energy (TKE) and shear stress () above and within different types of vegetation, measured by an Acoustic Doppler Velocimeter (Sontek Instruments). Different experimental conditions were considered: two vegetation models (rigid and flexible), vegetation heights (14 and 30 cm, corresponding to submerged and emergent vegetation), plants densities (SPF = 1, 5, 10%) and three oscillatory frequencies (f = 0.8, 1 and 1.4Hz). Our observations suggest that the presence of submerged vegetation alter the flow structure within and above the canopy when the ratio of orbital excursion above the canopy to stem center-center spacing is higher than 1, corresponding to SPF = 5 and 10%. Above the vegetation, the mean current is always higher than without vegetation, whereas within the canopy the mean current is damped by submerged vegetation. The TKE decreases with depth and above the canopy it is higher with vegetation until 2 cm below the top of the canopy, compared to what it is found without vegetation. The presence of vegetation produces a peak of shear stress at the top of the canopy. High levels of shear stress together with fast mean current near the top of the

  20. Investigation on the near-wake flow structures of a utility-scale wind turbine using snowflake based flow visualization

    NASA Astrophysics Data System (ADS)

    Dasari, Teja; Toloui, Mostafa; Guala, Michele; Hong, Jiarong

    2015-11-01

    Super-large-scale particle image velocimetry and flow visualization techniques using natural snow particles have been shown as an effective tool to probe the structure of the flow around full-scale wind turbines (Hong et al. Nature Comm. 2014). Here we present a follow-up study based on the data collected during a deployment around the 2.5 MW wind turbine at EOLOS Wind Energy Research Station on April, 4th, 2014. The dataset includes the snow visualization of flow fields from different perspectives in the near wake of the turbine. The motions of the dominant coherent structures including tip, blade root, hub and tower vortices, represented by the snow voids, are examined with the objective of quantifying and correlating their behavior with the meteorological and turbine operating conditions. Some preliminary studies on flow-structure interaction are also performed by correlating the data from strain gauges, accelerometers mounted on the turbine blades, with the flow measurements. The statistical analysis of the motions of blade induced vortices shows a clear impact of atmospheric turbulence and vortex interaction on flow development in the near wake. The result further indicates a strong connection between near-wake vorticity field, turbine operation and structure deformations. The work was supported by National Science Foundation (NSF-CBET-1454259) and the research infrastructure was supported by Department of Energy.

  1. Slat Cove Unsteadiness Effect of 3D Flow Structures

    NASA Technical Reports Server (NTRS)

    Choudhari, Meelan M.; Khorrami, Mehdi R.

    2006-01-01

    Previous studies have indicated that 2D, time accurate computations based on a pseudo-laminar zonal model of the slat cove region (within the framework of the Reynolds-Averaged Navier-Stokes equations) are inadequate for predicting the full unsteady dynamics of the slat cove flow field. Even though such computations could capture the large-scale, unsteady vorticity structures in the slat cove region without requiring any external forcing, the simulated vortices were excessively strong and the recirculation zone was unduly energetic in comparison with the PIV measurements for a generic high-lift configuration. To resolve this discrepancy and to help enable physics based predictions of slat aeroacoustics, the present paper is focused on 3D simulations of the slat cove flow over a computational domain of limited spanwise extent. Maintaining the pseudo-laminar approach, current results indicate that accounting for the three-dimensionality of flow fluctuations leads to considerable improvement in the accuracy of the unsteady, nearfield solution. Analysis of simulation data points to the likely significance of turbulent fluctuations near the reattachment region toward the generation of broadband slat noise. The computed acoustic characteristics (in terms of the frequency spectrum and spatial distribution) within short distances from the slat resemble the previously reported, subscale measurements of slat noise.

  2. Flow structures and sandbar dynamics in a canyon river during a controlled flood, Colorado River, Arizona

    USGS Publications Warehouse

    Wright, S.A.; Kaplinski, M.

    2011-01-01

    In canyon rivers, debris fan constrictions create rapids and downstream pools characterized by secondary flow structures that are closely linked to channel morphology. In this paper we describe detailed measurements of the three-dimensional flow structure and sandbar dynamics of two pools along the Colorado River in the Grand Canyon during a controlled flood release from Glen Canyon Dam. Results indicate that the pools are characterized by large lateral recirculation zones (eddies) resulting from flow separation downstream from the channel constrictions, as well as helical flow structures in the main channel and eddy. The lateral recirculation zones are low-velocity areas conducive to fine sediment deposition, particularly in the vicinity of the separation and reattachment points and are thus the dominant flow structures controlling sandbar dynamics. The helical flow structures also affect morphology but appear secondary in importance to the lateral eddies. During the controlled flood, sandbars in the separation and reattachment zones at both sites tended to build gradually during the rising limb and peak flow. Deposition in shallow water on the sandbars was accompanied by erosion in deeper water along the sandbar slope at the interface with the main channel. Erosion occurred via rapid mass failures as well as by gradual boundary shear stress driven processes. The flow structures and morphologic links at our study sites are similar to those identified in other river environments, in particular sharply curved meanders and channel confluences where the coexistence of lateral recirculation and helical flows has been documented. Copyright 2011 by the American Geophysical Union.

  3. Flow structures and sandbar dynamics in a canyon river during a controlled flood, Colorado River, Arizona

    NASA Astrophysics Data System (ADS)

    Wright, Scott A.; Kaplinski, Matt

    2011-03-01

    In canyon rivers, debris fan constrictions create rapids and downstream pools characterized by secondary flow structures that are closely linked to channel morphology. In this paper we describe detailed measurements of the three-dimensional flow structure and sandbar dynamics of two pools along the Colorado River in the Grand Canyon during a controlled flood release from Glen Canyon Dam. Results indicate that the pools are characterized by large lateral recirculation zones (eddies) resulting from flow separation downstream from the channel constrictions, as well as helical flow structures in the main channel and eddy. The lateral recirculation zones are low-velocity areas conducive to fine sediment deposition, particularly in the vicinity of the separation and reattachment points and are thus the dominant flow structures controlling sandbar dynamics. The helical flow structures also affect morphology but appear secondary in importance to the lateral eddies. During the controlled flood, sandbars in the separation and reattachment zones at both sites tended to build gradually during the rising limb and peak flow. Deposition in shallow water on the sandbars was accompanied by erosion in deeper water along the sandbar slope at the interface with the main channel. Erosion occurred via rapid mass failures as well as by gradual boundary shear stress driven processes. The flow structures and morphologic links at our study sites are similar to those identified in other river environments, in particular sharply curved meanders and channel confluences where the coexistence of lateral recirculation and helical flows has been documented.

  4. Deterministic modelling of the cumulative impacts of underground structures on urban groundwater flow and the definition of a potential state of urban groundwater flow: example of Lyon, France

    NASA Astrophysics Data System (ADS)

    Attard, Guillaume; Rossier, Yvan; Winiarski, Thierry; Cuvillier, Loann; Eisenlohr, Laurent

    2016-08-01

    Underground structures have been shown to have a great influence on subsoil resources in urban aquifers. A methodology to assess the actual and the potential state of the groundwater flow in an urban area is proposed. The study develops a three-dimensional modeling approach to understand the cumulative impacts of underground infrastructures on urban groundwater flow, using a case in the city of Lyon (France). All known underground structures were integrated in the numerical model. Several simulations were run: the actual state of groundwater flow, the potential state of groundwater flow (without underground structures), an intermediate state (without impervious structures), and a transient simulation of the actual state of groundwater flow. The results show that underground structures fragment groundwater flow systems leading to a modification of the aquifer regime. For the case studied, the flow systems are shown to be stable over time with a transient simulation. Structures with drainage systems are shown to have a major impact on flow systems. The barrier effect of impervious structures was negligible because of the small hydraulic gradient of the area. The study demonstrates that the definition of a potential urban groundwater flow and the depiction of urban flow systems, which involves understanding the impact of underground structures, are important issues with respect to urban underground planning.

  5. SAXS/WAXS studies of flow-induced crystallization of poly(1-butene) in shear flow

    NASA Astrophysics Data System (ADS)

    Luo, Binbin; Burghardt, Wesley

    2013-03-01

    Flow-induced crystallization of poly(1-butene) was studied in shear flow. Flow was produced using a Linkam shear cell that has been modified to allow x-ray access for in situ studies of polymer structure using synchrotron x-ray scattering techniques. After loading in the the shear cell, samples were first heated well into the melt, and then cooled to a crystallization temperature selected such that negligible quiescent crystallization would occur on reasonable time scales. A short burst of shear flow was then applied at various rates, after which simultaneous wide- and small-angle x-ray scattering (SAXS and WAXS) data were collected to study the resulting accelerated crystallization kinetics, as well as the morphology of the resulting crystallites (e.g. degree of crystallite orientation). The impact of both deformation rate and total applied strain on the crystallization process were examined.

  6. Study of the velocity gradient tensor in turbulent flow

    NASA Technical Reports Server (NTRS)

    Cheng, Wei-Ping; Cantwell, Brian

    1996-01-01

    The behavior of the velocity gradient tensor, A(ij)=delta u(i)/delta x(j), was studied using three turbulent flows obtained from direct numerical simulation The flows studies were: an inviscid calculation of the interaction between two vortex tubes, a homogeneous isotropic flow, and a temporally evolving planar wake. Self-similar behavior for each flow was obtained when A(ij) was normalized with the mean strain rate. The case of the interaction between two vortex tubes revealed a finite sized coherent structure with topological characteristics predictable by a restricted Euler model. This structure was found to evolve with the peak vorticity as the flow approached singularity. Invariants of A(ij) within this structure followed a straight line relationship of the form: gamma(sup 3)+gammaQ+R=0, where Q and R are the second and third invariants of A(ij), and the eigenvalue gamma is nearly constant over the volume of this structure. Data within this structure have local strain topology of unstable-node/saddle/saddle. The characteristics of the velocity gradient tensor and the anisotropic part of a related acceleration gradient tensor H(ij) were also studied for a homogeneous isotropic flow and a temporally evolving planar wake. It was found that the intermediate principal eigenvalue of the rate-of-strain tensor of H(ij) tended to be negative, with local strain topology of the type stable-node/saddle/saddle. There was also a preferential eigenvalue direction. The magnitude of H(ij) in the wake flow was found to be very small when data were conditioned at high local dissipation regions. This result was not observed in the relatively low Reynolds number simulation of homogeneous isotropic flow. A restricted Euler model of the evolution of A(ij) was found to reproduce many of the topological features identified in the simulations.

  7. Investigations of coherent structures in free turbulent shear flows

    NASA Technical Reports Server (NTRS)

    Hussain, A. K. M. F.

    1979-01-01

    The dynamics of large-scale coherent structures in general, and studies based on flow-visualization and phase-locked hot-wire measurements of the structures in the near fields of circular jets are considered. A study involving the nature of coherent structures under conditions of stable vortex pairing induced by controlled axisymmetric acoustic excitation reveals that azimuthal coherence initially enhanced by the excitation is lost before the end of the potential core through evolution of azimuthal lobe structures and turbulent breakdown. The evolution of a spark-induced spot in an axisymmetric turbulent mixing layer is also investigated, and the coherent Reynolds stress associated with the spot is found to be much higher than the background turbulence Reynolds stress. In addition, the state of organization in a high Reynolds number unperturbed axisymmetric mixing layer is examined, and it is shown that the shear layer is infrequently organized and the motions are intensely three-dimensional, while tearing and fractional pairing occur as frequently as complete pairing.

  8. Heat flow anomalies in oil- and gas-bearing structures

    SciTech Connect

    Sergiyenko, S.I.

    1988-02-01

    The main features of the distribution of heat flow values in oil, gas and gas-condensate fields on the continents have been discussed by Makarenko and Sergiyenko. The method of analysis used made it possible to establish that the presence of hydrocarbons in formations leads to high heat-flow, regardless of the age of folding of the potentially oil- and gas-bearing zones. Only in regions adjacent to marginal Cenozoic folded mountain structures and in zones of Cenozoic volcanism is the world average higher, by 2.5 to 10%, than in the oil- and gas-bearing structures in those regions. The earlier analysis of the distribution of heat flow values in oil and gas structures was based on 403 measurements. The author now has nearly doubled the sample population, enabling him substantially to revise the ideas on the distribution of heat flow values and the development of the thermal regime of local oil and gas structures. He notes that the method previously used, comparing heat flow values on young continental platforms with values in local oil and gas structures, makes it possible to estimate the thermal effect of the presence of oil and gas. This conclusion stems from the fact that the overwhelming majority of heat flow measurements were made on various kinds of positive structural forms, and distortions of the thermal field caused by thermal anisotropy phenomena are equally characteristic of both productive and nonproductive structures. As a result, for the first time a continuous time series of heat flow measurements over oil and gas structures in various tectonic regions, with ages of consolidation ranging from the Precambrian to the Cenozoic, was established. 26 references.

  9. Numerical and Experimental Investigation of Flow Structures During Insect Flight

    NASA Astrophysics Data System (ADS)

    Badrya, Camli; Baeder, James D.

    2015-11-01

    Insect flight kinematics involves complex interplay between aerodynamics structural response and insect body control. Features such as cross-coupling kinematics, high flapping frequencies and geometrical small-scales, result in experiments being challenging to perform. In this study OVERTURNS, an in-house 3D compressible Navier-Stokes solver is utilized to simulate the simplified kinematics of an insect wing in hover and forward flight. The flapping wings simulate the full cycle of wing motion, i.e., the upstroke, downstroke, pronation and supination.The numerical results show good agreement against experimental data in predicting the lift and drag over the flapping cycle. The flow structures around the flapping wing are found to be highly unsteady and vortical. Aside from the tip vortex on the wings, the formation of a prominent leading edge vortex (LEV) during the up/down stroke portions, and the shedding of a trailing edge vortex (TEV) at end of each stroke were observed. Differences in the insect dynamics and the flow features of the LEV are observed between hover and forward flight. In hover the up and downstroke cycles are symmetric, whereas in forward flight, these up and downstroke are asymmetric and LEV strength varies as a function of the kinematics and advance ratio. This work was supported by the Micro Autonomous Systems and Technology (MAST) CTA at the Univer- sity of Maryland.

  10. Final Report - Investigation of Intermittent Turbulence and Turbulent Structures in the Presence of Controlled Sheared Flows

    SciTech Connect

    Gilmore, Mark A.

    2013-06-27

    Final Report for grant DE-FG02-06ER54898. The dynamics and generation of intermittent plasma turbulent structures, widely known as "blobs" have been studied in the presence of sheared plasma flows in a controlled laboratory experiment.

  11. Flow structure on a rotating wing: Effect of steady incident flow

    NASA Astrophysics Data System (ADS)

    Bross, M.; Ozen, C. A.; Rockwell, D.

    2013-08-01

    The flow structure along a rotating wing in steady incident flow is compared to the structure on a rotating wing in quiescent fluid, in order to clarify the effect of advance ratio J (ratio of free-stream velocity to tip velocity of wing). Stereoscopic particle image velocimetry leads to patterns of vorticity, velocity, and Q-criterion (constant values of the second invariant of the velocity gradient tensor), as well as streamlines, which allow identification of critical points of the flow. The effective angle of attack is held constant over the range of J, and the wing rotates from rest to a large angle that corresponds to attainment of the asymptotic state of the flow structure. Prior to the onset of motion, the wing is at high angle of attack and the steady incident flow yields a fully stalled state along the wing. After the onset of rotation, the stalled region quickly gives rise to a stable leading edge vortex. Throughout the rotation maneuver, the development of the flow structure in the leading edge region is relatively insensitive to the value of J. In the trailing-edge region, however, the structure of the shed vorticity layer is strongly dependent on the value of J. Further insight into the effects of J is provided by three-dimensional patterns of spanwise-oriented vorticity, spanwise velocity, and Q-criterion.

  12. Biomimetic structures for fluid drag reduction in laminar and turbulent flows.

    PubMed

    Jung, Yong Chae; Bhushan, Bharat

    2010-01-27

    Biomimetics allows one to mimic nature to develop materials and devices of commercial interest for engineers. Drag reduction in fluid flow is one of the examples found in nature. In this study, nano, micro, and hierarchical structures found in lotus plant surfaces, as well as shark skin replica and a rib patterned surface to simulate shark skin structure were fabricated. Drag reduction efficiency studies on the surfaces were systematically carried out using water flow. An experimental flow channel was used to measure the pressure drop in laminar and turbulent flows, and the trends were explained in terms of the measured and predicted values by using fluid dynamics models. The slip length for various surfaces in laminar flow was also investigated based on the measured pressure drop. For comparison, the pressure drop for various surfaces was also measured using air flow.

  13. Correlations of Flow Structure and Particle Deposition with Structural Alterations in Severe Asthmatic Lungs

    NASA Astrophysics Data System (ADS)

    Choi, Sanghun; Miyawaki, Shinjiro; Choi, Jiwoong; Hoffman, Eric A.; Wenzel, Sally; Lin, Ching-Long

    2014-11-01

    Severe asthmatics are characterized by alterations of bifurcation angle, hydraulic diameter, circularity of the airways, and local shift of air-volume functional change. The characteristics altered against healthy human subjects can affect flow structure and particle deposition. A large-eddy-simulation (LES) model for transitional and turbulent flows is utilized to study flow characteristics and particle deposition with representative healthy and severe asthmatic lungs. For the subject-specific boundary condition, local air-volume changes are derived with two computed tomography images at inspiration and expiration. Particle transport simulations are performed on LES-predicted flow fields. In severe asthmatics, the elevated air-volume changes of apical lung regions affect the increased particle distribution toward upper lobes, especially for small particles. The constricted airways are significantly correlated with high wall shear stress, leading to the increased pressure drop and particle deposition. The structural alterations of bifurcation angle, circularity and hydraulic diameter in severe asthmatics are associated with the increase of particle deposition, wall shear stress and wall thickness. NIH Grants: U01-HL114494, R01-HL094315 and S10-RR022421. Computer time: XSEDE.

  14. Flow Structure on a Flapping Wing: Quasi-Steady Limit

    NASA Astrophysics Data System (ADS)

    Ozen, Cem; Rockwell, Donald

    2011-11-01

    The flapping motion of an insect wing typically involves quasi-steady motion between extremes of unsteady motion. This investigation characterizes the flow structure for the quasi-steady limit via a rotating wing in the form of a thin rectangular plate having a low aspect ratio (AR =1). Particle Image Velocimetry (PIV) is employed, in order to gain insight into the effects of centripetal and Coriolis forces. Vorticity, velocity and streamline patterns are used to describe the overall flow structure with an emphasis on the leading-edge vortex. A stable leading-edge vortex is maintained over effective angles of attack from 30° to 75° and it is observed that at each angle of attack the flow structure remains relatively same over the Reynolds number range from 3,600 to 14,500. The dimensionless circulation of the leading edge vortex is found to be proportional to the effective angle of attack. Quasi-three-dimensional construction of the flow structure is used to identify the different regimes along the span of the wing which is then complemented by patterns on cross flow planes to demonstrate the influence of root and tip swirls on the spanwise flow. The rotating wing results are also compared with the equivalent of translating wing to further illustrate the effects of the rotation.

  15. Study on flow instability and countermeasure in a draft tube with swirling flow

    NASA Astrophysics Data System (ADS)

    Nakashima, T.; Matsuzaka, R.; Miyagawa, K.; Yonezawa, K.; Tsujimoto, Y.

    2014-03-01

    The swirling flow in the draft tube of a Francis turbine can cause the flow instability and the cavitation surge and has a larger influence on hydraulic power operating system. In this paper, the cavitating flow with swirling flow in the diffuser was studied by the draft tube component experiment, the model Francis turbine experiment and the numerical simulation. In the component experiment, several types of fluctuations were observed, including the cavitation surge and the vortex rope behaviour by the swirling flow. While the cavitation surge and the vortex rope behaviour were suppressed by the aeration into the diffuser, the loss coefficient in the diffuser increased by the aeration. In the model turbine test the aeration decreased the efficiency of the model turbine by several percent. In the numerical simulation, the cavitating flow was studied using Scale-Adaptive Simulation (SAS) with particular emphasis on understanding the unsteady characteristics of the vortex rope structure. The generation and evolution of the vortex rope structures have been investigated throughout the diffuser using the iso-surface of vapor volume fraction. The pressure fluctuation in the diffuser by numerical simulation confirmed the cavitation surge observed in the experiment. Finally, this pressure fluctuation of the cavitation surge was examined and interpreted by CFD.

  16. Effect of volumetric electromagnetic forces on shock wave structure of hypersonic air flow near plate

    NASA Astrophysics Data System (ADS)

    Fomichev, Vladislav; Yadrenkin, Mikhail; Shipko, Evgeny

    2016-10-01

    Summarizing of experimental studies results of the local MHD-interaction at hypersonic air flow near the plate is presented. Pulsed and radiofrequency discharge have been used for the flow ionization. It is shown that MHD-effect on the shock-wave structure of the flow is significant at test conditions. Using of MHD-interaction parameter enabled to defining characteristic modes of MHD-interaction by the force effect: weak, moderate and strong.

  17. An experimental study on downward slug flow in inclined pipes

    SciTech Connect

    Roumazeilles, P.M.; Yang, J.; Sarica, C.; Chen, X.T.; Wilson, J.F.; Brill, J.P.

    1996-08-01

    The downward simultaneous flow of gas and liquid is often encountered in hilly terrain pipelines and injection wells. Most of the methods for predicting pressure drop in gas/liquid, two-phase flow in pipes have been developed for either upward vertical or upward inclined pipes. This study experimentally investigated downward cocurrent slug flow in inclined pipes. A new test facility was designed and built to acquire data for the entire range of pipe inclination angles. A series of slug flow experiments was conducted in a 2-in. diameter, 65-ft long clear PVC pipe installed on an inclinable structure. Liquid holdup and pressure drop measurements were obtained for downward inclination angles from 0{degree} to {minus}30{degree} at different flow conditions. Translational velocity and liquid-slug holdup correlations were investigated based on the acquired data for different inclination angles.

  18. Fundamentals of free flux flow: proposed studies

    NASA Astrophysics Data System (ADS)

    Alexander, J. A.; Gafarov, O.; Gapud, A. A.; Wu, J. Z.

    2013-03-01

    Although much is known about free flux flow (FFF) in superconductors - in which pinning is insignificant compared to interactions between quantized vortices - there still remain questions concerning fundamental dynamics. Building on our previous work in correlating FFF with vortex core size (PRB 80, 134524), we propose three new studies examining more deeply the normal state in the vortex core and interactions between vortices. A correlation between scattering inside cores and the viscosity of FFF has not been explicitly determined; this may be investigated by probing the effect of scattering centers created by proton irradiation. Using results of previous irradiation work, one could control the extent of normal state scattering while monitoring effects on FFF. Questions also exist concerning vortex motion in channels with widths approaching that of individual vortices - as determined solely by inter-vortex interactions. Studies have suggested that flux flow through constrictions could imitate ``jamming'' in the collective motion of grains: Under certain conditions, it is possible for grains to form a barrier, blocking flow. More than just qualitatively comparing flux flow and granular flow to find evidence of jamming, we propose a new experiment for quantitatively modeling flux jamming by realizing the flux flow equivalent of granular jamming in a ``hopper''. In the same way, we also propose a FFF equivalent of another granular-flow phenomenon, ``non-Newtonian'' fluids, where rapid shear causes jamming. Funded by NSF-RUI grant, DMR-0907038.

  19. High frequency flow-structural interaction in dense subsonic fluids

    NASA Technical Reports Server (NTRS)

    Liu, Baw-Lin; Ofarrell, J. M.

    1995-01-01

    Prediction of the detailed dynamic behavior in rocket propellant feed systems and engines and other such high-energy fluid systems requires precise analysis to assure structural performance. Designs sometimes require placement of bluff bodies in a flow passage. Additionally, there are flexibilities in ducts, liners, and piping systems. A design handbook and interactive data base have been developed for assessing flow/structural interactions to be used as a tool in design and development, to evaluate applicable geometries before problems develop, or to eliminate or minimize problems with existing hardware. This is a compilation of analytical/empirical data and techniques to evaluate detailed dynamic characteristics of both the fluid and structures. These techniques have direct applicability to rocket engine internal flow passages, hot gas drive systems, and vehicle propellant feed systems. Organization of the handbook is by basic geometries for estimating Strouhal numbers, added mass effects, mode shapes for various end constraints, critical onset flow conditions, and possible structural response amplitudes. Emphasis is on dense fluids and high structural loading potential for fatigue at low subsonic flow speeds where high-frequency excitations are possible. Avoidance and corrective measure illustrations are presented together with analytical curve fits for predictions compiled from a comprehensive data base.

  20. Flow structure and vorticity transport on a plunging wing

    NASA Astrophysics Data System (ADS)

    Eslam Panah, Azar

    The structure and dynamics of the flow field created by a plunging flat plate airfoil are investigated at a chord Reynolds number of 10,000 while varying plunge amplitude and Strouhal number. Digital particle image velocimetry measurements are used to characterize the shedding patterns and the interactions between the leading and trailing edge vortex structures (LEV and TEV), resulting in the development of a wake classification system based on the nature and timing of interactions between the leading- and trailing-edge vortices. The convection speed of the LEV and its resulting interaction with the TEV is primarily dependent on reduced frequency; however, at Strouhal numbers above approximately 0.4, a significant influence of Strouhal number (or plunge amplitude) is observed in which LEV convection is retarded, and the contribution of the LEV to the wake is diminished. It is shown that this effect is caused by an enhanced interaction between the LEV and the airfoil surface, due to a significant increase in the strength of the vortices in this Strouhal number range, for all plunge amplitudes investigated. Comparison with low-Reynolds-number studies of plunging airfoil aerodynamics reveals a high degree of consistency and suggests applicability of the classification system beyond the range examined in the present work. Some important differences are also observed. The three-dimensional flow field was characterized for a plunging two-dimensional flat-plate airfoil using three-dimensional reconstructions of planar PIV data. Whereas the phase-averaged description of the flow field shows the secondary vortex penetrating the leading-edge shear layer to terminate LEV formation on the airfoil, time-resolved, instantaneous PIV measurements show a continuous and growing entrainment of secondary vorticity into the shear layer and LEV. A planar control volume analysis on the airfoil indicated that the generation of secondary vorticity produced approximately one half the

  1. Structural characteristics of cohesive flow deposits, and a sedimentological approach on their flow mechanisms.

    NASA Astrophysics Data System (ADS)

    Tripsanas, E. K.; Bryant, W. R.; Prior, D. B.

    2003-04-01

    A large number of Jumbo Piston cores (up to 20 m long), acquired from the continental slope and rise of the Northwest Gulf of Mexico (Bryant Canyon area and eastern Sigsbee Escarpment), have recovered various mass-transport deposits. The main cause of slope instabilities over these areas is oversteepening of the slopes due to the seaward mobilization of the underlying allochthonous salt masses. Cohesive flow deposits were the most common recoveries in the sediment cores. Four types of cohesive flow deposits have been recognized: a) fluid debris flow, b) mud flow, c) mud-matrix dominated debris flow, and d) clast-dominated debris flow deposits. The first type is characterized by its relatively small thickness (less than 1 m), a mud matrix with small (less than 0.5 cm) and soft mud-clasts, and a faint layering. The mud-clasts reveal a normal grading and become more abundant towards the base of each layer. That reveals that their deposition resulted by several successive surges/pulses, developed in the main flow, than the sudden “freezing” of the whole flow. The main difference between mud flow and mud-matrix dominated debris flow deposits is the presence of small to large mud-clasts in the later. Both deposits consist of a chaotic mud-matrix, and a basal shear laminated zone, where the strongest shearing of the flow was exhibited. Convolute laminations, fault-like surfaces, thrust faults, and microfaults are interpreted as occurring during the “freezing” of the flows and/or by adjustments of the rested deposits. Clast-dominated debris flow deposits consist of three zones: a) an upper plug-zone, characterized by large interlocked clasts, b) a mid-zone, of higher reworked, inversely graded clasts, floating in a mud-matrix, and c) a lower shear laminated zone. The structure of the last three cohesive flow deposits indicate that they represent deposition of typical Bingham flows, consisting of an upper plug-zone in which the yield stress is not exceeded and an

  2. Flow structure, performance and scaling of acoustic jets

    NASA Astrophysics Data System (ADS)

    Muller, Michael Oliver

    Acoustic jets are studied, with an emphasis on their flow structure, performance, and scaling. The ultimate goal is the development of a micromachined acoustic jet for propulsion of a micromachined airborne platform, as well as integrated cooling and pumping applications. Scaling suggests an increase in performance with decreasing size, motivating the use of micro-technology. Experimental studies are conducted at three different orders of magnitude in size, each closely following analytic expectations. The jet creates a periodic vortical structure, the details of which are a function of amplitude. At small actuation amplitude, but still well above the linear acoustic regime, the flow structure consists of individual vortex rings, propagating away from the nozzle, formed during the outstroke of the acoustic cavity. At large amplitude, a trail of vorticity forms between the periodic vortex rings. Approximately corresponding to these two flow regions are two performance regimes. At low amplitude, the jet thrust increases with the fourth power of the amplitude; and at large amplitude, the thrust equals the momentum flux ejected during the output stroke, and increases as the square of the amplitude. Resonance of the cavity, at Reynolds numbers greater than approximately 10, enhances the jet performance beyond the incompressible behavior. Gains of an order of magnitude in the jet velocity occur at Reynolds numbers of approximately 100, and the data suggest further gains with increasing Reynolds number. The smallest geometries tested are micromachined acoustic jets, manufactured using MEMS technology. The throat dimensions are 50 by 200 mum, and the overall device size is approximately 1 mm 2, with eight throats per device. Several jets are manufactured in an array, to suit any given application. The performance is very dependent on frequency, with a sharp peak at the system resonance, occurring at approximately 70 kHz (inaudible). The mean jet velocity of these devices

  3. Spectacular ionospheric flow structures associated with substorm auroral onset

    NASA Astrophysics Data System (ADS)

    Gallardo-Lacourt, B. I.; Nishimura, Y.; Lyons, L. R.; Zou, Y.; Angelopoulos, V.; Donovan, E.; Mende, S. B.; Ruohoniemi, J.; McWilliams, K. A.; Nishitani, N.

    2013-12-01

    Auroral observations have shown that brightening at substorm auroral onset consists of azimuthally propagating beads forming along a pre-existing arc. However, the ionospheric flow structure related to this wavy auroral structure has not been previously identified. We present 2-d line-of-sight flow observations and auroral images from the SuperDARN radars and the THEMIS ground-based all-sky-imager array to investigate the ionospheric flow pattern associated with the onset. We have selected events where SuperDARN was operating in the THEMIS mode, which provides measurements along the northward looking radar beam that have time resolution (6 s) comparable to the high time resolution of the imagers and gives us a unique tool to detect properties of flows associated with the substorm onset instability. We find very fast flows (~1000 m/s) that initiated simultaneously with the onset arc beads propagating across the THEMIS-mode beam meridian. The flows show oscillations at ~9 mHz, which corresponds to the periodicity of the auroral beads propagating across the radar beam. 2-d radar measurements also show a wavy pattern in the azimuthal direction with a wavelength of ~74 km, which is close to the azimuthal separation of individual beads, although this determination is limited by the 2 minute radar scan period. These strong correlations (in time and space) between auroral beading and the fast ionospheric flows suggest that these spectacular flows are an important feature of the substorm onset instability within the inner plasma sheet. Also, a clockwise flow shear was observed in association with individual auroral beads, suggesting that such flow shear is a feature of the unstable substorm onset waves.

  4. A numerical approach for flow-induced vibration of pipe structures

    NASA Astrophysics Data System (ADS)

    Ting, E. C.; Hosseinipour, A.

    1983-06-01

    A structural impedance approach is extended for the dynamic analysis of pipe structures conveying fluid flow. The method is efficient in computation and convenient for studying transient responses. Thus, it is possible to study the transition from a stable condition to an unstable condition of the pipe structure as the flow speed increases. The structure may also exhibit different modes of instability. The present approach predicts the mode without prior assumption. Numerical examples are given for a hanging cantilever and a simply supported pipe. The critical speed associated with the dynamic stability is calculated and compared with available analytical and experimental results.

  5. Structure and dynamics of low Reynolds number turbulent pipe flow.

    PubMed

    Duggleby, Andrew; Ball, Kenneth S; Schwaenen, Markus

    2009-02-13

    Using large-scale numerical calculations, we explore the proper orthogonal decomposition of low Reynolds number turbulent pipe flow, using both the translational invariant (Fourier) method and the method of snapshots. Each method has benefits and drawbacks, making the 'best' choice dependent on the purpose of the analysis. Owing to its construction, the Fourier method includes all the flow fields that are translational invariants of the simulated flow fields. Thus, the Fourier method converges to an estimate of the dimension of the chaotic attractor in less total simulation time than the method of snapshots. The converse is that for a given simulation, the method of snapshots yields a basis set that is more optimal because it does not include all of the translational invariants that were not a part of the simulation. Using the Fourier method yields smooth structures with definable subclasses based upon Fourier wavenumber pairs, and results in a new dynamical systems insight into turbulent pipe flow. These subclasses include a set of modes that propagate with a nearly constant phase speed, act together as a wave packet and transfer energy from streamwise rolls. It is these interactions that are responsible for bursting events and Reynolds stress generation. These structures and dynamics are similar to those found in turbulent channel flow. A comparison of structures and dynamics in turbulent pipe and channel flows is reported to emphasize the similarities and differences.

  6. Observations and Measurements on Unsteady Cloud Cavitation Flow Structures

    NASA Astrophysics Data System (ADS)

    Gu, L. X.; Yan, G. J.; Huang, B.

    2015-12-01

    The objectives of this paper are to investigate the unsteady structures and hydrodynamics of cavitating flows. Experimental results are presented for a Clark-Y hydrofoil, which is fixed at α=0°, 5° and 8°. The high-speed video camera and Particle Image Velocimetry (PIV) are applied to investigate the transient flow structures. The dynamic measurement system is used to record the dynamic characteristics. The cloud cavitation exhibits noticeable unsteady characteristics. For the case of α=0°, there exit strong interactions between the attached cavity and the re-entrant flow. While for the case of α=8°, the re-entrant flow is relatively thin and the interaction between the cavity and re-entrant flow is limited. The results also present that the periodic collapse and shedding of the large-scale cloud cavitation, which leads to substantial increase of turbulent velocity fluctuations in the cavity region. Experimental evidence indicates that the hydrodynamics are clearly affected by the cavitating flow structures, the amplitude of load fluctuation are much higher for the cloud cavitating cases.

  7. Rapid Flow Analysis Studies with Spectroscopic Detectors.

    NASA Astrophysics Data System (ADS)

    Thalib, Amlius

    A rapid flow analysis study based on segmented flow and flow injection principles is described in this thesis. The main objective of this study was to establish the response characteristics in continuous flow analysis systems in order to improve sampling rates with several types of spectroscopic detectors. It was found from flame photometric studies that non-segmented flowing streams are applicable to rapid flow analysis with automatic sample aspiration. Calcium was used as a typical example and determined at sampling rates up to 360 h('-1) with a detection limit of 0.05 mg L(' -1). A rapid flow system is reported using direct aspiration for AAS analysis with both manual injection and automatic aspiration techniques, and found to give sampling rates of up to 600-720 samples h('-1). Speed of analysis was reduced by about 50% when using an external peristaltic pump in the flow system design, due to increased sample dispersion. A novel aspect of a rapid flow injection approach reported with ICPAES detection includes the method of injecting samples via a peristaltic pump with simultaneous computer data processing. Determination of serum cations (Na, K, Ca, Mg and Fe) was demonstrated as an example of an application of the technique at sampling rates of 240 h('-1). Precision and detection limits for 13 elements in a single standard solution are reported. The use of automated aspiration sampling is also reported in this method for comparison. Further studies on flow characteristics were carried out by a combination of the rapid flow system with very short sampling times as low as 2 seconds using UV-visible spectrophotometric detection. Analysis of human blood serum samples was used as an example where total protein and inorganic phosphate were determined at sampling rates of 240 h('-1) and 360 h('-1) respectively. The novel aspects of the results from these studies include the very rapid sample throughput developed with simple and inexpensive experimental approaches in

  8. Flow over periodic hills: an experimental study

    NASA Astrophysics Data System (ADS)

    Rapp, Ch.; Manhart, M.

    2011-07-01

    Two-dimensional flow over periodically arranged hills was investigated experimentally in a water channel. Two-dimensional particle image velocimetry (PIV) and one-dimensional laser Doppler anemometry (LDA) measurements were undertaken at four Reynolds numbers ({5,600} le Re le {37,000}). Two-dimensional PIV field measurements were thoroughly validated by means of point-by-point 1D LDA measurements at certain positions of the flow. A detailed study of the periodicity and the homogeneity was undertaken, which demonstrates that the flow can be regarded as two-dimensional and periodic for Re ge {10,000}. We found a decreasing reattachment length with increasing Reynolds number. This is connected to a higher momentum in the near-wall zone close to flow separation which comes from the velocity speed up above the obstacle. This leads to a velocity overshoot directly above the hill crest which increases with Reynolds number as the inner layer depth decreases. The flow speed up above that layer is independent of the Reynolds number which supports the assumption of inviscid flow disturbance in the outer layer usually made in asymptotic theory for flow over small hills.

  9. Englacial Structures as Indicators of the Controls on Ice Flow

    NASA Astrophysics Data System (ADS)

    Holschuh, N.; Parizek, B. R.; Alley, R. B.; Anandakrishnan, S.

    2015-12-01

    Direct sampling of the subglacial environment is costly, and will therefore never supply the spatial coverage needed to determine the basal boundary conditions required for large-scale ice-sheet modeling. Studies of the West Antarctic Ice Sheet (WAIS) show that the frictional and rheologic properties of the bed are a leading control on the evolution of the system, so developing geophysical methods to help constrain the basal characteristics of WAIS will reduce uncertainty in predictions of the timing and magnitude of future sea-level rise. Radar-imaged structures within the ice are an attractive data set for this pursuit, as they contain information about the flow dynamics that transform the horizontally deposited layers to their modern configuration; however, they can be challenging to interpret, given the number of processes acting to deform the internal layers and the difficulty in automating their analysis. In this study, we move away from the layer-tracing paradigm in favor of an automated slope extraction algorithm. This has several advantages: it does not require feature-continuity, providing a more stable result in regions of intense deformation, and it results in a data product that maps directly to model output. For steady-state features, layer slopes reflect the horizontal and vertical velocity structure, making quantitative comparison of the model and observations simple compared to the more qualitative, particle tracer comparisons done in the past. Using a higher order ice-flow model, we attempt to refine our understanding of basal properties using reflector slope fields at the grounding line of Whillans Ice Stream and the shear margin of the North East Greenland Ice Stream, with the hope of eventually using this method for basin-scale inversions.

  10. Asymmetrical reverse vortex flow due to induced-charge electro-osmosis around carbon stacking structures

    NASA Astrophysics Data System (ADS)

    Sugioka, Hideyuki

    2011-05-01

    Broken symmetry of vortices due to induced-charge electro-osmosis (ICEO) around stacking structures is important for the generation of a large net flow in a microchannel. Following theoretical predictions in our previous study, we herein report experimental observations of asymmetrical reverse vortex flows around stacking structures of carbon posts with a large height (~110 μm) in water, prepared by the pyrolysis of a photoresist film in a reducing gas. Further, by the use of a coupled calculation method that considers boundary effects precisely, the experimental results, except for the problem of anomalous flow reversal, are successfully explained. That is, unlike previous predictions, the precise calculations here show that stacking structures accelerate a reverse flow rather than suppressing it for a microfluidic channel because of the deformation of electric fields near the stacking portions; these structures can also generate a large net flow theoretically in the direction opposite that of a previous prediction for a standard vortex flow. Furthermore, by solving the one-dimensional Poisson-Nernst-Plank (PNP) equations in the presence of ac electric fields, we find that the anomalous flow reversal occurs by the phase retardation between the induced diffuse charge and the tangential electric field. In addition, we successfully explain the nonlinearity of the flow velocity on the applied voltage by the PNP analysis. In the future, we expect to improve the pumping performance significantly by using stacking structures of conductive posts along with a low-cost process.

  11. Shock-Induced Separated Structures in Symmetric Corner Flows

    NASA Technical Reports Server (NTRS)

    DAmbrosio, Domenic; Marsilio, Roberto

    1995-01-01

    Three-dimensional supersonic viscous laminar flows over symmetric corners are considered in this paper. The characteristic features of such configurations are discussed and an historical survey on the past research work is presented. A new contribution based on a numerical technique that solves the parabolized form of the Navier-Stokes equations is presented. Such a method makes it possible to obtain very detailed descriptions of the flowfield with relatively modest CPU time and memory storage requirements. The numerical approach is based on a space-marching technique, uses a finite volume discretization and an upwind flux-difference splitting scheme (developed for the steady flow equations) for the evaluation of the inviscid fluxes. Second order accuracy is reached following the guidelines of the ENO schemes. Different free-stream conditions and geometrical configurations are considered. Primary and secondary streamwise vortical structures embedded in the boundary layer and originated by the interaction of the latter with shock waves are detected and studied. Computed results are compared with experimental data taken from literature.

  12. Effect of submerged flexible vegetation on flow structure and resistance

    NASA Astrophysics Data System (ADS)

    Järvelä, Juha

    2005-06-01

    Flume studies were carried out to investigate flow structure above flexible vegetation. A new data set of mean velocity profiles and turbulence characteristics is reported from experiments with wheat. The flow above the wheat reasonably followed the log law. Maximum values of the turbulence intensity urms and Reynolds stress -uw¯ were found approximately at the level of the maximum observed deflected plant height. A recent approach for describing vertical velocity profiles above aquatic vegetation [Stephan, U., 2002. Zum Fließwiderstandsverhalten flexibler Vegetation. Wiener Mitteilungen 180. Doctoral Thesis. Institute of Hydraulics, Hydrology and Water Resources Management, Faculty of Civil Engineering, Technical University of Vienna.] was evaluated with these new data, which represent a different vegetal roughness type. The approach proved to be successful beyond the original scope. However, a new definition for the shear velocity based on the deflected plant height is suggested. The benefit of this modification is that complex turbulence measurements can be avoided, which enhances the practical applicability of the approach.

  13. Numerical study of free surface flow around large obstacles

    NASA Astrophysics Data System (ADS)

    Zhang, Yanming

    In this thesis a numerical model was developed to study three-dimensional turbulent flows around large obstacles in an open channel. With this numerical model, a series of numerical tests was carried out, and the properties of turbulent flows around a single obstacle or a cluster of obstacles were investigated. The origin of this study was to study the flow properties around fish habitat structures. Actually, the numerical model can be applied to the study of general turbulent flows under free surfaces. In the numerical model the three-dimensional Reynolds-averaged Navier-Stokes equations in conjunction with k-epsilon turbulence model were solved in a free surface fitted coordinate system. First, different forms of governing equations for turbulent flow were investigated, and a concise form of fully transformed governing equations in a general curvilinear coordinate system was derived. In the numerical solution the FAVOR (Fractional Area/Volume Obstacle Representation) technique was extended into the free surface fitted coordinate system. With this feature the problem of complex turbulent flow with a free surface and general shaped obstacles could be solved efficiently. To locate the free surface, a method based on integrating the momentum equation in the vertical direction was developed. After study and tests of several popular difference schemes, a QUICK scheme with UMIST limiter was adopted in this numerical model. Several test cases were presented to demonstrate the present numerical model. The first test case was to simulate a submerged hydraulic jump. The calculated velocity, free surface profile and turbulence properties of the flow showed a close match with the experimental data. The second test was a submerged hydraulic jump with a baffle sill. The comparison between numerical and experimental data indicated that the current numerical model could catch the general flow structures of the submerged hydraulic jumps. The last two test cases were flows around a

  14. Simulated tornado debris tracks: implications for inferring corner flow structure

    NASA Astrophysics Data System (ADS)

    Zimmerman, Michael; Lewellen, David

    2011-11-01

    A large collection of three-dimensional large eddy simulations of tornadoes with fine debris have been recently been performed as part of a longstanding effort at West Virginia University to understand tornado corner flow structure and dynamics. Debris removal and deposition is accounted for at the surface, in effect simulating formation of tornado surface marks. Physical origins and properties of the most prominent marks will be presented, and the possibility of inferring tornado corner flow structure from real marks in the field will be discussed. This material is based upon work supported by the National Science Foundation under Grants No. 0635681 and AGS-1013154.

  15. A study of thin liquid sheet flows

    NASA Technical Reports Server (NTRS)

    Chubb, Donald L.; Calfo, Frederick D.; Mcconley, Marc W.; Mcmaster, Matthew S.; Afjeh, Abdollah A.

    1993-01-01

    This study was a theoretical and experimental investigation of thin liquid sheet flows in vacuum. A sheet flow created by a narrow slit of width, W, coalesces to a point at a distance, L, as a result of surface tension forces acting at the sheet edges. As the flow coalesces, the fluid accumulates in the sheet edges. The observed triangular shape of the sheet agrees with the calculated triangular result. Experimental results for L/W as a function of Weber number, We, agree with the calculated result, L/W = the sq. root of 8We. The edge cross sectional shape is found to oscillate from elliptic to 'cigar' like to 'peanut' like and then back to elliptic in the flow direction. A theoretical one-dimensional model was developed that yielded only elliptic solutions for the edge cross section. At the points where the elliptic shapes occur, there is agreement between theory and experiment.

  16. Comparative Study of Airfoil Flow Separation Criteria

    NASA Astrophysics Data System (ADS)

    Laws, Nick; Kahouli, Waad; Epps, Brenden

    2015-11-01

    Airfoil flow separation impacts a multitude of applications including turbomachinery, wind turbines, and bio-inspired micro-aerial vehicles. In order to achieve maximum performance, some devices operate near the edge of flow separation, and others use dynamic flow separation advantageously. Numerous criteria exist for predicting the onset of airfoil flow separation. This talk presents a comparative study of a number of such criteria, with emphasis paid to speed and accuracy of the calculations. We evaluate the criteria using a two-dimensional unsteady vortex lattice method, which allows for rapid analysis (on the order of seconds instead of days for a full Navier-Stokes solution) and design of optimal airfoil geometry and kinematics. Furthermore, dynamic analyses permit evaluation of dynamic stall conditions for enhanced lift via leading edge vortex shedding, commonly present in small flapping-wing flyers such as the bumblebee and hummingbird.

  17. Studies of magnetopause structure

    NASA Technical Reports Server (NTRS)

    Speiser, Theodore W.

    1991-01-01

    From the International Sun-Earth Explorers (ISEE) 1 magnetopause crossings on November 10, 1977, three-dimensional distribution functions for energetic ions were studied in the magnetosphere, through the magnetopause, and in the magnetosheath (Speiser and Williams, 1982). The particle distributions were particularly examined at and near the times that Russell and Elphic (1978) identified as flux transfer events (FTE). Using a simple, one-dimensional, quasi-static model, particle orbits were followed numerically, from the magnetosphere into the sheath. The inner, trapped, distribution initializes the distribution function. Liouville's theorem allows the inner distribution to be mapped into the sheath following the orbits. This mapping is shown for four mangetosheath ion flows (MIF's) corresponding to four flux transfer events. Results from the studies are discussed. A brief discussion of current sheet particle motion is presented.

  18. Studies of the structure of attached and separated regions of viscous/inviscid interaction and the effects of combined surface roughness and blowing in high-Reynolds-number hypersonic flows. Final report, 1 August 1985-1 June 1988

    SciTech Connect

    Holden, M.S.; Bergman, R.; Harvey, J.; Duryea, G.; Moselle, J.

    1988-12-02

    The first of these 2 studies examined the detailed structure of the hypersonic boundary layer over a large cone/flare configuration. Emphasis was on development and use of instrumentation with which to obtain flow-field measurements of the mean and fluctuating properties of the attached and separated shear layers. Development and use of holographic interferometry and electron-beam techniques in the high Mach number and Reynolds number environment developed in the shock tunnel are described. In the second study, detailed measurements of heat transfer, pressure, and skin friction were made on a unique 'blowing and roughness' model constructed to simulate the aerothermal phenomena associated with a rough ablating maneuverable reentry vehicle. In this study emphasis was placed on development and use of unique heat transfer and skin-friction instrumentation to obtain measurements of the combined effects of blowing and roughness and to understand how such effects influence boundary-layer separation in regions of shock wave/boundary layer interaction. Each focused around providing information with which to construct and evaluate the modeling required in time-averaged Navier-Stokes equations to predict the structure of compressible hypersonic boundary layers in regions of strong pressure gradient, shock-wave/boundary-layer interaction and flow separation over smooth, rough, and ablating surfaces.

  19. Dynamics of generalized Gaussian polymeric structures in random layered flows

    NASA Astrophysics Data System (ADS)

    Katyal, Divya; Kant, Rama

    2015-04-01

    We develop a formalism for the dynamics of a flexible branched polymer with arbitrary topology in the presence of random flows. This is achieved by employing the generalized Gaussian structure (GGS) approach and the Matheron-de Marsily model for the random layered flow. The expression for the average square displacement (ASD) of the center of mass of the GGS is obtained in such flow. The averaging is done over both the thermal noise and the external random flow. Although the formalism is valid for branched polymers with various complex topologies, we mainly focus here on the dynamics of the flexible star and dendrimer. We analyze the effect of the topology (the number and length of branches for stars and the number of generations for dendrimers) on the dynamics under the influence of external flow, which is characterized by their root-mean-square velocity, persistence flow length, and flow exponent α . Our analysis shows two anomalous power-law regimes, viz., subdiffusive (intermediate-time polymer stretching and flow-induced diffusion) and superdiffusive (long-time flow-induced diffusion). The influence of the topology of the GGS is unraveled in the intermediate-time regime, while the long-time regime is only weakly dependent on the topology of the polymer. With the decrease in the value of α , the magnitude of the ASD decreases, while the temporal exponent of the ASD increases in both the time regimes. Also there is an increase in both the magnitude of the ASD and the crossover time (from the subdiffusive to the superdiffusive regime) with an increase in the total mass of the polymeric structure.

  20. A high-performance flow-field structured iron-chromium redox flow battery

    NASA Astrophysics Data System (ADS)

    Zeng, Y. K.; Zhou, X. L.; An, L.; Wei, L.; Zhao, T. S.

    2016-08-01

    Unlike conventional iron-chromium redox flow batteries (ICRFBs) with a flow-through cell structure, in this work a high-performance ICRFB featuring a flow-field cell structure is developed. It is found that the present flow-field structured ICRFB reaches an energy efficiency of 76.3% with a current density of 120 mA cm-2 at 25 °C. The energy efficiency can be as high as 79.6% with an elevated current density of 200 mA cm-2 at 65 °C, a record performance of the ICRFB in the existing literature. In addition, it is demonstrated that the energy efficiency of the battery is stable during the cycle test, and that the capacity decay rate of the battery is 0.6% per cycle. More excitingly, the high performance of the flow-field structured battery significantly lowers the capital cost at 137.6 kWh-1, which is 28.2% lower than that of the conventional ICRFB for 8-h energy storage.

  1. A high-performance flow-field structured iron-chromium redox flow battery

    NASA Astrophysics Data System (ADS)

    Zeng, Y. K.; Zhou, X. L.; An, L.; Wei, L.; Zhao, T. S.

    2016-08-01

    Unlike conventional iron-chromium redox flow batteries (ICRFBs) with a flow-through cell structure, in this work a high-performance ICRFB featuring a flow-field cell structure is developed. It is found that the present flow-field structured ICRFB reaches an energy efficiency of 76.3% with a current density of 120 mA cm-2 at 25 °C. The energy efficiency can be as high as 79.6% with an elevated current density of 200 mA cm-2 at 65 °C, a record performance of the ICRFB in the existing literature. In addition, it is demonstrated that the energy efficiency of the battery is stable during the cycle test, and that the capacity decay rate of the battery is 0.6% per cycle. More excitingly, the high performance of the flow-field structured battery significantly lowers the capital cost at 137.6 kWh-1, which is 28.2% lower than that of the conventional ICRFB for 8-h energy storage.

  2. Study on an undershot cross-flow water turbine

    NASA Astrophysics Data System (ADS)

    Nishi, Yasuyuki; Inagaki, Terumi; Li, Yanrong; Omiya, Ryota; Fukutomi, Junichiro

    2014-06-01

    This study aims to develop a water turbine suitable for ultra-low heads in open channels, with the end goal being the effective utilization of unutilized hydroelectric energy in agricultural water channels. We performed tests by applying a cross-flow runner to an open channel as an undershot water turbine while attempting to simplify the structure and eliminate the casing. We experimentally investigated the flow fields and performance of water turbines in states where the flow rate was constant for the undershot cross-flow water turbine mentioned above. In addition, we compared existing undershot water turbines with our undershot cross-flow water turbine after attaching a bottom plate to the runner. From the results, we were able to clarify the following. Although the effective head for cross-flow runners with no bottom plate was lower than those found in existing runners equipped with a bottom plate, the power output is greater in the high rotational speed range because of the high turbine efficiency. Also, the runner with no bottom plate differed from runners that had a bottom plate in that no water was being wound up by the blades or retained between the blades, and the former received twice the flow due to the flow-through effect. As a result, the turbine efficiency was greater for runners with no bottom plate in the full rotational speed range compared with that found in runners that had a bottom plate.

  3. Near field flow structure of isothermal swirling flows and reacting non-premixed swirling flames

    SciTech Connect

    Olivani, Andrea; Solero, Giulio; Cozzi, Fabio; Coghe, Aldo

    2007-04-15

    Two confined lean non-premixed swirl-stabilized flame typologies were investigated in order to achieve detailed information on the thermal and aerodynamic field in the close vicinity of the burner throat and provide correlation with the exhaust emissions. Previous finding indicated the generation of a partially premixed flame with radial fuel injection and a purely diffusive flame with co-axial injection in a swirling co-flow. In the present work, the experimental study is reported which has been conducted on a straight exit laboratory burner with no quarl cone, fuelled by natural gas and air, and fired vertically upwards with the flame stabilized at the end of two concentric pipes with the annulus supplying swirled air and the central pipe delivering the fuel. Two fuel injection typologies, co-axial and radial (i.e., transverse), leading to different mixing mechanisms, have been characterized through different techniques: particle image velocimetry (PIV) and laser Doppler velocimetry (LDV) for a comprehensive analysis of the velocity field, still photography for the detection of flame front and main visible features, and thermocouples for the temperature distribution. Isothermal flow conditions have been included in the experimental investigation to provide a basic picture of the flow field and to comprehend the modifications induced by the combustion process. The results indicated that, although the global mixing process and the main flame structure are governed by the swirl motion imparted to the air stream, the two different fuel injection methodologies play an important role on mixture formation and flame stabilization in the primary mixing zone. Particularly, it has been found that, in case of axial injection, the turbulent interaction between the central fuel jet and the backflow generated by the swirl can induce an intermittent fuel penetration in the recirculated hot products and the formation of a central sooting luminous plume, a phenomenon totally

  4. Numerical study of secondary flows in curved ducts

    SciTech Connect

    Hur, N.

    1988-01-01

    The secondary flow of an incompressible viscous fluid in a curved duct with and without sidewall heating is studied by using a finite-volume method. It is known that for low Dean numbers, the secondary flow is characterized by a pair of counter-rotating vortices. This study shows that, as the Dean number is increased, the secondary-flow structure evolves into a double vortex pair for low-aspect-ratio ducts and roll cells for ducts of high aspect ratio. A stability diagram is obtained in the domain of curvature ratio and Reynolds number. It is found that, for ducts of high curvature, the onset of instability depends on the Dean number and the curvature ratio while, for ducts of small curvature, the onset can be characterized by the Dean number alone. A comparison with the available theoretical and experimental results indicates good agreement. When there is sidewall heating, the interaction between the centrifugal and the buoyancy forces characterizes the secondary flow structure. As the Grashof number is increased, the friction factor can decrease due to the transition from centrifugally dominant flow to buoyancy-dominated flow. Also, for curved ducts the inertial effect dominates and the heat transfer may be enhanced at lower Grashof numbers.

  5. Two-Phase Flow within Geological Flow Analogies--A Computational Study

    SciTech Connect

    Crandall, D.M.; Ahmadi, G.; Smith, D.H.; Ferer, M.V.; Richards, M.; Bromhal, G.S.

    2006-10-01

    Displacement of a viscous fluid in heterogeneous geological media by a less viscous one does not evacuate 100% of the defending fluid due to capillary and viscous fingering. This is of importance in geological flows that are encountered in secondary oil recovery and carbon dioxide sequestration in saturated brine fields. Hele-Shaw and pore/throat cells are commonly used to study this in the labratory. Numerical simulations of this flow phenomenon with pore-throat models have been prevalent for over two decades. This current work solves the full Navier-Stokes equations of conservation within random pore-throat geometries with varying properties to study the resulting flow properties. Verification of the solution method is performed by comparison of the model predictions with the available experimental data in the literature. Experimental flows in a pore-throat cell with a known geometrical structure are shown to be in good agreement with the model. Dynamic comparisons to a computational pore-throat model have been shown to be in good agreement as well. There are also additional two-phase immiscible flow patterns that can be identified from the current solutions for which the corresponding laboratory counter part or the pore-throat model predictions are not available. The identification of these flow patterns may allow more accurate modeling of fluid displacement on the reservoir scale.

  6. Control of Flow Structure on Low Swept Delta Wing with Steady Leading Edge Blowing

    NASA Astrophysics Data System (ADS)

    Ozturk, Ilhan; Zharfa, Mohammadreza; Yavuz, Mehmet Metin

    2014-11-01

    Interest in unmanned combat air vehicles (UCAVs) and micro air vehicles (MAVs) has stimulated investigation of the flow structure, as well as its control, on delta wings having low and moderate values of sweep angle. In the present study, the flow structure is characterized on a delta wing of low sweep 35-degree angle, which is subjected to steady leading edge blowing. The techniques of laser illuminated smoke visualization, laser Doppler anemometry (LDA), and surface pressure measurements are employed to investigate the steady and unsteady nature of the flow structure on delta wing, in relation to the dimensionless magnitude of the blowing coefficient. Using statistics and spectral analysis, unsteadiness of the flow structure is studied in detail. Different injection locations are utilized to apply different blowing patterns in order to identify the most efficient control, which provides the upmost change in the flow structure with the minimum energy input. The study aims to find the optimum flow control strategy to delay or to prevent the stall and possibly to reduce the buffeting on the wing surface. Since the blowing set-up is computer controlled, the unsteady blowing patterns compared to the present steady blowing patterns will be studied next. This project was supported by the Scientific and Technological Research Council of Turkey (Project Number: 3501 111M732).

  7. Vortex structures in turbulent channel flow behind an orifice

    NASA Astrophysics Data System (ADS)

    Makino, Soichiro; Iwamoto, Kaoru; Kawamura, Hiroshi

    2006-11-01

    Direct numerical simulation of a channel flow with an orifice has been performed for Reτ0=10 - 600, where uτ0 is the friction velocity calculated from the mean pressure gradient, δ the channel half width and ν the kinematic viscosity. In the wake region, the mean flow becomes asymmetric by the Coanda effect. The degree of asymmetry increases with increasing the Reynolds number for the laminar flow at Reτ0< 50. The degree decreases abruptly at Reτ0=50, where the transition from the laminar to the turbulent flow take places. Large-scale spanwise vortices generated at the orifice edges. They become deformed and break up into disordered small-scale structures in shear layer. The small-scale vortices are convected towards the channel center. The large-scale vortices have an important effect upon the reattachment locations and streamwise vortices near the wall in the wake region.

  8. Structural integrated sensor and actuator systems for active flow control

    NASA Astrophysics Data System (ADS)

    Behr, Christian; Schwerter, Martin; Leester-Schädel, Monika; Wierach, Peter; Dietzel, Andreas; Sinapius, Michael

    2016-04-01

    An adaptive flow separation control system is designed and implemented as an essential part of a novel high-lift device for future aircraft. The system consists of MEMS pressure sensors to determine the flow conditions and adaptive lips to regulate the mass flow and the velocity of a wall near stream over the internally blown Coanda flap. By the oscillating lip the mass flow in the blowing slot changes dynamically, consequently the momentum exchange of the boundary layer over a high lift flap required mass flow can be reduced. These new compact and highly integrated systems provide a real-time monitoring and manipulation of the flow conditions. In this context the integration of pressure sensors into flow sensing airfoils of composite material is investigated. Mechanical and electrical properties of the integrated sensors are investigated under mechanical loads during tensile tests. The sensors contain a reference pressure chamber isolated to the ambient by a deformable membrane with integrated piezoresistors connected as a Wheatstone bridge, which outputs voltage signals depending on the ambient pressure. The composite material in which the sensors are embedded consists of 22 individual layers of unidirectional glass fiber reinforced plastic (GFRP) prepreg. The results of the experiments are used for adapting the design of the sensors and the layout of the laminate to ensure an optimized flux of force in highly loaded structures primarily for future aeronautical applications. It can be shown that the pressure sensor withstands the embedding process into fiber composites with full functional capability and predictable behavior under stress.

  9. Power flows and Mechanical Intensities in structural finite element analysis

    NASA Technical Reports Server (NTRS)

    Hambric, Stephen A.

    1989-01-01

    The identification of power flow paths in dynamically loaded structures is an important, but currently unavailable, capability for the finite element analyst. For this reason, methods for calculating power flows and mechanical intensities in finite element models are developed here. Formulations for calculating input and output powers, power flows, mechanical intensities, and power dissipations for beam, plate, and solid element types are derived. NASTRAN is used to calculate the required velocity, force, and stress results of an analysis, which a post-processor then uses to calculate power flow quantities. The SDRC I-deas Supertab module is used to view the final results. Test models include a simple truss and a beam-stiffened cantilever plate. Both test cases showed reasonable power flow fields over low to medium frequencies, with accurate power balances. Future work will include testing with more complex models, developing an interactive graphics program to view easily and efficiently the analysis results, applying shape optimization methods to the problem with power flow variables as design constraints, and adding the power flow capability to NASTRAN.

  10. Flow structures around a flapping wing considering ground effect

    NASA Astrophysics Data System (ADS)

    Van Truong, Tien; Kim, Jihoon; Kim, Min Jun; Park, Hoon Cheol; Yoon, Kwang Joon; Byun, Doyoung

    2013-07-01

    Over the past several decades, there has been great interest in understanding the aerodynamics of flapping flight, namely the two flight modes of hovering and forward flight. However, there has been little focus on the aerodynamic characteristics during takeoff of insects. In a previous study we found that the Rhinoceros Beetle ( Trypoxylusdichotomus) takes off without jumping, which is uncommon for other insects. In this study we built a scaled-up electromechanical model of a flapping wing and investigated fluid flow around the beetle's wing model. In particular, the present dynamically scaled mechanical model has the wing kinematics pattern achieved from the real beetle's wing kinematics during takeoff. In addition, we could systematically change the three-dimensional inclined motion of the flapping model through each stroke. We used digital particle image velocimetry with high spatial resolution, and were able to qualitatively and quantitatively study the flow field around the wing at a Reynolds number of approximately 10,000. The present results provide insight into the aerodynamics and the evolution of vortical structures, as well as the ground effect experienced by a beetle's wing during takeoff. The main unsteady mechanisms of beetles have been identified and intensively analyzed as the stability of the leading edge vortex (LEV) during strokes, the delayed stall during upstroke, the rotational circulation in pronation periods, and wake capture in supination periods. Due to the ground effect, the LEV was enhanced during half downstroke, and the lift force could thus be increased to lift the beetle during takeoff. This is useful for researchers in developing a micro air vehicle that has a beetle-like flapping wing motion.

  11. Two-phase flow interfacial structures in a rod bundle geometry

    NASA Astrophysics Data System (ADS)

    Paranjape, Sidharth S.

    Interfacial structure of air-water two-phase flow in a scaled nuclear reactor rod bundle geometry was studied in this research. Global and local flow regimes were obtained for the rod bundle geometry. Local two-phase flow parameters were measured at various axial locations in order to understand the transport of interfacial structures. A one-dimensional two-group interfacial area transport model was evaluated using the local parameter database. Air-water two-phase flow experiments were performed in an 8 X 8 rod bundle test section to obtain flow regime maps at various axial locations. Area averaged void fraction was measured using parallel plate type impedance void meters. The cumulative probability distribution functions of the signals from the impedance void meters were used along with a self organizing neural network to identify flow regimes. Local flow regime maps revealed the cross-sectional distribution of flow regimes in the bundle. Local parameters that characterize interfacial structure, that is, void fraction alpha, interfacial area concentration, ai, bubble Sauter mean diameter, DSm and bubble velocity, vg were measured using four sensor conductivity probe technique. The local data revealed the distribution of the interfacial structure in the radial direction, as well as its development in the axial direction. In addition to this, the effect of spacer grid on the flow structure at different gas and liquid velocities was revealed by local parameter measurements across the spacer grids. A two-group interfacial area transport equation (IATE) specific to rod bundle geometry was derived. The derivation of two-group IATE required certain assumption on the bubble shapes in the subchannels and the bubbles spanning more than a subchannel. It was found that the geometrical relationship between the volume and the area of a cap bubble distorted by rods was similar to the one derived for a confined channel under a specific geometrical transformation. The one

  12. Simulation and study of stratified flows around finite bodies

    NASA Astrophysics Data System (ADS)

    Gushchin, V. A.; Matyushin, P. V.

    2016-06-01

    The flows past a sphere and a square cylinder of diameter d moving horizontally at the velocity U in a linearly density-stratified viscous incompressible fluid are studied. The flows are described by the Navier-Stokes equations in the Boussinesq approximation. Variations in the spatial vortex structure of the flows are analyzed in detail in a wide range of dimensionless parameters (such as the Reynolds number Re = Ud/ ν and the internal Froude number Fr = U/( Nd), where ν is the kinematic viscosity and N is the buoyancy frequency) by applying mathematical simulation (on supercomputers of Joint Supercomputer Center of the Russian Academy of Sciences) and three-dimensional flow visualization. At 0.005 < Fr < 100, the classification of flow regimes for the sphere (for 1 < Re < 500) and for the cylinder (for 1 < Re < 200) is improved. At Fr = 0 (i.e., at U = 0), the problem of diffusion-induced flow past a sphere leading to the formation of horizontal density layers near the sphere's upper and lower poles is considered. At Fr = 0.1 and Re = 50, the formation of a steady flow past a square cylinder with wavy hanging density layers in the wake is studied in detail.

  13. Aircraft energy efficiency laminar flow control wing design study

    NASA Technical Reports Server (NTRS)

    Bonner, T. F., Jr.; Pride, J. D., Jr.; Fernald, W. W.

    1977-01-01

    An engineering design study was performed in which laminar flow control (LFC) was integrated into the wing of a commercial passenger transport aircraft. A baseline aircraft configuration was selected and the wing geometry was defined. The LFC system, with suction slots, ducting, and suction pumps was integrated with the wing structure. The use of standard aluminum technology and advanced superplastic formed diffusion bonded titanium technology was evaluated. The results of the design study show that the LFC system can be integrated with the wing structure to provide a structurally and aerodynamically efficient wing for a commercial transport aircraft.

  14. Fluid Structural Analysis of Urine Flow in a Stented Ureter.

    PubMed

    Gómez-Blanco, J Carlos; Martínez-Reina, F Javier; Cruz, Domingo; Pagador, J Blas; Sánchez-Margallo, Francisco M; Soria, Federico

    2016-01-01

    Many urologists are currently studying new designs of ureteral stents to improve the quality of their operations and the subsequent recovery of the patient. In order to help during this design process, many computational models have been developed to simulate the behaviour of different biological tissues and provide a realistic computational environment to evaluate the stents. However, due to the high complexity of the involved tissues, they usually introduce simplifications to make these models less computationally demanding. In this study, the interaction between urine flow and a double-J stented ureter with a simplified geometry has been analysed. The Fluid-Structure Interaction (FSI) of urine and the ureteral wall was studied using three models for the solid domain: Mooney-Rivlin, Yeoh, and Ogden. The ureter was assumed to be quasi-incompressible and isotropic. Data obtained in previous studies from ex vivo and in vivo mechanical characterization of different ureters were used to fit the mentioned models. The results show that the interaction between the stented ureter and urine is negligible. Therefore, we can conclude that this type of models does not need to include the FSI and could be solved quite accurately assuming that the ureter is a rigid body and, thus, using the more simple Computational Fluid Dynamics (CFD) approach.

  15. Fluid Structural Analysis of Urine Flow in a Stented Ureter

    PubMed Central

    Gómez-Blanco, J. Carlos; Martínez-Reina, F. Javier; Cruz, Domingo; Pagador, J. Blas; Sánchez-Margallo, Francisco M.; Soria, Federico

    2016-01-01

    Many urologists are currently studying new designs of ureteral stents to improve the quality of their operations and the subsequent recovery of the patient. In order to help during this design process, many computational models have been developed to simulate the behaviour of different biological tissues and provide a realistic computational environment to evaluate the stents. However, due to the high complexity of the involved tissues, they usually introduce simplifications to make these models less computationally demanding. In this study, the interaction between urine flow and a double-J stented ureter with a simplified geometry has been analysed. The Fluid-Structure Interaction (FSI) of urine and the ureteral wall was studied using three models for the solid domain: Mooney-Rivlin, Yeoh, and Ogden. The ureter was assumed to be quasi-incompressible and isotropic. Data obtained in previous studies from ex vivo and in vivo mechanical characterization of different ureters were used to fit the mentioned models. The results show that the interaction between the stented ureter and urine is negligible. Therefore, we can conclude that this type of models does not need to include the FSI and could be solved quite accurately assuming that the ureter is a rigid body and, thus, using the more simple Computational Fluid Dynamics (CFD) approach. PMID:27127535

  16. Fluid flow structure around the mixer in a reactor with mechanical mixing

    SciTech Connect

    Lecheva, A.; Zheleva, I.

    2015-10-28

    Fluid flow structure around the mixer in a cylindrical reactor with mechanical mixing is studied and numerical results are presented in this article. The model area is complex because of the presence of convex corners of the mixer in the fluid flow. Proper boundary conditions for the vorticity calculated on the base of the stream function values near solid boundaries of the examined area are presented. The boundary value problem of motion of swirling incompressible viscous fluid in a vertical tank reactor with a mixer is solved numerically. The calculations are made by a computer code, written in MATLAB. The complex structure of the flow around the mixing disk is described and commented.

  17. Fluid flow structure around the mixer in a reactor with mechanical mixing

    NASA Astrophysics Data System (ADS)

    Lecheva, A.; Zheleva, I.

    2015-10-01

    Fluid flow structure around the mixer in a cylindrical reactor with mechanical mixing is studied and numerical results are presented in this article. The model area is complex because of the presence of convex corners of the mixer in the fluid flow. Proper boundary conditions for the vorticity calculated on the base of the stream function values near solid boundaries of the examined area are presented. The boundary value problem of motion of swirling incompressible viscous fluid in a vertical tank reactor with a mixer is solved numerically. The calculations are made by a computer code, written in MATLAB. The complex structure of the flow around the mixing disk is described and commented.

  18. Review: Impact of underground structures on the flow of urban groundwater

    NASA Astrophysics Data System (ADS)

    Attard, Guillaume; Winiarski, Thierry; Rossier, Yvan; Eisenlohr, Laurent

    2016-02-01

    Property economics favours the vertical development of cities but flow of groundwater can be affected by the use of underground space in them. This review article presents the state of the art regarding the impact of disturbances caused by underground structures (tunnels, basements of buildings, deep foundations, etc.) on the groundwater flow in urban aquifers. The structures built in the underground levels of urban areas are presented and organised in terms of their impact on flow: obstacle to the flow or disturbance of the groundwater budget of the flow system. These two types of disturbance are described in relation to the structure area and the urban area. The work reviewed shows, on one hand, the individual impacts of different urban underground structures, and on the other, their cumulative impacts on flow, using real case studies. Lastly, the works are placed in perspective regarding the integration of underground structures with the aim of operational management of an urban aquifer. The literature presents deterministic numerical modelling as a tool capable of contributing to this aim, in that it helps to quantify the effect of an underground infrastructure project on groundwater flow, which is crucial for decision-making processes. It can also be an operational decision-aid tool for choosing construction techniques or for formulating strategies to manage the water resource.

  19. An Immersed Boundary Finite-Element Solver for Flow-Induced Deformation of Soft Structures with Application in Cardiac Flows

    NASA Astrophysics Data System (ADS)

    Bhardwaj, Rajneesh; Mittal, Rajat

    2011-11-01

    The modeling of complex biological phenomena such as cardiac mechanics is challenging. It involves complex three dimensional geometries, moving structure boundaries inside the fluid domain and large flow-induced deformations of the structure. We present a fluid-structure interaction solver (FSI) which couples a sharp-interface immersed boundary method for flow simulation with a powerful finite-element based structure dynamics solver. An implicit partitioned (or segregated) approach is implemented to ensure the stability of the solver. We validate the FSI solver with published benchmark for a configuration which involves a thin elastic plate attached to a rigid cylinder. The frequency and amplitude of the oscillations of the plate are in good agreement with published results and non-linear dynamics of the plate and its coupling with the flow field are discussed. The FSI solver is used to understand left-ventricular hemodynamics and flow-induced dynamics of mitral leaflets during early diastolic filling and results from this study are presented.

  20. Study of two-phase flows in reduced gravity

    NASA Astrophysics Data System (ADS)

    Roy, Tirthankar

    have been done in the past to understand the global structure of gas-liquid two-phase flows under reduced gravity conditions, using experimental setups aboard drop towers or aircrafts flying parabolic flights, detailed data on local structure of such two-phase flows are extremely rare. Hence experiments were carried out in a 304 mm inner diameter (ID) test facility on earth. Keeping in mind the detailed experimental data base that needs to be generated to evaluate two-fluid model along with IATE, ground based simulations provide the only economic path. Here the reduced gravity condition is simulated using two-liquids of similar densities (water and Therminol 59 RTM in the present case). Only adiabatic two-phase flows were concentrated on at this initial stage. Such a large diameter test section was chosen to study the development of drops to their full extent (it is to be noted that under reduced gravity conditions the stable bubble size in gas-liquid two-phase flows is much larger than that at normal gravity conditions). Twelve flow conditions were chosen around predicted bubbly flow to cap-bubbly flow transition region. Detailed local data was obtained at ten radial locations for each of three axial locations using state-of-the art multi-sensor conductivity probes. The results are presented and discussed. Also one-group as well as two-group, steady state, one-dimensional IATE was evaluated against data obtained here and by other researchers, and the results presented and discussed.

  1. Experiments and 3D simulations of flow structures in junctions and their influence on location of flowmeters.

    PubMed

    Mignot, E; Bonakdari, H; Knothe, P; Lipeme Kouyi, G; Bessette, A; Rivière, N; Bertrand-Krajewski, J-L

    2012-01-01

    Open-channel junctions are common occurrences in sewer networks and flow rate measurement often occurs near these singularities. Local flow structures are 3D, impact on the representativeness of the local flow measurements and thus lead to deviations in the flow rate estimation. The present study aims (i) to measure and simulate the flow pattern in a junction flow, (ii) to analyse the impact of the junction on the velocity distribution according to the distance from the junction and thus (iii) to evaluate the typical error derived from the computation of the flow rate close to the junction. PMID:22828313

  2. Low-level atmospheric flows studied by pulsed Doppler lidar

    NASA Technical Reports Server (NTRS)

    Banta, Robert M.; Olivier, Lisa D.; Hardesty, R. Michael

    1992-01-01

    A pulsed Doppler radar gains a tremendous advantage in studying atmospheric flows when it has the ability to scan. The Wave Propagation Laboratory (WPL) has been operating a scanning, 10.59 micron CO2 system for over 10 years. Recently, the WPL lidar has been a featured instrument in several investigations of mesoscale wind fields in the lowest 3-4 km of the atmosphere. These include four experiments: a study of the initiation and growth of the sea breeze off the coast of California, a study of the snake column of a prescribed forest fire, a study of the nighttime flow over the complex terrain near Rocky Flats, Colorado as it affects the dispersion of atmospheric contaminants, and a study of the wind flow in the Grand Canyon. We have analyzed much data from these experiments, and we have found that the lidar provides new insight into the structure of these flows. Many of these studies took place in rugged or mountainous terrain, thus using one of the major benefits of the lidar: the narrow, 90 microrad beam of the lidar makes it an ideal instrument for studying flow close to topography.

  3. Structure and Mixing Characterization of Variable Density Transverse Jet Flows

    NASA Astrophysics Data System (ADS)

    Gevorkyan, Levon

    (CVP) and the generation of strong upstream shear layer instability. In contrast, weak, convectively unstable upstream shear layers corresponded with asymmetries in the jet cross-sectional shape and/or lack of a CVP structure. While momentum flux ratio J and density ratio S most significantly determined the strength of the instabilities and CVP structures, an additional dependence on jet Reynolds number for CVP formation was found, with significant increases in jet Reynolds number resulting in enhanced symmetry and CVP generation. The mixing characteristics of Rej = 1900 jets of various J, S, and injector type were explored in detail in the present studies using jet centerplane and cross-sectional PLIF measurements. Various mixing metrics such as the jet fluid centerline concentration decay, Unmixedness, and Probability Density Function (PDF) were applied systematically using a novel method for comparing jets with different mass flux characteristics. It was found that when comparing mixing metrics along the jet trajectory, strengthening the upstream shear layer instability by reducing J, and achieving absolutely unstable conditions, enhanced overall mixing. Reducing density ratio S for larger J values, which under equidensity (S = 1.00) conditions would create a convectively unstable shear layer, was also observed to enhance mixing. On the other hand, reducing S for low J conditions, which are known to produce absolutely unstable upstream shear layers even for equidensity cases, was actually observed to reduce mixing, a result attributed to a reduction in crossfiow fluid entrainment into shear layer vortex cores as jet density was reduced. Comparing injectors, the flush-mounted pipe was generally the best mixer, whereas the worst mixer was the nozzle that was elevated above the crossfiow boundary layer due to upstream shear layer co-flow generated by the elevated nozzle contour; this co-flow was observed here and in prior studies to stabilize the shear layer. The

  4. Invariant-tori-like Lagrangian coherent structures in geophysical flows.

    PubMed

    Beron-Vera, Francisco J; Olascoaga, María J; Brown, Michael G; Koçak, Huseyin; Rypina, Irina I

    2010-03-01

    The term "Lagrangian coherent structure" (LCS) is normally used to describe numerically detected structures whose properties are similar to those of stable and unstable manifolds of hyperbolic trajectories. The latter structures are invariant curves, i.e., material curves of fluid that serve as transport barriers. In this paper we use the term LCS to describe a different type of structure whose properties are similar to those of invariant tori in certain classes of two-dimensional incompressible flows. Like stable and unstable manifolds, invariant tori are invariant curves that serve as transport barriers. There are many differences, however, between traditional LCSs and invariant-tori-like LCSs. These differences are discussed with an emphasis on numerical techniques that can be used to identify invariant-tori-like LCSs. Structures of this type are often present in geophysical flows where zonal jets are present. A prime example of an invariant-torus-like LCS is the transport barrier near the core of the polar night jet in the Earth's lower and middle stratospheres in the austral winter and early spring; this is the barrier that traps ozone-depleted air inside the ozone hole. This example is investigated using both a simple analytically prescribed flow and a velocity field produced by a general circulation model of the Earth's atmosphere. PMID:20370304

  5. Experimental study of turbulent axisymmetric cavity flow

    NASA Astrophysics Data System (ADS)

    Lee, D. H.; Sung, H. J.

    1994-08-01

    An experimental study is made of turbulent axisymmetric cavity flow. The flow configuration consists of a sudden expansion and contraction pipe joint. In using the LDV system, in an effort to minimize refraction of laser beams at the curved interface, a refraction correction formula for the Reynolds shear stress is devised. Three values of the cavity length ( L = 300, 600 and 900 mm) are chosen, and the cavity height ( H) is fixed at 55 mm. Both open and closed cavities are considered. Special attention is given to the critical case L = 600 mm, where the cavity length L is nearly equal to the reattachment length of the flow. The Reynolds number, based on the inlet diameter ( D = 110 mm) is 73,000. Measurement data are presented for the static wall pressure, mean velocity profiles, vorticity thickness distributions, and turbulence quantities.

  6. Computer model for selecting flow measuring structures in open channels

    SciTech Connect

    Hickey, M. J.

    1980-01-01

    Quantifying various pollutants in natural waterways has received increased emphasis with more stringent regulations issued by the Environmental Protection Agency (E.P.A.). Measuring natural stream fows presents a magnitude of problems, the most significant is the type of structure needed to measure the flows at the desired level of accuracy. A computer model designed to select a structure to best fit the engineer's needs is under development. This model, given the pertinent boundary conditions, will pinpoint the structure most suitable, if one exists. This selection process greatly facilitates the old selection process of trial and error.

  7. The effect of structural and rheological properties on blood flow distributions in capillary networks

    NASA Astrophysics Data System (ADS)

    Goldman, Daniel

    2001-11-01

    In various tissues microvascular structure, both geometric and topological, has been shown to be an important determinant of microcirculatory hemodynamics. In addition, blood rheology affects flow and hematocrit distributions in the microcirculation. Here we study steady-state hemodynamics in capillary networks modeled on the three-dimensional structure of the hamster cheek pouch retractor muscle. Capillary diameter is fixed while other structural properties are varied and an ensemble of similar random networks is generated for each parameter set. Using an experimentally derived two-phase continuum model for the flow of blood plasma and red cells, we investigate the effects of network size and topology on blood flow distributions and their variability. We also use typical capillary network structures to examine the importance of rheological effects under varying conditions. Our results indicate the relative importance of microvascular structure and blood rheology in determining the hemodynamic properties of capillary networks in striated muscle.

  8. Flow-Structure-Acoustic Interaction Computational Modeling of Voice Production inside an Entire Airway

    NASA Astrophysics Data System (ADS)

    Jiang, Weili; Zheng, Xudong; Xue, Qian

    2015-11-01

    Human voice quality is directly determined by the interplay of dynamic behavior of glottal flow, vibratory characteristics of VFs and acoustic characteristics of upper airway. These multiphysics constituents are tightly coupled together and precisely coordinate to produce understandable sound. Despite many years' research effort, the direct relationships among the detailed flow features, VF vibration and aeroacoustics still remains elusive. This study utilizes a first-principle based, flow-structure-acoustics interaction computational modeling approach to study the process of voice production inside an entire human airway. In the current approach, a sharp interface immersed boundary method based incompressible flow solver is utilized to model the glottal flow; A finite element based solid mechanics solver is utilized to model the vocal vibration; A high-order immersed boundary method based acoustics solver is utilized to directly compute sound. These three solvers are fully coupled to mimic the complex flow-structure-acoustic interaction during voice production. The geometry of airway is reconstructed based on the in-vivo MRI measurement reported by Story et al. (1995) and a three-layer continuum based vocal fold model is taken from Titze and Talkin (1979). Results from these simulations will be presented and further analyzed to get new insight into the complex flow-structure-acoustic interaction during voice production. This study is expected to improve the understanding of fundamental physical mechanism of voice production and to help to build direct cause-effect relationship between biomechanics and voice sound.

  9. Numerical Study of Tip Vortex Flows

    NASA Technical Reports Server (NTRS)

    Dacles-Mariani, Jennifer; Hafez, Mohamed

    1998-01-01

    This paper presents an overview and summary of the many different research work related to tip vortex flows and wake/trailing vortices as applied to practical engineering problems. As a literature survey paper, it outlines relevant analytical, theoretical, experimental and computational study found in literature. It also discusses in brief some of the fundamental aspects of the physics and its complexities. An appendix is also included. The topics included in this paper are: 1) Analytical Vortices; 2) Experimental Studies; 3) Computational Studies; 4) Wake Vortex Control and Management; 5) Wake Modeling; 6) High-Lift Systems; 7) Issues in Numerical Studies; 8) Instabilities; 9) Related Topics; 10) Visualization Tools for Vertical Flows; 11) Further Work Needed; 12) Acknowledgements; 13) References; and 14) Appendix.

  10. Pulsed Flows Along a Cusp Structure Observed with SOO/AIA

    NASA Technical Reports Server (NTRS)

    Thompson, Barbara; Demoulin, P.; Mandrini, C. H.; Mays, M. L.; Ofman, L.; Driel-Gesztelyi, L. Van; Viall, N. M.

    2011-01-01

    We present observations of a cusp-shaped structure that formed after a flare and coronal mass ejection on 14 February 2011. Throughout the evolution of the cusp structure, blob features up to a few Mm in size were observed flowing along the legs and stalk of the cusp at projected speeds ranging from 50 to 150 km/sec. Around two dozen blob features, on order of 1 - 3 minutes apart, were tracked in multiple AlA EUV wavelengths. The blobs flowed outward (away from the Sun) along the cusp stalk, and most of the observed speeds were either constant or decelerating. We attempt to reconstruct the 3-D magnetic field of the evolving structure, discuss the possible drivers of the flows (including pulsed reconnect ion and tearing mode instability), and compare the observations to studies of pulsed reconnect ion and blob flows in the solar wind and the Earth's magnetosphere.

  11. Turbulent statistics and flow structures in spanwise-rotating turbulent plane Couette flows

    NASA Astrophysics Data System (ADS)

    Gai, Jie; Xia, Zhenhua; Cai, Qingdong; Chen, Shiyi

    2016-09-01

    A series of direct numerical simulations of spanwise-rotating turbulent plane Couette flows at a Reynolds number of 1300 with rotation numbers Ro between 0 and 0.9 is carried out to investigate the effects of anticyclonic rotation on turbulent statistics and flow structures. Several typical turbulent statistics are presented, including the mean shear rate at the centerline, the wall-friction Reynolds number, and volume-averaged kinetic energies with respect to the secondary flow field, turbulent field, and total fluctuation field. Our results show that the rotation changes these quantities in different manners. Volume-averaged balance equations for kinetic energy are analyzed and it turns out that the interaction term acts as a kinetic energy bridge that transfers energy from the secondary flow to the turbulent fluctuations. Several typical flow regimes are identified based on the correlation functions across the whole channel and flow visualizations. The two-dimensional roll cells are observed at weak rotation Ro=0.01 , where alternant clustering of vortices appears. Three-dimensional roll cells emerge around Ro≈0.02 , where the clustering of vortices shows the meandering and bifurcating behavior. For moderate rotation 0.07 ≲Ro≲0.36 , well-organized structures are observed, where the herringbonelike vortices are clustered between streaks from the top view of three-dimensional flow visualization and form annuluses. More importantly, the vortices are rather confined to one side of the walls when Ro≤0.02 and are inclined from the bottom to upper walls when Ro≥0.07 .

  12. Flow structure and mixing at the confluence of unequal density rivers (Invited)

    NASA Astrophysics Data System (ADS)

    Best, J.; Parsons, D. R.; Amsler, M.; Kostaschuk, R.; Lane, S. N.; Orfeo, O.; Szupiany, R.; Hardy, R. J.

    2010-12-01

    River channel confluences are vital components of all river networks and are often sites of significant hydraulic, morphological and ecological change. Past work has identified the principal controls on flow mixing at river junctions, with the confluence angle, discharge or momentum ratio between the two channels and junction bed morphology being critical. However, little attention has been devoted to the influence of density differences between the two confluent flows, which may exist due to differences in suspended sediment concentration. This paper details a case study of the Río Bermejo and Río Paraguay, Argentina, where there is always a density contrast between the two flows, and shows how this dominates the flow structure, turbulence and flow mixing. Field surveys employed acoustic Doppler current profiling, single- and multi- beam echo sounding and direct sampling of the water column to measure the flow structure. This work reveals the distortion of the mixing layer between the flows as the denser Río Bermejo fluid forms a density underflow that moves beneath that of the clearer water Río Paraguay. Upwellings of dense turbid flow occur in the downstream main channel due to bed roughness, mixing instabilities on the top of the underflow and interaction of the flow with the channel margins. These mixing processes, and the techniques used to visualize and quantify them at such river confluences, will be discussed.

  13. A study of intermittent flow in downward inclined pipes

    SciTech Connect

    Yang, J.; Sarica, C.; Chen, X.; Brill, J.P.

    1996-12-31

    The downward simultaneous flow of gas and liquid is often encountered in hilly terrain pipelines and steam injection wells. Most of the available methods for predicting the behavior of gas-liquid flow in pipes have been developed for horizontal and upward inclined pipes. In this study, co-current steady state slug flow in downward inclined pipes is investigated, experimentally and theoretically. A series of slug flow experiments are conducted with an air-kerosene system in a 2-in. diameter, 75-ft long pipe installed on an inclinable structure. Liquid holdup and pressure drop measurements are obtained for downward inclination angles from 0{degree} to {minus}90{degree} at different flow conditions. Correlations for slug flow characteristics are obtained based on the experimental data. A mechanistic model based on a unit cell approach has been proposed for the prediction of the detailed slug structure, and subsequently the pressure gradient. Fully developed slug flow could not be observed from {minus}50{degree} to {minus}90{degree}. A correlation was obtained for slug liquid holdup, and an analytical model and a correlation were developed for slug translational velocity. The lognormal distribution was found to best fit all the experimental slug length data. Equations for mean and design slug length were derived from the lognormal distribution function for inclination angles ranging from 0{degree} to {minus}30{degree}. A slug frequency correlation was also developed. The model can be used to predict intermittent flow behavior in downward inclined pipes. The correlations for slug liquid holdup, slug translational velocity, and slug length and frequency are closure relationships applicable to any model. Slug frequency information is also imperative for erosion and corrosion rate predictions.

  14. CFD study on flow characteristics of pump sump and performance analysis of the mixed flow pump

    NASA Astrophysics Data System (ADS)

    Zhao, Y. X.; Kim, C. G.; Lee, Y. H.

    2013-12-01

    Head-capacity curves provided by the pump manufacturer are obtained on the condition of no vortices flowing into the pump intake. The efficiency and performance of pumping stations depend not only on the performance of the selected pumps but also on the proper design of the intake sumps. A faulty design of pump sump can lead to the occurrence of swirl and vortices, which reduce the pump performance. Therefore, sump model test is necessary in order to check the flow condition around intake structure. Numerical simulation is a good facility for reducing the time and cost involved throughout the design process. In this study, the commercial software ANSYS CFX-13.0 has been used for the CFD analysis of the pump sump. The effect of an anti-vortex device (AVD) for the submerged vortex has been examined. Hydraulic performances for the head rise, shaft power, pump efficiencies versus flow rate are studied by the performance curves. In addition, numerical simulation of cavitation phenomenon in a mixed flow pump has been performed by calculating the full cavitation model with k-ε turbulence model. According to the result, the efficacy of the AVD to ensure the uniform flow conditions around the pump intake is confirmed. From the numerical analysis, the inception of cavitation is observed on the suction surface where the leading edges meet the tip, and then the cavitation zone expands.

  15. Comparative study of pressure-flow parameters.

    PubMed

    Eri, Lars M; Wessel, Nicolai; Tysland, Ole; Berge, Viktor

    2002-01-01

    Methods for quantification of bladder outlet obstruction (BOO) are still controversial. Parameters such as detrusor opening pressure (p(det.open)), maximum detrusor pressure (p(det.max)), minimum voiding pressure (p(det.min.void)), and detrusor pressure at maximum flow rate (P(det.Qmax)) separate obstructed from nonobstructed patients to some extent, but two nomograms, the Abrams-Griffiths nomogram and the linearized passive urethral resistance relation (LinPURR), are more accepted for this purpose, along with the urethral resistance algorithm. In this retrospective, methodologic study, we evaluated the properties of these parameters with regard to test-retest reproducibility and ability to detect a moderate (pharmacologic) and a pronounced (surgical) relief of bladder outlet obstruction. We studied the pressure-flow charts of 42 patients who underwent 24 weeks of androgen suppressive therapy, 42 corresponding patients who received placebo, and 30 patients who had prostate surgery. The patients performed repeat void pressure-flow examinations before and after treatment or placebo. The various parameters were compared. Among the bladder pressure parameters, P(det.Qmax) seemed to have some advantages, supporting the belief that it is the most relevant detrusor pressure parameter to include in nomograms to quantify BOO. In assessment of a large decrease in urethral resistance, such as after TURp, resistance parameters that are based on maximum flow rate as well as detrusor pressure are preferable. PMID:11948710

  16. B-1 AFT Nacelle Flow Visualization Study

    NASA Technical Reports Server (NTRS)

    Celniker, Robert

    1975-01-01

    A 2-month program was conducted to perform engineering evaluation and design tasks to prepare for visualization and photography of the airflow along the aft portion of the B-1 nacelles and nozzles during flight test. Several methods of visualizing the flow were investigated and compared with respect to cost, impact of the device on the flow patterns, suitability for use in the flight environment, and operability throughout the flight. Data were based on a literature search and discussions with the test personnel. Tufts were selected as the flow visualization device in preference to several other devices studied. A tuft installation pattern has been prepared for the right-hand aft nacelle area of B-1 air vehicle No.2. Flight research programs to develop flow visualization devices other than tufts for use in future testing are recommended. A design study was conducted to select a suitable motion picture camera, to select the camera location, and to prepare engineering drawings sufficient to permit installation of the camera. Ten locations on the air vehicle were evaluated before the selection of the location in the horizontal stabilizer actuator fairing. The considerations included cost, camera angle, available volume, environmental control, flutter impact, and interference with antennas or other instrumentation.

  17. Structural modelling of a compliant flexure flow energy harvester

    NASA Astrophysics Data System (ADS)

    Chatterjee, Punnag; Bryant, Matthew

    2015-09-01

    This paper presents the concept of a flow-induced vibration energy harvester based on a one-piece compliant flexure structure. This energy harvester utilizes the aeroelastic flutter phenomenon to convert flow energy to structural vibrational energy and to electrical power output through piezoelectric transducers. This flexure creates a discontinuity in the structural stiffness and geometry that can be used to tailor the mode shapes and natural frequencies of the device to the desired operating flow regime while eliminating the need for discrete hinges that are subject to fouling and friction. An approximate representation of the flexure rigidity is developed from the flexure link geometry, and a model of the complete discontinuous structure and integrated flexure is formulated based on the transfer matrix method. The natural frequencies and mode shapes predicted by the model are validated using finite element simulations and are shown to be in close agreement. A proof-of-concept energy harvester incorporating the proposed flexure design has been fabricated and investigated in wind tunnel testing. The aeroelastic modal convergence, critical flutter wind speed, power output and limit cycle behavior of this device is experimentally determined and discussed.

  18. Granular flows on erodible layers: type and evolution of flow and deposit structures

    NASA Astrophysics Data System (ADS)

    Crosta, G.; De Blasio, F.; De Caro, M.; Volpi, G.; Frattini, P.

    2012-04-01

    The interaction of a fast moving landslide mass with the basal layer over which movement takes place has been discussed in previous contributions. Nevertheless, the evolution of the structures within the moving mass and the erodible layer are still to be described in detail (Hungr and Evans, 2004; Crosta et al., 1992, 2006, 2009, 2011; Dufresne et al., 2010; Mangeney et al., 2010) and modeling results (Crosta et al., 2006, 2009, 2011; Mangeney et al., 2010). We present some of the results from a campaign of laboratory experiments aimed at studying the evolution of a granular flow at the impact with and during the successive spreading over a cohesionless erodible layer. We performed these test to study the processes and to collect data and evidences to compare them with the results of numerical simulations and to verify capabilities of numerical codes. The laboratory setup consists of an inclined slope and an horizontal sector where release and transport, and deposition take place, respectively. Materials used for the tests are: a uniform rounded siliceous sand (Hostun sand; 0.125-0.5 mm) commonly adopted in lab tests because free of scale effects, and a gravel made of angular elements (12 mm in ave. size). Both the materials have been tested in dry conditions. Different slope angles have been tested (40, 45, 50, 55, 50, 66°) as well as different thicknesses of the erodible layer (0, 0.5, 1, 2 cm) and volumes of the released material (1.5, 3, 5, 9.6 liters). Tests have been monitored by means of a high speed camera and the pre- and post-failure geometries have been surveyed by means of a laser scanner. Deposit description allowed also the computation of volumes and the characterization of the different structures developed and frozen into the deposit. Experiments allowed us to observe the extreme processes occurring during the movement and the mise en place of the deposits. In particular, we observe the formation of a clear wave-like feature developing during the

  19. Experimental study of complex flow and turbulence structure around a turbomachine rotor blade operating behind a row of Inlet Guide Vanes (IGVS)

    NASA Astrophysics Data System (ADS)

    Soranna, Francesco

    The flow and turbulence around a rotor blade operating downstream of a row of Inlet Guide Vanes (IGV) are investigated experimentally in a refractive index matched turbomachinery facility that provides unobstructed view of the entire flow field. High resolution 2D and Stereoscopic PIV measurements are performed both at midspan and in the tip region of the rotor blade, focusing on effects of wake-blade, wake-boundary-layer and wake-wake interactions. We first examine the modification to the shape of an IGV-wake as well as to the spatial distribution of turbulence within it as the wake propagates along the rotor blade. Due to the spatially non-uniform velocity distribution, the IGV wake deforms through the rotor passage, expanding near the leading edge and shrinking near the trailing edge. The turbulence within this wake becomes spatially non-uniform and highly anisotropic as a result of interaction with the non-uniform strain rate field within the rotor passage. Several mechanisms, which are associated with rapid straining and highly non-uniform production rate (P), including negative production on the suction side of the blade, contribute to the observed trends. During IGV-wake impingement, the suction side boundary layer near the trailing edge becomes significantly thinner, with lower momentum thickness and more stable profile compared to other phases at the same location. Analysis of available terms in the integral momentum equation indicates that the phase-averaged unsteady term is the main contributor to the decrease in momentum thickness within the impinging wake. Thinning of the boundary/shear layer extends into the rotor near wake, making it narrower and increasing the phase averaged shear velocity gradients and associated production term just downstream of the trailing edge. Consequently, the turbulent kinetic energy (TKE) increases causing as much as 75% phase-dependent variations in peak TKE magnitude. Further away from the blade, the rotor wake is bent

  20. Performance study of a data flow architecture

    NASA Technical Reports Server (NTRS)

    Adams, George

    1985-01-01

    Teams of scientists studied data flow concepts, static data flow machine architecture, and the VAL language. Each team mapped its application onto the machine and coded it in VAL. The principal findings of the study were: (1) Five of the seven applications used the full power of the target machine. The galactic simulation and multigrid fluid flow teams found that a significantly smaller version of the machine (16 processing elements) would suffice. (2) A number of machine design parameters including processing element (PE) function unit numbers, array memory size and bandwidth, and routing network capability were found to be crucial for optimal machine performance. (3) The study participants readily acquired VAL programming skills. (4) Participants learned that application-based performance evaluation is a sound method of evaluating new computer architectures, even those that are not fully specified. During the course of the study, participants developed models for using computers to solve numerical problems and for evaluating new architectures. These models form the bases for future evaluation studies.

  1. Accuracy of flow convergence estimates of mitral regurgitant flow rates obtained by use of multiple color flow Doppler M-mode aliasing boundaries: an experimental animal study.

    PubMed

    Zhang, J; Jones, M; Shandas, R; Valdes-Cruz, L M; Murillo, A; Yamada, I; Kang, S U; Weintraub, R G; Shiota, T; Sahn, D J

    1993-02-01

    The proximal flow convergence method of multiplying color Doppler aliasing velocity by flow convergence surface area has yielded a new means of quantifying flow rate by noninvasively derived measurements. Unlike previous methods of visualizing the turbulent jet of mitral regurgitation on color flow Doppler mapping, flow convergence methods are less influenced by machine factors because of the systematic structure of the laminar flow convergence region. However, recent studies have demonstrated that the flow rate calculated from the first aliasing boundary of color flow Doppler imaging is dependent on orifice size, flow rate, aliasing velocity and therefore on the distance from the orifice chosen for measurement. In this study we calculated the regurgitant flow rates acquired by use of multiple proximal aliasing boundaries on color Doppler M-mode traces and assessed the effect of distances of measurement and aliasing velocities on the calculated regurgitant flow rate. Six sheep with surgically induced mitral regurgitation were studied. The distances from the mitral valve leaflet M-mode line to the first, second, and third sequential aliasing boundaries on color Doppler M-mode traces were measured and converted to the regurgitant flow rates calculated by applying the hemispheric flow equation and averaging instantaneous flow rates throughout systole. The flow rates that were calculated from the first, second, and third aliasing boundaries correlated well with the actual regurgitant flow rates (r = 0.91 to 0.96). The mean percentage error from the actual flow rates were 151% for the first aliasing boundary, 7% for the second aliasing boundary, and -43% for the third aliasing boundary; and the association between aliasing velocities and calculated flow rates indicates an inverse relationship, which suggests that in this model, there were limited velocity-distance combinations that fit with a hemispheric assumption for flow convergence geometry. The second aliasing

  2. Numerical Studies of a Fluidic Diverter for Flow Control

    NASA Technical Reports Server (NTRS)

    Gokoglu, Suleyman A.; Kuczmarski, Maria A.; Culley, Dennis E.; Raghu, Surya

    2009-01-01

    The internal flow structure in a specific fluidic diverter is studied over a range from low subsonic to sonic inlet conditions by a time-dependent numerical analysis. The understanding will aid in the development of fluidic diverters with minimum pressure losses and advanced designs of flow control actuators. The velocity, temperature and pressure fields are calculated for subsonic conditions and the self-induced oscillatory behavior of the flow is successfully predicted. The results of our numerical studies have excellent agreement with our experimental measurements of oscillation frequencies. The acoustic speed in the gaseous medium is determined to be a key factor for up to sonic conditions in governing the mechanism of initiating the oscillations as well as determining its frequency. The feasibility of employing plasma actuation with a minimal perturbation level is demonstrated in steady-state calculations to also produce oscillation frequencies of our own choosing instead of being dependent on the fixed-geometry fluidic device.

  3. Dislocation structures and anomalous flow in L12 compounds

    NASA Astrophysics Data System (ADS)

    Dimiduk, D. M.

    1991-06-01

    The theory of the anomalous flow behavior of LI2 compounds has developed over the last 30 years. This theory has a foundation in the early estimates of the crystallographic anisotropy of antiphase boundary (APB) energy in these compounds. In spite of this critical aspect of the theory, it is only in the last five years that electron microscopy has been employed to quantify the APB energies and to determine the detailed nature of dislocation structures at each stage of deformation. The recent studies of several research groups have provided essentially consistent new details about the nature of dislocations in Ni3AI and a few other LI2 compounds which exhibit anomalous flow behavior. These studies have introduced several new concepts for the controlling dislocation mechanisms. Additionally, these studies have shown that in Ni3AI, the APB energies have only small variations in magnitude with change of the APB plane (they are nearly isotropic), are relatively insensitive to changes in solute content, and the anisotropy ratio does not correlate with alloy strength. The present manuscript provides a critical review of the new transmission electron microscopy (TEM) results along with the new concepts for the mechanism of anomalous flow. Inconsistencies and deficiencies within these new concepts are identified and discussed. The collective set of electron-microscopy results is discussed within the context of both the mechanical behavior of LI2 compounds and the Greenberg and Paidar, Pope and Vitek (PPV) models for anomalous flow. Conceptual consistency with these models can only be constructed if the Kear-Wilsdorf (K-W) configurations are treated as an irreversible work hardening or relaxation artifact and, specific details of these two models cannot be shown by electron microscopy. Alternatively, the structural features recently revealed by electron microscopy have not been assembled into a self-consistent model for yielding which fully addresses the mechanical behavior

  4. Flow-structure-acoustic interaction in a human voice model.

    PubMed

    Becker, Stefan; Kniesburges, Stefan; Müller, Stefan; Delgado, Antonio; Link, Gerhard; Kaltenbacher, Manfred; Döllinger, Michael

    2009-03-01

    For the investigation of the physical processes of human phonation, inhomogeneous synthetic vocal folds were developed to represent the full fluid-structure-acoustic coupling. They consisted of polyurethane rubber with a stiffness in the range of human vocal folds and were mounted in a channel, shaped like the vocal tract in the supraglottal region. This test facility permitted extensive observations of flow-induced vocal fold vibrations, the periodic flow field, and the acoustic signals in the far field of the channel. Detailed measurements were performed applying particle-image velocimetry, a laser-scanning vibrometer, a microphone, unsteady pressure sensors, and a hot-wire probe, with the aim of identifying the physical mechanisms in human phonation. The results support the existence of the Coanda effect during phonation, with the flow attaching to one vocal fold and separating from the other. This behavior is not linked to one vocal fold and changes stochastically from cycle to cycle. The oscillating flow field generates a tonal sound. The broadband noise is presumed to be caused by the interaction of the asymmetric flow with the downstream-facing surfaces of the vocal folds, analogous to trailing-edge noise. PMID:19275292

  5. Coherent structures in flow over two-dimensional dunes

    NASA Astrophysics Data System (ADS)

    Chang, Kyungsik; Constantinescu, George

    2013-05-01

    The instantaneous turbulent flow fields over a smooth bed and a bed containing large-scale roughness elements are characterized by the presence of elongated low and high streamwise momentum regions or streaks. If the bed contains large-scale roughness elements (e.g., dunes), the size of the streaks increases and is of the order of the size of these elements and the flow depth. The present large eddy simulation (LES) study focuses on the case of developing flow within wide channels containing at the bottom a long array of spanwise-oriented sinusoidal 2-D dunes (2a/h = 0.1, λ/h = 1, λ is the wavelength, 2a is the dune height, and h is the mean flow depth) and an array of 2-D asymmetric dunes (2a/h = 0.25, λ/h = 3.75) of closer shape to the ones observed in natural streams. For the case of an incoming steady flow, the instantaneous flow fields, in the region where the flow transitions toward a fully developed turbulent flow regime, contain arrays of highly organized hairpin vortices, whose dimensions are larger than the dune height. The LES shows that for relatively shallow channels (e.g., channels with 2a/h = 0.25), the large-scale hairpins and the streaks penetrate regularly up to the free surface, thus affecting mass transport and mixing over the whole water column. This paper explained the mechanism for the formation of these arrays of hairpin vortices and discussed the changes between a case with asymmetric dunes that are characterized by a large value of λ/2a (= 15) and a long upslope face and a case with symmetric dunes for which λ/2a = 10, the upslope face is relatively short, and the rate of change of the bed curvature around the dune's crest is relatively small. The study discusses the main mechanisms through which large-scale hairpin form and how these mechanisms change between two dune geometries (sinusoidal versus asymmetric dunes). This study also shows that hairpin eddies play the primary role in the formation of the streaks over the region

  6. Axial compressor middle stage secondary flow study

    NASA Technical Reports Server (NTRS)

    Wagner, J. H.; Dring, R. P.; Joslyn, H. D.

    1983-01-01

    This report describes an experimental investigation of the secondary flow within and aft of an axial compressor model with thick endwall boundary layers. The objective of the study was to obtain detailed aerodynamic and trace gas concentration traverse data aft of a well documented isolated rotor for the ultimate purpose of improving the design phases of compressor development based on an improved physical understanding of secondary flow. It was determined from the flow visualization, aerodynamic, and trace gas concentration results that the relative unloading of the midspan region of the airfoil inhibitied a fullspan separation at high loading preventing the massive radial displacement of the hub corner stall to the tip. Radial distribution of high and low total pressure fluid influenced the magnitude of the spanwise distribution of loss, such that, there was a general decreases in loss near the hub to the extent that for the least loaded case a negative loss (increase in total pressure) was observed. The ability to determine the spanwise distribution of blockage was demonstrated. Large blockage was present in the endwall regions due to the corner stall and tip leakage with little blockage in the core flow region. Hub blockage was found to increase rapidly with loading.

  7. Structure and response to flow of the glycocalyx layer.

    PubMed

    Cruz-Chu, Eduardo R; Malafeev, Alexander; Pajarskas, Tautrimas; Pivkin, Igor V; Koumoutsakos, Petros

    2014-01-01

    The glycocalyx is a sugar-rich layer located at the luminal part of the endothelial cells. It is involved in key metabolic processes and its malfunction is related to several diseases. To understand the function of the glycocalyx, a molecular level characterization is necessary. In this article, we present large-scale molecular-dynamics simulations that provide a comprehensive description of the structure and dynamics of the glycocalyx. We introduce the most detailed, to-date, all-atom glycocalyx model, composed of lipid bilayer, proteoglycan dimers, and heparan sulfate chains with realistic sequences. Our results reveal the folding of proteoglycan ectodomain and the extended conformation of heparan sulfate chains. Furthermore, we study the glycocalyx response under shear flow and its role as a flypaper for binding fibroblast growth factors (FGFs), which are involved in diverse functions related to cellular differentiation, including angiogenesis, morphogenesis, and wound healing. The simulations show that the glycocalyx increases the effective concentration of FGFs, leading to FGF oligomerization, and acts as a lever to transfer mechanical stimulus into the cytoplasmic side of endothelial cells.

  8. Experimental Study of Flow in a Bifurcation

    NASA Astrophysics Data System (ADS)

    Fresconi, Frank; Prasad, Ajay

    2003-11-01

    An instability known as the Dean vortex occurs in curved pipes with a longitudinal pressure gradient. A similar effect is manifest in the flow in a converging or diverging bifurcation, such as those found in the human respiratory airways. The goal of this study is to characterize secondary flows in a bifurcation. Particle image velocimetry (PIV) and laser-induced fluorescence (LIF) experiments were performed in a clear, plastic model. Results show the strength and migration of secondary vortices. Primary velocity features are also presented along with dispersion patterns from dye visualization. Unsteadiness, associated with a hairpin vortex, was also found at higher Re. This work can be used to assess the dispersion of particles in the lung. Medical delivery systems and pollution effect studies would profit from such an understanding.

  9. Liquid-Gas Relative Permeabilities in Fractures: Effects of Flow Structures, Phase Transformation and Surface Roughness

    SciTech Connect

    Chih-Ying Chen

    2005-06-30

    Two-phase flow through fractured media is important in petroleum, geothermal, and environmental applications. However, the actual physics and phenomena that occur inside fractures are poorly understood, and oversimplified relative permeability curves are commonly used in fractured reservoir simulations. In this work, an experimental apparatus equipped with a high-speed data acquisition system, real-time visualization, and automated image processing technology was constructed to study three transparent analog fractures with distinct surface roughnesses: smooth, homogeneously rough, and randomly rough. Air-water relative permeability measurements obtained in this study were compared with models suggested by earlier studies and analyzed by examining the flow structures. A method to evaluate the tortuosities induced by the blocking phase, namely the channel tortuosity, was proposed from observations of the flow structure images. The relationship between the coefficients of channel tortuosity and the relative permeabilities was studied with the aid of laboratory experiments and visualizations. Experimental data from these fractures were used to develop a broad approach for modeling two-phase flow behavior based on the flow structures. Finally, a general model deduced from these data was proposed to describe two-phase relative permeabilities in both smooth and rough fractures. For the theoretical analysis of liquid-vapor relative permeabilities, accounting for phase transformations, the inviscid bubble train models coupled with relative permeability concepts were developed. The phase transformation effects were evaluated by accounting for the molecular transport through liquid-vapor interfaces. For the steam water relative permeabilities, we conducted steam-water flow experiments in the same fractures as used for air-water experiments. We compared the flow behavior and relative permeability differences between two-phase flow with and without phase transformation effects

  10. Three-dimensional structure of dominant instabilities in turbulent flow over smooth and rough boundaries

    NASA Astrophysics Data System (ADS)

    Grass, A. J.; Stuart, R. J.; Mansour-Tehrani, M.

    1991-01-01

    The current status of knowledge regarding coherent vortical structures in turbulent boundary layers and their role in turbulence generation are reviewed. The investigations reported in the study concentrate attention on rough-wall flows prevailing in the geophysical environment and include an experiment determining the three-dimensional form of the turbulence structures linked to the ejection and inrush events observed over rough walls and an experiment concerned with measuring the actual spanwise scale of the near-wall structures for boundary conditions ranging from hydrodynamically smooth to fully rough. It is demonstrated that horseshoe vortical structures are present and play an important role in rough-wall flows and they increase in scale with increasing wall distance, while a dominant spanwise wavelength occurs in the instantaneous cross-flow distribution of streamwise velocity close to the rough wall.

  11. Local flow structures defined by kinematic events in isotropic turbulence

    NASA Technical Reports Server (NTRS)

    Adrian, R. J.; Ditter, J. L.

    1988-01-01

    The spatial structure of turbulent motion in incompressible isotropic turbulence is investigated using a conditional average in which the conditional event specifies the local deformation tensor in addition to the local velocity vector. This average gives the best estimate of the flow field around a fixed point x given the kinematic state at x. Estimates are calculated for various kinematic states in isotropic turbulence, including pure translation, pure shear, plane strain, axisymmetric strain, and pure rotation. It is demonstrated that the large-scale motion is dominated by a vortex ring structure associated with the translational component, except at critical points of the velocity vector field.

  12. Study of argon-oxygen flowing afterglow

    NASA Astrophysics Data System (ADS)

    Mazánková, V.; Trunec, D.; Navrátil, Z.; Raud, J.; Krčma, F.

    2016-06-01

    The reaction kinetics in argon-oxygen flowing afterglow (post-discharge) was studied using NO titration and optical emission spectroscopy. The flowing DC post-discharge in argon-oxygen mixture was created in a quartz tube at the total gas pressure of 1000 Pa and discharge power of 90 W. The O(3P) atom concentration was determined by NO titration at different places along the flow tube. The optical emission spectra were also measured along the flow tube. Argon spectral lines, oxygen lines at 777 nm and 844.6 nm and atmospheric A-band of {{\\text{O}}2} were identified in the spectra. Rotational temperature of {{\\text{O}}2} was determined from the oxygen atmospheric A-band and also the outer wall temperature of the flow tube was measured by a thermocouple and by an IR thermometer. A zero-dimensional kinetic model for the reactions in the afterglow was developed. This model allows the time dependencies of particle concentrations and of gas temperature to be calculated. The wall recombination probability for O(3P) atoms {γ\\text{O≤ft(\\text{P}\\right)}}=≤ft(1.63+/- 0.06\\right)× {{10}-3} and wall deactivation probability for {{\\text{O}}2} (b {{}1}Σ\\text{g}+ ) molecules {γ{{\\text{O}2}≤ft(\\text{b}\\right)}}=≤ft(1.7+/- 0.1\\right)× {{10}-3} were determined from the fit of model results to experimental data. Sensitivity analysis was applied for the analysis of kinetic model in order to reveal the most important reactions in the model. The calculated gas temperature increases in the afterglow and then decreases at later afterglow times after reaching the maximum. This behavior is in good agreement with the spatial rotational temperature dependence. A similar trend was also observed at outer wall temperature measurement.

  13. Study of argon–oxygen flowing afterglow

    NASA Astrophysics Data System (ADS)

    Mazánková, V.; Trunec, D.; Navrátil, Z.; Raud, J.; Krčma, F.

    2016-06-01

    The reaction kinetics in argon–oxygen flowing afterglow (post-discharge) was studied using NO titration and optical emission spectroscopy. The flowing DC post-discharge in argon–oxygen mixture was created in a quartz tube at the total gas pressure of 1000 Pa and discharge power of 90 W. The O(3P) atom concentration was determined by NO titration at different places along the flow tube. The optical emission spectra were also measured along the flow tube. Argon spectral lines, oxygen lines at 777 nm and 844.6 nm and atmospheric A-band of {{\\text{O}}2} were identified in the spectra. Rotational temperature of {{\\text{O}}2} was determined from the oxygen atmospheric A-band and also the outer wall temperature of the flow tube was measured by a thermocouple and by an IR thermometer. A zero-dimensional kinetic model for the reactions in the afterglow was developed. This model allows the time dependencies of particle concentrations and of gas temperature to be calculated. The wall recombination probability for O(3P) atoms {γ\\text{O≤ft(\\text{P}\\right)}}=≤ft(1.63+/- 0.06\\right)× {{10}-3} and wall deactivation probability for {{\\text{O}}2} (b {{}1}Σ\\text{g}+ ) molecules {γ{{\\text{O}2}≤ft(\\text{b}\\right)}}=≤ft(1.7+/- 0.1\\right)× {{10}-3} were determined from the fit of model results to experimental data. Sensitivity analysis was applied for the analysis of kinetic model in order to reveal the most important reactions in the model. The calculated gas temperature increases in the afterglow and then decreases at later afterglow times after reaching the maximum. This behavior is in good agreement with the spatial rotational temperature dependence. A similar trend was also observed at outer wall temperature measurement.

  14. Experimental study of vortex breakdown in a cylindrical, swirling flow

    NASA Technical Reports Server (NTRS)

    Stevens, J. L.; Celik, Z. Z.; Cantwell, B. J.; Lopez, J. M.

    1996-01-01

    The stability of a steady, vortical flow in a cylindrical container with one rotating endwall has been experimentally examined to gain insight into the process of vortex breakdowwn. The dynamics of the flow are governed by the Reynolds number (Re) and the aspect ratio of the cylinder. Re is given by Omega R(sup 2)/nu, where Omega is the speed of rotation of the endwall, R is the cylinder radius, and nu is the kinematic viscosity of the fluid filling the cylinder. The aspect ratio is H/R, where H is the height of the cylinder. Numerical simulation studies disagree whether or not the steady breakdown is stable beyond a critical Reynolds number, Re(sub c). Previous experimental researches have considered the steady and unsteady flows near Re(sub c), but have not explored the stability of the steady breakdown structures beyond this value. In this investigation, laser induced fluorescence was utilized to observe both steady and unsteady vortex breakdown at a fixed H/R of 2.5 with Re varying around Re(sub c). When the Re of a steady flow was slowly increased beyond Re(sub c), the breakdown structure remained steady even though unsteadiness was possible. In addition, a number of hysteresis events involving the oscillation periods of the unsteady flow were noted. The results show that both steady and unsteady vortex breakdown occur for a limited range of Re above Re(sub c). Also, with increasing Re, complex flow transformations take place that alter the period at which the unsteady flow oscillates.

  15. Flow visualization of time-varying structural characteristics of dean vortices in a curved channel

    NASA Astrophysics Data System (ADS)

    Bella, David Wayne

    1988-12-01

    The time varying development and structure of Dean vortices were studied using flow visualization. Observations were made over a range of Dean numbers from 40 to 200 using a transparent channel with mild curvature, 40:1 aspect ratio, and an inner to outer radius ratio of 0.979. Seven flow visualization techniques were tried but only one, a wood burning smoke generator, produced usable results. Different vortex characteristics were observed and documented in sequences of photographs spaced one quarter of a second apart at locations ranging from 85 to 135 degrees from the start of curvature. Evidence is presented that supports the twisting/rocking nature of the flow.

  16. Correlation of optical phase distortion with turbulent structure in a homogeneous shear flow

    NASA Technical Reports Server (NTRS)

    Truman, C. Randall; Lee, Moon J.

    1989-01-01

    The relative importance of small-scale and large-scale turbulent structure to phase distortion in propagation through the homogeneous shear flow is the focus of this study. The importance of large-scale vortical structure and the associated scalar distribution to optical distortion induced by propagation through a turbulent shear flow has been established (Truman and Lee 1989). Phase errors induced in a coherent optical beam by these turbulent fluctuations are computed. This scalar field shows elongated regions of intense fluctuations which have an inclination with respect to the mean flow similar to that of the characteristic hairpin eddies. Long-term plans include an examination of the effects of inhomogeneity through consideration of direct numerical simulations of the channel flow, boundary layer or mixing layer.

  17. Cross-flow vortex structure and transition measurements using multi-element hot films

    NASA Technical Reports Server (NTRS)

    Agarwal, Naval K.; Mangalam, Siva M.; Maddalon, Dal V.; Collier, Fayette S., Jr.

    1991-01-01

    An experiment on a 45-degree swept wing was conducted to study three-dimensional boundary-layer characteristics using surface-mounted, micro-thin, multi-element hot-film sensors. Cross-flow vortex structure and boundary-layer transition were measured from the simultaneously acquired signals of the hot films. Spanwise variation of the root-mean-square (RMS) hot-film signal show a local minima and maxima. The distance between two minima corresponds to the stationary cross-flow vortex wavelength and agrees with naphthalene flow-visualization results. The chordwise and spanwise variation of amplified traveling (nonstationary) cross-flow disturbance characteristics were measured as Reynolds number was varied. The frequency of the most amplified cross-flow disturbances agrees with linear stability theory.

  18. Cell-cell interaction in blood flow in patients with coronary heart disease (in vitro study)

    NASA Astrophysics Data System (ADS)

    Malinova, Lidia I.; Simonenko, Georgy V.; Denisova, Tatyana P.; Tuchin, Valery V.

    2007-02-01

    Blood cell-cell and cell-vessel wall interactions are one of the key patterns in blood and vascular pathophysiology. We have chosen the method of reconstruction of pulsative blood flow in vitro in the experimental set. Blood flow structure was studied by PC integrated video camera with following slide by slide analysis. Studied flow was of constant volumetric blood flow velocity (1 ml/h). Diameter of tube in use was comparable with coronary arteries diameter. Glucose solution and unfractured heparin were used as the nonspecial irritants of studied flow. Erythrocytes space structure in flow differs in all groups of patients in our study (men with stable angina pectoris (SAP), myocardial infarction (MI) and practically healthy men (PHM). Intensity of erythrocytes aggregate formation was maximal in patients with SAP, but time of their "construction/deconstruction" at glucose injection was minimal. Phenomena of primary clotting formation in patients with SAP of high function class was reconstructed under experimental conditions. Heparin injection (10 000 ED) increased linear blood flow velocity both in patients with SAP, MI and PHP but modulated the cell profile in the flow. Received data correspond with results of animal model studies and noninvasive blood flow studies in human. Results of our study reveal differences in blood flow structure in patients with coronary heart disease and PHP under irritating conditions as the possible framework of metabolic model of coronary blood flow destabilization.

  19. Eddy structure and mean flow effects in strong convection

    NASA Astrophysics Data System (ADS)

    Hunt, J.; Zilitinkevich, S.; Nieuwstadt, F.; Fernando, H.; Princevac, M.

    2003-04-01

    Recent research has shown how in turbulent thermal convection above a horizontal plane where a buoyancy flux is produced (e.g. by heat or by diffusion of dense fluid) characteristic forms of eddy structure interact with processes at the horizontal plane and with horizontal mean velocity field (1). If the flux is produced through a diffusive solid geophysical flow, surface, (e.g. in the solid part of Earth's core or in freezing ice) the eddy structure takes the form of unsteady puffs, because the fluid motion causes variations in the temperature buoyancy at the liquid/solid interface. But if the flux is constant and independent of the fluid motion (e.g. by radiative flux) then the usual quasi-steady plumes are formed. A geophysically significant effect of these differences in eddy structure is the influence on the entrainment rate at inversion layers/thermocline bounding the convective turbulent regions. In the presence of a weak mean velocity gradient no greater than the turbulence intensity, any plumes may be advected (and their structure changed to become puff-like) and/or may be bent over, depending on the strength and vertical extent of the shear. Laboratory experiments, numerical simulation and a simple model demonstrate that in the latter situation the mean flow is amplified by the turbulence, a form of anisotropic, inhomogeneous upscale eddy transport with wide geophysical applications (2). (1) Hunt, J.C.R., Vrieling, A.J., Nieuwstadt, F.T.M. and Fernando, H.J.S., `The influence of the thermal conductivity of the lower boundary on eddy motion in convection', J. Fluid Mech. - submitted 2003. (2) Krishnamurti, R. and Howard, L.N., `Mean flow set up by tilted plumes in a confined space', Proc. Nat. Acad. Sci., 78, 1981.

  20. EDITORIAL: Experimental studies of zonal flow and turbulence

    NASA Astrophysics Data System (ADS)

    Itoh, Sanae-I.

    2006-04-01

    There has been remarkable progress made in the research of structure formation by turbulence in nonequilibrium plasmas. One of the highlights has been the physics of zonal flow and drift wave turbulence in toroidal plasmas. Extensive theoretical as well as computational studies have revealed the various mechanisms in the system of turbulence and zonal flows, as highlighted in the recent review paper `Zonal flows in plasma—a review' by P H Diamond et al (2005 Plasma Phys. Control. Fusion} 47 R35). There has also been increasing research in experimental studies of zonal flows, geodesic acoustic modes, and the generation of global electric field by turbulence. In recognition of this a cluster Plasma Physics and Controlled Fusion occasionally publishes a small collection of articles on a specific topic. These special sections highlight a specific area of research that is of importance to the journal either as a new or growing research area. The subjects are selected by the Editorial Board and managed by a Guest Editor, Professor Itoh in this case. of 15 papers on `Experimental studies of zonal flow and turbulence' is presented in this issue of Plasma Physics and Controlled Fusion. Each paper in this special cluster describes the present research status and new scientific knowledge/results on the authors' machine involved, on the subject of experimental studies of zonal flows, electric field and nonlinear interactions with turbulence (including studies of Reynolds-Maxwell stresses, etc). Readers of, and contributors to, Plasma Physics and Controlled Fusion have been facing a new phase of plasma physics, with the expanding application of plasma physics to the explosive growth of our knowledge of the astronomical, space and laboratory plasmas, and the approach of ITER. The evolution of modern plasma physics into the new arena is backed up by extensive research as illustrated by this cluster of papers and review papers. We believe that this group of articles will

  1. Coherent structures in ion temperature gradient turbulence-zonal flow

    SciTech Connect

    Singh, Rameswar; Singh, R.; Kaw, P.; Gürcan, Ö. D.; Diamond, P. H.

    2014-10-15

    Nonlinear stationary structure formation in the coupled ion temperature gradient (ITG)-zonal flow system is investigated. The ITG turbulence is described by a wave-kinetic equation for the action density of the ITG mode, and the longer scale zonal mode is described by a dynamic equation for the m = n = 0 component of the potential. Two populations of trapped and untrapped drift wave trajectories are shown to exist in a moving frame of reference. This novel effect leads to the formation of nonlinear stationary structures. It is shown that the ITG turbulence can self-consistently sustain coherent, radially propagating modulation envelope structures such as solitons, shocks, and nonlinear wave trains.

  2. Social dilemma structure hidden behind traffic flow with route selection

    NASA Astrophysics Data System (ADS)

    Tanimoto, Jun; Nakamura, Kousuke

    2016-10-01

    Several traffic flows contain social dilemma structures. Herein, we explored a route-selection problem using a cellular automaton simulation dovetailed with evolutionary game theory. In our model, two classes of driver-agents coexist: D agents (defective strategy), which refer to traffic information for route selection to move fast, and C agents (cooperative strategy), which are insensitive to information and less inclined to move fast. Although no evidence suggests that the social dilemma structure in low density causes vehicles to move freely and that in high density causes traffic jams, we found a structure that corresponds to an n-person (multiplayer) Chicken (n-Chicken) game if the provided traffic information is inappropriate. If appropriate traffic information is given to the agents, the n-Chicken game can be solved. The information delivered to vehicles is crucial for easing the social dilemma due to urban traffic congestion when developing technologies to support the intelligent transportation system (ITS).

  3. SAXS/WAXS studies of flow-induced crystallization of poly(1-butene) in uniaxial extensional flow

    NASA Astrophysics Data System (ADS)

    McCready, Erica; Burghardt, Wesley

    2013-03-01

    We report studies of flow-induced crystallization of poly(1-butene) in uniaxial extensional flow. Flow was produced using an SER extensional flow fixture housed in a custom built convection oven designed to provide x-ray access for in situ studies of polymer structure using synchrotron x-ray scattering techniques. Samples were loaded into the SER fixture, heated well into the melt, and then cooled to a temperature at which quiescent crystallization would be prohibitively slow. A short interval of uniaxial extensional flow was then applied, after which simultaneous wide- and small-angle x-ray scattering (SAXS and WAXS) patterns were collected to study the phase transformation kinetics and morphology of the subsequent accelerated crystallization. The impact of both deformation rate and total applied strain on the crystallization process were examined.

  4. Space shuttle orbiter flow visualization study. [water tunnel study of vortex flow during atmospheric entry

    NASA Technical Reports Server (NTRS)

    Lorincz, D. J.

    1980-01-01

    The vortex flows generated at subsonic speed during the final portion of atmospheric reentry were defined using a 0.01 scale model of the orbiter in a diagnostic water tunnel. Flow visualization photographs were obtained over an angle-of-attack range to 40 deg and sideslip angles up to 10 deg. The vortex flow field development, vortex path, and vortex breakdown characteristics were determined as a function of angle-of-attack at zero sideslip. Vortex flows were found to develop on the highly swept glove, on the wing, and on the upper surface of the fuselage. No significant asymmetries were observed at zero sideslip in the water tunnel tests. The sensitivity of the upper surface vortex flow fields to variations in sideslip angle was also studied. The vortex formed on the glove remained very stable in position above the wing up through the 10 deg of sideslip tested. There was a change in the vortex lifts under sideslip due to effective change in leading-edge sweep angles. Asymmetric flow separation occurred on the upper surface of the fuselage at small sideslip angles. The influence of vortex flow fields in sideslip on the lateral/ directional characteristics of the orbiter is discussed.

  5. Structure parameters in rotating Couette-Poiseuille channel flow

    NASA Technical Reports Server (NTRS)

    Knightly, George H.; Sather, D.

    1986-01-01

    It is well-known that a number of steady state problems in fluid mechanics involving systems of nonlinear partial differential equations can be reduced to the problem of solving a single operator equation of the form: v + lambda Av + lambda B(v) = 0, v is the summation of H, lambda is the summation of one-dimensional Euclid space, where H is an appropriate (real or complex) Hilbert space. Here lambda is a typical load parameter, e.g., the Reynolds number, A is a linear operator, and B is a quadratic operator generated by a bilinear form. In this setting many bifurcation and stability results for problems were obtained. A rotating Couette-Poiseuille channel flow was studied, and it showed that, in general, the superposition of a Poiseuille flow on a rotating Couette channel flow is destabilizing.

  6. Structure parameters in rotating Couette-Poiseuille channel flow

    NASA Astrophysics Data System (ADS)

    Knightly, George H.; Sather, D.

    It is well-known that a number of steady state problems in fluid mechanics involving systems of nonlinear partial differential equations can be reduced to the problem of solving a single operator equation of the form: v + lambda Av + lambda B(v) = 0, v is the summation of H, lambda is the summation of one-dimensional Euclid space, where H is an appropriate (real or complex) Hilbert space. Here lambda is a typical load parameter, e.g., the Reynolds number, A is a linear operator, and B is a quadratic operator generated by a bilinear form. In this setting many bifurcation and stability results for problems were obtained. A rotating Couette-Poiseuille channel flow was studied, and it showed that, in general, the superposition of a Poiseuille flow on a rotating Couette channel flow is destabilizing.

  7. Solar Coronal Structure Study

    NASA Technical Reports Server (NTRS)

    Nitta, Nariaki; Bruner, Marilyn E.; Saba, Julia; Strong, Keith; Harvey, Karen

    2000-01-01

    The subject of this investigation is to study the physics of the solar corona through the analysis of the EUV and UV data produced by two flights (12 May 1992 and 25 April 1994) of the Lockheed Solar Plasma Diagnostics Experiment (SPDE) sounding rocket payload, in combination with Yohkoh and ground-based data. Each rocket flight produced both spectral and imaging data. These joint datasets are useful for understanding the physical state of various features in the solar atmosphere at different heights ranging from the photosphere to the corona at the time of the, rocket flights, which took place during the declining phase of a solar cycle, 2-4 years before the minimum. The investigation is narrowly focused on comparing the physics of small- and medium-scale strong-field structures with that of large-scale, weak fields. As we close th is investigation, we have to recall that our present position in the understanding of basic solar physics problems (such as coronal heating) is much different from that in 1995 (when we proposed this investigation), due largely to the great success of SOHO and TRACE. In other words, several topics and techniques we proposed can now be better realized with data from these missions. For this reason, at some point of our work, we started concentrating on the 1992 data, which are more unique and have more supporting data. As a result, we discontinued the investigation on small-scale structures, i.e., bright points, since high-resolution TRACE images have addressed more important physics than SPDE EUV images could do. In the final year, we still spent long time calibrating the 1992 data. The work was complicated because of the old-fashioned film, which had problems not encountered with more modern CCD detectors. After our considerable effort on calibration, we were able to focus on several scientific topics, relying heavily on the SPDE UV images. They include the relation between filaments and filament channels, the identification of hot

  8. Quasi-Steady Limit of Flow Structure on Flapping Wing in Mean Flow

    NASA Astrophysics Data System (ADS)

    Bross, Matthew; Ozen, Cem; Rockwell, Donald

    2012-11-01

    A limiting case of flapping motion of a wing (low aspect ratio plate) in presence of incident steady flow is compared to a rotating wing in quiescent fluid, in order to clarify the effect of advance ratio J (ratio of free-stream velocity to tangential velocity of wing) on the structure of the leading-edge vortex. Stereoscopic particle image velocimetry leads to patterns of vorticity, velocity contours, and streamlines. For each value of J, the effective angle of attack is held constant at 45°, while the wing rotates from rest through 270°. While at rest, the wing at high angle of attack in the presence of a steady free-stream gives rise to fully stalled flow. After the onset of rotation, the fully stalled region very quickly transforms to a stable leading edge vortex. Despite the change in advance ratio, the development of the flow structure around the wing throughout the rotation maneuver is similar, especially in the leading edge vortex region, as evidenced by patterns of streamline topology. To further demonstrate the effect of J, three-dimensional representations of of spanwise-oriented vorticity, spanwise velocity, and Q were constructed for hovering flight and forward flight.

  9. Numerical Study of Flow Motion and Patterns Driven by a Rotating Permanent Helical Magnetic Field

    NASA Astrophysics Data System (ADS)

    Yang, Wenzhi; Wang, Xiaodong; Wang, Bo; Baltaretu, Florin; Etay, Jacqueline; Fautrelle, Yves

    2016-10-01

    Liquid metal magnetohydrodynamic flow driven by a rotating permanent helical magnetic field in a cylindrical container is numerically studied. A three-dimensional numerical simulation provides insight into the visualization of the physical fields, including the magnetic field, the Lorentz force density, and the flow structures, especially the flow patterns in the meridional plane. Because the screen parameter is sufficiently small, the model is decoupled into electromagnetic and hydrodynamic components. Two flow patterns in the meridional plane, i.e., the global flow and the secondary flow, are discovered and the impact of several system parameters on their transition is investigated. Finally, a verifying model is used for comparison with the previous experiment.

  10. Numerical Study of Flow Motion and Patterns Driven by a Rotating Permanent Helical Magnetic Field

    NASA Astrophysics Data System (ADS)

    Yang, Wenzhi; Wang, Xiaodong; Wang, Bo; Baltaretu, Florin; Etay, Jacqueline; Fautrelle, Yves

    2016-08-01

    Liquid metal magnetohydrodynamic flow driven by a rotating permanent helical magnetic field in a cylindrical container is numerically studied. A three-dimensional numerical simulation provides insight into the visualization of the physical fields, including the magnetic field, the Lorentz force density, and the flow structures, especially the flow patterns in the meridional plane. Because the screen parameter is sufficiently small, the model is decoupled into electromagnetic and hydrodynamic components. Two flow patterns in the meridional plane, i.e., the global flow and the secondary flow, are discovered and the impact of several system parameters on their transition is investigated. Finally, a verifying model is used for comparison with the previous experiment.

  11. Structural efficiency of percolated landscapes in flow networks.

    PubMed

    Serrano, M Angeles; De Los Rios, Paolo

    2008-01-01

    The large-scale structure of complex systems is intimately related to their functionality and evolution. In particular, global transport processes in flow networks rely on the presence of directed pathways from input to output nodes and edges, which organize in macroscopic connected components. However, the precise relation between such structures and functional or evolutionary aspects remains to be understood. Here, we investigate which are the constraints that the global structure of directed networks imposes on transport phenomena. We define quantitatively under minimal assumptions the structural efficiency of networks to determine how robust communication between the core and the peripheral components through interface edges could be. Furthermore, we assess that optimal topologies in terms of access to the core should look like "hairy balls" so to minimize bottleneck effects and the sensitivity to failures. We illustrate our investigation with the analysis of three real networks with very different purposes and shaped by very different dynamics and time-scales-the Internet customer-provider set of relationships, the nervous system of the worm Caenorhabditis elegans, and the metabolism of the bacterium Escherichia coli. Our findings prove that different global connectivity structures result in different levels of structural efficiency. In particular, biological networks seem to be close to the optimal layout. PMID:18985157

  12. Gold recycling; a materials flow study

    USGS Publications Warehouse

    Amey, Earle B.

    2000-01-01

    This materials flow study includes a description of trends in consumption, loss, and recycling of gold-containing materials in the United States in 1998 in order to illustrate the extent to which gold is presently being recycled and to identify recycling trends. The quantity of gold recycled, as a percent of the apparent supply of gold, was estimated to be about 30 percent. Of the approximately 446 metric tons of gold refined in the United States in 1998, the fabricating and industrial use losses were 3 percent.

  13. Flow field studies on yawed, stranded cables

    NASA Astrophysics Data System (ADS)

    Batill, S. M.; Nelson, R. C.; Nebres, J. V.

    A study of the flowfield near yawed, stranded cables was conducted in order to investigate the mechanisms associated with the generation of both steady and unsteady fluid forces on the cables. Rigid cable models and a circular cylinder were tested in a wind tunnel at four different cable angles over a Reynolds number range from 6000 to 14,600 based on the nominal cable diameter. The smoke-wire and the kerosene smoke flow visualization techniques were used to qualitatively evaluate the flowfields associated with each cable geometry.

  14. Flow structure in canopy models dominated by progressive waves

    NASA Astrophysics Data System (ADS)

    Pujol, Dolors; Serra, Teresa; Colomer, Jordi; Casamitjana, Xavier

    2013-04-01

    SummaryLaboratory experiments were carried out to study the flow structure both inside and above different canopy models which were dominated by progressive waves. A set of experimental conditions were considered in a laboratory flume: three vegetation models (submerged rigid, submerged flexible and emergent rigid), three plant densities (128, 640 and 1280 stems m-2) and three wave frequencies (f = 0.8, 1 and 1.4 Hz). The progressive waves followed the second-order Stokes theory in the intermediate depth range. The observations revealed that submerged and emergent rigid vegetation models modified the wave-induced velocities i.e., both mean current and wave velocity. The submerged rigid vegetation model for plant densities higher than 640 plants m-2 and wave frequency higher than 1 Hz acted akin to a false floor, confining the mean current to above the plant bed. A penetration depth around 2 cm below the top of submerged rigid vegetation was found. For the other runs, the vertical profile of mean current did not present changes with respect to runs without plants. The emergent rigid vegetation model reversed the direction of the induced mean current, with the highest velocity corresponding to the highest plant density. In contrast, the submerged flexible vegetation model had a weak effect on the mean current, with the vertical velocity profile similar to that found in experiments without vegetation. The wave velocities inside the vegetation for the densest submerged rigid vegetation were found to be reduced by 20%, when compared to the wave velocities without vegetation, while in emergent rigid vegetation this reduction was of 45%.

  15. Flow structure interaction around an axial-flow hydrokinetic turbine: Experiments and CFD simulations

    NASA Astrophysics Data System (ADS)

    Kang, S.; Chamorro, L.; Hill, C.; Arndt, R.; Sotiropoulos, F.

    2014-12-01

    We carry out large-eddy simulation of turbulent flow past a complete hydrokinetic turbine mounted on the bed of a straight rectangular open channel. The complex turbine geometry, including the rotor and all stationary components, is handled by employing the curvilinear immersed boundary (CURVIB) method [1], and velocity boundary conditions near all solid surfaces are reconstructed using a wall model based on solving the simplified boundary layer equations [2]. In this study we attempt to directly resolve flow-blade interactions without introducing turbine parameterization methods. The computed wake profiles of velocities and turbulent stresses agree well with the experimentally measured values.

  16. Flow structure and unsteadiness in the supersonic wake of a generic space launcher

    NASA Astrophysics Data System (ADS)

    Schreyer, Anne-Marie; Stephan, Sören; Radespiel, Rolf

    2015-11-01

    At the junction between the rocket engine and the main body of a classical space launcher, a separation-dominated and highly unstable flow field develops and induces strong wall-pressure oscillations. These can excite structural vibrations detrimental to the launcher. It is desirable to minimize these effects, for which a better understanding of the flow field is required. We study the wake flow of a generic axisymmetric space-launcher model with and without propulsive jet (cold air). Experimental investigations are performed at Mach 2.9 and a Reynolds number ReD = 1 . 3 .106 based on model diameter D. The jet exits the nozzle at Mach 2.5. Velocity measurements by means of Particle Image Velocimetry and mean and unsteady wall-pressure measurements on the main-body base are performed simultaneously. Additionally, we performed hot-wire measurements at selected points in the wake. We can thus observe the evolution of the wake flow along with its spectral content. We describe the mean and turbulent flow topology and evolution of the structures in the wake flow and discuss the origin of characteristic frequencies observed in the pressure signal at the launcher base. The influence of a propulsive jet on the evolution and topology of the wake flow is discussed in detail. The German Research Foundation DFG is gratefully acknowledged for funding this research within the SFB-TR40 ``Technological foundations for the design of thermally and mechanically highly loaded components of future space transportation systems.''

  17. A study of grout flow pattern analysis

    SciTech Connect

    Lee, S. Y.; Hyun, S.

    2013-01-10

    A new disposal unit, designated as Salt Disposal Unit no. 6 (SDU6), is being designed for support of site accelerated closure goals and salt nuclear waste projections identified in the new Liquid Waste System plan. The unit is cylindrical disposal vault of 380 ft diameter and 43 ft in height, and it has about 30 million gallons of capacity. Primary objective was to develop the computational model and to perform the evaluations for the flow patterns of grout material in SDU6 as function of elevation of grout discharge port, and slurry rheology. A Bingham plastic model was basically used to represent the grout flow behavior. A two-phase modeling approach was taken to achieve the objective. This approach assumes that the air-grout interface determines the shape of the accumulation mound. The results of this study were used to develop the design guidelines for the discharge ports of the Saltstone feed materials in the SDU6 facility. The focusing areas of the modeling study are to estimate the domain size of the grout materials radially spread on the facility floor under the baseline modeling conditions, to perform the sensitivity analysis with respect to the baseline design and operating conditions such as elevation of discharge port, discharge pipe diameter, and grout properties, and to determine the changes in grout density as it is related to grout drop height. An axi-symmetric two-phase modeling method was used for computational efficiency. Based on the nominal design and operating conditions, a transient computational approach was taken to compute flow fields mainly driven by pumping inertia and natural gravity. Detailed solution methodology and analysis results are discussed here.

  18. The role of coherent flow structures in the sensible heat fluxes of an Alaskan boreal forest

    NASA Astrophysics Data System (ADS)

    Starkenburg, Derek; Fochesatto, Gilberto J.; Prakash, Anupma; Cristóbal, Jordi; Gens, Rudiger; Kane, Douglas L.

    2013-08-01

    Accelerations in the flow over forests generate coherent structures which locally enhance updrafts and downdrafts, forcing rapid exchanges of energy and matter. Here, observations of the turbulent flow are made in a highly heterogeneous black spruce boreal forest in Fairbanks, Alaska at ~2.6 h (12 m) and ~0.6 h (3 m), where h is the mean canopy height of 4.7 m. Wavelet analysis is used to detect coherent structures. The sonic temperature and wind data cover 864 half-hour periods spanning winter, spring, and summer. When mean global statistics of structures are analyzed at the two levels independently, results are similar to other studies. Specifically, an average of eight structures occurs per period, their mean duration is 85 s, and their mean heat flux contribution is 48%. However, this analysis suggests that 31% of the structures detected at 2.6 h, and 13% at 0.6 h, may be influenced by wave-like flow organization. Remarkably, less than 25% of the structures detected occur synchronously in the subcanopy and above canopy levels, which speaks robustly to the lack of flow interaction within only nine vertical meters of the forest.

  19. Bodies in flowing plasmas - Laboratory studies

    NASA Technical Reports Server (NTRS)

    Stone, N. H.; Samir, U.

    1981-01-01

    A brief review of early rudimentary laboratory studies of bodies in flowing, rarefied plasmas is presented (e.g., Birkeland, 1908), along with a discussion of more recent parametric studies conducted in steady plasma wind tunnels, which includes the study by Hall et al. (1964), in which a strong ion density enhancement in the center of the ion void created downstream from the body was observed. Good agreement was found between the experimental results and theoretical calculations which omit ion thermal motion. Examples in which in situ data on the interaction between satellites and the ionospheric plasma have been elucidated by the laboratory results are presented, and include evidence for a midwake axial ion peak, and ion current density in the near-wake region. The application of the ionospheric laboratory to basic space plasma physics is discussed, and its application to some types of solar system plasma phenomena is illustrated.

  20. Multi-scale geometry of flow structures in a flat-plate turbulent boundary layer

    NASA Astrophysics Data System (ADS)

    Bermejo-Moreno, Ivan; Atkinson, Callum; Chumakov, Sergei; Soria, Julio; Wu, Xiaohua

    2010-11-01

    We study the geometry of structures educed from the enstrophy and dissipation fields obtained from a DNS of a flat-plate turbulent boundary layer (J. Fluid Mech. 630, 5-41, 2009) following the non-local multi-scale methodology introduced in J. Fluid Mech. 603, 101-135, 2008. We compare the results with those of homogeneous isotropic turbulence. In the present analysis, geometric parameters are combined with physical quantities associated with the flow structures. Their evolution in time is studied through a series of snapshots obtained from the simulation, following a moving subdomain. Individual structures are tracked in time, relating their physical and geometric properties at the local and structure levels. The validity of two local identification criteria for the eduction of vortex tubes and sheets in wall-bounded flows is also evaluated.

  1. Relationships Between Watershed Emergy Flow and Coastal New England Salt Marsh Structure, Function, and Condition

    EPA Science Inventory

    This study evaluated the link between watershed activities and salt marsh structure, function, and condition using spatial emergy flow density (areal empower density) in the watershed and field data from 10 tidal salt marshes in Narragansett Bay, RI. The field-collected data wer...

  2. Structural Relationships among E-Learners' Sense of Presence, Usage, Flow, Satisfaction, and Persistence

    ERIC Educational Resources Information Center

    Joo, Young Ju; Joung, Sunyoung; Kim, Eun Kyung

    2013-01-01

    This study aimed to investigate the structural relationships among teaching presence, cognitive presence, usage, learning flow, satisfaction, and learning persistence in corporate e-learners. The research participants were 462 e-learners registered for cyber-lectures through an electronics company in South Korea. The extrinsic variables were sense…

  3. Characteristics of electrohydrodynamic roll structures in laminar planar Couette flow

    NASA Astrophysics Data System (ADS)

    Kourmatzis, Agisilaos; Shrimpton, John S.

    2016-02-01

    The behaviour of an incompressible dielectric liquid subjected to a laminar planar Couette flow with unipolar charge injection is investigated numerically in two dimensions. The computations show new morphological characteristics of roll structures that arise in this forced electro-convection problem. The charge and velocity magnitude distributions between the two parallel electrodes are discussed as a function of the top wall velocity and the EHD Rayleigh number, T for the case of strong charge injection. A wide enough parametric space is investigated such that the observed EHD roll structures progress through three regimes. These regimes are defined by the presence of a single or double-roll free convective structure as observed elsewhere (Vazquez et al 2008 J. Phys. D 41 175303), a sheared or stretched roll structure, and finally by a regime where the perpendicular velocity gradient is sufficient to prevent the generation of a roll. These three regimes have been delineated as a function of the wall to ionic drift velocity {{U}\\text{W}}/κ E , and the T number. In the stretched regime, an increase in {{U}\\text{W}}/κ E can reduce charge and momentum fluctuations whilst in parallel de-stratify charge in the region between the two electrodes. The stretched roll regime is also characterised by a substantial influence of {{U}\\text{W}}/κ E on the steady development time, however in the traditional non-stretched roll structure regime, no influence of {{U}\\text{W}}/κ E on the development time is noted.

  4. Experimental Investigation of the Unsteady Flow Structures of Two Interacting Pitching Wings

    NASA Astrophysics Data System (ADS)

    Kurt, Melike; Moored, Keith

    2015-11-01

    Birds, insects and fish propel themselves with unsteady motions of their wings and fins. Many of these animals are also found to fly or swim in three-dimensional flocks and schools. Numerous studies have explored the three-dimensional steady flow interactions and the two-dimensional unsteady flow interactions in collectives. Yet, the characterization of the three-dimensional unsteady interactions remains relatively unexplored. This study aims to characterize the flow structures and interactions between two sinusoidally pitching finite-span wings. The arrangement of the wings varies from a tandem to a bi-plane configuration. The vortex structures for these various arrangements are quantified by using particle image velocimetry. The vortex-wing interactions are also characterized as the synchrony between the wings is modified.

  5. Laser direct writing 3D structures for microfluidic channels: flow meter and mixer

    NASA Astrophysics Data System (ADS)

    Lin, Chih-Lang; Liu, Yi-Jui; Lin, Zheng-Da; Wu, Bo-Long; Lee, Yi-Hsiung; Shin, Chow-Shing; Baldeck, Patrice L.

    2015-03-01

    The 3D laser direct-writing technology is aimed at the modeling of arbitrary three-dimensional (3D) complex microstructures by scanning a laser-focusing point along predetermined trajectories. Through the perspective technique, the details of designed 3D structures can be properly fabricated in a microchannel. This study introduces a direct reading flow meter and a 3D passive mixer fabricated by laser direct writing for microfluidic applications. The flow meter consists of two rod-shaped springs, a pillar, an anchor, and a wedge-shaped indicator, installed inside a microfluidic channel. The indicator is deflected by the flowing fluid while restrained by the spring to establish an equilibrium indication according to the flow rate. The measurement is readily carried out by optical microscopy observation. The 3D passive Archimedes-screw-shaped mixer is designed to disturb the laminar flow 3D direction for enhancing the mixing efficiency. The simulation results indicate that the screw provides 3D disturbance of streamlines in the microchannel. The mixing demonstration for fluids flowing in the micrchannel approximately agrees with the simulation result. Thanks to the advantage of the laser direct writing technology, this study performs the ingenious applications of 3D structures for microchannels.

  6. Preferential flow in connected soil structures and the principle of "maximum energy dissipation": A thermodynamic perspective

    NASA Astrophysics Data System (ADS)

    Zehe, E.; Blume, T.; Bloeschl, G.

    2009-04-01

    Helmholtz free energy. Thermodynamic equilibrium is a state of minimum free energy. The latter is determined by potential energy and capillary energy in soil, which in turn strongly depends on soil moisture, pore size distribution and depth to groundwater. The objective of this study is threefold. First, we will introduce the necessary theoretical background. Second we suggest ? based on simulations with a physically based hydrological model ? that water flow in connected preferential pathways assures a faster relaxation towards thermodynamic equilibrium through a faster drainage of ?excess water? and a faster redistribution of ?capillary water? within the soil. The latter process is of prime importance in case of cohesive soils where the pore size distribution is dominated by medium and small pores. Third, an application of a physically based hydrological model to predict water flow and runoff response from a pristine catchment in the Chilenean Andes underpins this hypothesis. Behavioral model structures that allow a good match of the observed hydrographs turned out to be most efficient in dissipating free energy by means of preferential flow. It seems that a population of connected preferential pathways is favourable both for resilience and stability of these soils during extreme events and to retain water resources for the ecosystem at the same time. We suggest that this principle of ?maximum energy dissipation? may on the long term help us to better understand why soil structures remain stable, threshold nature of preferential as well as offer a means to further reduce model structural uncertainty. Bloeschl, G. 2006. Idle thoughts on a unifying theory of catchment Hydrology. Geophysical Research Abstracts, Vol. 8, 10677, 2006 SRef-ID: 1607-7962/gra/EGU06-A-10677 European Geosciences Union 2006 Kleidon, A., and S. Schymanski (2008), Thermodynamics and optimality of the water budget on land: A review, Geophys. Res. Lett., 35, L20404, doi:10.1029/ 2008GL035393.

  7. A study of temporal estaurine flow dynamics

    NASA Technical Reports Server (NTRS)

    Mairs, R. L.; Clark, D. K.

    1972-01-01

    Multispectral photography,infrared imagery, image enhancement, and oceanographic, radiometric, and meteorological data were used in the study of temporal estuarine flow dynamics, nearshore circulation, and the resulting dispersal of suspended and dissolved substances introduced from the continent. Repetitive multispectral photography, IR imagery, total radiance and irradiance, water surface temperatures, salinity, total suspended solids, visibility, current velocity, winds, dye implants, and high contrast image enhancement were used to observe and describe water mass boundaries in the nearshore zone and to attempt to establish on what repetitive scale these coastal features should be observed to better understand their behavior. Water mass variability patterns, seen naturally and with the use of dyes, along the North Carolina coast and in the Chesapeake Bay are being studied as synoptic data on the basic dynamics of circulation, flushing, and mixing in coastal waters.

  8. Numerical Studies of a Supersonic Fluidic Diverter Actuator for Flow Control

    NASA Technical Reports Server (NTRS)

    Gokoglu, Suleyman A.; Kuczmarski, Maria A.; Culley, Dennis e.; Raghu, Surya

    2010-01-01

    The analysis of the internal flow structure and performance of a specific fluidic diverter actuator, previously studied by time-dependent numerical computations for subsonic flow, is extended to include operation with supersonic actuator exit velocities. The understanding will aid in the development of fluidic diverters with minimum pressure losses and advanced designs of flow control actuators. The self-induced oscillatory behavior of the flow is successfully predicted and the calculated oscillation frequencies with respect to flow rate have excellent agreement with our experimental measurements. The oscillation frequency increases with Mach number, but its dependence on flow rate changes from subsonic to transonic to supersonic regimes. The delay time for the initiation of oscillations depends on the flow rate and the acoustic speed in the gaseous medium for subsonic flow, but is unaffected by the flow rate for supersonic conditions

  9. Turbulent boundary-layer structure of flows over freshwater biofilms

    NASA Astrophysics Data System (ADS)

    Walker, J. M.; Sargison, J. E.; Henderson, A. D.

    2013-12-01

    The structure of the turbulent boundary-layer for flows over freshwater biofilms dominated by the diatom Tabellaria flocculosa was investigated. Biofilms were grown on large test plates under flow conditions in an Australian hydropower canal for periods up to 12 months. Velocity-profile measurements were obtained using LDV in a recirculating water tunnel for biofouled, smooth and artificially sandgrain roughened surfaces over a momentum thickness Reynolds number range of 3,000-8,000. Significant increases in skin friction coefficient of up to 160 % were measured over smooth-wall values. The effective roughnesses of the biofilms, k s, were significantly higher than their physical roughness measured using novel photogrammetry techniques and consisted of the physical roughness and a component due to the vibration of the biofilm mat. The biofilms displayed a k-type roughness function, and a logarithmic relationship was found between the roughness function and roughness Reynolds number based on the maximum peak-to-valley height of the biofilm, R t. The structure of the boundary layer adhered to Townsend's wall-similarity hypothesis even though the scale separation between the effective roughness height and the boundary-layer thickness was small. The biofouled velocity-defect profiles collapsed with smooth and sandgrain profiles in the outer region of the boundary layer. The Reynolds stresses and quadrant analysis also collapsed in the outer region of the boundary layer.

  10. Continuous-Flow Bioseparation Using Microfabricated Anisotropic Nanofluidic Sieving Structures

    PubMed Central

    Fu, Jianping; Mao, Pan; Han, Jongyoon

    2010-01-01

    The anisotropic nanofluidic filter (nanofilter) array (ANA) is a unique molecular sieving structure for separating biomolecules. Here we describe fabrication of planar and vertical ANA chips and how to perform continuous-flow bioseparation using them. This protocol is most useful for bioengineers that are interested in developing automated multistep chip-based bioanalysis systems and assumes prior cleanroom microfabrication knowledge. The ANA consists of a two-dimensional periodic nanofilter array, and the designed structural anisotropy of the ANA causes different sized- or charged-biomolecules to follow distinct trajectories under applied electric fields, leading to efficient continuous-flow separation. Using microfluidic channels surrounding the ANA, the fractionated biomolecule streams are collected and routed to different fluid channels or reservoirs for convenient sample recovery and downstream bioanalysis. The ANA is physically robust and can be reused repeatedly. Compared to conventional gel-based separation techniques, the ANA offers the potential for faster separation, higher throughput, and more convenient sample recovery. PMID:19876028

  11. Robust Feedback Control of Flow Induced Structural Radiation of Sound

    NASA Technical Reports Server (NTRS)

    Heatwole, Craig M.; Bernhard, Robert J.; Franchek, Matthew A.

    1997-01-01

    A significant component of the interior noise of aircraft and automobiles is a result of turbulent boundary layer excitation of the vehicular structure. In this work, active robust feedback control of the noise due to this non-predictable excitation is investigated. Both an analytical model and experimental investigations are used to determine the characteristics of the flow induced structural sound radiation problem. The problem is shown to be broadband in nature with large system uncertainties associated with the various operating conditions. Furthermore the delay associated with sound propagation is shown to restrict the use of microphone feedback. The state of the art control methodologies, IL synthesis and adaptive feedback control, are evaluated and shown to have limited success for solving this problem. A robust frequency domain controller design methodology is developed for the problem of sound radiated from turbulent flow driven plates. The control design methodology uses frequency domain sequential loop shaping techniques. System uncertainty, sound pressure level reduction performance, and actuator constraints are included in the design process. Using this design method, phase lag was added using non-minimum phase zeros such that the beneficial plant dynamics could be used. This general control approach has application to lightly damped vibration and sound radiation problems where there are high bandwidth control objectives requiring a low controller DC gain and controller order.

  12. Cell Structure Study.

    ERIC Educational Resources Information Center

    Ekstrom, James V.

    2000-01-01

    Presents an activity in which students use microscopes and digital images to examine Elodea, a fresh water plant, before and after the process of plasmolysis, identify plant cellular structures before and after plasmolysis, and calculate the size of the plant's vacuole. (ASK)

  13. Flow around new wind fence with multi-scale fractal structure in an atmospheric boundary layer

    NASA Astrophysics Data System (ADS)

    McClure, Sarah; Lee, Sang-Joon; Zhang, Wei

    2015-11-01

    Understanding and controlling atmospheric boundary-layer flows with engineered structures, such as porous wind fences or windbreaks, has been of great interest to the fluid mechanics and wind engineering community. Previous studies found that the regular mono-scale grid fence of 50% porosity and a bottom gap of 10% of the fence height are considered to be optimal over a flat surface. Significant differences in turbulent flow structure have recently been noted behind multi-scale fractal wind fences, even with the same porosity. In this study, wind-tunnel tests on the turbulent flow and the turbulence kinetic energy transport of 1D and 2D multi-scale fractal fences under atmospheric boundary-layer were conducted. Velocity fields around the fractal fences were systematically measured using Particle Image Velocimetry to uncover effects of key parameters on turbulent flows around the fences at a Reynolds number of approximately 3.6x104 based on the free-stream speed and fence height. The turbulent flow structures induced by specific 1D/2D multi-scale fractal wind fences were compared to those of a conventional grid fence. The present results would contribute to the design of new-generation wind fences to reduce snow/sand deposition on critical infrastructure such as roads and bridges.

  14. Effect of blood flow parameters on flow patterns at arterial bifurcations--studies in models.

    PubMed

    Liepsch, D W

    1990-01-01

    Atherosclerotic lesions are found primarily at arterial bends and bifurcations. Flow disturbances at these anatomic sites play a major role in atherogenesis. How hemodynamic factors such as vessel geometry, the pulsatile nature of blood flow, vessel wall elasticity and the non-Newtonian flow behavior of blood influence the flow field at these sites must be clarified. We have performed fundamental studies using a birefringent solution in a simplified rigid 90 degree T-bifurcation and pulsatile flow. The velocity distribution was measured with a laser Doppler anemometer. Flow in an elastic abdominal aorta model has been visualized using magnetic resonance imaging. In both flow studies, zones with negative velocity were found. These model measurements demonstrate that no flow parameter can be neglected. Further detailed studies are necessary to examine the interaction between fluid dynamic and cellular surface properties. PMID:2404201

  15. Performance Mapping Studies in Redox Flow Cells

    NASA Technical Reports Server (NTRS)

    Hoberecht, M. A.; Thaller, L. H.

    1981-01-01

    Pumping power requirements in any flow battery system constitute a direct parasitic energy loss. It is therefore useful to determine the practical lower limit for reactant flow rates. Through the use of a theoretical framework based on electrochemical first principles, two different experimental flow mapping techniques were developed to evaluate and compare electrodes as a function of flow rate. For the carbon felt electrodes presently used in NASA-Lewis Redox cells, a flow rate 1.5 times greater than the stoichiometric rate seems to be the required minimum.

  16. Coherent Flow Structures and Suspension Events over Low-angle Dunes: Fraser River, Canada

    NASA Astrophysics Data System (ADS)

    Bradley, R. W.; Venditti, J. G.; Kostaschuk, R. A.; Hendershot, M. L.; Allison, M. A.; Church, M. A.

    2012-12-01

    Increasing observations show that dunes with low-angle lee-sides (< 30°) and symmetrical shapes are the most common bedform morphology in large sand-bedded alluvial channels. Flume studies have revealed much about flow and sediment dynamics over high-angle (~30°) asymmetric dunes, however much less is known about low-angle dune dynamics. This study examines mean flow, coherent flow structures and suspension events over low-angle dunes in the unsteady flow of the estuarine reach of the Fraser River, Canada. Dune field topography was mapped using a multibeam echo sounder (MBES) while an acoustic Doppler current profiler (aDcp) simultaneously provided flow and suspended sediment measurements over a range of flows through tidal cycles. At high tide, river flow nearly ceases and a salt wedge enters the channel, forcing plumes of salt water towards the surface into the downstream moving fresh water above as the wedge moves upstream over the dunes. The salt wedge persists in the channel causing stratification in water column and one-sided instabilities along the saline-fresh water interface until the late in the falling tide. At low tide, mean velocities peak and force the saline water out of the channel. Flow over the low-angle dunes displays topographically induced flow patterns similar to previously observed over high-angle dunes, but permanent flow separation is notably absent. Sediment-laden kolks emerge as important suspended sediment transport agents during low tide but become more coherent, yet less frequent, structures as the tide begins to rise. Kolks appear to form downstream of dune crests along the shear layer that is likely formed by intermittent flow separation. Kolks also form at the reattachment point and grow over the stoss slope of the dunes. This is consistent with the generation of hairpin vortices formed near the bed that lift into the flow and grow to the surface through an 'autogeneration' mechanism. Persistent downwelling and periodic sweeps at

  17. Qualitative comparison of intra-aneurysmal flow structures determined from conventional and virtual angiograms

    NASA Astrophysics Data System (ADS)

    Cebral, Juan R.; Radaelli, Alessandro; Frangi, Alejandro; Putman, Christopher M.

    2007-03-01

    In this study we qualitatively compare the flow structures observed in cerebral aneurysms using conventional angiography and virtual angiograms produced from patient-specific computational fluid dynamics (CFD) models. For this purpose, high frame rate biplane angiograms were obtained during a rapid injection of contrast agent in three patients with intracranial aneurysms. Patient-specific CFD models were then constructed from 3D rotational angiography images of each aneurysm. Time dependent flow fields were obtained from the numerical solution of the incompressible Navier-Stokes equations under pulsatile flow conditions derived from phase-contrast magnetic resonance measurements performed on normal subjects. These flow fields were subsequently used to simulate the transport of a contrast agent by solving the advection-diffusion equation. Both the fluid and transport equations were solved with an implicit finite element formulation on unstructured grids. Virtual angiograms were then constructed by volume rendering of the simulated dye concentration field. The flow structures observed in the conventional and virtual angiograms were then qualitatively compared. It was found that the finite element models showed distinct flow types for each aneurysm, ranging from simple to complex. The virtual angiograms showed good agreement with the images from the conventional angiograms for all three aneurysms. Analogous size and orientation of the inflow jet, regions of flow impaction, major intraaneurysmal vortices and regions of outflow were observed in both the conventional and virtual angiograms. In conclusion, patient-specific image-based computational models of intracranial aneurysms can realistically reproduce the major intraaneurysmal flow structures observed with conventional angiography.

  18. Undulating fins produce off-axis thrust and flow structures.

    PubMed

    Neveln, Izaak D; Bale, Rahul; Bhalla, Amneet Pal Singh; Curet, Oscar M; Patankar, Neelesh A; MacIver, Malcolm A

    2014-01-15

    While wake structures of many forms of swimming and flying are well characterized, the wake generated by a freely swimming undulating fin has not yet been analyzed. These elongated fins allow fish to achieve enhanced agility exemplified by the forward, backward and vertical swimming capabilities of knifefish, and also have potential applications in the design of more maneuverable underwater vehicles. We present the flow structure of an undulating robotic fin model using particle image velocimetry to measure fluid velocity fields in the wake. We supplement the experimental robotic work with high-fidelity computational fluid dynamics, simulating the hydrodynamics of both a virtual fish, whose fin kinematics and fin plus body morphology are measured from a freely swimming knifefish, and a virtual rendering of our robot. Our results indicate that a series of linked vortex tubes is shed off the long edge of the fin as the undulatory wave travels lengthwise along the fin. A jet at an oblique angle to the fin is associated with the successive vortex tubes, propelling the fish forward. The vortex structure bears similarity to the linked vortex ring structure trailing the oscillating caudal fin of a carangiform swimmer, though the vortex rings are distorted because of the undulatory kinematics of the elongated fin.

  19. Undulating fins produce off-axis thrust and flow structures.

    PubMed

    Neveln, Izaak D; Bale, Rahul; Bhalla, Amneet Pal Singh; Curet, Oscar M; Patankar, Neelesh A; MacIver, Malcolm A

    2014-01-15

    While wake structures of many forms of swimming and flying are well characterized, the wake generated by a freely swimming undulating fin has not yet been analyzed. These elongated fins allow fish to achieve enhanced agility exemplified by the forward, backward and vertical swimming capabilities of knifefish, and also have potential applications in the design of more maneuverable underwater vehicles. We present the flow structure of an undulating robotic fin model using particle image velocimetry to measure fluid velocity fields in the wake. We supplement the experimental robotic work with high-fidelity computational fluid dynamics, simulating the hydrodynamics of both a virtual fish, whose fin kinematics and fin plus body morphology are measured from a freely swimming knifefish, and a virtual rendering of our robot. Our results indicate that a series of linked vortex tubes is shed off the long edge of the fin as the undulatory wave travels lengthwise along the fin. A jet at an oblique angle to the fin is associated with the successive vortex tubes, propelling the fish forward. The vortex structure bears similarity to the linked vortex ring structure trailing the oscillating caudal fin of a carangiform swimmer, though the vortex rings are distorted because of the undulatory kinematics of the elongated fin. PMID:24072799

  20. 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.

  1. Reconstructing Flow Patterns from Tsunami Deposits with No Visible Sedimentary Structure

    NASA Astrophysics Data System (ADS)

    Kain, C. L.; Chague-Goff, C.; Goff, J. R.; Wassmer, P.; Gomez, C. A.; Hart, D. E.

    2014-12-01

    High energy coastal events, such as tsunamis, commonly leave sediment deposits in the landscape that may be preserved in the geological record. A set of anomalous sand and silt layers intercalated between soil units was identified alongside an estuary in Okains Bay, Banks Peninsula, New Zealand. Okains Bay, comprised of a coastal plain of Holocene progradational dune ridges, was flooded by tsunamis in 1868 and 1960. Previous research has assessed the relationship between tsunami flow patterns and sediment deposits for recent events, and we aim to extend this application to older deposits where flow patterns were not recorded and sedimentary structures are not visually apparent. A multi-proxy approach was used to investigate the sediment deposits at twelve sites along a 2 km length of the estuary margin and map inundation patterns. Measurements of Magnetic Fabric (MF: Anisotropy of Magnetic Susceptibility) were used to determine the flow direction during deposition, alongside stratigraphy and particle size analyses to assess wave energy. Flow direction results were overlaid on a digital elevation model of the study site to interpret flow patterns. Deposits became thinner and particle size decreased with distance from the coast, indicating waning flow energy with distance inland. MF results indicate that inundation occurred via the estuary channel, with primary flow directions oriented perpendicular or sub-perpendicular to the channel at each site. On a smaller scale, results showed evidence of current reversal at some sites, with flow directed alternately away from and towards the estuary channel. This is consistent with uprush and backwash patterns observed in tsunami wave sequences. Topographic control of flow patterns is also evident from the data. This research demonstrates a method for investigating older, structurally-degraded deposits and has implications for the reconstruction of paleotsunami inundation from their sedimentary deposits.

  2. Effect of Iron(II) on Arsenic Sequestration by δ-MnO2: Desorption Studies Using Stirred-Flow Experiments and X-Ray Absorption Fine-Structure Spectroscopy.

    PubMed

    Wu, Yun; Li, Wei; Sparks, Donald L

    2015-11-17

    Arsenic (As) mobility in the environment is greatly affected by its oxidation state and the degree to which it is sorbed on metal oxide surfaces. Manganese (Mn) and iron (Fe) oxides are ubiquitous solids in terrestrial systems and have high sorptive capacities for many trace metals, including As. Although numerous studies have studied the effects of As adsorption and desorption onto Fe and Mn oxides individually, the fate of As within mixed systems representative of natural environments has not been resolved. In this research, As(III) was initially reacted with a poorly crystalline phyllomanganate (δ-MnO2) in the presence of Fe(II) prior to desorption. This initial reaction resulted in the sorption of both As(III) and As(V) on mixed Fe/Mn-oxides surfaces. A desorption study was carried out using two environmentally significant ions, phosphate (PO4(3-)) and calcium (Ca(2+)). Both a stirred-flow technique and X-ray absorption fine-structure spectroscopy (XAFS) analysis were used to investigate As desorption behavior. Results showed that when As(III)/Fe(II) = 1:1 in the initial reaction, only As(V) was desorbed, agreeing with a previous study showing that As(III) is not associated with the Fe/Mn-oxides. When As(III)/Fe(II) = 1:10 in the initial reaction, both As(III) and As(V) can be desorbed from the Fe/Mn-oxide surface, and more As(III) is desorbed than As(V). Neither of the desorbents used in this study completely removed As(III) or As(V) from the Fe/Mn-oxides surface. However, the As desorption fraction decreases with increasing Fe(II) concentration in the initial reactions.

  3. Effect of Iron(II) on Arsenic Sequestration by δ-MnO2: Desorption Studies Using Stirred-Flow Experiments and X-Ray Absorption Fine-Structure Spectroscopy.

    PubMed

    Wu, Yun; Li, Wei; Sparks, Donald L

    2015-11-17

    Arsenic (As) mobility in the environment is greatly affected by its oxidation state and the degree to which it is sorbed on metal oxide surfaces. Manganese (Mn) and iron (Fe) oxides are ubiquitous solids in terrestrial systems and have high sorptive capacities for many trace metals, including As. Although numerous studies have studied the effects of As adsorption and desorption onto Fe and Mn oxides individually, the fate of As within mixed systems representative of natural environments has not been resolved. In this research, As(III) was initially reacted with a poorly crystalline phyllomanganate (δ-MnO2) in the presence of Fe(II) prior to desorption. This initial reaction resulted in the sorption of both As(III) and As(V) on mixed Fe/Mn-oxides surfaces. A desorption study was carried out using two environmentally significant ions, phosphate (PO4(3-)) and calcium (Ca(2+)). Both a stirred-flow technique and X-ray absorption fine-structure spectroscopy (XAFS) analysis were used to investigate As desorption behavior. Results showed that when As(III)/Fe(II) = 1:1 in the initial reaction, only As(V) was desorbed, agreeing with a previous study showing that As(III) is not associated with the Fe/Mn-oxides. When As(III)/Fe(II) = 1:10 in the initial reaction, both As(III) and As(V) can be desorbed from the Fe/Mn-oxide surface, and more As(III) is desorbed than As(V). Neither of the desorbents used in this study completely removed As(III) or As(V) from the Fe/Mn-oxides surface. However, the As desorption fraction decreases with increasing Fe(II) concentration in the initial reactions. PMID:26477604

  4. Mach Number Dependence of Near Wall Structure in Compressible Channel Flows

    NASA Astrophysics Data System (ADS)

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

    2011-09-01

    A newly developed statistical correlation structure is used to analyze compressible channel flows up to M = 3.0. Using velocity-vorticity correlation structure (VVCS), the Mach number dependence of the characteristic scales of near wall structure are analyzed. The detailed results show that the length scale and the spanwise spacing of VVCS exponentially increase with Mach number in the near wall region. For example, for VVCSuωx, the length scale of the statistical streamwise structure is Lxuωx = e6.5 + M/2.8 + (M/4.1)2, and spacing between the structure is Dxuωx = 60eM/2.2 + 13.3, where the parameters 2.8, 4.1 and 2.2 are characteristic Mach numbers to be explained further. The geometrical features of the statistical structure are consistent with the observations of Coleman et al., and it is also argued that the quantitative relationship between the characteristic scales of VVCS and Mach number is important to consider in performing numerical computation of compressible flows. This study also suggests that a set of geometrical structures should be invoked for modeling inhomogeneous compressible shear flows.

  5. Secondary flow structure in a model curved artery: 3D morphology and circulation budget analysis

    NASA Astrophysics Data System (ADS)

    Bulusu, Kartik V.; Plesniak, Michael W.

    2015-11-01

    In this study, we examined the rate of change of circulation within control regions encompassing the large-scale vortical structures associated with secondary flows, i.e. deformed Dean-, Lyne- and Wall-type (D-L-W) vortices at planar cross-sections in a 180° curved artery model (curvature ratio, 1/7). Magnetic resonance velocimetry (MRV) and particle image velocimetry (PIV) experiments were performed independently, under the same physiological inflow conditions (Womersley number, 4.2) and using Newtonian blood-analog fluids. The MRV-technique performed at Stanford University produced phase-averaged, three-dimensional velocity fields. Secondary flow field comparisons of MRV-data to PIV-data at various cross-sectional planes and inflow phases were made. A wavelet-decomposition-based approach was implemented to characterize various secondary flow morphologies. We hypothesize that the persistence and decay of arterial secondary flow vortices is intrinsically related to the influence of the out-of-plane flow, tilting, in-plane convection and diffusion-related factors within the control regions. Evaluation of these factors will elucidate secondary flow structures in arterial hemodynamics. Supported by the National Science Foundation under Grant Number CBET-0828903, and GW Center for Biomimetics and Bioinspired Engineering (COBRE). The MRV data were acquired at Stanford University in collaboration with Christopher Elkins and John Eaton.

  6. Rheology and flow-induced structure in a polystyrene-polyisoprene biocontinuous microemulsion

    NASA Astrophysics Data System (ADS)

    Brinker, Kristin

    2005-03-01

    Polymer bicontinuous microemulsions are blends of immiscible polymers compatibilized with diblock copolymer in such a way as to produce an equilibrium interconnected morphology. Previous experiments on a microemulsion of poly(ethyl ethylene) (PEE) and poly(dimethyl siloxane) (PDMS) have revealed a fascinating array of rheological and flow-induced structural phenomena. We have prepared a new microemulsion sample from low molecular weight polystyrene (PS) and polyisoprene (PI) and their corresponding block copolymer. Despite the fact that the constituent homopolymers are strictly Newtonian, the microemulsion exhibits substantial viscoelasticity associated with flow-induced deformation of the supramolecular organization. The linear viscoelastic properties of the PS-PI microemulsion closely resemble those previously found in the PEE- PDMS system. Under even fairly weakly nonlinear flow conditions, the PS-PI microemulsion exhibits a flow-induced phase transition. In situ small-angle x-ray scattering is used to probe both the flow-induced deformation of the equilibrium microemulsion structure as well as the onset and development of a flow-induced bulk phase separation. The higher suscepibility of the PS-PI system to phase separation may be related to a higher viscosity contrast between its constituents and those in the previously studied PEE-PDMS system.

  7. Magnetic structure and origin of counter-streaming mass flows in solar prominences

    NASA Astrophysics Data System (ADS)

    Shen, Yuandeng

    2015-08-01

    The magnetic structure and origin of counter-streaming mass flows in solar prominences are hitherto unknown, however, these issues are vitally important for understanding the instability and eruption of solar and stellar prominences, as well as the associated coronal mass ejections (CMEs). Here we report high-resolution observations of a quiescent solar prominence that clearly manifests the magnetic structure and origin of counter-streaming mass flows in solar prominences. Based on the observational results, we propose a new prominence model in the present paper, which can reconcile many discrepancies in previous studies, for example, the distribution of magnetic fields in solar prominences, the relationship between the photospheric magnetic fields and the ends of prominence feet, as well as the origin of counterstreaming mass flows in solar prominences. In addition, we also find that the photospheric pressure-driven three and five minutes oscillations can effectively modulate the kinematics of solar prominences.

  8. Aeroacoustics of Turbulent Jets: Flow Structure, Noise Sources, and Control

    NASA Astrophysics Data System (ADS)

    Gutmark, Ephraim Jeff; Callender, Bryan William; Martens, Steve

    The paper reviews research performed to advance the understanding of state-of-the-art technologies capable of reducing coaxial jet noise simulating the exhaust flow of turbofan engines. The review focuses on an emerging jet noise passive control technology known as chevron nozzles. The fundamental physical mechanisms responsible for the acoustic benefits provided by these nozzles are discussed. Additionally, the relationship between these physical mechanisms and some of the primary chevron geometric parameters are highlighted. Far-field acoustic measurements over a wide range of nozzle operating conditions illustrated the ability of the chevron nozzles to provide acoustic benefits. Detailed mappings of the acoustic near-field provided more insight into the chevron noise suppression mechanisms by successfully identifying two primary chevron effects consistent with the results of the far-field measurements: chevrons penetration and shear velocity across them. Mean and turbulence data identified the physical flow mechanisms responsible for the effects documented in the far- and near-field studies.

  9. Visualization studies of turbulent transition flows in a porous medium

    NASA Technical Reports Server (NTRS)

    Bilardo, V. J.

    1983-01-01

    Results are reported for flow-visualization studies of the flow regimes of water passing through a porous medium consisting of cylindrical glass and plexiglas rods arranged in a complex and fixed three-dimensional geometry. The Reynolds number (Re) varied from 50 to 700; the flow was visualized by injecting a 5% potassium permanganate dye solution into the pores and photographing the resulting dye streaklines with both a still camera and a movie camera. The results indicate that four distinct flow regimes exist in the porous medium: (1) Darcy or creeping flow up to Re = 3; (2) steady inertia-dominated laminar flow for Re = 3-150; (3) unsteady transitional laminar flow for Re = 150-250; and (4) fully turbulent flow for Re greater than 250. It is concluded that a laminar wake instability mechanism typical of the external flow about bluff bodies may be responsible for the overall transition from laminar to turbulent flow in porous media.

  10. Coherent structures near the wall in a turbulent channel flow

    NASA Astrophysics Data System (ADS)

    Jeong, J.; Hussain, F.; Schoppa, W.; Kim, J.

    1997-02-01

    Coherent structures (CS) near the wall (i.e. y+ [less-than-or-eq, slant] 60) in a numerically simulated turbulent channel flow are educed using a conditional sampling scheme which extracts the entire extent of dominant vortical structures. Such structures are detected from the instantaneous flow field using our newly developed vortex definition (Jeong & Hussain 1995) a region of negative [lambda]2, the second largest eigenvalue of the tensor SikSkj + [Omega]ik[Omega]kj which accurately captures the structure details (unlike velocity-, vorticity- or pressure-based eduction). Extensive testing has shown that [lambda]2 correctly captures vortical structures, even in the presence of the strong shear occurring near the wall of a boundary layer. We have shown that the dominant near-wall educed (i.e. ensemble averaged after proper alignment) CS are highly elongated quasi-streamwise vortices; the CS are inclined 9° in the vertical (x, y)-plane and tilted ±4° in the horizontal (x, z)-plane. The vortices of alternating sign overlap in x as a staggered array; there is no indication near the wall of hairpin vortices, not only in the educed data but also in instantaneous fields. Our model of the CS array reproduces nearly all experimentally observed events reported in the literature, such as VITA, Reynolds stress distribution, wall pressure variation, elongated low-speed streaks, spanwise shear, etc. In particular, a phase difference (in space) between streamwise and normal velocity fluctuations created by CS advection causes Q4 (‘sweep’) events to dominate Q2 (‘ejection’) and also creates counter-gradient Reynolds stresses (such as Q1 and Q3 events) above and below the CS. We also show that these effects are adequately modelled by half of a Batchelor's dipole embedded in (and decoupled from) a background shear U(y). The CS tilting (in the (x, z)-plane) is found to be responsible for sustaining CS through redistribution of streamwise turbulent kinetic energy to

  11. Quantitative visualization of coherent flow structures in alluvial channels using multibeam echo-sounding

    NASA Astrophysics Data System (ADS)

    Parsons, D. R.; Simmons, S.; Best, J.

    2010-12-01

    Multibeam Echo-Sounder systems have developed rapidly over recent decades and are routinely deployed to provide high-resolution bathymetric details in range of aquatic environments. Modern data handling and storage technologies now facilitate the logging of the raw acoustic back-scatter information that was previously discarded by these systems. This paper describes methodologies that exploit this logging capability to quantify the concentration and dynamics of suspended sediment within the water column and presents a novel method that also allows for quantification of 2D flow velocities. This development provides a multi-purpose tool for the holistic surveying of the process linkages between flow, sediment transport and bed morphology. The application of this new technique is illustrated with reference to flow over alluvial sand dunes, which allows, for the first time in a field study, quantitative visualization of larg-scale, whole flow field, turbulent coherent flow structures, associated with the dune leeside, that are responsible for suspending bed sediment. This methodology holds great potential for use in a wide range of aqueous geophysical flows. CFS captured by MBES in the lee of an alluvial dune. Contours of suspended sediment concentration and superimposed 2D flow velocity vectors

  12. Experimental and theoretical studies of isothermal upward gas-liquid flows in vertical tubes

    SciTech Connect

    Fernandes, R.C.

    1981-01-01

    In two-phase flow technolgy, two important problems exist which must be solved as a function of the various physical and system parameters associated with the phenomenon, and which stand as prerequisites for proper modelling of two-phase processes: Prediction of the flow pattern under existing operating conditions and prediction of the holdup for each given flow pattern. Modelling studies of steady isothermal upward gas-liquid flows in vertical pipes, at low pressures, were undertaken. Experimental data on liquid holdup over a wide range of flow rates were taken for all observed flow patterns-bubbly, slug, churn, and annular - by means of a specially designed Quick-Closing Valves System. This technique also allowed the detection of a unique phenomenon occurring in the form of fast-flowing slugs of gas-liquid mixture, in both the churn and annular flow patterns, which was called the lump phenomenon. The lump holdup was measured and a qualitative theory regarding the nature, formation and propagation of these structures was proposed. A photographic method was applied to the slug flow pattern in order to determine both the rise velocity and length of Taylor bubbles and liquid slugs characteristic of this flow regime. Assisted by the measured data, flow pattern-based physical models were developed for predicting holdup of bubbly flows and the detailed structure of slug flows. The latter was accomplished by means of a fairly complete analysis which enabled the prediction of several variables of interest such as void fractions, velocities, film thicknesses and the length ratio between Taylor bubbles and liquid slugs. The average holdup for churn flow was predicted by directly applying the slug flow model to that flow pattern. A simplified framework for calculating the holdup in annular flows was also proposed. The comparison between theory and experiment showed that for bubbly, slug and churn flows the predicted results are in good agreement with the data.

  13. Fluid Flow through Porous Sandstone with Overprinting and Intersecting Geological Structures of Various Types

    NASA Astrophysics Data System (ADS)

    Zhou, X.; Karimi-Fard, M.; Durlofsky, L.; Aydin, A.

    2010-12-01

    Impact of a wide variety of structural heterogeneities on fluid flow in an aeolian sandstone in the Valley of Fire State Park (NV), such as (1) dilatant fractures (joints), (2) shear fractures (faults), and (3) contraction/compaction structures (compaction bands), are considered. Each type of these structures has its own geometry, spacing, distribution, connectivity, and hydraulic properties, which either enhance or impede subsurface fluid flow. Permeability of these structures may, on average, be a few orders of magnitude higher or lower than those of the corresponding matrix rocks. In recent years, the influence of a single type of these heterogeneities on fluid flow has been studied individually, such as joints, compaction bands or faults. However, as different types of geological structures are commonly present together in the same rock volume, their combined effect requires a more detailed assessment. In this study, fluid flow simulations are performed using a special finite-volume discretization technique that was developed by Karimi-Fard et al. (2004; 2006). Using this approach, thin features such as fractures and compaction bands are represented as linear elements in unstructured 2D models and as planar elements in 3D models, which significantly reduces the total number of cells and simplifies grid generation. The cell geometric information and the cell-to-cell transmissibility obtained from this discretization technique are input to Stanford’s General Purpose Research Simulator (GPRS) for fluid flow simulation. To account for the effects of the various geological structures on subsurface flow, we perform permeability upscaling over regions corresponding to large-scale simulation grid blocks in order to obtain equivalent permeability components in two principal directions. We will focus on the following problems: (1) compaction bands of multisets; (2) compartmentalization of compaction bands of high-angle, low-angle and horizontal; (3) joints overprinting

  14. Development of laminar flow control wing surface composite structures

    NASA Technical Reports Server (NTRS)

    Lineberger, L. B.

    1984-01-01

    The dramatic increases in fuel costs and the potential for periods of limited fuel availability provided the impetus to explore technologies to reduce transport aircraft fuel consumption. NASA sponsored the Aircraft Energy Efficiency (ACEE) program beginning in 1976 to develop technologies to improve fuel efficiency. This report documents the Lockheed-Georgia Company accomplishments under NAS1-16235 LFC Laminar-Flow-Control Wing Panel Structural Design And Development (WSSD); Design, manufacturing, and testing activities. An in-depth preliminary design of the baseline 1993 LFC wing was accomplished. A surface panel using the Lockheed graphite/epoxy integrated LFC wing box structural concept was designed. The concept was shown by analysis to be structurally efficient and cost effective. Critical details of the surface and surface joints were demonstrated by fabricating and testing complex, concept selection specimens. Cost of the baseline LFC aircraft was estimated and compared to the turbulent aircraft. The mission fuel weight was 21.7 percent lower for the LFC aircraft. The calculation shows that the lower fuel costs for LFC offset the higher incremental costs of LFC in less than six months.

  15. Fluid-structure interactions in compressible cavity flows

    SciTech Connect

    Wagner, Justin L.; Casper, Katya Marie; Beresh, Steven J.; Hunter, Patrick S.; Spillers, Russell Wayne; Henfling, John F.; Mayes, Randall L.

    2015-06-08

    Experiments were performed to understand the complex fluid-structure interactions that occur during aircraft internal store carriage. A cylindrical store was installed in a rectangular cavity having a length-to-depth ratio of 3.33 and a length-to-width ratio of 1. The Mach number ranged from 0.6 to 2.5 and the incoming boundary layer was turbulent. Fast-response pressure measurements provided aeroacoustic loading in the cavity, while triaxial accelerometers provided simultaneous store response. Despite occupying only 6% of the cavity volume, the store significantly altered the cavity acoustics. The store responded to the cavity flow at its natural structural frequencies, and it exhibited a directionally dependent response to cavity resonance. Specifically, cavity tones excited the store in the streamwise and wall-normal directions consistently, whereas a spanwise response was observed only occasionally. Also, the streamwise and wall-normal responses were attributed to the longitudinal pressure waves and shear layer vortices known to occur during cavity resonance. Although the spanwise response to cavity tones was limited, broadband pressure fluctuations resulted in significant spanwise accelerations at store natural frequencies. As a result, the largest vibrations occurred when a cavity tone matched a structural natural frequency, although energy was transferred more efficiently to natural frequencies having predominantly streamwise and wall-normal motions.

  16. Fluid-structure interactions in compressible cavity flows

    DOE PAGESBeta

    Wagner, Justin L.; Casper, Katya Marie; Beresh, Steven J.; Hunter, Patrick S.; Spillers, Russell Wayne; Henfling, John F.; Mayes, Randall L.

    2015-06-08

    Experiments were performed to understand the complex fluid-structure interactions that occur during aircraft internal store carriage. A cylindrical store was installed in a rectangular cavity having a length-to-depth ratio of 3.33 and a length-to-width ratio of 1. The Mach number ranged from 0.6 to 2.5 and the incoming boundary layer was turbulent. Fast-response pressure measurements provided aeroacoustic loading in the cavity, while triaxial accelerometers provided simultaneous store response. Despite occupying only 6% of the cavity volume, the store significantly altered the cavity acoustics. The store responded to the cavity flow at its natural structural frequencies, and it exhibited a directionallymore » dependent response to cavity resonance. Specifically, cavity tones excited the store in the streamwise and wall-normal directions consistently, whereas a spanwise response was observed only occasionally. Also, the streamwise and wall-normal responses were attributed to the longitudinal pressure waves and shear layer vortices known to occur during cavity resonance. Although the spanwise response to cavity tones was limited, broadband pressure fluctuations resulted in significant spanwise accelerations at store natural frequencies. As a result, the largest vibrations occurred when a cavity tone matched a structural natural frequency, although energy was transferred more efficiently to natural frequencies having predominantly streamwise and wall-normal motions.« less

  17. Commodity Flow Study - Clark County, Nevada, USA

    SciTech Connect

    Conway, S.Ph.D.; Navis, I.

    2008-07-01

    The United States Department of Energy has designated Clark County, Nevada as an 'Affected Unit of Local Government' due to the potential for impacts by activities associated with the Yucca Mountain High Level Nuclear Waste Repository project. Urban Transit, LLC has led a project team of transportation including experts from the University of Nevada Las Vegas Transportation Research Center to conduct a hazardous materials community flow study along Clark County's rail and truck corridors. In addition, a critical infrastructure analysis has also been carried out in order to assess the potential impacts of transportation within Clark County of high level nuclear waste and spent nuclear fuel to a proposed repository 90 miles away in an adjacent county on the critical infrastructure in Clark County. These studies were designed to obtain information relating to the transportation, identification and routing of hazardous materials through Clark County. Coordinating with the United States Department of Energy, the U.S. Department of Agriculture, the U. S. Federal Highway Administration, the Nevada Department of Transportation, and various other stakeholders, these studies and future research will examine the risk factors along the entire transportation corridor within Clark County and provide a context for understanding the additional vulnerability associated with shipping spent fuel through Clark County. (authors)

  18. Flow structures in the wake of heaving and pitching foils

    NASA Astrophysics Data System (ADS)

    Najdzin, Derek; Pardo, Enrique; Leftwich, Megan C.; Bardet, Philippe M.

    2012-11-01

    A 10-bar mechanism drives a cambering hydrofoil in an oscillatory heaving and pitching motion that replicates the flapping motion of a dolphin tail. The mechanism sits on a force-balance with six strain gages that together measure the forces and moments experienced by the fin during an oscillation. Planar Laser-Induced Fluorescence is used to image the flow structures created downstream of the cambering fin for a range of Reynolds and Strouhal numbers. The images are taken in the mid-plane, parallel to the bottom of the water tunnel. These results are compared to a rigid foil at matching conditions to investigate the role of camber changes during the flapping cycle.

  19. The development of laser speckle velocimetry for the study of vortical flows

    NASA Technical Reports Server (NTRS)

    Krothapalli, A.

    1991-01-01

    A new experimental technique commonly known as PIDV (particle image displacement velocity) was developed to measure an instantaneous two dimensional velocity fluid in a selected plane of the flow field. This technique was successfully applied to the study of several problems: (1) unsteady flows with large scale vortical structures; (2) the instantaneous two dimensional flow in the transition region of a rectangular air jet; and (3) the instantaneous flow over a circular bump in a transonic flow. In several other experiments PIDV is routinely used as a non-intrusive measurement technique to obtain instantaneous two dimensional velocity fields.

  20. The Effect of Flow on Periphyton Structure and Nitrate Removal

    NASA Astrophysics Data System (ADS)

    Arnon, S.; Packman, A.; Gray, K.

    2005-05-01

    High nutrient levels in surface waters are a persistent worldwide problem. Natural and constructed wetlands are frequently employed to reduce nutrients levels from non-point sources, such as agriculture activity. However, there is little understanding of the variation in nitrate removal with flow conditions, and it is difficult to control peaks of nitrogen, especially in the spring when flows tend to be high and there is substantial agricultural nutrient input. Observations of nitrogen transformations in the Des Plaines River Wetland Demonstration Project (Wadsworth, IL) indicate that the emplacement of benthic mesh netting increases the rate of denitrification by providing a favorable and uniform substrate for thick periphyton growth, which, in turn, promotes a superior habitat and carbon source for denitrifying bacteria. We are evaluating this hypothesis in a series of studies designed to improve understanding of the interplay between periphyton assemblage characteristics, overlying flow conditions, and the rate of denitrification. We are conducting laboratory experiments in a model wetland system (250 cm long and 20 cm wide). Nitrate removal is evaluated by monitoring changes in the concentrations of nitrate, nitrite, ammonium and total nitrogen in the system under different fluid velocities (0.05, 0.5 and 5 cm/s). Temporal changes in the periphyton assemblage characteristics are quantified using a combination of confocal microscopy, algal identification, and microbial enumeration. We also utilize micro-profiling with oxygen and nitrate micro-sensors to evaluate chemical heterogeneity in the periphyton and sediments. Combined knowledge of the response of the microbial system and bulk denitrification rates to the system geometry and flow conditions will support the development of improved strategies that rely on periphytic growth to enhance denitrification rates in natural and constructed wetlands.

  1. A survey of air flow models for multizone structures

    SciTech Connect

    Feustel, H.E.; Dieris, J.

    1991-03-01

    Air flow models are used to simulate the rates of incoming and outgoing air flows for a building with known leakage under given weather and shielding conditions. Additional information about the flow paths and air-mass flows inside the building can only by using multizone air flow models. In order to obtain more information on multizone air flow models, a literature review was performed in 1984. A second literature review and a questionnaire survey performed in 1989, revealed the existence of 50 multizone air flow models, all developed since 1966, two of which are still under development. All these programs use similar flow equations for crack flow but differ in the versatility to describe the full range of flow phenomena and the algorithm provided for solving the set of nonlinear equations. This literature review was found that newer models are able to describe and simulate the ventilation systems and interrelation of mechanical and natural ventilation. 27 refs., 2 figs., 1 tab.

  2. [Correlation of substrate structure and hydraulic characteristics in subsurface flow constructed wetlands].

    PubMed

    Bai, Shao-Yuan; Song, Zhi-Xin; Ding, Yan-Li; You, Shao-Hong; He, Shan

    2014-02-01

    The correlation of substrate structure and hydraulic characteristics was studied by numerical simulation combined with experimental method. The numerical simulation results showed that the permeability coefficient of matrix had a great influence on hydraulic efficiency in subsurface flow constructed wetlands. The filler with a high permeability coefficient had a worse flow field distribution in the constructed wetland with single layer structure. The layered substrate structure with the filler permeability coefficient increased from surface to bottom could avoid the short-circuited flow and dead-zones, and thus, increased the hydraulic efficiency. Two parallel pilot-scale constructed wetlands were built according to the numerical simulation results, and tracer experiments were conducted to validate the simulation results. The tracer experiment result showed that hydraulic characteristics in the layered constructed wetland were obviously better than that in the single layer system, and the substrate effective utilization rates were 0.87 and 0.49, respectively. It was appeared that numerical simulation would be favorable for substrate structure optimization in subsurface flow constructed wetlands.

  3. Time-Dependent Thermally-Driven Interfacial Flows in Multilayered Fluid Structures

    NASA Technical Reports Server (NTRS)

    Haj-Hariri, Hossein; Borhan, A.

    1996-01-01

    A computational study of thermally-driven convection in multilayered fluid structures will be performed to examine the effect of interactions among deformable fluid-fluid interfaces on the structure of time-dependent flow in these systems. Multilayered fluid structures in two models configurations will be considered: the differentially heated rectangular cavity with a free surface, and the encapsulated cylindrical liquid bridge. An extension of a numerical method developed as part of our recent NASA Fluid Physics grant will be used to account for finite deformations of fluid-fluid interfaces.

  4. Integration of flow studies for robust selection of mechanoresponsive genes.

    PubMed

    Maimari, Nataly; Pedrigi, Ryan M; Russo, Alessandra; Broda, Krysia; Krams, Rob

    2016-03-01

    Blood flow is an essential contributor to plaque growth, composition and initiation. It is sensed by endothelial cells, which react to blood flow by expressing > 1000 genes. The sheer number of genes implies that one needs genomic techniques to unravel their response in disease. Individual genomic studies have been performed but lack sufficient power to identify subtle changes in gene expression. In this study, we investigated whether a systematic meta-analysis of available microarray studies can improve their consistency. We identified 17 studies using microarrays, of which six were performed in vivo and 11 in vitro. The in vivo studies were disregarded due to the lack of the shear profile. Of the in vitro studies, a cross-platform integration of human studies (HUVECs in flow cells) showed high concordance (> 90 %). The human data set identified > 1600 genes to be shear responsive, more than any other study and in this gene set all known mechanosensitive genes and pathways were present. A detailed network analysis indicated a power distribution (e. g. the presence of hubs), without a hierarchical organisation. The average cluster coefficient was high and further analysis indicated an aggregation of 3 and 4 element motifs, indicating a high prevalence of feedback and feed forward loops, similar to prokaryotic cells. In conclusion, this initial study presented a novel method to integrate human-based mechanosensitive studies to increase its power. The robust network was large, contained all known mechanosensitive pathways and its structure revealed hubs, and a large aggregate of feedback and feed forward loops. PMID:26842798

  5. Transition and acoustic response of recirculation structures in an unconfined co-axial isothermal swirling flow

    NASA Astrophysics Data System (ADS)

    Santhosh, R.; Miglani, Ankur; Basu, Saptarshi

    2013-08-01

    This paper reports the first observations of transition from a pre-vortex breakdown (Pre-VB) flow reversal to a fully developed central toroidal recirculation zone in a non-reacting, double-concentric swirling jet configuration and its response to longitudinal acoustic excitation. This transition proceeds with the formation of two intermediate, critical flow regimes. First, a partially penetrated vortex breakdown bubble (VBB) is formed that indicates the first occurrence of an enclosed structure as the centre jet penetration is suppressed by the growing outer roll-up eddy; resulting in an opposed flow stagnation region. Second, a metastable transition structure is formed that marks the collapse of inner mixing vortices. In this study, the time-averaged topological changes in the coherent recirculation structures are discussed based on the non-dimensional modified Rossby number (Rom) which appears to describe the spreading of the zone of swirl influence in different flow regimes. Further, the time-mean global acoustic response of pre-VB and VBB is measured as a function of pulsing frequency using the relative aerodynamic blockage factor (i.e., maximum radial width of the inner recirculation zone). It is observed that all flow modes except VBB are structurally unstable as they exhibit severe transverse radial shrinkage (˜20%) at the burner Helmholtz resonant modes (100-110 Hz). In contrast, all flow regimes show positional instability as seen by the large-scale, asymmetric spatial shifting of the vortex core centres. Finally, the mixing transfer function M (f) and magnitude squared coherence λ2(f) analysis is presented to determine the natural coupling modes of the system dynamic parameters (u', p'), i.e., local acoustic response. It is seen that the pre-VB flow mode exhibits a narrow-band, low pass filter behavior with a linear response window of 100-105 Hz. However, in the VBB structure, presence of critical regions such as the opposed flow stagnation region

  6. Two-phase flow stability structure in a natural circulation system

    SciTech Connect

    Zhou, Zhiwei

    1995-09-01

    The present study reports a numerical analysis of two-phase flow stability structures in a natural circulation system with two parallel, heated channels. The numerical model is derived, based on the Galerkin moving nodal method. This analysis is related to some design options applicable to integral heating reactors with a slightly-boiling operation mode, and is also of general interest to similar facilities. The options include: (1) Symmetric heating and throttling; (2) Asymmetric heating and symmetric throttling; (3) Asymmetric heating and throttling. The oscillation modes for these variants are discussed. Comparisons with the data from the INET two-phase flow stability experiment have qualitatively validated the present analysis.

  7. A patterned anisotropic nanofluidic sieving structure for continuous-flow separation of DNA and proteins.

    PubMed

    Fu, Jianping; Schoch, Reto B; Stevens, Anna L; Tannenbaum, Steven R; Han, Jongyoon

    2007-02-01

    Microfabricated regular sieving structures hold great promise as an alternative to gels to improve the speed and resolution of biomolecule separation. In contrast to disordered porous gel networks, these regular structures also provide well defined environments ideal for the study of molecular dynamics in confining spaces. However, the use of regular sieving structures has, to date, been limited to the separation of long DNA molecules, however separation of smaller, physiologically relevant macromolecules, such as proteins, still remains a challenge. Here we report a microfabricated anisotropic sieving structure consisting of a two-dimensional periodic nanofluidic filter array. The designed structural anisotropy causes different-sized or -charged biomolecules to follow distinct trajectories, leading to efficient separation. Continuous-flow size-based separation of DNA and proteins, as well as electrostatic separation of proteins, was achieved, demonstrating the potential use of this device as a generic molecular sieving structure for an integrated biomolecule sample preparation and analysis system. PMID:18654231

  8. A patterned anisotropic nanofluidic sieving structure for continuous-flow separation of DNA and proteins

    NASA Astrophysics Data System (ADS)

    Fu, Jianping; Schoch, Reto B.; Stevens, Anna L.; Tannenbaum, Steven R.; Han, Jongyoon

    2007-02-01

    Microfabricated regular sieving structures hold great promise as an alternative to gels to improve the speed and resolution of biomolecule separation. In contrast to disordered porous gel networks, these regular structures also provide well defined environments ideal for the study of molecular dynamics in confining spaces. However, the use of regular sieving structures has, to date, been limited to the separation of long DNA molecules, however separation of smaller, physiologically relevant macromolecules, such as proteins, still remains a challenge. Here we report a microfabricated anisotropic sieving structure consisting of a two-dimensional periodic nanofluidic filter array. The designed structural anisotropy causes different-sized or -charged biomolecules to follow distinct trajectories, leading to efficient separation. Continuous-flow size-based separation of DNA and proteins, as well as electrostatic separation of proteins, was achieved, demonstrating the potential use of this device as a generic molecular sieving structure for an integrated biomolecule sample preparation and analysis system.

  9. Strongly coupled partitioned approach for fluid structure interaction in free surface flows

    NASA Astrophysics Data System (ADS)

    Facci, Andrea Luigi; Ubertini, Stefano

    2016-06-01

    In this paper we describe and validate a methodology for the numerical simulation of the fluid structure interaction in free surface flows. Specifically, this study concentrates on the vertical impact of a rigid body on the water surface, (i.e. on the hull slamming problem). The fluid flow is modeled through the volume of fluid methodology, and the structure dynamics is described by the Newton's second law. An iterative algorithm guarantees the tight coupling between the fluid and solid solvers, allowing the simulations of lightweight (i.e. buoyant) structures. The methodology is validated comparing numerical results to experimental data on the free fall of different rigid wedges. The correspondence between numerical results and independent experimental findings from literature evidences the reliability and the accuracy of the proposed approach.

  10. Basic studies of microstructure of combusting turbulent flows

    NASA Astrophysics Data System (ADS)

    Hussain, Fazle

    1991-03-01

    The goal is to develop a state-of-the-art measurement technique, Holographic Particle Displacement Velocimetry (HPV), which can provide instantaneous velocities everywhere in the flow field simultaneously. Another goal is to use the power of supercomputers to simulate 3D flows with heat release to study the physics of combusting turbulent flows. Computations suffer from limited flow times and Reynolds number but can provide flow properties in more detail than possible by any existing experimental techniques. Moreover, numerical simulations can provide quantities almost impossible to measure experimentally. This article discusses efforts to develop the holographic particle displacement velocimetry system and results of direct numerical numerical simulations of combusting flows.

  11. Experimental Investigation on Near-wall Turbulent Flow Structures over Deformable Roughness

    NASA Astrophysics Data System (ADS)

    Toloui, Mostafa; John, Nolan; Hong, Jiarong

    2015-11-01

    Wall-bounded turbulent flows over rough surfaces have been studied for almost a century. However, in most of the prior studies, little attention has been paid to the role of roughness mechanical properties, e.g. deformability, in altering the flow characteristics including both general turbulent statistics and near-wall flow structures. In this study, high resolution time-resolved digital in-line holographic PIV is employed to investigate the near-wall turbulent structures as well as turbulent statistics around and above deforming roughness structures. The rough wall samples consisting of tapered cylinders of size 0.5 mm in diameter and 3 mm in height are manufactured from transparent PDMS with similar geometrical features but various deformability levels. The experiments are conducted within an optically index-matched facility (using NaI solution) operating with different Reynolds numbers where roughness samples of different deformability are placed downstream of a 1.2 m long acrylic channel of 50 mm square cross section. The follow-up research envisions a large dataset including various Reynolds numbers and deformability to elucidate the role of roughness deformability on near-wall coherent structures and turbulent energy transport within and above the roughness sublayer. This work is supported by the startup package of Jiarong Hong and the MnDrive Fellowship of Mostafa Toloui from University of Minnesota.

  12. Interfacial structures of confined air-water two-phase bubbly flow

    SciTech Connect

    Kim, S.; Ishii, M.; Wu, Q.; McCreary, D.; Beus, S.G.

    2000-08-01

    The interfacial structure of the two-phase flows is of great importance in view of theoretical modeling and practical applications. In the present study, the focus is made on obtaining detailed local two-phase parameters in the air-water bubbly flow in a rectangular vertical duct using the double-sensor conductivity probe. The characteristic wall-peak is observed in the profiles of the interracial area concentration and the void fraction. The development of the interfacial area concentration along the axial direction of the flow is studied in view of the interfacial area transport and bubble interactions. The experimental data is compared with the drift flux model with C{sub 0} = 1.35.

  13. Ultrasonic flow imaging system: A feasibility study

    SciTech Connect

    Sheen, S.H.; Lawrence, W.P.; Chien, H.T.; Raptis, A.C.

    1991-09-01

    This report examines the feasibility and potential problems in developing a real-time ultrasonic flow imaging instrument for on-line monitoring of mixed-phased flows such as coal slurries. State-of-the-art ultrasonic imaging techniques are assessed for this application. Reflection and diffraction tomographies are proposed for further development, including image-reconstruction algorithms and parallel processing systems. A conventional ultrasonic C-scan technique is used to demonstrate the feasibility of imaging the particle motion in a solid/water flow. 13 refs., 11 figs.

  14. Experimental measurement of structural power flow on an aircraft fuselage

    NASA Technical Reports Server (NTRS)

    Cuschieri, J. M.

    1989-01-01

    An experimental technique is used to measure the structural power flow through an aircraft fuselage with the excitation near the wing attachment location. Because of the large number of measurements required to analyze the whole of an aircraft fuselage, it is necessary that a balance be achieved between the number of measurement transducers, the mounting of these transducers, and the accuracy of the measurements. Using four transducers mounted on a bakelite platform, the structural intensity vectors at locations distributed throughout the fuselage are measured. To minimize the errors associated with using a four transducers technique the measurement positions are selected away from bulkheads and stiffeners. Because four separate transducers are used, with each transducer having its own drive and conditioning amplifiers, phase errors are introduced in the measurements that can be much greater than the phase differences associated with the measurements. To minimize these phase errors two sets of measurements are taken for each position with the orientation of the transducers rotated by 180 deg and an average taken between the two sets of measurements. Results are presented and discussed.

  15. Cosmic Flows and the Structure of the Local Universe

    NASA Astrophysics Data System (ADS)

    Steinmetz, Matthias

    2016-03-01

    The Local Volume is the area of the cosmos we can analyze in most detail with respect to the properties of its galaxy population, their abundance, their inner structure, their distribution, and their formation. Indeed, many challenges of the cosmological concordance model such as the substructure crisis or the surprising occurrence of vast planes of satellite galaxies are intimately linked to observations of the local galaxy population. However, owing to the peculiar environment of our Milky Way system and its cosmic neighborhood, the Local Volume may also be severely biased. Cosmography, i.e. the reconstruction of the local cosmic web from cosmic flows, and constrained simulations of structure formation as a tool to produce simulated local group analogues provide a powerful method to analyze and quantify these biases. Possible applications include the analysis of the local distribution of dwarf galaxies around luminous galaxies and the characterization of the mass accretion history of these objects. Thanks to the extension of galaxy velocity data out to distances in excess of 200Mpc, we are now capable to reconstruct the 3D matter distribution out to these distances, thus constraining the formation history of object such as the Virgo Cluster.

  16. Structural properties of mobile armors formed at different flow strengths in gravel-bed rivers

    NASA Astrophysics Data System (ADS)

    Powell, D. Mark; Ockelford, Annie; Rice, Stephen P.; Hillier, John K.; Nguyen, Thao; Reid, Ian; Tate, Nicholas J.; Ackerley, David

    2016-08-01

    Differences in the structure of mobile armors formed at three different flow strengths have been investigated in a laboratory flume. The temporal evolution of the bed surfaces and the properties of the final beds were compared using metrics of surface grain size, microtopography, and bed organization at both grain and mesoscales. Measurements of the bed condition were obtained on nine occasions during each experiment to describe the temporal evolution of the beds. Structured mobile armors formed quickly in each experiment. At the grain scale (1-45 mm; 9 ≤ Ds50 ≤ 17 mm where Ds50 is the median surface particle size), surface complexity decreased and bed roughness increased in response to surface coarsening and the development of the mobile armor. Particles comprising the armor also became flow aligned and developed imbrication. At a larger scale (100-200 mm), the surface developed a mesoscale topography through the development of bed patches with lower and higher elevations. Metrics of mobile armor structure showed remarkable consistency over prolonged periods of near-constant transport, demonstrating for the first time that actively transporting surfaces maintain an equilibrium bed structure. Bed structuring was least developed in the experiments conducted at the lowest flow strength. However, little difference was observed in the structural metrics of the mobile armors generated at higher flows. Although the range of transport rates studied was limited, the results suggest that the structure of mobile armors is insensitive to the formative transport rate except when rates are low (τ* ≈ 0.03 where τ* is the dimensionless shear stress).

  17. Comparative study of heat transfer and pressure drop during flow boiling and flow condensation in minichannels

    NASA Astrophysics Data System (ADS)

    Mikielewicz, Dariusz; Andrzejczyk, Rafał; Jakubowska, Blanka; Mikielewicz, Jarosław

    2014-09-01

    In the paper a method developed earlier by authors is applied to calculations of pressure drop and heat transfer coefficient for flow boiling and also flow condensation for some recent data collected from literature for such fluids as R404a, R600a, R290, R32,R134a, R1234yf and other. The modification of interface shear stresses between flow boiling and flow condensation in annular flow structure are considered through incorporation of the so called blowing parameter. The shear stress between vapor phase and liquid phase is generally a function of nonisothermal effects. The mechanism of modification of shear stresses at the vapor-liquid interface has been presented in detail. In case of annular flow it contributes to thickening and thinning of the liquid film, which corresponds to condensation and boiling respectively. There is also a different influence of heat flux on the modification of shear stress in the bubbly flow structure, where it affects bubble nucleation. In that case the effect of applied heat flux is considered. As a result a modified form of the two-phase flow multiplier is obtained, in which the nonadiabatic effect is clearly pronounced.

  18. A Method for Flow Simulation About Complex Geometries Using Both Structured and Unstructured Grids

    NASA Technical Reports Server (NTRS)

    Debonis, James R.

    1994-01-01

    A computational fluid dynamics code which utilizes both structured and unstructured grids was developed. The objective of this study was to develop and demonstrate the ability of such a code to achieve solutions about complex geometries in two dimensions. An unstructured grid generator and flow solver were incorporated into the PARC2D structured flow solver. This new unstructured grid generator capability allows for easier generation and manipulation of complex grids. Several examples of the grid generation capabilities are provided. The coupling of different grid topologies and the manipulation of individual grids is shown. Also, grids for realistic geometries, a NACA 0012 airfoil and a wing/nacelle installation, were created. The flow over a NACA 0012 airfoil was used as a test case for the flow solver. Eight separate cases were run. They were both the inviscid and viscous solutions for two freestream Mach numbers and airfoil angle of attacks of 0 to 3.86 degrees. The Mach numbers chosen were for a subsonic case, Mach 0.6, and a case where supersonic regions and a shock wave exists, Mach 0.8. These test case conditions were selected to match experimentally obtained data for code comparison. The results show that the code accurately predicts the flow field for all cases.

  19. Buoyancy Effects on Flow Structure and Instability of Low-Density Gas Jets

    NASA Technical Reports Server (NTRS)

    Pasumarthi, Kasyap Sriramachandra

    2004-01-01

    A low-density gas jet injected into a high-density ambient gas is known to exhibit self-excited global oscillations accompanied by large vortical structures interacting with the flow field. The primary objective of the proposed research is to study buoyancy effects on the origin and nature of the flow instability and structure in the near-field of low-density gas jets. Quantitative rainbow schlieren deflectometry, Computational fluid dynamics (CFD) and Linear stability analysis were the techniques employed to scale the buoyancy effects. The formation and evolution of vortices and scalar structure of the flow field are investigated in buoyant helium jets discharged from a vertical tube into quiescent air. Oscillations at identical frequency were observed throughout the flow field. The evolving flow structure is described by helium mole percentage contours during an oscillation cycle. Instantaneous, mean, and RMS concentration profiles are presented to describe interactions of the vortex with the jet flow. Oscillations in a narrow wake region near the jet exit are shown to spread through the jet core near the downstream location of the vortex formation. The effects of jet Richardson number on characteristics of vortex and flow field are investigated and discussed. The laminar, axisymmetric, unsteady jet flow of helium injected into air was simulated using CFD. Global oscillations were observed in the flow field. The computed oscillation frequency agreed qualitatively with the experimentally measured frequency. Contours of helium concentration, vorticity and velocity provided information about the evolution and propagation of vortices in the oscillating flow field. Buoyancy effects on the instability mode were evaluated by rainbow schlieren flow visualization and concentration measurements in the near-field of self-excited helium jets undergoing gravitational change in the microgravity environment of 2.2s drop tower at NASA John H. Glenn Research Center. The jet

  20. Modeling Water Flow and Bromide Transport in a Two-Scale-Structured Lignitic Mine Soil

    NASA Astrophysics Data System (ADS)

    Dusek, J.; Gerke, H. H.; Vogel, T.; Maurer, T.; Buczko, U.

    2008-12-01

    Two-dimensional single- and dual-permeability simulations are used to analyze water and solute fluxes in heterogeneous lignitic mine soil at a forest-reclaimed mine spoil heap. The soil heterogeneity on this experimental site "Barenbrucker Hohe" resulted from inclined dumping structures and sediment mixtures that consist of sand with lignitic dust and embedded lignitic fragments. Observations on undisturbed field suction- cell lysimeters including tracer experiments revealed funneling-type preferential flow with lateral water and bromide movement along inclined sediment structures. The spatial distribution of soil structures and fragment distributions was acquired by a digital camera and identified by a supervised classification of the digital profile image. First, a classical single-domain modeling approach was proposed with spatially variable scaling factors inferred from image analyses. In the next step, a two-continuum scenario was constructed to examine additional effects of nonequilibrium on the flow regime. The scaling factors used for the preferential flow domain are here obtained from the gradient of the grayscale images. So far, the single domain scenarios failed to predict the bromide leaching patterns although water effluent could be described. Dual-permeability model allows the incorporation of structural effects and can be used as a tool to further testing other approaches that account for structure effects. The numerical study suggests that additional experiments are required to obtain better understanding of the highly complex transport processes on this experimental site.

  1. Cavitation, Flow Structure and Turbulence in the Tip Region of a Rotor Blade

    NASA Technical Reports Server (NTRS)

    Wu, H.; Miorini, R.; Soranna, F.; Katz, J.; Michael, T.; Jessup, S.

    2010-01-01

    Objectives: Measure the flow structure and turbulence within a Naval, axial waterjet pump. Create a database for benchmarking and validation of parallel computational efforts. Address flow and turbulence modeling issues that are unique to this complex environment. Measure and model flow phenomena affecting cavitation within the pump and its effect on pump performance. This presentation focuses on cavitation phenomena and associated flow structure in the tip region of a rotor blade.

  2. The art and science of flow control - case studies using flow visualization methods

    NASA Astrophysics Data System (ADS)

    Alvi, F. S.; Cattafesta, L. N., III

    2010-04-01

    Active flow control (AFC) has been the focus of significant research in the last decade. This is mainly due to the potentially substantial benefits it affords. AFC applications range from the subsonic to the supersonic (and beyond) regime for both internal and external flows. These applications are wide and varied, such as controlling flow transition and separation over various external components of the aircraft to active management of separation and flow distortion in engine components and over turbine and compressor blades. High-speed AFC applications include control of flow oscillations in cavity flows, supersonic jet screech, impinging jets, and jet-noise control. In this paper we review some of our recent applications of AFC through a number of case studies that illustrate the typical benefits as well as limitations of present AFC methods. The case studies include subsonic and supersonic canonical flowfields such as separation control over airfoils, control of supersonic cavity flows and impinging jets. In addition, properties of zero-net mass-flux (ZNMF) actuators are also discussed as they represent one of the most widely studied actuators used for AFC. In keeping with the theme of this special issue, the flowfield properties and their response to actuation are examined through the use of various qualitative and quantitative flow visualization methods, such as smoke, shadowgraph, schlieren, planar-laser scattering, and Particle image velocimetry (PIV). The results presented here clearly illustrate the merits of using flow visualization to gain significant insight into the flow and its response to AFC.

  3. Investigation on 3D t wake flow structures of swimming bionic fish

    NASA Astrophysics Data System (ADS)

    Shen, G.-X.; Tan, G.-K.; Lai, G.-J.

    2012-10-01

    A bionic experimental platform was designed for the purpose of investigating time accurate three-dimensional flow field, using digital particle image velocimetry (DSPIV). The wake behind the flapping trail of a robotic fish model was studied at high spatial resolution. The study was performed in a water channel. A robot fish model was designed and built. The model was fixed onto a rigid support framework using a cable-supporting method, with twelve stretched wires. The entire tail of the model can perform prescribed motions in two degrees of freedom, mainly in carangiform mode, by driving its afterbody and lunate caudal fin respectively. The DSPIV system was set up to operate in a translational manner, measuring velocity field in a series of parallel slices. Phase locked measurements were repeated for a number of runs, allowing reconstruction of phase average flow field. Vortex structures with phase history of the wake were obtained. The study reveals some new and complex three-dimensional flow structures in the wake of the fish, including "reverse hairpin vortex" and "reverse Karman S-H vortex rings", allowing insight into physics of this complex flow.

  4. Field Investigation of Flow Structure and Channel Morphology at Confluent-Meander Bends

    NASA Astrophysics Data System (ADS)

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

    2007-12-01

    The movement of water and sediment through drainage networks is inevitably influenced by the convergence of streams and rivers at channel confluences. These focal components of fluvial systems produce a complex hydrodynamic environment, where rapid changes in flow structure and sediment transport occur to accommodate the merging of separate channel flows. The inherent geometric and hydraulic change at confluences also initiates the development of distinct geomorphic features, reflected in the bedform and shape of the channel. An underlying assumption of previous experimental and theoretical models of confluence dynamics has been that converging streams have straight channels with angular configurations. This generalized conceptualization was necessary to establish confluence planform as symmetrical or asymmetrical and to describe subsequent flow structure and geomorphic features at confluences. However, natural channels, particularly those of meandering rivers, curve and bend. This property and observation of channel curvature at natural junctions have led to the hypothesis that natural stream and river confluences tend to occur on the concave outer bank of meander bends. The resulting confluence planform, referred to as a confluent-meander bend, was observed over a century ago but has received little scientific attention. This paper examines preliminary data on three-dimensional flow structure and channel morphology at two natural confluent-meander bends of varying size and with differing tributary entrance locations. The large river confluence of the Vermilion River and Wabash River in west central Indiana and the comparatively small junction of the Little Wabash River and Big Muddy Creek in southeastern Illinois are the location of study sites for field investigation. Measurements of time-averaged three-dimensional velocity components were obtained at these confluences with an acoustic Doppler current profiler for flow events with differing momentum ratios. Bed

  5. Large-Scale Flow Structure in Turbulent Nonpremixed Flames under Normal- And Low-Gravity Conditions

    NASA Technical Reports Server (NTRS)

    Clemens, N. T.; Idicheria, C. A.; Boxx, I. G.

    2001-01-01

    It is well known that buoyancy has a major influence on the flow structure of turbulent nonpremixed jet flames. Buoyancy acts by inducing baroclinic torques, which generate large-scale vortical structures that can significantly modify the flow field. Furthermore, some suggest that buoyancy can substantially influence the large-scale structure of even nominally momentum-dominated flames, since the low velocity flow outside of the flame will be more susceptible to buoyancy effects. Even subtle buoyancy effects may be important because changes in the large-scale structure affects the local entrainment and fluctuating strain rate, and hence the structure of the flame. Previous studies that have compared the structure of normal- and micro-gravity nonpremixed jet flames note that flames in microgravity are longer and wider than in normal-gravity. This trend was observed for jet flames ranging from laminar to turbulent regimes. Furthermore, imaging of the flames has shown possible evidence of helical instabilities and disturbances starting from the base of the flame in microgravity. In contrast, these characteristics were not observed in normal-gravity. The objective of the present study is to further advance our knowledge of the effects of weak levels of buoyancy on the structure of transitional and turbulent nonpremixed jet flames. In later studies we will utilize the drop tower facilities at NASA Glenn Research Center (GRC), but the preliminary work described in this paper was conducted using the 1.25-second drop tower located at the University of Texas at Austin. A more detailed description of these experiments can be found in Idicheria et al.

  6. Fluid structure interaction solver coupled with volume of fluid method for two-phase flow simulations

    NASA Astrophysics Data System (ADS)

    Cerroni, D.; Fancellu, L.; Manservisi, S.; Menghini, F.

    2016-06-01

    In this work we propose to study the behavior of a solid elastic object that interacts with a multiphase flow. Fluid structure interaction and multiphase problems are of great interest in engineering and science because of many potential applications. The study of this interaction by coupling a fluid structure interaction (FSI) solver with a multiphase problem could open a large range of possibilities in the investigation of realistic problems. We use a FSI solver based on a monolithic approach, while the two-phase interface advection and reconstruction is computed in the framework of a Volume of Fluid method which is one of the more popular algorithms for two-phase flow problems. The coupling between the FSI and VOF algorithm is efficiently handled with the use of MEDMEM libraries implemented in the computational platform Salome. The numerical results of a dam break problem over a deformable solid are reported in order to show the robustness and stability of this numerical approach.

  7. Numerical study of transient flow phenomena in shock tunnels

    NASA Technical Reports Server (NTRS)

    Tokarcik-Polsky, Susan; Cambier, Jean-Luc

    1994-01-01

    Computational fluid dynamics (CFD) was used to study some transient flow features that can occur during the startup process of a shoch tunnel. The investigation concentrated on two areas: (1) the flow near the endwall of the driven tube during shock reflection and (2) the transient flow in the nozzle. The driven tube calculations were inviscid and focused on the study of a vortex system that was seen to form at the driven tube's axis of symmetry. The nozzle flow calculations examined viscous and inviscid effects during nozzle startup. The CFD solutions of the nozzle flows were compared with experimental data to demonstrate the effectiveness of the numerical analysis.

  8. Fluid flow and particle transport in mechanically ventilated airways. Part I. Fluid flow structures.

    PubMed

    Van Rhein, Timothy; Alzahrany, Mohammed; Banerjee, Arindam; Salzman, Gary

    2016-07-01

    A large eddy simulation-based computational study of fluid flow and particle transport in upper tracheobronchial airways is carried out to investigate the effect of ventilation parameters on pulmonary fluid flow. Respiratory waveforms commonly used by commercial mechanical ventilators are used to study the effect of ventilation parameters and ventilation circuit on pulmonary fluid dynamics. A companion paper (Alzahrany et al. in Med Biol Eng Comput, 2014) reports our findings on the effect of the ventilation parameters and circuit on particle transport and aerosolized drug delivery. The endotracheal tube (ETT) was found to be an important geometric feature and resulted in a fluid jet that caused an increase in turbulence and created a recirculation zone with high wall shear stress in the main bronchi. Stronger turbulence was found in lower airways than would be found under normal breathing conditions due to the presence of the jet caused by the ETT. The pressure-controlled sinusoidal waveform induced the lowest wall shear stress on the airways wall. PMID:26563199

  9. Local structure of turbulence in flows with large Reynolds numbers.

    PubMed

    Praskovsky, A. A.

    1991-08-01

    Results are reported on an experimental investigation of the characteristics of fine-scale pulsations of the velocity in several shear flows (mixing layer, boundary layer, planar, axially symmetric, and spatial wakes, and in the return channel of a large wind tunnel) in an interval of definite Reynolds numbers R(lambda) [approximately-equal-to] 70-3000 with respect to the Taylor microscale lambda. The characteristic scales of most of the studied flows are quite large, and the integral scale of the turbulence reaches 5 m. The apparatus had a high resolving power-the ratio of the hot-wire length to the Kolmogorov scale was varied in the range 0.8-2.5. It is shown that the Kolmogorov constant C in the "two thirds" law and the constants C(epsilon) and &mgr; in the energy-dissipation correlation function are not universal and have a systematic dependence on the coefficient of external intermittency. The same constants determined in a completely turbulent fluid are universal within the errors of the measurements.

  10. Passive urban ventilation by combined buoyancy-driven slope flow and wall flow: Parametric CFD studies on idealized city models

    NASA Astrophysics Data System (ADS)

    Luo, Zhiwen; Li, Yuguo

    2011-10-01

    This paper reports the results of a parametric CFD study on idealized city models to investigate the potential of slope flow in ventilating a city located in a mountainous region when the background synoptic wind is absent. Examples of such a city include Tokyo in Japan, Los Angeles and Phoenix in the US, and Hong Kong. Two types of buoyancy-driven flow are considered, i.e., slope flow from the mountain slope (katabatic wind at night and anabatic wind in the daytime), and wall flow due to heated/cooled urban surfaces. The combined buoyancy-driven flow system can serve the purpose of dispersing the accumulated urban air pollutants when the background wind is weak or absent. The microscopic picture of ventilation performance within the urban structures was evaluated in terms of air change rate (ACH) and age of air. The simulation results reveal that the slope flow plays an important role in ventilating the urban area, especially in calm conditions. Katabatic flow at night is conducive to mitigating the nocturnal urban heat island. In the present parametric study, the mountain slope angle and mountain height are assumed to be constant, and the changing variables are heating/cooling intensity and building height. For a typical mountain of 500 m inclined at an angle of 20° to the horizontal level, the interactive structure is very much dependent on the ratio of heating/cooling intensity as well as building height. When the building is lower than 60 m, the slope wind dominates. When the building is as high as 100 m, the contribution from the urban wall flow cannot be ignored. It is found that katabatic wind can be very beneficial to the thermal environment as well as air quality at the pedestrian level. The air change rate for the pedestrian volume can be as high as 300 ACH.

  11. CFD Validation Studies for Hypersonic Flow Prediction

    NASA Technical Reports Server (NTRS)

    Gnoffo, Peter A.

    2001-01-01

    A series of experiments to measure pressure and heating for code validation involving hypersonic, laminar, separated flows was conducted at the Calspan-University at Buffalo Research Center (CUBRC) in the Large Energy National Shock (LENS) tunnel. The experimental data serves as a focus for a code validation session but are not available to the authors until the conclusion of this session. The first set of experiments considered here involve Mach 9.5 and Mach 11.3 N2 flow over a hollow cylinder-flare with 30 degree flare angle at several Reynolds numbers sustaining laminar, separated flow. Truncated and extended flare configurations are considered. The second set of experiments, at similar conditions, involves flow over a sharp, double cone with fore-cone angle of 25 degrees and aft-cone angle of 55 degrees. Both sets of experiments involve 30 degree compressions. Location of the separation point in the numerical simulation is extremely sensitive to the level of grid refinement in the numerical predictions. The numerical simulations also show a significant influence of Reynolds number on extent of separation. Flow unsteadiness was easily introduced into the double cone simulations using aggressive relaxation parameters that normally promote convergence.

  12. CFD Validation Studies for Hypersonic Flow Prediction

    NASA Technical Reports Server (NTRS)

    Gnoffo, Peter A.

    2001-01-01

    A series of experiments to measure pressure and heating for code validation involving hypersonic, laminar, separated flows was conducted at the Calspan-University at Buffalo Research Center (CUBRC) in the Large Energy National Shock (LENS) tunnel. The experimental data serves as a focus for a code validation session but are not available to the authors until the conclusion of this session. The first set of experiments considered here involve Mach 9.5 and Mach 11.3 N, flow over a hollow cylinder-flare with 30 deg flare angle at several Reynolds numbers sustaining laminar, separated flow. Truncated and extended flare configurations are considered. The second set of experiments, at similar conditions, involves flow over a sharp, double cone with fore-cone angle of 25 deg and aft-cone angle of 55 deg. Both sets of experiments involve 30 deg compressions. Location of the separation point in the numerical simulation is extremely sensitive to the level of grid refinement in the numerical predictions. The numerical simulations also show a significant influence of Reynolds number on extent of separation. Flow unsteadiness was easily introduced into the double cone simulations using aggressive relaxation parameters that normally promote convergence.

  13. Water Flow Vibration Effect on the NLC RF Structure - Girder System

    SciTech Connect

    Boffo, C

    2004-07-16

    As part of the vibration budget study for the NLC Main Linac components, the vibration sources in the NLC modules (Girder) are under investigation. The activity is focused on the effect of cooling water flow on the structures (FXB type) stability, the transmission of vibrations to the adjacent components, and the effect of different materials of construction used for the supports. Experimental data and ANSYS simulations have been compared. This paper reports on the ongoing work.

  14. Water Flow Vibration Effect on the NLC RF Structure-Girder System

    SciTech Connect

    Cristian Boffo et al.

    2004-07-07

    As part of the vibration budget study for the NLC Main Linac components, the vibration sources in the NLC modules (Girder) are under investigation. The activity is focused on the effect of cooling water flow on the structures (FXB type) stability, the transmission of vibrations to the adjacent components, and the effect of different materials of construction used for the supports. Experimental data and ANSYS simulations have been compared. This paper reports on the ongoing work.

  15. The structure of separated flow regions occurring near the leading edge of airfoils, including transition

    NASA Technical Reports Server (NTRS)

    Mueller, T. J.

    1985-01-01

    The structure and behavior of the separation bubble including transition and the redeveloping boundary layer after reattachment over an airfoil at low Reynolds numbers was studied. The intent is to further the understanding of the complex flow phenomena so that analytic methods for predicting their formation and development can be improved. These analytic techniques have applications in the design and performance prediction of airfoils operating in the low Reynolds number flight regime.

  16. Numerical study of eccentric Couette Taylor flows and effect of eccentricity on flow patterns

    NASA Astrophysics Data System (ADS)

    Shu, C.; Wang, L.; Chew, Y. T.; Zhao, N.

    2004-10-01

    In this study, the differential quadrature (DQ) method was used to simulate the eccentric Couette Taylor vortex flow in an annulus between two eccentric cylinders with rotating inner cylinder and stationary outer cylinder. An approach combining the SIMPLE (semi-implicit method for pressure-linked equations) and DQ discretization on a non-staggered mesh was proposed to solve the time-dependent, three-dimensional incompressible Navier Stokes equations in the primitive variable form. The eccentric steady Couette Taylor flow patterns were obtained from the solution of three-dimensional Navier Stokes equations. The reported numerical results for steady Couette flow were compared with those from Chou [1], and San and Szeri [2]. Very good agreement was achieved. For steady eccentric Taylor vortex flow, detailed flow patterns were obtained and analyzed. The effect of eccentricity on the eccentric Taylor vortex flow pattern was also studied.

  17. Identifying Coherent Structures in a 3-Stream Supersonic Jet Flow using Time-Resolved Schlieren Imaging

    NASA Astrophysics Data System (ADS)

    Tenney, Andrew; Coleman, Thomas; Berry, Matthew; Magstadt, Andy; Gogineni, Sivaram; Kiel, Barry

    2015-11-01

    Shock cells and large scale structures present in a three-stream non-axisymmetric jet are studied both qualitatively and quantitatively. Large Eddy Simulation is utilized first to gain an understanding of the underlying physics of the flow and direct the focus of the physical experiment. The flow in the experiment is visualized using long exposure Schlieren photography, with time resolved Schlieren photography also a possibility. Velocity derivative diagnostics are calculated from the grey-scale Schlieren images are analyzed using continuous wavelet transforms. Pressure signals are also captured in the near-field of the jet to correlate with the velocity derivative diagnostics and assist in unraveling this complex flow. We acknowledge the support of AFRL through an SBIR grant.

  18. Fine-scale structures and material flows of quiescent filaments observed by the New Vacuum Solar Telescope

    NASA Astrophysics Data System (ADS)

    Yan, Xiao-Li; Xue, Zhi-Ke; Xiang, Yong-Yuan; Yang, Li-Heng

    2015-10-01

    Study of the small-scale structures and material flows associated with solar quiescent filaments is very important for understanding the formation and equilibrium of solar filaments. Using high resolution Hα data observed by the New Vacuum Solar Telescope, we present the structures of barbs and material flows along the threads across the spine in two quiescent filaments on 2013 September 29 and on 2012 November 2, respectively. During the evolution of the filament barb, several parallel tube-shaped structures formed and the width of the structures ranged from about 2.3 Mm to 3.3 Mm. The parallel tube-shaped structures merged together accompanied by material flows from the spine to the barb. Moreover, the boundary between the barb and surrounding atmosphere was very neat. The counter-streaming flows were not found to appear alternately in the adjacent threads of the filament. However, the large-scale patchy counter-streaming flows were detected in the filament. The flows in one patch of the filament have the same direction but flows in the adjacent patch have opposite direction. The patches of two opposite flows with a size of about 10″ were alternately exhibited along the spine of the filament. The velocity of these material flows ranged from 5.6 km s-1 to 15.0 km s-1. The material flows along the threads of the filament did not change their direction for about two hours and fourteen minutes during the evolution of the filament. Our results confirm that the large-scale counter-streaming flows with a certain width along the threads of solar filaments exist and are coaligned well with the threads.

  19. Lagrangian-based investigation of the transient flow structures around a pitching hydrofoil

    NASA Astrophysics Data System (ADS)

    Wu, Qin; Huang, Biao; Wang, Guoyu

    2016-02-01

    The objective of this paper is to address the transient flow structures around a pitching hydrofoil by combining physical and numerical studies. In order to predict the dynamic behavior of the flow structure effectively, the Lagrangian coherent structures (LCS) defined by the ridges of the finite-time Lyapunov exponent (FTLE) are utilized under the framework of Navier-Stokes flow computations. In the numerical simulations, the k-ω shear stress transport (SST) turbulence model, coupled with a two-equation γ {-Re}_θ transition model, is used for the turbulence closure. Results are presented for a NACA66 hydrofoil undergoing slowly and rapidly pitching motions from 0° to 15° then back to 0° at a moderate Reynolds number Re=7.5× 105. The results reveal that the transient flow structures can be observed by the LCS method. For the slowly pitching case, it consists of five stages: quasi-steady and laminar, transition from laminar to turbulent, vortex development, large-scale vortex shedding, and reverting to laminar. The observation of LCS and Lagrangian particle tracers elucidates that the trailing edge vortex is nearly attached and stable during the vortex development stage and the interaction between the leading and trailing edge vortex caused by the adverse pressure gradient forces the vortexes to shed downstream during the large-scale vortex shedding stage, which corresponds to obvious fluctuations of the hydrodynamic response. For the rapidly pitching case, the inflection is hardly to be observed and the stall is delayed. The vortex formation, interaction, and shedding occurred once instead of being repeated three times, which is responsible for just one fluctuation in the hydrodynamic characteristics. The numerical results also show that the FTLE field has the potential to identify the transient flows, and the LCS can represent the divergence extent of infinite neighboring particles and capture the interface of the vortex region.

  20. TANK MIXING STUDY WITH FLOW RECIRCULATION

    SciTech Connect

    Lee, S.

    2014-06-25

    The primary objective of this work is to quantify the mixing time when two miscible fluids are mixed by one recirculation pump and to evaluate adequacy of 2.5 hours of pump recirculation to be considered well mixed in SRS tanks, JT-71/72. The work scope described here consists of two modeling analyses. They are the steady state flow pattern analysis during pump recirculation operation of the tank liquid and transient species transport calculations based on the initial steady state flow patterns. The modeling calculations for the mixing time are performed by using the 99% homogeneity criterion for the entire domain of the tank contents.

  1. Flow and permeability structure of the Beowawe, Nevada hydrothermal system

    SciTech Connect

    Faulder, D.D.; Johnson, S.D.; Benoit, W.R.

    1997-05-01

    A review of past geologic, geochemical, hydrological, pressure transient, and reservoir engineering studies of Beowawe suggests a different picture of the reservoir than previously presented. The Beowawe hydrothermal contains buoyant thermal fluid dynamically balanced with overlying cold water, as shown by repeated temperature surveys and well test results. Thermal fluid upwells from the west of the currently developed reservoir at the intersection of the Malpais Fault and an older structural feature associated with mid-Miocene rifting. A tongue of thermal fluid rises to the east up the high permeability Malpais Fault, discharges at the Geysers area, and is in intimate contact with overlying cooler water. The permeability structure is closely related to the structural setting, with the permeability of the shallow hydrothermal system ranging from 500 to 1,000 D-ft, while the deeper system ranges from 200 to 400 D-ft.

  2. Algebraic structure of general electromagnetic fields and energy flow

    SciTech Connect

    Hacyan, Shahen

    2011-08-15

    Highlights: > Algebraic structure of general electromagnetic fields in stationary spacetime. > Eigenvalues and eigenvectors of the electomagnetic field tensor. > Energy-momentum in terms of eigenvectors and Killing vector. > Explicit form of reference frame with vanishing Poynting vector. > Application of formalism to Bessel beams. - Abstract: The algebraic structures of a general electromagnetic field and its energy-momentum tensor in a stationary space-time are analyzed. The explicit form of the reference frame in which the energy of the field appears at rest is obtained in terms of the eigenvectors of the electromagnetic tensor and the existing Killing vector. The case of a stationary electromagnetic field is also studied and a comparison is made with the standard short-wave approximation. The results can be applied to the general case of a structured light beams, in flat or curved spaces. Bessel beams are worked out as example.

  3. Flow structure due to dimple depressions on a channel surface

    NASA Astrophysics Data System (ADS)

    Ligrani, P. M.; Harrison, J. L.; Mahmmod, G. I.; Hill, M. L.

    2001-11-01

    Instantaneous, dynamic and time-averaged characteristics of the vortex structures which are shed from the dimples placed on one wall of a channel are described. The dimpled test surface contains 13 staggered rows of dimples in the streamwise direction, where each dimple has a print diameter of 5.08 cm, and a ratio of depth to print diameter of 0.2. Considered are Reynolds numbers (based on channel height) ReH from 600 to 11 000, and ratios of channel height to dimple print diameter H/D of 0.25, 0.50, and 1.00. For all three H/D, a primary vortex pair is periodically shed from the central portion of each dimple, including a large upwash region. This shedding occurs periodically and continuously, and is followed by inflow advection into the dimple cavity. The frequency of these events appears to scale on time-averaged bulk velocity and dimple print diameter, which gives nondimensional frequencies of 2.2-3.0 for all three H/D values considered. As H/D decreases, (i) the strength of the primary vortex pair increases, and (ii) two additional secondary vortex pairs (which form near the spanwise edges of each dimple) become significantly stronger, larger in cross section, and more apparent in flow visualization images and in surveys of time-averaged, streamwise vorticity. The locations of these primary and secondary vortex pairs near the dimpled surface coincide closely with locations where normalized Reynolds normal stress is augmented. This evidences an important connection between the vortices, Reynolds normal stress, and mixing. The large-scale unsteadiness associated with this mixing is then more pronounced, and encompasses larger portions of the vortex structure (and thus extends over larger volumes) as H/D increases from 0.25 to 1.0.

  4. Shear flow energy redistribution stipulated by the internal-gravity wavy structures in the dissipative ionosphere

    NASA Astrophysics Data System (ADS)

    Aburjania, G. D.; Chargazia, K. Z.; Kharshiladze, O. A.

    2013-07-01

    The linear mechanism of generation, intensification and further nonlinear dynamics of internal gravity waves (IGW) in stably stratified dissipative ionosphere with non-uniform zonal wind (shear flow) is studied. In case of the shear flows the operators of linear problem are non-selfadjoint, and the corresponding Eigen functions - nonorthogonal. Thus, canonical - modal approach is of less use studying such motions. Non-modal mathematical analysis becomes more adequate for such problems. On the basis of non-modal approach, the equations of dynamics and the energy transfer of IGW disturbances in the ionosphere with a shear flow is obtained. Exact analytical solutions of the linear as well as the nonlinear dynamic equations of the problem are built. The increment of shear instability of IGW is defined. It is revealed that the transient amplification of IGW disturbances due time does not flow exponentially, but in algebraic - power law manner. The effectiveness of the linear amplification mechanism of IGW at interaction with non-uniform zonal wind is analyzed. It is shown that at initial linear stage of evolution IGW effectively temporarily draws energy from the shear flow significantly increasing (by an order of magnitude) own amplitude and energy. With amplitude growth the nonlinear mechanism turns on and the process ends with self-organization of nonlinear solitary, strongly localized IGW vortex structures (the monopole vortex, the transverse vortex chain or the longitudinal vortex street). Accumulation of these vortices in the ionospheric medium can create the strongly turbulent state.

  5. Oscillatory flow through submerged canopies: 1. Velocity structure

    NASA Astrophysics Data System (ADS)

    Lowe, Ryan J.; Koseff, Jeffrey R.; Monismith, Stephen G.

    2005-10-01

    Many benthic organisms form very rough surfaces on the seafloor that can be described as submerged canopies. Recent evidence has shown that, compared with a unidirectional current, an oscillatory flow driven by surface waves can significantly enhance biological processes such as nutrient uptake. However, to date, the physical mechanisms responsible for this enhancement have not been established. This paper presents a theoretical model to estimate flow inside a submerged canopy driven by oscillatory flow. To reduce the complexity of natural canopies, an idealized canopy consisting of an array of vertical cylinders is used. The attenuation of the in-canopy oscillatory flow is shown to be governed by three dimensionless parameters defined on the basis of canopy geometry and flow parameters. The model predicts that an oscillatory flow will always generate a higher in-canopy flow when compared to a unidirectional current of the same magnitude, and specifically that the attenuation will monotonically increase as the wave orbital excursion length is increased. A series of laboratory experiments are conducted for a range of different unidirectional and oscillatory flow conditions, and the results confirm that oscillatory flow increases water motion inside a canopy. It is hypothesized that this higher in-canopy flow will enhance rates of mass transfer from the canopy elements, a problem formally investigated in a companion paper (Lowe et al., 2005b).

  6. Flow-induced vibration of circular cylindrical structures

    SciTech Connect

    Chen, S.S.

    1987-01-01

    This book presents the flow-induced vibration of circular cylinders in quiescent fluid, axial flow, and crossflow, and applications of the analytical methods and experimental data in design evaluation of various system components consisting of circular cylinders. The information is organized into five general topical areas: Introduction: Chapter 1 presents an overview of flow-induced vibration of circular cylinders. It includes examples of flow-induced vibration, various fluid force components, and nondimensional parameters as well as different excitation mechanisms. The general principles are applicable under different flow conditions. Quiescent Fluid: Fluid inertia and fluid damping are discussed in Chapters 2, 3 and 4. Various flow theories are applied in different situations. Axial Flow: Axial flow can cause subcritical vibration and instability. Chapter 5 summarizes the results for internal flow, while Chapter 6 considers external flow. Both theoretical results and experimental data are examined. Crossflow: Different excitation mechanisms can be dominant in different conditions for crossflow. Those include turbulent buffeting, acoustic resonance, vortex excitation, and dynamic instability. Design Considerations: Applications of the general methods of analysis in the design evaluation of system components are described and various techniques to avoid detrimental vibration are presented.

  7. Noninvasive measurement of cerebrospinal fluid flow using an ultrasonic transit time flow sensor: a preliminary study.

    PubMed

    Pennell, Thomas; Yi, Juneyoung L; Kaufman, Bruce A; Krishnamurthy, Satish

    2016-03-01

    OBJECT Mechanical failure-which is the primary cause of CSF shunt malfunction-is not readily diagnosed, and the specific reasons for mechanical failure are not easily discerned. Prior attempts to measure CSF flow noninvasively have lacked the ability to either quantitatively or qualitatively obtain data. To address these needs, this preliminary study evaluates an ultrasonic transit time flow sensor in pediatric and adult patients with external ventricular drains (EVDs). One goal was to confirm the stated accuracy of the sensor in a clinical setting. A second goal was to observe the sensor's capability to record real-time continuous CSF flow. The final goal was to observe recordings during instances of flow blockage or lack of flow in order to determine the sensor's ability to identify these changes. METHODS A total of 5 pediatric and 11 adult patients who had received EVDs for the treatment of hydrocephalus were studied in a hospital setting. The primary EVD was connected to a secondary study EVD that contained a fluid-filled pressure transducer and an in-line transit time flow sensor. Comparisons were made between the weight of the drainage bag and the flow measured via the sensor in order to confirm its accuracy. Data from the pressure transducer and the flow sensor were recorded continuously at 100 Hz for a period of 24 hours by a data acquisition system, while the hourly CSF flow into the drip chamber was recorded manually. Changes in the patient's neurological status and their time points were noted. RESULTS The flow sensor demonstrated a proven accuracy of ± 15% or ± 2 ml/hr. The flow sensor allowed real-time continuous flow waveform data recordings. Dynamic analysis of CSF flow waveforms allowed the calculation of the pressure-volume index. Lastly, the sensor was able to diagnose a blocked catheter and distinguish between the blockage and lack of flow. CONCLUSIONS The Transonic flow sensor accurately measures CSF output within ± 15% or ± 2 ml

  8. Noninvasive measurement of cerebrospinal fluid flow using an ultrasonic transit time flow sensor: a preliminary study.

    PubMed

    Pennell, Thomas; Yi, Juneyoung L; Kaufman, Bruce A; Krishnamurthy, Satish

    2016-03-01

    OBJECT Mechanical failure-which is the primary cause of CSF shunt malfunction-is not readily diagnosed, and the specific reasons for mechanical failure are not easily discerned. Prior attempts to measure CSF flow noninvasively have lacked the ability to either quantitatively or qualitatively obtain data. To address these needs, this preliminary study evaluates an ultrasonic transit time flow sensor in pediatric and adult patients with external ventricular drains (EVDs). One goal was to confirm the stated accuracy of the sensor in a clinical setting. A second goal was to observe the sensor's capability to record real-time continuous CSF flow. The final goal was to observe recordings during instances of flow blockage or lack of flow in order to determine the sensor's ability to identify these changes. METHODS A total of 5 pediatric and 11 adult patients who had received EVDs for the treatment of hydrocephalus were studied in a hospital setting. The primary EVD was connected to a secondary study EVD that contained a fluid-filled pressure transducer and an in-line transit time flow sensor. Comparisons were made between the weight of the drainage bag and the flow measured via the sensor in order to confirm its accuracy. Data from the pressure transducer and the flow sensor were recorded continuously at 100 Hz for a period of 24 hours by a data acquisition system, while the hourly CSF flow into the drip chamber was recorded manually. Changes in the patient's neurological status and their time points were noted. RESULTS The flow sensor demonstrated a proven accuracy of ± 15% or ± 2 ml/hr. The flow sensor allowed real-time continuous flow waveform data recordings. Dynamic analysis of CSF flow waveforms allowed the calculation of the pressure-volume index. Lastly, the sensor was able to diagnose a blocked catheter and distinguish between the blockage and lack of flow. CONCLUSIONS The Transonic flow sensor accurately measures CSF output within ± 15% or ± 2 ml

  9. Turbulent structures in wall-bounded shear flows observed via three-dimensional numerical simulators. [using the Illiac 4 computer

    NASA Technical Reports Server (NTRS)

    Leonard, A.

    1980-01-01

    Three recent simulations of tubulent shear flow bounded by a wall using the Illiac computer are reported. These are: (1) vibrating-ribbon experiments; (2) study of the evolution of a spot-like disturbance in a laminar boundary layer; and (3) investigation of turbulent channel flow. A number of persistent flow structures were observed, including streamwise and vertical vorticity distributions near the wall, low-speed and high-speed streaks, and local regions of intense vertical velocity. The role of these structures in, for example, the growth or maintenance of turbulence is discussed. The problem of representing the large range of turbulent scales in a computer simulation is also discussed.

  10. Effects of flow intermittency and pharmaceutical exposure on the structure and metabolism of stream biofilms.

    PubMed

    Corcoll, Natàlia; Casellas, Maria; Huerta, Belinda; Guasch, Helena; Acuña, Vicenç; Rodríguez-Mozaz, Sara; Serra-Compte, Albert; Barceló, Damià; Sabater, Sergi

    2015-01-15

    Increasing concentrations of pharmaceutical compounds occur in many rivers, but their environmental risk remains poorly studied in stream biofilms. Flow intermittency shapes the structure and functions of ecosystems, and may enhance their sensitivity to toxicants. This study evaluates the effects of a long-term exposure of biofilm communities to a mixture of pharmaceutical compounds at environmental concentrations on biofilm bioaccumulation capacity, the structure and metabolic processes of algae and bacteria communities, and how their potential effects were enhanced or not by the occurrence of flow intermittency. To assess the interaction between those two stressors, an experiment with artificial streams was performed. Stream biofilms were exposed to a mixture of pharmaceuticals, as well as to a short period of flow intermittency. Results indicate that biofilms were negatively affected by pharmaceuticals. The algal biomass and taxa richness decreased and unicellular green algae relatively increased. The structure of the bacterial (based on denaturing gradient gel electrophoresis of amplified 16S rRNA genes) changed and showed a reduction of the operational taxonomic units (OTUs) richness. Exposed biofilms showed higher rates of metabolic processes, such as primary production and community respiration, attributed to pharmaceuticals stimulated an increase of green algae and heterotrophs, respectively. Flow intermittency modulated the effects of chemicals on natural communities. The algal community became more sensitive to short-term exposure of pharmaceuticals (lower EC50 value) when exposed to water intermittency, indicating cumulative effects between the two assessed stressors. In contrast to algae, the bacterial community became less sensitive to short-term exposure of pharmaceuticals (higher EC50) when exposed to water intermittency, indicating co-tolerance phenomena. According to the observed effects, the environmental risk of pharmaceuticals in nature is high

  11. Ex-situ experimental studies on serpentine flow field design for redox flow battery systems

    NASA Astrophysics Data System (ADS)

    Jyothi Latha, T.; Jayanti, S.

    2014-02-01

    Electrolyte distribution using parallel flow field for redox flow battery (RFB) applications shows severe non-uniformity, while the conventional design of using the carbon felt itself as the flow distributor gives too high pressure drop. An optimized flow field design for uniform flow distribution at a minimal parasitic power loss is therefore needed for RFB systems. Since the materials and geometrical dimensions in RFBs are very different from those used in fuel cells, the hydrodynamics of the flow fields in RFBs is likely to be very different. In the present paper, we report on a fundamental study of the hydrodynamics of a serpentine flow field relevant to RFB applications. The permeability of the porous medium has been measured under different compression ratios and this is found to be in the range of 5-8 × 10-11 m2. The pressure drop in two serpentine flow fields of different geometric characteristics has been measured over a range of Reynolds numbers. Further analysis using computational fluid dynamics simulations brings out the importance of the compression of the porous medium as an additional parameter in determining the flow distribution and pressure drop in these flow fields.

  12. Study of transient flow and particle transport in continuous steel caster molds: Part I. Fluid flow

    NASA Astrophysics Data System (ADS)

    Yuan, Quan; Thomas, Brian G.; Vanka, S. P.

    2004-08-01

    Unsteady three-dimensional flow in the mold region of the liquid pool during continuous casting of steel slabs has been computed using realistic geometries starting from the submerged inlet nozzle. Three large-eddy simulations (LES) have been validated with measurements and used to compare results between full-pool and symmetric half-pool domains and between a full-scale water model and actual behavior in a thin-slab steel caster. First, time-dependent turbulent flow in the submerged nozzle is computed. The time-dependent velocities exiting the nozzle ports are then used as inlet conditions for the flow in the liquid pool. Complex time-varying flow structures are observed in the simulation results, in spite of the nominally steady casting conditions. Flow in the mold region is seen to switch between a “double-roll” recirculation zone and a complex flow pattern with multiple vortices. The computed time-averaged flow pattern agrees well with measurements obtained by hot-wire anemometry and dye injection in full-scale water models. Full-pool simulations show asymmetries between the left and right sides of the flow, especially in the lower recirculation zone. These asymmetries, caused by interactions between two halves of the liquid pool, are not present in the half-pool simulation. This work also quantifies differences between flow in the water model and the corresponding steel caster. The top-surface liquid profile and fluctuations are predicted in both systems and agree favorably with measurements. The flow field in the water model is predicted to differ from that in the steel caster in having higher upward velocities in the lower-mold region and a more uniform top-surface liquid profile. A spectral analysis of the computed velocities shows characteristics similar to previous measurements. The flow results presented here are later used (in Part II of this article) to investigate the transport of inclusion particles.

  13. Compressibility effects on large structures in free shear flows

    NASA Technical Reports Server (NTRS)

    Samimy, M.; Reeder, M. F.; Elliott, G. S.

    1992-01-01

    Space-time correlations were used to study compressibility effects on large structures in mixing layers. Two high-Reynolds number mixing layers with M(c) = 0.51 (case 1) and 0.86 (case 2) were studied. The results indicate that the structures in case 1 are similar to those in the incompressible case, but less organized. The structures in case 2 are highly three-dimensional, with a good spatial but a poor temporal orgnization. The streamwise correlations showed a decay rate four to five times greater for case 2 relative to case 1. While the spanwise correlations for case 1 showed trends similar to incompressible mixing layers, the behavior of case 2 was very different. The pressure fluctuations in the fully developed region of case 2 displayed significant rms variation in the spanwise direction with a well-defined pattern. Based on these measurements, the structures in case 2 seem to be of a horseshoe type, transversely spanning the mixing layer with the head in the low-speed side and the legs inclined in both the x-y and the x-z planes.

  14. On conditional sampling for turbulent flow studies

    NASA Technical Reports Server (NTRS)

    Wang, F. C.

    1974-01-01

    The conditional sampling technique is analyzed as a weighted time average for turbulent flow. The various conditional averages are obtained by using different types of weighting functions. A second averaging relation is obtained between the conventional averages and the conditional averages. A few examples are given in which simplified expressions are used.

  15. Structural study of ammonium metatungstate

    SciTech Connect

    Christian, Joel B. Whittingham, M. Stanley

    2008-08-15

    Several techniques have been used to study the structure of the Keggin-type polyoxometalate salt ammonium metatungstate (AMT)-(NH{sub 4}){sub 6}[H{sub 2}W{sub 12}O{sub 40}]*nH{sub 2}O, a potential fuel cell catalyst. The dehydrated salt is comprised of a mixture of crystallites of different unit cells in a centered eutactic cubic configuration, with an average unit cell of a{approx_equal}12.295. Varied orientations of the Keggin ions in the cubic arrangement create the differences, and orientational variation within each unit cell size represents an energy well. Progressive hydration of each crystallite leads to expansion of the lattice, with the degree of expansion depending on the locations of the water added in relation to the Keggin ion, which is influenced by cation location and hydrogen bonding. The structural hypothesis is supported by electron diffraction of single and multicrystal samples, by powder density measurements, X-ray powder diffraction studies, synchrotron powder X-ray diffraction, and a priori structural modeling studies. Based on the structure, projected active site densities are compared with nanostructured platinum catalysts for fuel cell application. - Graphical abstract: The structure of ammonium metatungstate powders are highly dependent on hydration and POM molecule rotation, with cation and hydrogen bonding forces directing a mixture of structures that have been studied with bulk and single-crystal methods. The illustration shows Monte Carlo simulated anion structural disorder for the fully dehydrated form of the title compound.

  16. An experimental study of flow around submerged grass vegetation

    NASA Astrophysics Data System (ADS)

    Lee, Julia; Mandre, Shreyas; Singh, Ravi

    2014-11-01

    Mixing of fluids through submerged vegetation caused by tidal currents facilitate various environmental and ecological transport processes. This fluid-vegetation interaction is believed to result from a Kelvin-Helmholtz instability from an inflection point in the flow profile. Recent studies suggest that flow in presence of grass can also become unstable due to shear instability of flow above the grass. We devise a two-dimensional lab scale analog of the fluid-vegetation interaction using ABS plastic filaments immersed in a soap film. We employ PIV of the surrounding flow to gain an understanding of the role of instabilities in the flow.

  17. Fluid-structure interaction for nonlinear response of shells conveying pulsatile flow

    NASA Astrophysics Data System (ADS)

    Tubaldi, Eleonora; Amabili, Marco; Païdoussis, Michael P.

    2016-06-01

    Circular cylindrical shells with flexible boundary conditions conveying pulsatile flow and subjected to pulsatile pressure are investigated. The equations of motion are obtained based on the nonlinear Novozhilov shell theory via Lagrangian approach. The flow is set in motion by a pulsatile pressure gradient. The fluid is modeled as a Newtonian pulsatile flow and it is formulated using a hybrid model that contains the unsteady effects obtained from the linear potential flow theory and the pulsatile viscous effects obtained from the unsteady time-averaged Navier-Stokes equations. A numerical bifurcation analysis employs a refined reduced order model to investigate the dynamic behavior. The case of shells containing quiescent fluid subjected to the action of a pulsatile transmural pressure is also addressed. Geometrically nonlinear vibration response to pulsatile flow and transmural pressure are here presented via frequency-response curves and time histories. The vibrations involving both a driven mode and a companion mode, which appear due to the axial symmetry, are also investigated. This theoretical framework represents a pioneering study that could be of great interest for biomedical applications. In particular, in the future, a more refined model of the one here presented will possibly be applied to reproduce the dynamic behavior of vascular prostheses used for repairing and replacing damaged and diseased thoracic aorta in cases of aneurysm, dissection or coarctation. For this purpose, a pulsatile time-dependent blood flow model is here considered by applying physiological waveforms of velocity and pressure during the heart beating period. This study provides, for the first time in literature, a fully coupled fluid-structure interaction model with deep insights in the nonlinear vibrations of circular cylindrical shells subjected to pulsatile pressure and pulsatile flow.

  18. Flow Structure over Moderate Swept Delta Wing: Effects of Reynolds Number and Attack Angle

    NASA Astrophysics Data System (ADS)

    Ozturk, Ilhan; Zharfa, Mohammadreza; Yavuz, Mehmet Metin

    2013-11-01

    Recent investigations have revealed the appearance of a distinctive type of leading edge vortex, dual vortex structure, over simple delta wing planforms having moderate sweep angles. Flow over a moderate swept 45-degree wing has been investigated using laser illuminated smoke visualization, Laser Doppler Anemometry (LDA), and surface pressure measurements. The effects of Reynolds number and attack angles on dual vortex structure, vortex breakdown, and poststall regime are reported. The footprint of flow regimes on the surface of the planform is captured by the pressure measurements, and the lift performance of the wing is tried to be extracted. The relation between surface pressure fluctuations and near surface velocity fluctuations is investigated. The reattachment region of the separated shear layer on the surface, vortex breakdown, and stall regime are studied with considering the aforementioned relation, which will enlighten some of the aspects of the buffeting on the wing planform.

  19. Micro/macroscopic fluid flow in open cell fibrous structures and porous media

    NASA Astrophysics Data System (ADS)

    Tamayol, Ali

    Fibrous porous materials are involved in a wide range of applications including composite fabrication, filtration, compact heat exchangers, fuel cell technology, and tissue engineering to name a few. Fibrous structures, such as metalfoams, have unique characteristics such as low weight, high porosity, high mechanical strength, and high surface to volume ratio. More importantly, in many applications the fibrous microstructures can be tailored to meet a range of requirements. Therefore, fibrous materials have the potential to be used in emerging sustainable energy conversion applications. The first step for analyzing transport phenomena in porous materials is to determine the micro/macroscopic flow-field inside the medium. In applications where the porous media is confined in a channel, the system performance is tightly related to the flow properties of the porous medium and its interaction with the channel walls, i.e., macroscopic velocity distribution. Therefore, the focus of the study has been on: developing new mechanistic model(s) for determining permeability and inertial coefficient of fibrous porous materials; investigating the effects of microstructural and mechanical parameters such as porosity, fiber orientation, mechanical compression, and fiber distribution on the flow properties and pressure drop of fibrous structures; determining the macroscopic flow-field in confined porous media where the porous structure fills the channel cross-section totally or partially. A systematic approach has been followed to study different aspects of the flow through fibrous materials. The complex microstructure of real materials has been modelled using unit cells that have been assumed to be repeated throughout the media. Implementing various exact and approximate analytical techniques such as integral technique, point matching, blending rules, and scale analysis the flow properties of such media have been modelled; the targeted properties include permeability and inertial

  20. Heat transfer enhancement and vortex flow structure over a heated cylinder oscillating in the crossflow direction

    SciTech Connect

    Gau, C.; Wu, J.M.; Liang, C.Y.

    1999-11-01

    Experiments are performed to study the flow structure and heat transfer over a heated oscillating cylinder. Both flow visualization using a smoke wire and local heat transfer measurements around the cylinder were made. The excitation frequencies of the cylinder are selected at F{sub e}/F{sub n} = 0, 0.5, 1, 1.5, 2, 2.5, and 3. These include excitations at harmonic, subharmonic, superharmonic, and non harmonic frequencies. Synchronization of vortex shedding with the cylinder excitation occurs not only at F{sub e}/F{sub n} = 1 but also at F{sub e}/F{sub n} = 3, which can greatly enhance the heat transfer. The simultaneous enhancement of heat transfer at the stagnation point, its downstream region, and the wake region of the flow suggests that different modes of instabilities occurring in the shear layer of the near wake are actually initiated and amplified far upstream in the stagnation point, which were suppressed in the accelerated flow region and re-amplified in the decelerated flow region. As long as the dominant mode of the instability is amplified by the excitation of cylinder, enhancement of heat transfer can be obtained. During the experiments, the Reynolds numbers vary from 1,600 to 4,800, the ratios of oscillation amplitude to diameter of the cylinder from 0.064 to 0.016.

  1. Genetic structure of eelgrass Zostera marina meadows in an embayment with restricted water flow

    USGS Publications Warehouse

    Munoz-Salazar, R.; Talbot, S.L.; Sage, G.K.; Ward, D.H.; Cabello-Pasini, Alejandro

    2006-01-01

    Genetic structure of the seagrass Zostera marina in a coastal lagoon with restricted water flow, and with heterogeneous water residence times and oceanographic characteristics, was assessed using 8 polymorphic microsatellite loci. Analyses of genetic differentiation (??) and Bayesian clustering suggested that the Z. marina population in San Quintin Bay (SQB) is genetically substructured, with at least 4 genetically different groups: (1) West Head, (2) Mouth, (3) East Arm, and (4) East Head. The greatest ?? value was observed between the most distant sites (?? = 0.095). The lowest values were found among sites closest to the mouth of the coastal lagoon (?? = 0.000 to 0.009). The maximum likelihood approach showed that the sites at the mouth have a mixed pattern of gene flow without a unidirectional pattern. In contrast, there was a clear pattern of asymmetrical gene flow from the mouth towards the West Head. These results suggested that the restriction of water flow at the heads, current pattern, and the distance between sites can reduce genetic flow and promote genetic differences within Z. marina meadows in small water embayments such as SQB. Though the population is genetically substructured and a 14 % decline in cover has been detected, this study did not show evidence of a recent genetic bottleneck. In contrast, mouth sites have experienced a recent expansion in their population size, and also perhaps a recent influx of rare alleles from genetically distinct immigrants. ?? Inter-Research 2006.

  2. Effect of Gravity on the Near Field Flow Structure of Helium Jet in Air

    NASA Technical Reports Server (NTRS)

    Agrawal, Ajay K.; Parthasarathy, Ramkumar; Griffin, DeVon

    2002-01-01

    Experiments have shown that a low-density jet injected into a high-density surrounding medium undergoes periodic oscillations in the near field. Although the flow oscillations in these jets at Richardson numbers about unity are attributed to the buoyancy, the direct physical evidence has not been acquired in the experiments. If the instability were indeed caused by buoyancy, the near-field flow structure would undergo drastic changes upon removal of gravity in the microgravity environment. The present study was conducted to investigate this effect by simulating microgravity environment in the 2.2-second drop tower at the NASA Glenn Research Center. The non-intrusive, rainbow schlieren deflectometry technique was used for quantitative measurements of helium concentrations in buoyant and non-buoyant jets. Results in a steady jet show that the radial growth of the jet shear layer in Earth gravity is hindered by the buoyant acceleration. The jet in microgravity was 30 to 70 percent wider than that in Earth gravity. The microgravity jet showed typical growth of a constant density jet shear layer. In case of a self-excited helium jet in Earth gravity, the flow oscillations continued as the jet flow adjusted to microgravity conditions in the drop tower. The flow oscillations were however not present at the end of the drop when steady microgravity conditions were reached.

  3. Transition and development processes of turbulence structure from flat bed to vegetation flows

    NASA Astrophysics Data System (ADS)

    Maegawa, Takuya; Nezu, Iehisa; Katayama, Aki

    A lot of aquatic plants are observed in actual rivers, and they are responsible for water quality, nutrient and particle removal, and can reduce turbidity and sediment transport. Recently, the importance of flow and turbulence to the ecology of aquatic benthic organism has been widely reported. For submerged vegetation, a shear-layer is generated near the vegetation edge, and it generates coherent vortices by Kelvin-Helmholtz (KH) instability. These large-scale eddies control mass and momentum exchange between the vegetated and non-vegetated zone, influencing the mean velocity profile, as well as the turbulent diffusivity. Therefore, it is very important to reveal the coherent eddies in vegetated flows. However, the transition from boundary-layer flow upstream of the vegetation canopy region to a mixing-layer-type flow within the vegetation canopy has not been fully investigated. So, in this study, turbulence measurements were conducted intensively in vegetated open-channel flows by using PIV. The present data provide insight into spatial growth of coherent structure.

  4. NMR studies of multiphase flows II

    SciTech Connect

    Altobelli, S.A.; Caprihan, A.; Fukushima, E.

    1995-12-31

    NMR techniques for measurements of spatial distribution of material phase, velocity and velocity fluctuation are being developed and refined. Versions of these techniques which provide time average liquid fraction and fluid phase velocity have been applied to several concentrated suspension systems which will not be discussed extensively here. Technical developments required to further extend the use of NMR to the multi-phase flow arena and to provide measurements of previously unobtainable parameters are the focus of this report.

  5. Flow-induced vibration of circular cylindrical structures

    SciTech Connect

    Chen, S.S.

    1985-06-01

    This report summarizes the flow-induced vibration of circular cylinders in quiescent fluid, axial flow, and crossflow, and applications of the analytical methods and experimental data in design evaluation of various system components consisting of circular cylinders. 219 figs., 30 tabs. (JDB)

  6. Flow Structure and Channel Change in a Chute Cutoff along a Large Meandering River

    NASA Astrophysics Data System (ADS)

    Rhoads, B. L.; Best, J.; Johnson, K.; Engel, F. L.

    2009-12-01

    Meander cutoffs, which develop when flow cuts across the narrow neck of a bend, are common features along actively migrating meandering rivers. Despite the importance of cutoffs in the dynamics of river meandering and floodplain sedimentation, few, if any, studies have documented in detail the fluvial processes involved in the development of a meander cutoff. This paper examines the morphodynamics of a chute cutoff along the Wabash River, Illinois-Indiana, immediately following initiation of the cutoff. The original cutoff channel formed across the neck of Mackey Bend, a meander loop immediately upstream of the confluence with the Ohio River, during a major flood in June 2008. The formation of the cutoff channel likely involved migration of a headcut from the downstream side to the upstream side of the meander neck along the path of a floodplain slough. A key focus of the investigation has been to document flow structure at the upstream and downstream ends of the cutoff channel so that patterns of flow can be related to morphological change. Three separate measurement campaigns using an acoustic doppler current profiler (ADCP) and single-beam echosounder were conducted between January and May 2009 to determine 3D flow structure and bed morphology during events with different discharges and flow stages. In addition, channel dimensions were surveyed using a dGPS system in September 2008 and in August 2009. Results indicate that the cutoff channel has widened dramatically over a one-year period, increasing its width by as much as 100 percent. Curvature of flow into the entrance of the cutoff channel from the Wabash River generates strong helical motion that advects momentum toward the outer bank, resulting in high velocities near the bank toe and ongoing bank retreat through slab failures. This flow pattern, accentuated by dramatic widening of the cutoff channel, has resulted in deposition along the inner bank and development of a large bar platform at this location

  7. Flow past an array of catalyst blocks with a honeycomb structure

    SciTech Connect

    Bespalov, A.V.

    1992-07-10

    There is interest in an organized stationary catalyst beds consisting of block catalysts with a honeycomb structure: The flow is directed between vertically positioned blocks, in which the through channels are oriented perpendicularly to the direction of the incident flow ({alpha} = 90{degrees}). Calculations of the flow past a single block of honey comb structure were performed for this case, and it has been shown that the surface of the through channel is accessible to the reaction flow. The authors continued this effort to quantitate the flow with honeycomb catalysts. 9 refs., 2 figs.

  8. A new methodology for the quantitative visualization of coherent flow structures in alluvial channels using multibeam echo-sounding (MBES)

    NASA Astrophysics Data System (ADS)

    Best, Jim; Simmons, Stephen; Parsons, Daniel; Oberg, Kevin; Czuba, Jonathan; Malzone, Chris

    2010-03-01

    In order to investigate the interactions between turbulence and suspended sediment transport in natural aqueous environments, we ideally require a technique that allows simultaneous measurement of fluid velocity and sediment concentration for the whole flow field. Here, we report on development of a methodology using the water column acoustic backscatter signal from a multibeam echo sounder to simultaneously quantify flow velocities and sediment concentrations. The application of this new technique is illustrated with reference to flow over the leeside of an alluvial sand dune, which allows, for the first time in a field study, quantitative visualization of large-scale, whole flow field, turbulent coherent flow structures associated with the dune leeside that are responsible for suspending bed sediment. This methodology holds great potential for use in a wide range of aqueous geophysical flows.

  9. A new methodology for the quantitative visualization of coherent flow structures in alluvial channels using multibeam echo-sounding (MBES)

    USGS Publications Warehouse

    Best, Jim; Simmons, Stephen; Parsons, Daniel; Oberg, Kevin; Czuba, Jonathan; Malzone, Chris

    2010-01-01

    In order to investigate the interactions between turbulence and suspended sediment transport in natural aqueous environments, we ideally require a technique that allows simultaneous measurement of fluid velocity and sediment concentration for the whole flow field. Here, we report on development of a methodology using the water column acoustic backscatter signal from a multibeam echo sounder to simultaneously quantify flow velocities and sediment concentrations. The application of this new technique is illustrated with reference to flow over the leeside of an alluvial sand dune, which allows, for the first time in a field study, quantitative visualization of large-scale, whole flow field, turbulent coherent flow structures associated with the dune leeside that are responsible for suspending bed sediment. This methodology holds great potential for use in a wide range of aqueous geophysical flows.

  10. Structural Controls on Groundwater Flow in Basement Terrains: Geophysical, Remote Sensing, and Field Investigations in Sinai

    NASA Astrophysics Data System (ADS)

    Mohamed, Lamees; Sultan, Mohamed; Ahmed, Mohamed; Zaki, Abotalib; Sauck, William; Soliman, Farouk; Yan, Eugene; Elkadiri, Racha; Abouelmagd, Abdou

    2015-09-01

    An integrated [very low frequency (VLF) electromagnetic, magnetic, remote sensing, field, and geographic information system (GIS)] study was conducted over the basement complex in southern Sinai (Feiran watershed) for a better understanding of the structural controls on the groundwater flow. The increase in satellite-based radar backscattering values following a large precipitation event (34 mm on 17-18 January 2010) was used to identify water-bearing features, here interpreted as preferred pathways for surface water infiltration. Findings include: (1) spatial analysis in a GIS environment revealed that the distribution of the water-bearing features (conductive features) corresponds to that of fractures, faults, shear zones, dike swarms, and wadi networks; (2) using VLF (43 profiles), magnetic (7 profiles) techniques, and field observations, the majority (85 %) of the investigated conductive features were determined to be preferred pathways for groundwater flow; (3) northwest-southeast- to north-south-trending conductive features that intersect the groundwater flow (southeast to northwest) at low angles capture groundwater flow, whereas northeast-southwest to east-west features that intersect the flow at high angles impound groundwater upstream and could provide potential productive well locations; and (4) similar findings are observed in central Sinai: east-west-trending dextral shear zones (Themed and Sinai Hinge Belt) impede south to north groundwater flow as evidenced by the significant drop in hydraulic head (from 467 to 248 m above mean sea level) across shear zones and by reorientation of regional flow (south-north to southwest-northeast). The adopted integrated methodologies could be readily applied to similar highly fractured basement arid terrains elsewhere.

  11. Entrainment of granular substrate by pyroclastic flows: an experimental study and its implications for flow dynamics

    NASA Astrophysics Data System (ADS)

    Roche, O.; Niño, Y.; Mangeney, A.; Brand, B. D.; Valentine, G. A.

    2012-12-01

    -defined basal layer consisting of a mixture of fine particles and coarse steel beads. Further experiments with substrates of glass beads of diameter of 80 μm or 700 μm showed that particles were not dragged individually and were not uplifted. Shear at the top of the substrate caused the formation of structures of small height (1-3 mm) formed by numerous beads, which could have rendered the upward pressure gradient non operant and hence would have inhibited individual particle uplift. The height of these shear structures decreased with the size of the beads and they strongly elongated horizontally with time so that almost no evidence of entrainment was preserved in the deposits for substrates of beads of 80 μm. These results are consistent with field observations as unconsolidated granular substrates of fine particles (ash, lapillis) at the base of pyroclastic flow deposits can be well preserved whereas those made of large blocks are commonly reworked, as shown by the Peach Springs tuff for instance. At Mt St Helens, the 1980 pyroclastic flows emplaced on a debris avalanche deposit and entrained dense lava blocks of size up to several tens of cm on local slopes of only a few degrees. Application of our model assuming a bulk flow density of 500-1500 kg/m3 indicates flow velocities of ~12-27 m/s, which matches field observations.

  12. Structural dynamics verification facility study

    NASA Technical Reports Server (NTRS)

    Kiraly, L. J.; Hirchbein, M. S.; Mcaleese, J. M.; Fleming, D. P.

    1981-01-01

    The need for a structural dynamics verification facility to support structures programs was studied. Most of the industry operated facilities are used for highly focused research, component development, and problem solving, and are not used for the generic understanding of the coupled dynamic response of major engine subsystems. Capabilities for the proposed facility include: the ability to both excite and measure coupled structural dynamic response of elastic blades on elastic shafting, the mechanical simulation of various dynamical loadings representative of those seen in operating engines, and the measurement of engine dynamic deflections and interface forces caused by alternative engine mounting configurations and compliances.

  13. The population genomics of begomoviruses: global scale population structure and gene flow

    PubMed Central

    2010-01-01

    Background The rapidly growing availability of diverse full genome sequences from across the world is increasing the feasibility of studying the large-scale population processes that underly observable pattern of virus diversity. In particular, characterizing the genetic structure of virus populations could potentially reveal much about how factors such as geographical distributions, host ranges and gene flow between populations combine to produce the discontinuous patterns of genetic diversity that we perceive as distinct virus species. Among the richest and most diverse full genome datasets that are available is that for the dicotyledonous plant infecting genus, Begomovirus, in the Family Geminiviridae. The begomoviruses all share the same whitefly vector, are highly recombinogenic and are distributed throughout tropical and subtropical regions where they seriously threaten the food security of the world's poorest people. Results We focus here on using a model-based population genetic approach to identify the genetically distinct sub-populations within the global begomovirus meta-population. We demonstrate the existence of at least seven major sub-populations that can further be sub-divided into as many as thirty four significantly differentiated and genetically cohesive minor sub-populations. Using the population structure framework revealed in the present study, we further explored the extent of gene flow and recombination between genetic populations. Conclusions Although geographical barriers are apparently the most significant underlying cause of the seven major population sub-divisions, within the framework of these sub-divisions, we explore patterns of gene flow to reveal that both host range differences and genetic barriers to recombination have probably been major contributors to the minor population sub-divisions that we have identified. We believe that the global Begomovirus population structure revealed here could facilitate population genetics studies

  14. Rare gas flow structuration in plasma jet experiments

    NASA Astrophysics Data System (ADS)

    Robert, E.; Sarron, V.; Darny, T.; Riès, D.; Dozias, S.; Fontane, J.; Joly, L.; Pouvesle, J.-M.

    2014-02-01

    Modifications of rare gas flow by plasma generated with a plasma gun (PG) are evidenced through simultaneous time-resolved ICCD imaging and schlieren visualization. The geometrical features of the capillary inside which plasma propagates before in-air expansion, the pulse repetition rate and the presence of a metallic target are playing a key role on the rare gas flow at the outlet of the capillary when the plasma is switched on. In addition to the previously reported upstream offset of the laminar to turbulent transition, we document the reverse action leading to the generation of long plumes at moderate gas flow rates together with the channeling of helium flow under various discharge conditions. For higher gas flow rates, in the l min-1 range, time-resolved diagnostics performed during the first tens of ms after the PG is turned on, evidence that the plasma plume does not start expanding in a laminar neutral gas flow. Instead, plasma ignition leads to a gradual laminar-like flow build-up inside which the plasma plume is generated. The impact of such phenomena for gas delivery on targets mimicking biological samples is emphasized, as well as their consequences on the production and diagnostics of reactive species.

  15. A Study of Bubble and Slug Gas-Liquid Flow in a Microgravity Environment

    NASA Technical Reports Server (NTRS)

    McQuillen, J.

    2000-01-01

    The influence of gravity on the two-phase flow dynamics is obvious.As the gravity level is reduced,there is a new balance between inertial and interfacial forces, altering the behavior of the flow. In bubbly flow,the absence of drift velocity leads to spherical-shaped bubbles with a rectilinear trajectory.Slug flow is a succession of long bubbles and liquid slug carrying a few bubbles. There is no flow reversal in the thin liquid film as the long bubble and liquid slug pass over the film. Although the flow structure seems to be simpler than in normal gravity conditions,the models developed for the prediction of flow behavior in normal gravity and extended to reduced gravity flow are unable to predict the flow behavior correctly.An additional benefit of conducting studies in microgravity flows is that these studies aide the development of understanding for normal gravity flow behavior by removing the effects of buoyancy on the shape of the interface and density driven shear flows between the gas and the liquid phases. The proposal calls to study specifically the following: 1) The dynamics of isolated bubbles in microgravity liquid flows will be analyzed: Both the dynamics of spherical isolated bubbles and their dispersion by turbulence, their interaction with the pipe wall,the behavior of the bubbles in accelerated or decelerated flows,and the dynamics of isolated cylindrical bubbles, their deformation in accelerated/decelerated flows (in converging or diverging channels), and bubble/bubble interaction. Experiments will consist of the use of Particle Image Velocimetry (PIV) and Laser Doppler Velocimeters (LDV) to study single spherical bubble and single and two cylindrical bubble behavior with respect to their influence on the turbulence of the surrounding liquid and on the wall 2) The dynamics of bubbly and slug flow in microgravity will be analyzed especially for the role of the coalescence in the transition from bubbly to slug flow (effect of fluid properties and

  16. Mobility power flow analysis of an L-shaped plate structure subjected to acoustic excitation

    NASA Technical Reports Server (NTRS)

    Cuschieri, J. M.

    1989-01-01

    An analytical investigation based on the Mobility Power Flow method is presented for the determination of the vibrational response and power flow for two coupled flat plate structures in an L-shaped configuration, subjected to acoustical excitation. The principle of the mobility power flow method consists of dividing the global structure into a series of subsystems coupled together using mobility functions. Each separate subsystem is analyzed independently to determine the structural mobility functions for the junction and excitation locations. The mobility functions, together with the characteristics of the junction between the subsystems, are then used to determine the response of the global structure and the power flow. In the coupled plate structure considered here, mobility power flow expressions are derived for excitation by an incident acoustic plane wave. In this case, the forces (acoustic pressures) acting on the structure are dependent on the response of the structure because of the scattered pressure component. The interaction between the structure and the fluid leads to the derivation of a corrected mode shape for the plates' normal surface velocity and also for the structure mobility functions. The determination of the scattered pressure components in the expressions for the power flow represents an additional component in the power flow balance for the source plate and the receiver plate. This component represents the radiated acoustical power from the plate structure.

  17. The Ongoing Lava Flow Eruption of Sinabung Volcano (Sumatra, Indonesia): Observations from Structure-from-Motion and Satellite Remote Sensing

    NASA Astrophysics Data System (ADS)

    Carr, B. B.; Clarke, A. B.; Arrowsmith, R.; Vanderkluysen, L.

    2015-12-01

    Sinabung is a 2460 m high andesitic stratovolcano in North Sumatra, Indonesia. Its ongoing eruption has produced a 2.9 km long lava flow with two active summit lobes and frequent pyroclastic flows (≤ 5 km long) with associated plumes over 5 km high. Large viscous lava flows of this type are common at volcanoes around the world, but are rarely observed while active. This eruption therefore provides a special opportunity to observe and study the mechanisms of emplacement and growth of an active lava flow. In September 2014, we conducted a field campaign to collect ground-based photographs to analyze with Structure-from-Motion photogrammetric techniques. We built multiple 3D models from which we estimate the volume of the lava flow and identify areas where the flow was most active. Thermal infrared and visual satellite images provide information on the effusive eruption from its initiation in December 2013 to the present and allow us to estimate the eruption rate, advance rate and rheological characteristics of the flow. According to our DEMs the flow volume as of September 2014 was 100 Mm3, providing an average flow rate of 4.5 m3/s, while comparison of two DEMs from that month suggests that most growth occurred at the SE nose of the flow. Flow advancement was initially controlled by the yield strength of the flow crust while eruption and flow advance rates were at their highest in January-March 2014. A period of slow front advancement and inflation from March - October 2014 suggests that the flow's interior had cooled and that propagation was limited by the interior yield strength. This interpretation is supported by the simultaneous generation of pyroclastic flows due to collapse of the upper portion of the lava flow and consequent lava breakout and creation of new flow lobes originating from the upper reaches in October 2014 and June 2015. Both lobes remain active as of August 2015 and present a significant hazard for collapse and generation of pyroclastic flows

  18. Asymmetric energy flow in liquid alkylbenzenes: A computational study

    SciTech Connect

    Leitner, David M.; Pandey, Hari Datt

    2015-10-14

    Ultrafast IR-Raman experiments on substituted benzenes [B. C. Pein et al., J. Phys. Chem. B 117, 10898–10904 (2013)] reveal that energy can flow more efficiently in one direction along a molecule than in others. We carry out a computational study of energy flow in the three alkyl benzenes, toluene, isopropylbenzene, and t-butylbenzene, studied in these experiments, and find an asymmetry in the flow of vibrational energy between the two chemical groups of the molecule due to quantum mechanical vibrational relaxation bottlenecks, which give rise to a preferred direction of energy flow. We compare energy flow computed for all modes of the three alkylbenzenes over the relaxation time into the liquid with energy flow through the subset of modes monitored in the time-resolved Raman experiments and find qualitatively similar results when using the subset compared to all the modes.

  19. Evaluation of a universal flow-through model for predicting and designing phosphorus removal structures.

    PubMed

    Penn, Chad; Bowen, James; McGrath, Joshua; Nairn, Robert; Fox, Garey; Brown, Glenn; Wilson, Stuart; Gill, Clinton

    2016-05-01

    Phosphorus (P) removal structures have been shown to decrease dissolved P loss from agricultural and urban areas which may reduce the threat of eutrophication. In order to design or quantify performance of these structures, the relationship between discrete and cumulative removal with cumulative P loading must be determined, either by individual flow-through experiments or model prediction. A model was previously developed for predicting P removal with P sorption materials (PSMs) under flow-through conditions, as a function of inflow P concentration, retention time (RT), and PSM characteristics. The objective of this study was to compare model results to measured P removal data from several PSM under a range of conditions (P concentrations and RT) and scales ranging from laboratory to field. Materials tested included acid mine drainage residuals (AMDRs), treated and non-treated electric arc furnace (EAF) steel slag at different size fractions, and flue gas desulfurization (FGD) gypsum. Equations for P removal curves and cumulative P removed were not significantly different between predicted and actual values for any of the 23 scenarios examined. However, the model did tend to slightly over-predict cumulative P removal for calcium-based PSMs. The ability of the model to predict P removal for various materials, RTs, and P concentrations in both controlled settings and field structures validate its use in design and quantification of these structures. This ability to predict P removal without constant monitoring is vital to widespread adoption of P removal structures, especially for meeting discharge regulations and nutrient trading programs.

  20. SAXS/WAXS studies of flow-induced crystallization of poly(1-butene) in uniaxial extensional flow

    NASA Astrophysics Data System (ADS)

    McCready, Erica; Burghardt, Wesley

    2014-03-01

    We report studies of flow-induced crystallization of poly(1-butene) in uniaxial extensional flow. Flow was produced using an SER extensional flow fixture housed in a custom built convection oven designed to provide x-ray access for in situ studies of polymer structure using synchrotron x-ray scattering techniques. Samples were loaded into the SER fixture, heated well into the melt, and then cooled to a temperature at which quiescent crystallization would be prohibitively slow. A short interval of uniaxial extensional flow was then applied, after which simultaneous wide- and small-angle x-ray scattering (SAXS and WAXS) patterns were collected to study the phase transformation kinetics and morphology of the subsequent accelerated crystallization. The degree of crystallite orientation was generally found to decrease over the course of the crystallization. WAXS measurements yielded systematically higher degrees of crystallite orientation than SAXS. Both SAXS and WAXS gave generally consistent results for the extent of crystallization, although the SAXS invariant showed a decrease at long times that is not mirrored in the WAXS data. The impact of both deformation rate and total applied strain on the crystallization process were examined.

  1. Performance improvement of IPMC flow sensors with a biologically-inspired cupula structure

    NASA Astrophysics Data System (ADS)

    Lei, Hong; Sharif, Montassar Aidi; Paley, Derek A.; McHenry, Matthew J.; Tan, Xiaobo

    2016-04-01

    Ionic polymer-metal composites (IPMCs) have inherent underwater sensing and actuation properties. They can be used as sensors to collect flow information. Inspired by the hair-cell mediated receptor in the lateral line system of fish, the impact of a flexible, cupula-like structure on the performance of IPMC flow sensors is experimentally explored. The fabrication method to create a silicone-capped IPMC sensor is reported. Experiments are conducted to compare the sensing performance of the IPMC flow sensor before and after the PDMS coating under the periodic flow stimulus generated by a dipole source in still water and the laminar flow stimulus generated in a flow tank. Experimental results show that the performance of IPMC flow sensors is significantly improved under the stimulus of both periodic flow and laminar flow by the proposed silicone-capping.

  2. Structure of supersonic turbulent flow past a swept compression corner

    NASA Technical Reports Server (NTRS)

    Knight, Doyle D.; Horstman, C. C.; Bogdonoff, Seymour

    1992-01-01

    The structure of the shock wave/turbulent boundary-layer interaction generated by a 3D swept compression corner has been investigated through a combined experimental and theoretical research program. The flowfield geometry is defined by the streamwise compression angle alpha and the sweep angle lambda of the corner. The present study examines two different configurations, namely (alpha, lambda) = (24 deg, 40 deg) and (24 deg, 60 deg) at Mach 3 and Re sigma infinity about 9 x 10 exp 5. The theoretical model is the 3D Reynolds-averaged compressible Navier-Stokes equations with turbulence incorporated using a turbulent eddy viscosity. The calculated flowfields display general agreement with experimental data for surface pressure and good agreement with experimental flowfield profiles of pitot pressure and yaw angle. The principal feature of the flowfield is a large vortical structure approximately aligned with the corner. The entrainment of incoming fluid into the vortical structure is strongly affected by the sweep angle lambda. Viscous (turbulent and molecular) effects appear to be important only in the immediate vicinity of the surface and in an isolated region within the interaction and near the corner.

  3. Flow structure of water in carbon nanotubes: Poiseuille type or plug-like?

    NASA Astrophysics Data System (ADS)

    Hanasaki, Itsuo; Nakatani, Akihiro

    2006-04-01

    We have conducted molecular dynamics simulations of water flow in carbon nanotubes (CNTs) for (6,6) to (20,20) CNTs at a streaming velocity of 100m/s. The fluidized piston model (FPM) and the ice piston model (IPM) are employed to drive flow through the CNTs. The results show that the single-file water flow inside (6,6) CNT has a convex upward streaming velocity profile, whereas the velocity profiles in (10,10) to (20,20) CNTs are flat except near the tube wall. The flow structure of cylindrical water in the (8,8) CNT is intermediate between that for the (6,6) CNT and the larger CNTs. The flow parameters are found not to exhibit any dependence on streaming velocity at up to 300m/s in the (12,12) CNT. The hydrogen bond lifetimes of water flowing in CNTs tend to be longer than for the corresponding equilibrium states, and nonzero flow does not reduce the microscopic structure or structural robustness (hydrogen bond lifetime). Although the atomic density profile varies with tube diameter, reflecting the change in static microscopic structure of flow from single file to cylindrical, tube diameter does not induce a clear transition in streaming velocity, temperature, or hydrogen bond lifetime over this diameter range. The results suggest that water flow in CNTs of this size is more pluglike than Poiseuille type, although the flow structure does not strictly accord with either definition.

  4. Flows in a tube structure: Equation on the graph

    NASA Astrophysics Data System (ADS)

    Panasenko, Grigory; Pileckas, Konstantin

    2014-08-01

    The steady-state Navier-Stokes equations in thin structures lead to some elliptic second order equation for the macroscopic pressure on a graph. At the nodes of the graph the pressure satisfies Kirchoff-type junction conditions. In the non-steady case the problem for the macroscopic pressure on the graph becomes nonlocal in time. In the paper we study the existence and uniqueness of a solution to such one-dimensional model on the graph for a pipe-wise network. We also prove the exponential decay of the solution with respect to the time variable in the case when the data decay exponentially with respect to time.

  5. Schlieren System For Flow Studies In Round Glass Pipes

    NASA Technical Reports Server (NTRS)

    Costen, Robert C.; Rhodes, David B.; Jones, Stephen B.

    1990-01-01

    In schlieren system for studying flow of gas in transparent pipe of circular cross section, cylindrical lenses placed on opposite sides of pipe compensate for refraction caused by wall of pipe. Enables direct visualization of such phenomena as laminar or turbulent flow, shock waves, vortexes, and flow separations in systems having inherently cylindrical geometry; potentially unreliable extrapolations from results in flat-sided test cells no longer necessary.

  6. Study of unsteady flow conditions for slurry fuels

    SciTech Connect

    Ekmann, J.M.; Wildman, D.J.; Klinzing, G.E.

    1985-01-01

    During the past three years, transport characteristics of coal-water mixtures (CWMs) have been studied at the Pittsburgh Energy Technology Center. The effort has concentrated predominantly on studying flow conditions in straight horizontal and vertical sections, and to a lesser extent on studying the flow patterns around elbows of a one-inch-diameter loop and a two-inch-diameter loop. Steady-state flow was characterized for in-house prepared slurries and commercially prepared slurries. For lower concentrated slurries (55 wt % to 60 wt %) and coarse particle size distributions (50% finer than 75 microns), nonhomogeneous flow conditions were encountered across horizontal test sections. Since nonhomogeneous conditions existed in straight sections during steady-state flow, it was decided to further investigate flow conditions during changes in velocity (magnitude and direction). This paper concentrates on nonuniform flow conditions of two types. The first nonuniform flow condition arises from sudden increases in the magnitude of the flow velocity. Pressure measurements recorded at a fixed position in the vertical section of the two-inch-diameter loop during sudden changes in velocity can be analyzed via classic control theory to evaluate the dynamic properties of the CWM. The second nonuniform flow condition occurs as the CWM passes through a bend. Both long-radius bends and 90-degree elbows made of glass and steel have been studied. Pressure-loss data around the long-radius bends and elbows were analyzed with a modified version of the model developed by Ito for single-phase flow around bends. Flow patterns around glass bends and elbows were observed for slurries prepared of vinyl coating powder and water. They are described in an effort to increase understanding of the pressure-loss data. 8 refs., 11 figs., 1 tab.

  7. Studies in Transition and Time Varying Turbulent Flows

    NASA Technical Reports Server (NTRS)

    Grosch, Chester E.

    2004-01-01

    The research focused on two areas: (a) the dynamics of forced turbulent flows and (b) time filtered Large Eddy Simulations (TLES). The dynamics of turbulent flows arising from external forcing of the turbulence are poorly understood. In particular, here are many unanswered questions relating the basic dynamical balances and the existence or nonexistence of statistical equilibrium of forced turbulent flows. The research used direct numerical simulations to explore these questions. The properties of the temporally filtered Navier-Stokes equations were also studied.

  8. USANS study of wood structure

    NASA Astrophysics Data System (ADS)

    Garvey, Christopher J.; Knott, Robert B.; Searson, Matthew; Conroy, Jann P.

    2006-11-01

    Wood performs a vascular and structural function in trees. In this study we used the double-crystal diffractometer BT5 at the NIST Center for Neutron Scattering (Gaithersburg, USA) to study the pore structure inside wood sections. The slit-smeared intensity of scattered neutrons was measured from wood sections in directions parallel, orthogonal and transverse to the tree's trunk axis over a scattering vector range 0.00004-0.002 Å -1. The interpretation of the data in terms of a reductionist model consisting of infinitely long cylinders (cell lumens) is discussed.

  9. Spatiotemporal cascades of the Poiseuille-Hagen flow in invariant elliptic structures

    NASA Astrophysics Data System (ADS)

    Miroshnikov, Victor

    2011-11-01

    Spatiotemporal cascades of the transitional Poiseuille-Hagen flow are considered in elliptic structures, which are invariant with respect to differential and nonlinear algebraic operations. Differentiation and algebra of the invariant structures and decomposition of smooth velocity profiles in the invariant structures are treated both theoretically and symbolically. Reduction of the invariant elliptic structures to invariant trigonometric structures and invariant hyperbolic structures is also considered. By using the invariant structures, the displayed and hidden perturbations of the basic Poiseuille-Hagen flow are represented as dual perturbations, while the series solution for the perturbed flow converges uniformly. The cascade solution for the Poiseuille-Hagen flow is constructed in a multiscale form, which explicitly shows the effect of various factors at multiple scales.

  10. The prescribed output pattern regulates the modular structure of flow networks

    NASA Astrophysics Data System (ADS)

    Beber, Moritz Emanuel; Armbruster, Dieter; Hütt, Marc-Thorsten

    2013-11-01

    Modules are common functional and structural properties of many social, technical and biological networks. Especially for biological systems it is important to understand how modularity is related to function and how modularity evolves. It is known that time-varying or spatially organized goals can lead to modularity in a simulated evolution of signaling networks. Here, we study a minimal model of material flow in networks. We discuss the relation between the shared use of nodes, i.e., the cooperativity of modules, and the orthogonality of a prescribed output pattern. We study the persistence of cooperativity through an evolution of robustness against local damages. We expect the results to be valid for a large class of flow-based biological and technical networks.

  11. The prescribed output pattern regulates the modular structure of flow networks

    NASA Astrophysics Data System (ADS)

    Emanuel Beber, Moritz; Armbruster, Dieter; Hütt, Marc-Thorsten

    2013-11-01

    Modules are common functional and structural properties of many social, technical and biological networks. Especially for biological systems it is important to understand how modularity is related to function and how modularity evolves. It is known that time-varying or spatially organized goals can lead to modularity in a simulated evolution of signaling networks. Here, we study a minimal model of material flow in networks. We discuss the relation between the shared use of nodes, i.e., the cooperativity of modules, and the orthogonality of a prescribed output pattern. We study the persistence of cooperativity through an evolution of robustness against local damages. We expect the results to be valid for a large class of flow-based biological and technical networks. Supplementary material in the form of one pdf file available from the Journal web page at http://dx.doi.org/10.1140/epjb/e2013-40672-3

  12. Similarity analysis of compressor tip clearance flow structure

    NASA Technical Reports Server (NTRS)

    Chen, G. T.; Greitzer, E. M.; Tan, C. S.; Marble, F. E.

    1991-01-01

    A new approach is presented for analyzing compressor tip clearance flow. The basic idea is that the clearance velocity field can be (approximately) decomposed into independent throughflow and crossflow, since chordwise pressure gradients are much smaller than normal pressure gradients in the clearance region. As in the slender body approximation in external aerodynamics, this description implies that the three-dimensional steady clearance flow can be viewed as a two-dimensional, unsteady flow. Using this approach, a similarity scaling for the crossflow in the clearance region is developed and a generalized description of the clearance vortex is derived. Calculations based on the similarity scaling agree well with a wide range of experimental data in regard to flow features such as crossflow velocity field, static pressure field, and tip clearance vortex trajectory.

  13. Trend of heat flow in france: relation with deep structures

    NASA Astrophysics Data System (ADS)

    Vasseur, Guy; Nouri, Yamina; Groupe Fluxchaf

    1980-06-01

    The trend of heat flow over France is discussed using both direct measurements at equilibrium in boreholes and file data. The two types of data are found to be in agreement. They exhibit high heat flow values over the Massif Central and the Vosges. An E-W cross section across the Massif Central allows us to observe the relationship between the high heat flow values, the thinning of the crust and the uprising of the asthenosphere deduced from seismic and gravity measurements. High heat flow values could be explained using a cinematic model where upward convection occurs in the upper mantle for a period of 40 m.y. with a vertical velocity reaching 5 mm/y.

  14. The current structure of stratified tidal planetary boundary layer flow

    SciTech Connect

    Myrhaug, D.; Slaattelid, O.H.

    1995-12-31

    The paper presents the bottom shear stress and velocity profiles in stratified tidal planetary boundary layer flow by using similarity theory. For a given seabed roughness length, free stream current velocity components, frequency of tidal oscillation, Coriolis parameter and stratification parameter the maximum bottom shear stress is determined for flow conditions in the rough, smooth and transitional smooth-to-rough turbulent regime. Further, the direction of the bottom shear stress and the velocity profiles are given. Comparison is made with data from field measurements of time-independent as well as tidal planetary boundary layer flow for neutral conditions, and the agreement between the predictions and the data is generally good. Further, an example of application for stable stratification is given, and qualitatively the predictions show, as expected, that the bottom shear stress and the thickness of the boundary layer become smaller for stable than for neutral stratification. Other features of the tidal planetary boundary layer flow are also discussed.

  15. Hamiltonian structure for rotational capillary waves in stratified flows

    NASA Astrophysics Data System (ADS)

    Martin, Calin Iulian

    2016-07-01

    We show that the governing equations of two-dimensional water waves driven by surface tension propagating over two-layered stratified flows admit a Hamiltonian formulation. Moreover, the underlying flows that we consider here, have piecewise constant distribution of vorticity, the jump in vorticity being located along the interface separating the fluid of bigger density at the bottom from the lighter fluid adjacent to the free surface.

  16. Structural studies of ciliary components.

    PubMed

    Mizuno, Naoko; Taschner, Michael; Engel, Benjamin D; Lorentzen, Esben

    2012-09-14

    Cilia are organelles found on most eukaryotic cells, where they serve important functions in motility, sensory reception, and signaling. Recent advances in electron tomography have facilitated a number of ultrastructural studies of ciliary components that have significantly improved our knowledge of cilium architecture. These studies have produced nanometer-resolution structures of axonemal dynein complexes, microtubule doublets and triplets, basal bodies, radial spokes, and nexin complexes. In addition to these electron tomography studies, several recently published crystal structures provide insights into the architecture and mechanism of dynein as well as the centriolar protein SAS-6, important for establishing the 9-fold symmetry of centrioles. Ciliary assembly requires intraflagellar transport (IFT), a process that moves macromolecules between the tip of the cilium and the cell body. IFT relies on a large 20-subunit protein complex that is thought to mediate the contacts between ciliary motor and cargo proteins. Structural investigations of IFT complexes are starting to emerge, including the first three-dimensional models of IFT material in situ, revealing how IFT particles organize into larger train-like arrays, and the high-resolution structure of the IFT25/27 subcomplex. In this review, we cover recent advances in the structural and mechanistic understanding of ciliary components and IFT complexes. PMID:22683354

  17. Structural Studies of Ciliary Components

    PubMed Central

    Mizuno, Naoko; Taschner, Michael; Engel, Benjamin D.; Lorentzen, Esben

    2012-01-01

    Cilia are organelles found on most eukaryotic cells, where they serve important functions in motility, sensory reception, and signaling. Recent advances in electron tomography have facilitated a number of ultrastructural studies of ciliary components that have significantly improved our knowledge of cilium architecture. These studies have produced nanometer‐resolution structures of axonemal dynein complexes, microtubule doublets and triplets, basal bodies, radial spokes, and nexin complexes. In addition to these electron tomography studies, several recently published crystal structures provide insights into the architecture and mechanism of dynein as well as the centriolar protein SAS-6, important for establishing the 9-fold symmetry of centrioles. Ciliary assembly requires intraflagellar transport (IFT), a process that moves macromolecules between the tip of the cilium and the cell body. IFT relies on a large 20-subunit protein complex that is thought to mediate the contacts between ciliary motor and cargo proteins. Structural investigations of IFT complexes are starting to emerge, including the first three‐dimensional models of IFT material in situ, revealing how IFT particles organize into larger train-like arrays, and the high-resolution structure of the IFT25/27 subcomplex. In this review, we cover recent advances in the structural and mechanistic understanding of ciliary components and IFT complexes. PMID:22683354

  18. A Numerical Study of Shear Flow in Partially Vegetated Open Channels

    NASA Astrophysics Data System (ADS)

    Qu, Jingfang; Chen, S.; Yu, Jie; Li, Xiaolin

    Shear flow at the interface between a porous layer and an open conduit is a problem of fundamental importance to problems ranging from natural to engineered flows. Such shear flows are known to be unstable, inducing waves and coherent vortices via Kelvin-Helmholtz instability. These coherent flow structures can strongly enhance the exchange of scalar variables and vector variable such as momentum in and out of the canopy, hence playing an important role in controlling environmental quality of these system. We developed a numerical model using finite difference method for flow in open channel occupied by a vegetation canopy. We apply the method to simulate the shear flow and compare with the experimental study by White and Nepf in 2007. Preliminary comparisons with the experimental data show good agreements.

  19. Macroscopic effects of the spectral structure in turbulent flows

    NASA Astrophysics Data System (ADS)

    Tran, T.; Chakraborty, P.; Guttenberg, N.; Prescott, A.; Kellay, H.; Goldburg, W.; Goldenfeld, N.; Gioia, G.

    2010-11-01

    There is a missing link between macroscopic properties of turbulent flows, such as the frictional drag of a wall-bounded flow, and the turbulent spectrum. To seek the missing link we carry out unprecedented experimental measurements of the frictional drag in turbulent soap-film flows over smooth walls. These flows are effectively two-dimensional, and we are able to create soap-film flows with the two types of turbulent spectrum that are theoretically possible in two dimensions: the "enstrophy cascade," for which the spectral exponent α= 3, and the "inverse energy cascade," for which the spectral exponent α= 5/3. We find that the functional relation between the frictional drag f and the Reynolds number Re depends on the spectral exponent: where α= 3, f ˜Re-1/2; where α= 5/3, f ˜Re-1/4. Each of these scalings may be predicted from the attendant value of α by using a recently proposed spectral theory of the frictional drag. In this theory the frictional drag of turbulent flows on smooth walls is predicted to be f ˜Re^(1-α)/(1+α).

  20. Structural-acoustic optimization of structures excited by turbulent boundary layer flow

    NASA Astrophysics Data System (ADS)

    Shepherd, Micah R.

    In order to reduce noise radiation of aircraft or marine panels, a general structural-acoustic optimization technique is presented. To compute the structural-acoustic response, a modal approach based on finite element / boundary element analysis is used which can easily incorporate fluid loading, added structures and static pre-loads. Simple deterministic or complex random forcing functions are included in the analysis by transforming their cross-spectral density matrices to modal space. Particular emphasis is placed in this dissertation on structures excited by the fluctuating pressures due to turbulent boundary layer (TBL) flow. An efficient frequency-spacing is also used to minimize evaluation time but ensure accuracy. The response from the structural-acoustic analysis is coupled to an evolutionary strategy with covariance matrix adaptation (CMA-ES) to find the best design for low noise and weight. CMA-ES, a stochastic optimizer with robust search properties, samples candidate solutions from a multi-variate normal distribution and adapts the covariance matrix to favor good solutions. The optimization procedure is validated by minimizing the sound radiated by a point-driven ribbed panel and comparing the optimization results to an exhaustive search of the design space. Structural-acoustic optimization is then performed on a curved marine panel with heavy fluid loading excited by slow TBL flow. A weighted combination of noise radiation and mass are minimized by changing the thickness of strips and patches of elements. An uncorrelated pressure approximation is used to estimate the modal force due to TBL flow thus reducing the evaluation time required to compute the objective function. The results show that the best noise reduction is achieved by minimizing the modal acceptance of energy by the panel. This is equivalent to pushing the structural modes away from the peak frequency range of the forcing function. Additionally, the Pareto trade-off curve between total

  1. Turbulent Compressible Convection with Rotation. Part 1; Flow Structure and Evolution

    NASA Technical Reports Server (NTRS)

    Brummell, Nicholas H.; Hurlburt, Neal E.; Toomre, Juri

    1996-01-01

    The effects of Coriolis forces on compressible convection are studied using three-dimensional numerical simulations carried out within a local modified f-plane model. The physics is simplified by considering a perfect gas occupying a rectilinear domain placed tangentially to a rotating sphere at various latitudes, through which a destabilizing heat flux is driven. The resulting convection is considered for a range of Rayleigh, Taylor, and Prandtl (and thus Rossby) numbers, evaluating conditions where the influence of rotation is both weak and strong. Given the computational demands of these high-resolution simulations, the parameter space is explored sparsely to ascertain the differences between laminar and turbulent rotating convection. The first paper in this series examines the effects of rotation on the flow structure within the convection, its evolution, and some consequences for mixing. Subsequent papers consider the large-scale mean shear flows that are generated by the convection, and the effects of rotation on the convective energetics and transport properties. It is found here that the structure of rotating turbulent convection is similar to earlier nonrotating studies, with a laminar, cellular surface network disguising a fully turbulent interior punctuated by vertically coherent structures. However, the temporal signature of the surface flows is modified by inertial motions to yield new cellular evolution patterns and an overall increase in the mobility of the network. The turbulent convection contains vortex tubes of many scales, including large-scale coherent structures spanning the full vertical extent of the domain involving multiple density scale heights. Remarkably, such structures align with the rotation vector via the influence of Coriolis forces on turbulent motions, in contrast with the zonal tilting of streamlines found in laminar flows. Such novel turbulent mechanisms alter the correlations which drive mean shearing flows and affect the

  2. STRUCTURAL HETEROGENEITIES AND PALEO FLUID FLOW IN AN ANALOG SANDSTONE RESERVOIR 2001-2004

    SciTech Connect

    Pollard, David; Aydin, Atilla

    2005-02-22

    Fractures and faults are brittle structural heterogeneities that can act both as conduits and barriers with respect to fluid flow in rock. This range in the hydraulic effects of fractures and faults greatly complicates the challenges faced by geoscientists working on important problems: from groundwater aquifer and hydrocarbon reservoir management, to subsurface contaminant fate and transport, to underground nuclear waste isolation, to the subsurface sequestration of CO2 produced during fossil-fuel combustion. The research performed under DOE grant DE-FG03-94ER14462 aimed to address these challenges by laying a solid foundation, based on detailed geological mapping, laboratory experiments, and physical process modeling, on which to build our interpretive and predictive capabilities regarding the structure, patterns, and fluid flow properties of fractures and faults in sandstone reservoirs. The material in this final technical report focuses on the period of the investigation from July 1, 2001 to October 31, 2004. The Aztec Sandstone at the Valley of Fire, Nevada, provides an unusually rich natural laboratory in which exposures of joints, shear deformation bands, compaction bands and faults at scales ranging from centimeters to kilometers can be studied in an analog for sandstone aquifers and reservoirs. The suite of structures there has been documented and studied in detail using a combination of low-altitude aerial photography, outcrop-scale mapping and advanced computational analysis. In addition, chemical alteration patterns indicative of multiple paleo fluid flow events have been mapped at outcrop, local and regional scales. The Valley of Fire region has experienced multiple episodes of fluid flow and this is readily evident in the vibrant patterns of chemical alteration from which the Valley of Fire derives its name. We have successfully integrated detailed field and petrographic observation and analysis, process-based mechanical modeling, and numerical

  3. Study flow diagrams in Cochrane systematic review updates: an adapted PRISMA flow diagram.

    PubMed

    Stovold, Elizabeth; Beecher, Deirdre; Foxlee, Ruth; Noel-Storr, Anna

    2014-05-29

    Cochrane systematic reviews are conducted and reported according to rigorous standards. A study flow diagram must be included in a new review, and there is clear guidance from the PRISMA statement on how to do this. However, for a review update, there is currently no guidance on how study flow diagrams should be presented. To address this, a working group was formed to find a solution and produce guidance on how to use these diagrams in review updates.A number of different options were devised for how these flow diagrams could be used in review updates, and also in cases where multiple searches for a review or review update have been conducted. These options were circulated to the Cochrane information specialist community for consultation and feedback. Following the consultation period, the working group refined the guidance and made the recommendation that for review updates an adapted PRISMA flow diagram should be used, which includes an additional box with the number of previously included studies feeding into the total. Where multiple searches have been conducted, the results should be added together and treated as one set of results.There is no existing guidance for using study flow diagrams in review updates. Our adapted diagram is a simple and pragmatic solution for showing the flow of studies in review updates.

  4. Colloidal Suspensions in Shear Flow : a Real Space Study

    NASA Astrophysics Data System (ADS)

    Derks, D.

    2006-09-01

    We investigate the effect of shear flow on the microstructure of colloidal suspensions by means of microscopy. Systems of nearly equally sized particles are used, whose interactions and phase behavior are predominantly determined by their size and shape, and can further be tuned by the addition of polymers. Recently, a new type of shear cell was developed to study flowing suspensions in real space. The key property of this setup is the counter-rotating principle of the cone and plate, opening up the possibility to create a stationary layer in the bulk of the cell. In Chapter 2, we elaborate on the details of this setup and its performance. Fluorescence confocal microscopy is used to visualize the sheared suspension, and allows imaging of individual particles in the bulk in the stationary plane for a prolonged time. This way, the particle positions in a layer of, for example, a sheared colloidal crystal can be tracked. The particle dynamics in colloidal crystals in shear flow are the subject of Chapter 3. Here, the particles interact through a (nearly) hard sphere potential. Apart from the alignment of the crystal in the shear field and the collective zigzag motion, which had also been deduced from early scattering experiments, we find that random particle displacements increase with shear rate. Those increased fluctuations result in shear induced melting when their mean square displacement has reached about 13 % of the particle separation. Apart from hard spheres, we investigate mixtures of colloids and polymers in shear flow. The polymers cause an effective attraction between the spheres, leading to phase separation into a colloid rich (polymer poor) and a colloid poor (polymer rich) phase at sufficiently high colloid and polymer concentration. In Chapter 4, we study the demixing process in the (spinodal) two-phase region of the phase diagram. The system is quenched from an initially almost homogeneous state at very high shear rate to a low shear rate. A spinodal

  5. Turbulence production near walls: The role of flow structures with spanwise asymmetry

    NASA Technical Reports Server (NTRS)

    Alfredsson, P. Henrik; Johansson, Arne V.; Kim, John

    1988-01-01

    Space-time evolution of near wall flow structures is described by conditional sampling methods, in which conditional averages are formed at various stages of development of shear layer structures. The development of spanwise asymmetry of the structures was found to be important in the creation of the structures and for the process of turbulence production.

  6. Experimental and theoretical study of dispersion in potential flows

    NASA Astrophysics Data System (ADS)

    Eames, Ian; Woods, Andy

    1998-11-01

    We examine tracer dispersion in a potential flow, where the velocity field may be writted in terms of the gradient of a scalar function. A range of relevant environmental flows, such as the flow through porous media or thin cracks, may be described to leading order as potential flows. In such flows, tracer dispersion is significantly affected by diverging and converging streamlines which may occur due to variations in permeability, crack thickness or the thickness of a porous layer. We build upon previous studies of dispersion in potential flows in order to examine the effect of geometry of porous inclusions or the spatial variation of crack thickness on plume dispersion. Complementary experimental work is also present using a Hele-Shaw cell, which consists of a uniform viscid flow between two rigid plates. By introducing various shaped obstacles of prescribed thickness between the plates, we are able to study the effect of geometry and permeability on plume dispersion. Here the streamlines correspond to the flow past porous inclusions (and the magnetic field lines past paramagnetic materials), however the velocity field is not similar. These aspects of the flow are included in our analysis.

  7. A Study in Structured Discussion.

    ERIC Educational Resources Information Center

    Gutzmer, Willard Ernest

    This study tested the hypothesis that group interaction skill and useful learning occur in a discussion group which is academically structured. A class procedure involving a cognitive map, member skills and roles, and group etiquette was incorporated into a class ("Education and the Contemporary Scene," Fall Quarter, 1968) at the University of…

  8. Gravitational Effects on Near Field Flow Structure of Low Density Gas Jets

    NASA Technical Reports Server (NTRS)

    Yep, Tze-Wing; Agrawal, Ajay K.; Griffin, DeVon; Salzman, Jack (Technical Monitor)

    2001-01-01

    Experiments were conducted in Earth gravity and microgravity to acquire quantitative data on near field flow structure of helium jets injected into air. Microgravity conditions were simulated in the 2.2-second drop tower at NASA Glenn Research Center. The jet flow was observed by quantitative rainbow schlieren deflectometry, a non-intrusive line of site measurement technique for the whole field. The flow structure was characterized by distributions of angular deflection and helium mole percentage obtained from color schlieren images taken at 60 Hz. Results show that the jet flow was significantly influenced by the gravity. The jet in microgravity was up to 70 percent wider than that in Earth gravity. The jet flow oscillations observed in Earth gravity were absent in microgravity, providing direct experimental evidence that the flow instability in the low density jet was buoyancy induced. The paper provides quantitative details of temporal flow evolution as the experiment undergoes a change in gravity in the drop tower.

  9. Development of a modular MR valve using meandering flow path structure

    NASA Astrophysics Data System (ADS)

    Ichwan, B.; Mazlan, S. A.; Imaduddin, F.; Ubaidillah; Koga, T.; Idris, M. H.

    2016-03-01

    The extensive development of the magnetorheological (MR) valve has successfully introduced a new high-performance compact-class MR valve using a meandering flow path structure. Aside from the performance improvement, in real applications, the ease of performance adjustment also needs to be improved. This study focused on the development of a new design of a modular MR valve using a meandering flow path to improve the adjustability of the valve performance. The approach is proposed based on the high-performance advantages of a meandering flow path structure, while at the same time utilizing the benefit of the modular structure in terms of performance flexibility. In order to evaluate the performance of the modular structure, the analytical assessment was conducted for three different module stages: the single-stage module, the double-stage module, and triple-stage module. To predict the strength of the magnetic field in the effective area, the magnetic simulation was conducted through an open-source software called the FEMM (Finite Element Method Magnetics). The quasi-steady mathematical model of the proposed valve was also derived to conduct the analytical assessment as well as to predict the valve performance. In order to validate the simulation results, the prototypes of the proposed valve are experimentally tested with the aid of the hydraulic cylinder on a dynamic test machine. The results of the MR valve assessment from both the simulation and experimental test demonstrated that the pressure drop rating of the meandering type MR valve can be easily modified using modular structure by changing the number of module stages.

  10. Modelling of the flow structure in a composite jet behind two thrusters located near the spacecraft case

    NASA Astrophysics Data System (ADS)

    Gerasimov, Yu. I.; Yarygin, V. N.; Krylov, A. N.; Sagdullin, B. A.

    2009-09-01

    The gasdynamic flow structure is studied experimentally and numerically in the zone of jet interaction flowing with considerable underexpansion from two supersonic nozzles located near the spacecraft case. Longitudinal and transversal distributions of the density are obtained by the method of electron beam. They are compared with calculation results for inviscid gas. Generalized dependencies for determination of gas density within the zone of two jets interaction and boundary of this zone are obtained.

  11. An optical fiber Fabry-Perot flow measurement technology based on partial bend structure

    NASA Astrophysics Data System (ADS)

    Yang, Huijia; Jiang, Junfeng; Zhang, Xuezhi; Pan, Yuheng; Zhu, Wanshan; Zhou, Xiang; Liu, Tiegen

    2016-08-01

    An optical fiber Fabry-Perot (F-P) flow measurement technology is presented, which is based on partial bend structure. A 90° partial bend structure is designed to achieve the non-probe flow measurement with a pressure difference. The fluid simulation results of partial bend structure show that the error of the pressure difference is below 0.05 kPa during steady flow. The optical fiber F-P sensor mounted on the elbow with pressure test accuracy of 1% full scale is used to measure the fluid flow. Flow test results show that when the flow varies from 1 m3/h to 6.5 m3/h at ambient temperature of 25 °C, the response time is 1 s and the flow test accuracy is 4.5% of the F-P flow test system, proving that the F-P flow test method based on partial bend structure can be used in fluid flow measurement.

  12. An optical fiber Fabry-Perot flow measurement technology based on partial bend structure.

    PubMed

    Yang, Huijia; Jiang, Junfeng; Zhang, Xuezhi; Pan, Yuheng; Zhu, Wanshan; Zhou, Xiang; Liu, Tiegen

    2016-08-01

    An optical fiber Fabry-Perot (F-P) flow measurement technology is presented, which is based on partial bend structure. A 90° partial bend structure is designed to achieve the non-probe flow measurement with a pressure difference. The fluid simulation results of partial bend structure show that the error of the pressure difference is below 0.05 kPa during steady flow. The optical fiber F-P sensor mounted on the elbow with pressure test accuracy of 1% full scale is used to measure the fluid flow. Flow test results show that when the flow varies from 1 m(3)/h to 6.5 m(3)/h at ambient temperature of 25 °C, the response time is 1 s and the flow test accuracy is 4.5% of the F-P flow test system, proving that the F-P flow test method based on partial bend structure can be used in fluid flow measurement.

  13. An optical fiber Fabry-Perot flow measurement technology based on partial bend structure.

    PubMed

    Yang, Huijia; Jiang, Junfeng; Zhang, Xuezhi; Pan, Yuheng; Zhu, Wanshan; Zhou, Xiang; Liu, Tiegen

    2016-08-01

    An optical fiber Fabry-Perot (F-P) flow measurement technology is presented, which is based on partial bend structure. A 90° partial bend structure is designed to achieve the non-probe flow measurement with a pressure difference. The fluid simulation results of partial bend structure show that the error of the pressure difference is below 0.05 kPa during steady flow. The optical fiber F-P sensor mounted on the elbow with pressure test accuracy of 1% full scale is used to measure the fluid flow. Flow test results show that when the flow varies from 1 m(3)/h to 6.5 m(3)/h at ambient temperature of 25 °C, the response time is 1 s and the flow test accuracy is 4.5% of the F-P flow test system, proving that the F-P flow test method based on partial bend structure can be used in fluid flow measurement. PMID:27587096

  14. Compound Lava Flow Fields on Planetary Surfaces: Hawaiian Analogue Studies

    NASA Astrophysics Data System (ADS)

    Crown, D. A.; Byrnes, J. M.; Ramsey, M. S.

    2002-12-01

    Quantitative, process-oriented analyses of planetary volcanism have primarily been based on analogue studies of single-lobed lava flows emplaced as discrete units. Comparative analyses of compound lava flow fields on the Earth and terrestrial planets are being conducted in order to include volcanic styles characterized by complex distributary systems, stratigraphic relationships, and emplacement histories. Field observations, differential Global Positioning Systems (dGPS) measurements, and visible, thermal, and radar remote sensing are being used to characterize Hawaiian lava flow fields and develop techniques for analyses of planetary flow fields using datasets with high spatial and/or spectral resolution, such as MOC and THEMIS. These terrestrial studies allow flow field surface morphology, topography, and lava textures as well as detailed maps of distributary networks to be used to examine flow field growth and development. Information on flow field evolution is provided by delineating relationships between remote sensing signatures, surface morphology, and lava transport processes and by identifying input parameters for flowfield emplacement models. Investigations of the Mauna Ulu (1969-1974) and Puu Oo (1983-present) flow fields (Kilauea Volcano, HI) have focused on understanding the nature of distributary networks at various scales in order to determine spatial and temporal variations in lava transport. Initial work at Mauna Ulu has included analyses of 1) the distribution, network morphometry, and volumetric significance of lava channels in the medial zone of the flow field, and 2) the distribution, lava texture, and volumetric significance of breakouts from surface conduits and subsurface storage. Analyses of the temporal evolution of individual conduit systems provide the basis for interpretation of complex patterns of overlapping surface units that characterize local flow stratigraphy. Reconstruction of lava transport networks and relationships to surface

  15. A Phase-Field Method for Simulating Fluid-Structure Interactions in Multi-Phase Flow

    NASA Astrophysics Data System (ADS)

    Zheng, Xiaoning; Karniadakis, George

    2015-11-01

    We investigate two-phase flow instabilities by numerical simulations of fluid structure interactions in two-phase flow. The first case is a flexible pipe conveying two fluids, which exhibits self-sustained oscillations at high Reynolds number and tension related parameter. Well-defined two-phase flow patterns, i.e., slug flow and bubbly flow, are observed. The second case is external two-phase cross flow past a circular cylinder, which induces a Kelvin-Helmholtz instability due to density stratification. We solve the Navier-Stokes equation coupled with the Cahn-Hilliard equation and the structure equation in an arbitrary Lagrangian Eulerian (ALE) framework. For the fluid solver, a spectral/hp element method is employed for spatial discretization and backward differentiation for time discretization. For the structure solver, a Galerkin method is used in Lagrangian coordinates for spatial discretization and the Newmark- β scheme for time discretization.

  16. The Pilot Training Study: Personnel Flow and the PILOT Model.

    ERIC Educational Resources Information Center

    Mooz, W. E.

    The results of the Rand study of pilot flows and the computer-operated decision model, called the PILOT model, are described. The flows of pilots within the Air Force are caused by policies that require the career-development rotation of pilots from cockpit jobs to desk jobs, the maintenance of a supplement of pilots in excess of cockpit-related…

  17. Channel morphology and flow structure of an abandoned channel under varying stages

    NASA Astrophysics Data System (ADS)

    Costigan, Katie H.; Gerken, Joseph E.

    2016-07-01

    Abandoned channels are those channels left behind as meandering rivers migrate over their floodplains and remain among the most enigmatic features of the riverscape, especially related to their hydraulics and geomorphology. Abandoned channels are being considered and implemented as restoration and rehabilitation strategies for large rivers but we do not yet have a sound understanding of their hydromorphodynamics. The overall objectives of this work were to assess the bed morphology and flow structure of a large, dynamically connected abandoned channel (e.g., the channel is inundated during annual or decadal floods through bank overflow) under varying stages. Here we document the hydromorphodynamics of an abandoned channel during 3.4, 9.2, and 37.9 return interval discharges using an acoustic Doppler current profiler. Flow separation was observed along the channel entrance during the lowest flow surveying campaign but was not seen during the higher flow campaign. Width to depth ratio and channel width at the exit both progressively decreased from the first surveying campaign, despite the final campaign having the highest measured discharge. Large zones of flow stagnation and recirculation were observed, with depth-averaged velocity vectors not aligning in one direction, in the abandoned channel where water from the entrance was meeting water coming up from the exit during moderate discharges. The abandoned channel has been maintained for at least 25 years due to its low diversion angle and it being perched above the Kansas River. Results of this study provide insights of how flow hydraulics and physical characteristics of abandoned channel change under varying stages.

  18. On the dependence of structural and sensing properties of sputtered MoO3 thin films on argon gas flow

    NASA Astrophysics Data System (ADS)

    Khojier, K.; Savaloni, H.; Zolghadr, S.

    2014-11-01

    Nitrogen and carbon oxides (CO, NO and NO2), released from combustion facilities and automobiles, are known to be extremely harmful to the human body and also are the main cause of air pollution. Therefore, effective methods to monitor and suppress the carbon and nitrogen oxides have been highly demanded for atmospheric environmental measurements and controls. It is known that molybdenum oxide (MoO3) can be a good semiconductor material for use as a gas sensor in monitoring CO, NO and NO2. In this paper we report the structural characteristics and sensing properties of the sputtered MoO3 thin films as a function of argon gas flow. MoO3 thin films were deposited by DC reactive magnetron sputtering technique on glass substrates at different argon gas flows in the range of 5-20 sccm. X-ray diffraction (XRD) analysis was used for studying crystallographic structure. XRD results showed that all of our films were of polycrystalline structure and of α-MoO3 stable orthorhombic phase. Results also showed that crystallite size increases while compressive nano-strain in the structure of the films decreases with increasing the argon gas flow. Atomic force microscope and the field emission scanning electron microscope studies showed granular structures for all samples, which increased in size consistent with the XRD results, with argon gas flow, while the surface roughness of the films also increased with argon gas flow. Chemical composition study showed optimum reaction between oxygen and molybdenum atoms for films produced at 15 sccm flow of argon gas. The electrical response of samples was measured in the vacuum and the CO environments in the temperature range of 150-350 K. All samples showed Ohmic behavior and the electrical resistances of the films measured in the CO environment were lower than those measured in vacuum. This study showed that the sensing ability of MoO3 for CO improves with increasing the argon gas flow.

  19. Probing High School Students' Cognitive Structures and Key Areas of Learning Difficulties on Ethanoic Acid Using the Flow Map Method

    ERIC Educational Resources Information Center

    Zhou, Qing; Wang, Tingting; Zheng, Qi

    2015-01-01

    The purpose of this study was primarily to explore high school students' cognitive structures and to identify their learning difficulties on ethanoic acid through the flow map method. The subjects of this study were 30 grade 1 students from Dong Yuan Road Senior High School in Xi'an, China. The interviews were conducted a week after the students…

  20. Numerical simulation on macro-instability of coupling flow field structure in jet-stirred tank

    NASA Astrophysics Data System (ADS)

    Luan, D. Y.; Lu, J. P.; Bu, Q. X.; Zhang, S. F.; Zheng, S. X.

    2016-05-01

    The velocity field macro-instability (MI) can help to improve the mixing efficiency. In this work, the MI features of flow field induced by jet-stirred coupling action is studied by using computational fluid dynamics (CFD) simulations. The numerical simulation method of jet-stirred model was established based on standard turbulent equations, and the impeller rotation was modeled by means of the Sliding Mesh (SM) technology. The numerical results of test fluid (water) power consumption were compared with the data obtained by power test experiments. The effects of jet flow velocity and impeller speed on MI frequency were analyzed thoroughly. The results show that the calculated values of power consumption agree well with the experiment measured data, which validates the turbulent model, and the flow structure and MI frequency distribution are affected by both impeller speed and jet flow rate. The amplitude of MI frequency increases obviously with the increasing rotation speed of impeller and the eccentric jet rate, and it can be enhanced observably by eccentric jet rate, in condition of comparatively high impeller speed. At this time, the MI phenomenon disappears with the overall chaotic mixing.

  1. Probing the three-dimensional structure of a rotating turbulent flow

    NASA Astrophysics Data System (ADS)

    Ruppert-Felsot, Jori E.; Zhang, Hepeng

    2005-11-01

    We study laboratory produced fluid turbulence under the influence of rapid rotation. Three-dimensional turbulence was generated by strong pumping through sources and sinks at the bottom of a deep rotating tank (48.4 cm high, 39.4 cm diameter) filled with water. The resulting flow evolved toward quasi-two-dimensional (quasi-2D) turbulence with increasing height in the tank. The quasi-2D flow near the top of the tank contained many long-lived coherent vortices and jetsootnotetextJ. E. Ruppert- Felsot, O. Praud, E. Sharon, and H. L. Swinney, Phys. Rev. E 72, 016311 (2005). Digital particle image velocimetry measurements of the flow field were made using tracer particles illuminated by laser light-sheets. Measurements using two synchronized cameras and vertically separated horizontal light-sheets revealed that the coherent vortices were columnar and vertically extended throughout the tank. We found the simultaneously measured vertically separated horizontal projections of the velocity field to be well correlated even at moderate rotation. Further, a gradual spatial decay was observed in the correlation for increasing vertical separation, rather than a sharp transition. The findings were consistent with the effect of rotation to cause a quasi-2D column-like flow structure aligned along the axis of rotation.

  2. Stability of Brillouin flow in the presence of slow-wave structure

    NASA Astrophysics Data System (ADS)

    Simon, D. H.; Lau, Y. Y.; Greening, G.; Wong, P.; Hoff, B.; Gilgenbach, R. M.

    2016-09-01

    Including a slow-wave structure (SWS) on the anode in the conventional, planar, and inverted magnetron, we systematically study the linear stability of Brillouin flow, which is the prevalent flow in crossed-field devices. The analytic treatment is fully relativistic and fully electromagnetic, and it incorporates the equilibrium density profile, flow profile, and electric field and magnetic field profiles in the linear stability analysis. Using parameters similar to the University of Michigan's recirculating planar magnetron, the numerical data show that the resonant interaction of the vacuum circuit mode and the corresponding smooth-bore diocotron-like mode is the dominant cause for instability. This resonant interaction is far more important than the intrinsic negative (positive) mass property of electrons in the inverted (conventional) magnetron geometry. It is absent in either the smooth-bore magnetron or under the electrostatic assumption, one or both of which was almost always adopted in prior analytical formulation. This resonant interaction severely restricts the wavenumber for instability to the narrow range in which the cold tube frequency of the SWS is within a few percent of the corresponding smooth bore diocotron-like mode in the Brillouin flow.

  3. Effect of the wake flow on the soundproofing of aircraft structures

    NASA Astrophysics Data System (ADS)

    Generalov, A. V.

    The effect of the wake flow on the soundproofing of aircraft structures is calculated analytically for a single-layer structure for zero and nonzero Mach numbers. The results obtained indicate that the wake flow contributes to the sound insulation of aircraft structures. The greatest benefit from the standpoint of sound insulation is achieved when the powerplant is located in the tail section of the aircraft.

  4. The Influence of Nozzle Shape on the Shock Structure in Separated Flows

    NASA Astrophysics Data System (ADS)

    Nasuti, F.; Onofri, M.; Pietropaoli, E.

    2005-02-01

    The performance of liquid rocket engines is presently limited by the side loads that take place during the startup because of the coupling between the natural flow asymmetry and a peculiar shock structure inside the nozzle. The shock and flow structures of highly overexpandend nozzles are examined numerically, with a critical discussion on the reasons yielding the different possible configurations. The results confirm that a major role is played by the flow gradients ahead of the shock and thus by the nozzle geometry. Key words: Nozzle; Flow separation; Mach reflection.

  5. Methods for Computationally Efficient Structured CFD Simulations of Complex Turbomachinery Flows

    NASA Technical Reports Server (NTRS)

    Herrick, Gregory P.; Chen, Jen-Ping

    2012-01-01

    This research presents more efficient computational methods by which to perform multi-block structured Computational Fluid Dynamics (CFD) simulations of turbomachinery, thus facilitating higher-fidelity solutions of complicated geometries and their associated flows. This computational framework offers flexibility in allocating resources to balance process count and wall-clock computation time, while facilitating research interests of simulating axial compressor stall inception with more complete gridding of the flow passages and rotor tip clearance regions than is typically practiced with structured codes. The paradigm presented herein facilitates CFD simulation of previously impractical geometries and flows. These methods are validated and demonstrate improved computational efficiency when applied to complicated geometries and flows.

  6. Stochastic Aspects of Bridging Bonds of Induced Structure of Electro-Rheological Fluids in Shear Flow

    NASA Astrophysics Data System (ADS)

    Riha, P.; Kimura, H.; Takimoto, J.; Koyama, K.

    The bridging of electrodes by clusters of polarizable elements occurs to be a dominant feature of the response of certain electrorheological fluid suspensions and liquid polymeric blends to the imposed electric field. The evolution of the bridging structure in deformation and flow is described as a stochastic process and identified with the macroscopic flow behavior. The effect of structure is introduced into the rheological equation providing its non-linear modification. The comparisons are presented showing how the proposed rheological equation describes rheological characteristics measured at steady shearing flow and start-up shearing flow.

  7. Simulating nitrate leaching under winter wheat grown on a structured clay soil considering bypass flow

    NASA Astrophysics Data System (ADS)

    Ragab, R.; Coopers, D. M.; Harris, G. L.; Catt, J. A.

    1996-07-01

    Nitrate leaching from drained plots of structured clay soil under winter wheat is simulated for one growing season using the SOILN model. Results are compared with field measurements from two replicate plots. Soil water movement is simulated both with and without a bypass flow component using the SOIL model. Flow to field drains and soil water content in the root zone are simulated better when bypass flow is included. The results emphasise the importance of considering bypass flow in modelling leaching from structured clay soils. Simulations of nitrate leaching using the SOILN model show that the model captures the main features of the cumulative loss of nitrate over the year.

  8. Flow structure and heat exchange analysis in internal cooling channel of gas turbine blade

    NASA Astrophysics Data System (ADS)

    Szwaba, Ryszard; Kaczynski, Piotr; Doerffer, Piotr; Telega, Janusz

    2016-08-01

    This paper presents the study of the flow structure and heat transfer, and also their correlations on the four walls of a radial cooling passage model of a gas turbine blade. The investigations focus on heat transfer and aerodynamic measurements in the channel, which is an accurate representation of the configuration used in aeroengines. Correlations for the heat transfer coefficient and the pressure drop used in the design of radial cooling passages are often developed from simplified models. It is important to note that real engine passages do not have perfect rectangular cross sections, but include corner fillet, ribs with fillet radii and special orientation. Therefore, this work provides detailed fluid flow and heat transfer data for a model of radial cooling geometry which possesses very realistic features.

  9. Fluid-structure interaction analysis of the flow through a stenotic aortic valve

    NASA Astrophysics Data System (ADS)

    Maleki, Hoda; Labrosse, Michel R.; Durand, Louis-Gilles; Kadem, Lyes

    2009-11-01

    In Europe and North America, aortic stenosis (AS) is the most frequent valvular heart disease and cardiovascular disease after systemic hypertension and coronary artery disease. Understanding blood flow through an aortic stenosis and developing new accurate non-invasive diagnostic parameters is, therefore, of primarily importance. However, simulating such flows is highly challenging. In this study, we considered the interaction between blood flow and the valve leaflets and compared the results obtained in healthy valves with stenotic ones. One effective method to model the interaction between the fluid and the structure is to use Arbitrary Lagrangian-Eulerian (ALE) approach. Our two-dimensional model includes appropriate nonlinear and anisotropic materials. It is loaded during the systolic phase by applying pressure curves to the fluid domain at the inflow. For modeling the calcified stenotic valve, calcium will be added on the aortic side of valve leaflets. Such simulations allow us to determine the effective orifice area of the valve, one of the main parameters used clinically to evaluate the severity of an AS, and to correlate it with changes in the structure of the leaflets.

  10. Viscoelastic polymer flows and elastic turbulence in three-dimensional porous structures.

    PubMed

    Mitchell, Jonathan; Lyons, Kyle; Howe, Andrew M; Clarke, Andrew

    2016-01-14

    Viscoelastic polymer solutions flowing through reservoir rocks have been found to improve oil displacement efficiency when the aqueous-phase shear-rate exceeds a critical value. A possible mechanism for this enhanced recovery is elastic turbulence that causes breakup and mobilization of trapped oil ganglia. Here, we apply nuclear magnetic resonance (NMR) pulsed field gradient (PFG) diffusion measurements in a novel way to detect increased motion of disconnected oil ganglia. The data are acquired directly from a three-dimensional (3D) opaque porous structure (sandstone) when viscoelastic fluctuations are expected to be present in the continuous phase. The measured increase in motion of trapped ganglia provides unequivocal evidence of fluctuations in the flowing phase in a fully complex 3D system. This work provides direct evidence of elastic turbulence in a realistic reservoir rock - a measurement that cannot be readily achieved by conventional laboratory methods. We support the NMR data with optical microscopy studies of fluctuating ganglia in simple two-dimensional (2D) microfluidic networks, with consistent apparent rheological behaviour of the aqueous phase, to provide conclusive evidence of elastic turbulence in the 3D structure and hence validate the proposed flow-fluctuation mechanism for enhanced oil recovery. PMID:26477403

  11. Viscoelastic polymer flows and elastic turbulence in three-dimensional porous structures.

    PubMed

    Mitchell, Jonathan; Lyons, Kyle; Howe, Andrew M; Clarke, Andrew

    2016-01-14

    Viscoelastic polymer solutions flowing through reservoir rocks have been found to improve oil displacement efficiency when the aqueous-phase shear-rate exceeds a critical value. A possible mechanism for this enhanced recovery is elastic turbulence that causes breakup and mobilization of trapped oil ganglia. Here, we apply nuclear magnetic resonance (NMR) pulsed field gradient (PFG) diffusion measurements in a novel way to detect increased motion of disconnected oil ganglia. The data are acquired directly from a three-dimensional (3D) opaque porous structure (sandstone) when viscoelastic fluctuations are expected to be present in the continuous phase. The measured increase in motion of trapped ganglia provides unequivocal evidence of fluctuations in the flowing phase in a fully complex 3D system. This work provides direct evidence of elastic turbulence in a realistic reservoir rock - a measurement that cannot be readily achieved by conventional laboratory methods. We support the NMR data with optical microscopy studies of fluctuating ganglia in simple two-dimensional (2D) microfluidic networks, with consistent apparent rheological behaviour of the aqueous phase, to provide conclusive evidence of elastic turbulence in the 3D structure and hence validate the proposed flow-fluctuation mechanism for enhanced oil recovery.

  12. Flow over a backward-facing step: Mean separation bubble and evolution of coherent structures

    NASA Astrophysics Data System (ADS)

    Nadge, Pankaj; Govardhan, Raghuraman

    2013-11-01

    We present PIV measurements downstream of a backward-facing step at large step based Reynolds numbers. The structure of the mean separation bubble is mapped in detail, and the effect of Reynolds number and expansion ratio (ER) on it is studied; the ER being the primary geometrical parameter for this configuration. These measurements show that there exists a mean separation bubble structure that is nearly independent of ER at large Re. Further, these measurements permit evaluation of the forces acting on the mean separation bubble in the streamwise direction due to the Reynolds stresses. Towards understanding the coherent structures in the flow downstream of the step, time-resolved PIV measurements have been performed in a plane parallel to the lower wall. These show the presence of counter-rotating vortical structures, which may be thought of as signatures of three-dimensional hairpin-like structures. These counter-rotating pairs are observed to evolve as they convect downstream. Conditional averaging of these counter-rotating structures show that their length-scale increases with streamwise distance. Details about these structures and their evolution will be presented at the conference.

  13. Near-wake flow structure of elliptic cylinders close to a free surface: effect of cylinder aspect ratio

    NASA Astrophysics Data System (ADS)

    Daichin, K. V.; Lee, Sang Joon

    The flow fields behind elliptic cylinders adjacent to a free surface were investigated experimentally in a circulating water channel. A range of cylinder aspect ratios (AR=2, 3, 4) were considered, while the cross-sectional area of the elliptical cylinder was kept constant. The main objective of this study was to investigate the effect of cylinder aspect ratio and a free surface on the flow structure in the near-wake behind elliptic cylinders. For each elliptic cylinder, the flow structure was analyzed for various values of the submergence depth of the cylinder beneath the free surface. The flow fields were measured using a single-frame double-exposure PIV (Particle Image Velocimetry) system. For each experimental condition, 350 instantaneous velocity fields were obtained and ensemble-averaged to obtain the mean velocity field and spatial distribution of the mean vorticity statistics. The results show that near-wake can be classified into three typical flow patterns: formation of a Coanda flow, generation of substantial jet-like flow, and attachment of this jet flow to the free surface. The general flow structure observed behind the elliptic cylinders resembles the structure previously reported for a circular cylinder submerged near a free surface. However, the wake width and the angle of downward deflection of the shear layer developed from the lower surface of the elliptic cylinder differ from those observed for a circular cylinder. These trends are enhanced as cylinder aspect ratio is increased. In addition, the free surface distortion is also discussed in the paper.

  14. CFD study on electrolyte distribution in redox flow batteries

    NASA Astrophysics Data System (ADS)

    Bortolin, S.; Toninelli, P.; Maggiolo, D.; Guarnieri, M.; Del, D., Col

    2015-11-01

    The most important component in a redox flow battery (RFB) cell is the MEA (membrane electrode assembly), a sandwich consisting of two catalyzed electrodes with an interposed polymeric membrane. In order to allow electrolyte flow toward the electroactive sites, the electrodes have a porous structure that can be obtained with carbon base materials such as carbon felts. The RFB cell is closed by two plates containing the distribution flow channels. Considering that a uniform electrolyte distribution in the reaction region is a prerequisite for high-efficiency operation, the flow pattern is an important parameter to be investigated for the optimization of the cell. In the present work, the effect of different channels patterns on the electrolyte distribution and on the pressure drop is numerically investigated. Three-dimensional simulations have been carried out with ANSYS Fluent code and four different layouts have been considered. Calculations have been performed both in the distribution channels and in the felt porous region.

  15. Emissivity corrected infrared method for imaging anomalous structural heat flows

    DOEpatents

    Del Grande, Nancy K.; Durbin, Philip F.; Dolan, Kenneth W.; Perkins, Dwight E.

    1995-01-01

    A method for detecting flaws in structures using dual band infrared radiation. Heat is applied to the structure being evaluated. The structure is scanned for two different wavelengths and data obtained in the form of images. Images are used to remove clutter to form a corrected image. The existence and nature of a flaw is determined by investigating a variety of features.

  16. Study of flow patterns in fume hood enclosures

    SciTech Connect

    Pathanjali, C.; Rahman, M.M.

    1996-12-31

    A three-dimensional model for flow inside a fume hood enclosure was developed and numerical computations were carried out to explore the flow pattern and possible path of contaminant transport under different operating conditions of the hood. Equations for the conservation of mass and momentum were solved for different flow rate and opening conditions in the hood. The face velocity was maintained constant at its rated value of 0.4 m/s. The flow was assumed to enter through the front window opening (positive x-direction) and leave the cupboard through an opening on the top of the hood (positive z-direction). The flow was assumed to be fully turbulent. The {kappa}-{var_epsilon} model was used for the prediction of turbulence. The flow pattern for different sash openings were studied. The flow patterns around an object located at the bottom of the hood was studied for different locations of the object. In addition, the effect of a person standing in front of the hood on the flow pattern was investigated. It was found that air entering the hood proceeds directly to the back wall, impinges it and turns upward toward the top wall and exits through the outlet. The flow finds its way around any object forming a recirculating region at its trailing surface. With an increase in the sash opening, the velocity becomes higher and the fluid traces the path to the outlet more quickly. The volume occupied by recirculating flow decreases with increase in sash opening. The computed flow patterns will be very useful to design experiments with optimum sash opening providing adequate disposal of contaminants with minimum use of conditioned air from inside the room.

  17. Comparison of Comet Enflow and VA One Acoustic-to-Structure Power Flow Predictions

    NASA Technical Reports Server (NTRS)

    Grosveld, Ferdinand W.; Schiller, Noah H.; Cabell, Randolph H.

    2010-01-01

    Comet Enflow is a commercially available, high frequency vibroacoustic analysis software based on the Energy Finite Element Analysis (EFEA). In this method the same finite element mesh used for structural and acoustic analysis can be employed for the high frequency solutions. Comet Enflow is being validated for a floor-equipped composite cylinder by comparing the EFEA vibroacoustic response predictions with Statistical Energy Analysis (SEA) results from the commercial software program VA One from ESI Group. Early in this program a number of discrepancies became apparent in the Enflow predicted response for the power flow from an acoustic space to a structural subsystem. The power flow anomalies were studied for a simple cubic, a rectangular and a cylindrical structural model connected to an acoustic cavity. The current investigation focuses on three specific discrepancies between the Comet Enflow and the VA One predictions: the Enflow power transmission coefficient relative to the VA One coupling loss factor; the importance of the accuracy of the acoustic modal density formulation used within Enflow; and the recommended use of fast solvers in Comet Enflow. The frequency region of interest for this study covers the one-third octave bands with center frequencies from 16 Hz to 4000 Hz.

  18. Experimental Studies of Low-Pressure Turbine Flows and Flow Control

    NASA Technical Reports Server (NTRS)

    Volino, Ralph J.

    2012-01-01

    This report summarizes research performed in support of the NASA Glenn Research Center (GRC) Low-Pressure Turbine (LPT) Flow Physics Program. The work was performed experimentally at the U.S. Naval Academy faculties. The geometry corresponded to "Pak B" LPT airfoil. The test section simulated LPT flow in a passage. Three experimental studies were performed: (a) Boundary layer measurements for ten baseline cases under high and low freestream turbulence conditions at five Reynolds numbers of 25,000, 50,000, 100,000, 200,000, and 300,000, based on passage exit velocity and suction surface wetted length; (b) Passive flow control studies with three thicknesses of two-dimensional bars, and two heights of three-dimensional circular cylinders with different spanwise separations, at same flow conditions as the 10 baseline cases; (c) Active flow control with oscillating synthetic (zero net mass flow) vortex generator jets, for one case with low freestream turbulence and a low Reynolds number of 25,000. The Passive flow control was successful at controlling the separation problem at low Reynolds numbers, with varying degrees of success from case to case and varying levels of impact at higher Reynolds numbers. The active flow control successfully eliminated the large separation problem for the low Reynolds number case. Very detailed data was acquired using hot-wire anemometry, including single and two velocity components, integral boundary layer quantities, turbulence statistics and spectra, turbulent shear stresses and their spectra, and intermittency, documenting transition, separation and reattachment. Models were constructed to correlate the results. The report includes a summary of the work performed and reprints of the publications describing the various studies.

  19. Toward non-Newtonian effects on secondary flow structures in a 180 degree bent tube model for curved arteries

    NASA Astrophysics Data System (ADS)

    van Wyk, Stevin; Prahl Wittberg, Lisa; Fuchs, Laszlo; Bulusu, Kartik V.; Plesniak, Michael W.

    2013-11-01

    The purpose of this study is to investigate the development of vortical flow structures of blood like fluids in a 180 degree tube bend, analogous to the aortic arch. Cardiovascular diseases are localized to regions of curvature in the arterial tree. The pathology of atherogenesis is widely considered an inflammatory response, hypothesized to be modulated by the interplay between Wall Shear Stress (WSS) variations and particulate transport mechanisms from the bulk fluid core to the near wall. The WSS is determined by the local flow characteristics as well as the rheological properties of the blood, which in turn are dependent on the bulk secondary flows. In this work, the time dependent fluid flow under various physiological flow conditions are investigated both experimentally and numerically. A Newtonian blood analog fluid model is considered in both studies to validate both methods and thereby study flow structure development during steady as well as pulsatile conditions. Particle image velocimetry (2C - 2D PIV) is used to acquire velocity field data from an acrylic tube bend. The numerical study is extended to consider the non-Newtonian properties of blood according to an empirical model to identify the relative importance of the non-Newtonian behavior. The studies show complex Dean and Lyne vortex interaction that are enhanced with increasing peak Reynolds numbers.

  20. Factors influencing the structure and shape of stenotic and regurgitant jets: an in vitro investigation using Doppler color flow mapping and optical flow visualization.

    PubMed

    Krabill, K A; Sung, H W; Tamura, T; Chung, K J; Yoganathan, A P; Sahn, D J

    1989-06-01

    To evaluate factors influencing the structure and shape of stenotic and regurgitant jets, Doppler color flow mapping and optical flow visualization studies were performed with use of a syringe model with a constant rate of ejection to simulate jets of valvular regurgitation and a pulsatile flow model of the right heart chambers to simulate jets of mild, moderate and severe valvular pulmonary stenosis. Ink-(0 to 40%) glycerol-water jets (viscosity 1 to 3.5 centiPoise) were produced by injecting the fluid at a constant rate into a 10 gallon rectangular reservoir of the same still fluid through 1.4 and 3.4 mm needles. The Doppler color flow scanners imaged the laminar jet length within 3 mm of actual jet length (2 to 6 cm) and the jet width within 2 to 3 mm of the actual jet width. Jet flows with Reynolds numbers ranging from 230 to 1,200 injected into still fluid yielded jet length/width ratios that decreased with increasing Reynolds numbers and leveled off to a length/width ratio of 5-6:1 at a Reynolds number near 600. When the fluid reservoir was swirled to better mimic the effect of flow entering the same cardiac chamber from a second source, the jets showed diminution of the jet length/width ratio and a clearly defined zone of turbulence. Studies of the pulsatile flow model were performed at cardiac outputs of 1 to 6 liters/min for the normal and each stenotic valve. Mild stenosis had an orifice area of 2.8 cm2, moderate stenosis an area of 1.0 cm2 and severe stenosis an area of 0.5 cm2. Laminar jet length represented the length of the total jet, which had a symmetric width and was measured from the valve opening to a region where the jet exhibited a spray effect. Laminar jet lengths (0.2 to 1.1 cm) were imaged by Doppler color flow mapping and optical visualization only in the moderate and severely stenotic valves and only at flows less than or equal to 3 liters/min (mean Reynolds numbers less than or equal to 3,470). Beyond this flow rate the jets exhibited a

  1. Propulsion of micro-structures in Oscillatory Stokes Flow

    NASA Astrophysics Data System (ADS)

    Jo, Ikhee; Huang, Yangyang; Zimmerman, Walter; Kanso, Eva

    2015-11-01

    Drug delivery often necessitates specific site-targeting within the human body. The use of micro and/or nano devices swimming through the bloodstream provides an attractive mechanism for targeted drug targeting, however the design and practical implementation of such devices remain very challenging. Inspired by flapping wings, we construct a two-dimensional wedge-like device, consisting of two links connected by a linear torsional spring and released in an oscillatory Stokes flow. We vary the stiffness and rest angle of the linear spring and the oscillation amplitude and frequency of the background flow to explore the behavior of the device. We find that the device achieves a net displacement, or propulsion, in oscillatory flows even when no elastic energy is stored initially, thus breaking Purcell's scallop's theorem. More importantly, the vehicle tends to align with the background flow under perturbations. We conclude by commenting on how to control the parameters of the device and the fluid to achieve desired behavior of the device. These findings may have significant implications on the design of micro devices in viscous fluids.

  2. Turbulent Flow Structure Inside a Canopy with Complex Multi-Scale Elements

    NASA Astrophysics Data System (ADS)

    Bai, Kunlun; Katz, Joseph; Meneveau, Charles

    2015-06-01

    Particle image velocimetry laboratory measurements are carried out to study mean flow distributions and turbulent statistics inside a canopy with complex geometry and multiple scales consisting of fractal, tree-like objects. Matching the optical refractive indices of the tree elements with those of the working fluid provides unobstructed optical paths for both illuminations and image acquisition. As a result, the flow fields between tree branches can be resolved in great detail, without optical interference. Statistical distributions of mean velocity, turbulence stresses, and components of dispersive fluxes are documented and discussed. The results show that the trees leave their signatures in the flow by imprinting wake structures with shapes similar to the trees. The velocities in both wake and non-wake regions significantly deviate from the spatially-averaged values. These local deviations result in strong dispersive fluxes, which are important to account for in canopy-flow modelling. In fact, we find that the streamwise normal dispersive flux inside the canopy has a larger magnitude (by up to four times) than the corresponding Reynolds normal stress. Turbulent transport in horizontal planes is studied in the framework of the eddy viscosity model. Scatter plots comparing the Reynolds shear stress and mean velocity gradient are indicative of a linear trend, from which one can calculate the eddy viscosity and mixing length. Similar to earlier results from the wake of a single tree, here we find that inside the canopy the mean mixing length decreases with increasing elevation. This trend cannot be scaled based on a single length scale, but can be described well by a model, which considers the coexistence of multi-scale branches. This agreement indicates that the multi-scale information and the clustering properties of the fractal objects should be taken into consideration in flows inside multi-scale canopies.

  3. Intense transport of bed load - modeling based on experimentally observed flow structure

    NASA Astrophysics Data System (ADS)

    Matoušek, Václav

    2016-04-01

    A modeling approach is discussed which enables to predict characteristics of steady uniform open-channel flow carrying a large amount of sediment (bed load). The approach considers a layered structure of the sediment-laden flow and employs conditions at layer interfaces to evaluate the flow slope, depth, the thickness of the layers and flow rates of both the sediment and sediment-water mixture. It is based on experimental observations obtained for lightweight granular materials in a laboratory tilting flume. Besides visual observations of a development of the layered structure of the flow, detailed profiles of the longitudinal velocity were collected together with integral characteristics of the flow (depths and slopes, flow rates) in the flume. Values of the grain velocity and concentration at the interfaces were determined from the measurements and observations. In the upper plane bed regime of bed load transport, the flow structure appears to be composed of up to three distinct layers (water layer, linear collisional layer and dense sliding layer). Depending on a value of the bed Shields parameter (and associated flow conditions) the number of layers may change and the thicknesses of the particular layers vary. It appears that collisional layers in flows in which they dominate the flow depth (typically Shields bigger than 1) exhibit a virtually constant value of the collisional-layer Richardson number. Velocity and concentration profiles across the collisional layer can be considered linear. At the bottom of the flow, the Coulomb yield criterion with the assumption of the zero fluid contribution balances the bed shear stress applied by the flowing mixture of water and sediment. These features are employed in the discussed modeling approach and lead to a depth-averaged flow model composed of a set of balance and constitutive equations. A kinetic-theory based formula for granular shear stress at the bottom of the collisional layer is added to close the set of

  4. Transitional flow structure on classic and wavy wings at low Reynolds numbers

    NASA Astrophysics Data System (ADS)

    Zverkov, I.; Kozlov, V.; Kryukov, A.

    2015-06-01

    The paper presents experimental results on the boundary-layer structure and laminar-turbulent transition on a wavy wing designed for unmanned air vehicles (UAVs). The study has been performed at the chord Reynolds number of the order of 105 to compare the wings with smooth and wavy surfaces at similar conditions. The flow past Z-15-25 airfoil was investigated with a particle-image velocimetry (PIV). The method made it possible to obtain a spatial pattern of velocity perturbations on the wing with wavy surface.

  5. Turbulent structure of three-dimensional flow behind a model car: 1. Exposed to uniform approach flow

    NASA Astrophysics Data System (ADS)

    Kozaka, Orçun E.; Özkan, Gökhan; Özdemir, Bedii I.

    2004-01-01

    Turbulent structure of flow behind a model car is investigated with local velocity measurements with emphasis on large structures and their relevance to aerodynamic forces. Results show that two counter-rotating helical vortices, which are formed within the inner wake region, play a key role in determining the flux of kinetic energy. The turbulence is generated within the outermost shear layers due to the instabilities, which also seem to be the basic drive for these relatively organized structures. The measured terms of the turbulent kinetic energy production, which are only part of the full expression, indicate that vortex centres act similar to the manifolds draining the energy in the streamwise direction. As the approach velocity increases, the streamwise convection becomes the dominant means of turbulent transport and, thus, the acquisition of turbulence by relatively non-turbulent flow around the wake region is suppressed.

  6. Structural similarity and lifetimes of turbulence structures in fully developed pipe flow

    NASA Astrophysics Data System (ADS)

    Bullock, K. J.; Cooper, R. E.; Kronauer, R. E.; Lai, J. C. S.

    1987-10-01

    Cross correlation measurements of the longitudinal velocity fluctuations in fully developed pipe flow have been performed with a reference hot-wire probe at a distance y+1 =100 from the wall for five different y+2 locations (namely, 50, 100, 200, 400, and 600) of a second probe with zero longitudinal separation but nonzero transverse separations. The pipe flow Reynolds number is 69 000 based on the pipe radius and the centerline velocity. The covariant (Co) and quadrature (Quad) correlations, which have been determined for each of the seven frequencies ω+ used to constrain the longitudinal wavenumber k+x, have been Fourier transformed with the transverse wavenumber k+z, y+1, y+2, and ω+ as the independent variables. The data presented in this form enable similarity to be examined in terms of waves of different sizes and inclinations. By using a similarity variable k+y+, where k+=[k+2x k+2z]1/2, the relative phases determined from the Co and Quad correlations and the wave intensity function for various wave angles have been shown to collapse. These results support the similarity hypothesis that the phase and intensity of the turbulance components is scaled by wave size k+ and distance from the wall y+. The dimension over which a turbulence structure retains its coherence has been deduced from the correlation data for various wave angles. Two estimates for the lifetime of turbulence structures have been derived, one from the phase-shifting effects of shear contained in the relative phase data, and the other from spectral sheet thickness data. Their significance and implications have been discussed.

  7. Studies of Flame Structure in Microgravity

    NASA Technical Reports Server (NTRS)

    Law, C. K.; Sung, C. J.; Zhu, D. L.

    1997-01-01

    The present research endeavor is concerned with gaining fundamental understanding of the configuration, structure, and dynamics of laminar premixed and diffusion flames under conditions of negligible effects of gravity. Of particular interest is the potential to establish and hence study the properties of spherically- and cylindrically-symmetric flames and their response to external forces not related to gravity. For example, in an earlier experimental study of the burner-stabilized cylindrical premixed flames, the possibility of flame stabilization through flow divergence was established, while the resulting one-dimensional, adiabatic, stretchless flame also allowed an accurate means of determining the laminar flame speeds of combustible mixtures. We have recently extended our studies of the flame structure in microgravity along the following directions: (1) Analysis of the dynamics of spherical premixed flames; (2) Analysis of the spreading of cylindrical diffusion flames; (3) Experimental observation of an interesting dual luminous zone structure of a steady-state, microbuoyancy, spherical diffusion flame of air burning in a hydrogen/methane mixture environment, and its subsequent quantification through computational simulation with detailed chemistry and transport; (4) Experimental quantification of the unsteady growth of a spherical diffusion flame; and (5) Computational simulation of stretched, diffusionally-imbalanced premixed flames near and beyond the conventional limits of flammability, and the substantiation of the concept of extended limits of flammability. Motivation and results of these investigations are individually discussed.

  8. A structural study of gallstones.

    PubMed Central

    Bills, P M; Lewis, D

    1975-01-01

    A number of gallstones have been studied using methods which have not previously been applied to gallstones. In particular, the use of scanning electron microscopy and micro-x-radiography have allowed detailed observations to be made on the structure of the stones and the distribution of the various components within the stones. Large differences in structure have been shown to exist between stones having similar overall chemical compositions. In cholesterol gallstones containing calcium carbonate the crystalline nature, distribution and method of deposition of the calcium carbonate was studied and was found to vary from stone to stone. Evidence was found for the presence of fibrous material in the centre of many stones and it is possible that this material acted as a nucleus for the deposition of the other stone components. Images Fig 1 Fig 2 Fig 3 Fig 4 Fig 5 PMID:1183859

  9. Some specific features of the NMR study of fluid flows

    NASA Astrophysics Data System (ADS)

    Davydov, V. V.

    2016-07-01

    Some specific features of studying fluid flows with a NMR spectrometer are considered. The consideration of these features in the NMR spectrometer design makes it possible to determine the relative concentrations of paramagnetic ions and measure the longitudinal and transverse relaxation times ( T 1 and T 2, respectively) in fluid flows with an error no larger than 0.5%. This approach allows one to completely avoid errors in determining the state of a fluid from measured relaxation constants T 1 and T 2, which is especially urgent when working with medical suspensions and biological solutions. The results of an experimental study of fluid flows are presented.

  10. Numerical studies of transverse curvature effects on transonic flow stability

    NASA Technical Reports Server (NTRS)

    Macaraeg, M. G.; Daudpota, Q. I.

    1992-01-01

    A numerical study of transverse curvature effects on compressible flow temporal stability for transonic to low supersonic Mach numbers is presented for axisymmetric modes. The mean flows studied include a similar boundary-layer profile and a nonsimilar axisymmetric boundary-layer solution. The effect of neglecting curvature in the mean flow produces only small quantitative changes in the disturbance growth rate. For transonic Mach numbers (1-1.4) and aerodynamically relevant Reynolds numbers (5000-10,000 based on displacement thickness), the maximum growth rate is found to increase with curvature - the maximum occurring at a nondimensional radius (based on displacement thickness) between 30 and 100.

  11. Performance studies on an axial flow compressor stage

    NASA Astrophysics Data System (ADS)

    Sitaram, N.

    1986-12-01

    A low-speed, medium loaded axial flow compressor stage is studied experimentally and theoretically. The flow compressor facility, composed of an inlet guide vane row, a rotor blade row, and a stator blade row, and the principles of the streamline curvature method (SCM) and the Douglas-Neumann cascade program are described. The radial distribution of the flow properties, the rotor blade static pressure distribution, and the lift coefficient and relative flow angle derived experimentally and theoretically are compared. It is determined that there is good correlation between the experimental flow properties and the SCM data, the Douglas-Neumann cascade program and experimental rotor blade static pressure data, and the experimental and theoretical lift coefficients only in the midspan region. Modifications to the SCM and the Douglas-Neumann cascade program in order to improve their accuracy are discussed.

  12. Gravitational Effects on Near Field Flow Structure of Low Density Gas Jets

    NASA Technical Reports Server (NTRS)

    Griffin, D. W.; Yep, T. W.; Agrawal, A. K.

    2005-01-01

    Experiments were conducted in Earth gravity and microgravity to acquire quantitative data on near field flow structure of helium jets injected into air. Microgravity conditions were simulated in the 2.2- second drop tower at NASA Glenn Research Center. The jet flow was observed by quantitative rainbow schlieren deflectometry, a non-intrusive line of site measurement technique for the whole field. The flow structure was characterized by distributions of angular deflection and helium mole percentage obtained from color schlieren images taken at 60 Hz. Results show that the jet in microgravity was up to 70 percent wider than that in Earth gravity. The global jet flow oscillations observed in Earth gravity were absent in microgravity, providing direct experimental evidence that the flow instability in the low density jet was buoyancy induced. The paper provides quantitative details of temporal flow evolution as the experiment undergoes change in gravity in the drop tower.

  13. Survey of shock-wave structures of smooth-particle granular flows.

    PubMed

    Padgett, D A; Mazzoleni, A P; Faw, S D

    2015-12-01

    We show the effects of simulated supersonic granular flow made up of smooth particles passing over two prototypical bodies: a wedge and a disk. We describe a way of computationally identifying shock wave locations in granular flows and tabulate the shock wave locations for flow over wedges and disks. We quantify the shock structure in terms of oblique shock angle for wedge impediments and shock standoff distance for disk impediments. We vary granular flow parameters including upstream volume fraction, average upstream velocity, granular temperature, and the collision coefficient of restitution. Both wedges and disks have been used in the aerospace community as prototypical impediments to flowing air in order to investigate the fundamentally different shock structures emanating from sharp and blunt bodies, and we present these results in order to increase the understanding of the fundamental behavior of supersonic granular flow. PMID:26764684

  14. Structure of hydrogen-rich transverse jets in a vitiated turbulent flow

    DOE PAGESBeta

    Lyra, Sgouria; Wilde, Benjamin; Kolla, Hemanth; Seitzman, Jerry M.; Lieuwen, Timothy C.; Chen, Jacqueline H.

    2014-11-24

    Our paper reports the results of a joint experimental and numerical study of the flow characteristics and flame structure of a hydrogen rich jet injected normal to a turbulent, vitiated crossflow of lean methane combustion products. Simultaneous high-speed stereoscopic PIV and OH PLIF measurements were obtained and analyzed alongside three-dimensional direct numerical simulations of inert and reacting JICF with detailed H2/COH2/CO chemistry. Both the experiment and the simulation reveal that, contrary to most previous studies of reacting JICF stabilized in low-to-moderate temperature air crossflow, the present conditions lead to a burner-attached flame that initiates uniformly around the burner edge. Significantmore » asymmetry is observed, however, between the reaction zones located on the windward and leeward sides of the jet, due to the substantially different scalar dissipation rates. The windward reaction zone is much thinner in the near field, while also exhibiting significantly higher local and global heat release than the much broader reaction zone found on the leeward side of the jet. The unsteady dynamics of the windward shear layer, which largely control the important jet/crossflow mixing processes in that region, are explored in order to elucidate the important flow stability implications arising in the inert and reacting JICF. The paper concludes with an analysis of the ignition, flame characteristics, and global structure of the burner-attached flame. FurthermoreChemical explosive mode analysis (CEMA) shows that the entire windward shear layer, and a large region on the leeward side of the jet, are highly explosive prior to ignition and are dominated by non-premixed flame structures after ignition. The predominantly mixing limited nature of the flow after ignition is examined by computing the Takeno flame index, which shows that ~70% of the heat release occurs in non-premixed regions.« less

  15. Structure of hydrogen-rich transverse jets in a vitiated turbulent flow

    SciTech Connect

    Lyra, Sgouria; Wilde, Benjamin; Kolla, Hemanth; Seitzman, Jerry M.; Lieuwen, Timothy C.; Chen, Jacqueline H.

    2014-11-24

    Our paper reports the results of a joint experimental and numerical study of the flow characteristics and flame structure of a hydrogen rich jet injected normal to a turbulent, vitiated crossflow of lean methane combustion products. Simultaneous high-speed stereoscopic PIV and OH PLIF measurements were obtained and analyzed alongside three-dimensional direct numerical simulations of inert and reacting JICF with detailed H2/COH2/CO chemistry. Both the experiment and the simulation reveal that, contrary to most previous studies of reacting JICF stabilized in low-to-moderate temperature air crossflow, the present conditions lead to a burner-attached flame that initiates uniformly around the burner edge. Significant asymmetry is observed, however, between the reaction zones located on the windward and leeward sides of the jet, due to the substantially different scalar dissipation rates. The windward reaction zone is much thinner in the near field, while also exhibiting significantly higher local and global heat release than the much broader reaction zone found on the leeward side of the jet. The unsteady dynamics of the windward shear layer, which largely control the important jet/crossflow mixing processes in that region, are explored in order to elucidate the important flow stability implications arising in the inert and reacting JICF. The paper concludes with an analysis of the ignition, flame characteristics, and global structure of the burner-attached flame. FurthermoreChemical explosive mode analysis (CEMA) shows that the entire windward shear layer, and a large region on the leeward side of the jet, are highly explosive prior to ignition and are dominated by non-premixed flame structures after ignition. The predominantly mixing limited nature of the flow after ignition is examined by computing the Takeno flame index, which shows that ~70% of the heat release occurs in non-premixed regions.

  16. Fluid-thermal-structural study of aerodynamically heated leading edges

    NASA Technical Reports Server (NTRS)

    Deuchamphai, Pramote; Thornton, Earl A.; Wieting, Allan R.

    1988-01-01

    A finite element approach for integrated fluid-thermal-structural analysis of aerodynamically heated leading edges is presented. The Navier-Stokes equations for high speed compressible flow, the energy equation, and the quasi-static equilibrium equations for the leading edge are solved using a single finite element approach in one integrated, vectorized computer program called LIFTS. The fluid-thermal-structural coupling is studied for Mach 6.47 flow over a 3-in diam cylinder for which the flow behavior and the aerothermal loads are calibrated by experimental data. Issues of the thermal-structural response are studied for hydrogen-cooled, super thermal conducting leading edges subjected to intense aerodynamic heating.

  17. Emissivity corrected infrared method for imaging anomalous structural heat flows

    DOEpatents

    Del Grande, N.K.; Durbin, P.F.; Dolan, K.W.; Perkins, D.E.

    1995-08-22

    A method for detecting flaws in structures using dual band infrared radiation is disclosed. Heat is applied to the structure being evaluated. The structure is scanned for two different wavelengths and data obtained in the form of images. Images are used to remove clutter to form a corrected image. The existence and nature of a flaw is determined by investigating a variety of features. 1 fig.

  18. Ground Based Studies of Thermocapillary Flows in Levitated Drops

    NASA Technical Reports Server (NTRS)

    Sadhal, Satwindar Singh; Trinh, Eugene H.

    1996-01-01

    Ground-based experiments together with analytical studies are presently being conducted for levitated drops. Both acoustic and electrostatic techniques are being employed to achieve levitation of drops in a gaseous environment. The scientific effort is principally on the thermal and the fluid phenomena associated with the local heating of levitated drops, both at 1-g and at low-g. In particular, the thermocapillary flow associated with local spot heating is being studied. Fairly stable acoustic levitation of drops has been achieved with some exceptions when random rotational motion of the drop persists. The flow visualization has been carried out by light scattering from smoke particles for the exterior flow and fluorescent tracer particles in the drop. The results indicate a lack of axial symmetry in the internal flow even though the apparatus and the heating are symmetric. The theoretical studies for the past year have included fundamental analyses of acoustically levitated spherical drops. The flow associated with a particle near the velocity antinode is being investigated by the singular perturbation technique. As a first step towards understanding the effect of the particle displacement from the antinode, the flow field about the node has been calculated for the first time. The effect of the acoustic field on the interior of a liquid drop has also been investigated. The results predict that the internal flow field is very weak.

  19. Flow Structures and Energy Capture from an Oscillating Hydrofoil

    NASA Astrophysics Data System (ADS)

    Franck, Jennifer; Frank, Sarah; Mandre, Shreyas

    2013-11-01

    The flow surrounding an oscillating hydrofoil in a uniform freestream is computationally investigated for hydrokinetic energy capture. Simulations are performed on an elliptical hydrofoil using 2D Direct Numerical Simulation (DNS) for low Reynolds number and 3D Large-Eddy Simulations (LES) for high Reynolds number simulations at 80,000. A non-inertial reference frame is utilized for rigid-body motion of the hydrofoil, which is prescribed a sinusoidal motion in pitch and heave. The kinematic parameters are varied and the resulting flow features are correlated with positive or negative energy capture. In an effort to optimize the stroke, variations in the sinusoidal heave and pitch signals are systematically explored and analyzed for future closed-loop control.

  20. Analytical study of flow phenomena in SSME turnaround duct geometries

    NASA Astrophysics Data System (ADS)

    McLallin, K. L.

    1985-04-01

    The SSME fuel turbopump hot gas manifold was identified as a source of loss and flow distortion which significantly affects the performance and durability of both the drive turbine and the LOX injector area of the main combustion chamber. Two current SSME geometries were studied, the full power level (FPL) and the first manned orbital flight (FMOF) configuration. The effects of turnaround duct geometry on flow losses and distortions, by varying wall curvature and flow area variation in the 180 deg turnaround region were examined. The effects of the duct inlet flow phenomena such as the radial distortion of the inlet flow and inlet swirl level on turnaround duct performance were also investigated. It is shown that of the two current geometries, the FMOF configuration had lower pressure losses and generated less flow distortion, but had a small flow separation bubble at the 180 deg turnaround exit. It is found that by optimizing wall curvature and flow diffusion in the turnaround, improved duct performance can be achieved.

  1. Theoretical study on the constricted flow phenomena in arteries

    NASA Astrophysics Data System (ADS)

    Sen, S.; Chakravarty, S.

    2012-12-01

    The present study is dealt with the constricted flow characteristics of blood in arteries by making use of an appropriate mathematical model. The constricted artery experiences the generated wall shear stress due to flow disturbances in the presence of constriction. The disturbed flow in the stenosed arterial segment causes malfunction of the cardiovascular system leading to serious health problems in the form of heart attack and stroke. The flowing blood contained in the stenosed artery is considered to be non-Newtonian while the flow is treated to be two-dimensional. The present pursuit also accounts for the motion of the arterial wall and its effect on local fluid mechanics. The flow analysis applies the time-dependent, two-dimensional incompressible nonlinear Navier-Stokes equations for non-Newtonian fluid representing blood. An extensive quantitative analysis presented at the end of the paper based on large scale numerical computations of the quantities of major physiological significance enables one to estimate the constricted flow characteristics in the arterial system under consideration which deviates significantly from that of normal physiological flow conditions.

  2. Gene flow and population structure of a solitary top carnivore in a human-dominated landscape.

    PubMed

    McManus, Jeannine S; Dalton, Desiré L; Kotzé, Antoinette; Smuts, Bool; Dickman, Amy; Marshal, Jason P; Keith, Mark

    2015-01-01

    While African leopard populations are considered to be continuous as demonstrated by their high genetic variation, the southernmost leopard population exists in the Eastern and Western Cape, South Africa, where anthropogenic activities may be affecting this population's structure. Little is known about the elusive, last free-roaming top predator in the region and this study is the first to report on leopard population structuring using nuclear DNA. By analyzing 14 microsatellite markers from 40 leopard tissue samples, we aimed to understand the populations' structure, genetic distance, and gene flow (Nm). Our results, based on spatially explicit analysis with Bayesian methods, indicate that leopards in the region exist in a fragmented population structure with lower than expected genetic diversity. Three population groups were identified, between which low to moderate levels of gene flow were observed (Nm 0.5 to 3.6). One subpopulation exhibited low genetic differentiation, suggesting a continuous population structure, while the remaining two appear to be less connected, with low emigration and immigration between these populations. Therefore, genetic barriers are present between the subpopulations, and while leopards in the study region may function as a metapopulation, anthropogenic activities threaten to decrease habitat and movement further. Our results indicate that the leopard population may become isolated within a few generations and suggest that management actions should aim to increase habitat connectivity and reduce human-carnivore conflict. Understanding genetic diversity and connectivity of populations has important conservation implications that can highlight management of priority populations to reverse the effects of human-caused extinctions.

  3. Gene flow and population structure of a solitary top carnivore in a human-dominated landscape

    PubMed Central

    McManus, Jeannine S; Dalton, Desiré L; Kotzé, Antoinette; Smuts, Bool; Dickman, Amy; Marshal, Jason P; Keith, Mark

    2015-01-01

    While African leopard populations are considered to be continuous as demonstrated by their high genetic variation, the southernmost leopard population exists in the Eastern and Western Cape, South Africa, where anthropogenic activities may be affecting this population's structure. Little is known about the elusive, last free-roaming top predator in the region and this study is the first to report on leopard population structuring using nuclear DNA. By analyzing 14 microsatellite markers from 40 leopard tissue samples, we aimed to understand the populations' structure, genetic distance, and gene flow (Nm). Our results, based on spatially explicit analysis with Bayesian methods, indicate that leopards in the region exist in a fragmented population structure with lower than expected genetic diversity. Three population groups were identified, between which low to moderate levels of gene flow were observed (Nm 0.5 to 3.6). One subpopulation exhibited low genetic differentiation, suggesting a continuous population structure, while the remaining two appear to be less connected, with low emigration and immigration between these populations. Therefore, genetic barriers are present between the subpopulations, and while leopards in the study region may function as a metapopulation, anthropogenic activities threaten to decrease habitat and movement further. Our results indicate that the leopard population may become isolated within a few generations and suggest that management actions should aim to increase habitat connectivity and reduce human–carnivore conflict. Understanding genetic diversity and connectivity of populations has important conservation implications that can highlight management of priority populations to reverse the effects of human-caused extinctions. PMID:25691961

  4. Gene flow and population structure of a solitary top carnivore in a human-dominated landscape.

    PubMed

    McManus, Jeannine S; Dalton, Desiré L; Kotzé, Antoinette; Smuts, Bool; Dickman, Amy; Marshal, Jason P; Keith, Mark

    2015-01-01

    While African leopard populations are considered to be continuous as demonstrated by their high genetic variation, the southernmost leopard population exists in the Eastern and Western Cape, South Africa, where anthropogenic activities may be affecting this population's structure. Little is known about the elusive, last free-roaming top predator in the region and this study is the first to report on leopard population structuring using nuclear DNA. By analyzing 14 microsatellite markers from 40 leopard tissue samples, we aimed to understand the populations' structure, genetic distance, and gene flow (Nm). Our results, based on spatially explicit analysis with Bayesian methods, indicate that leopards in the region exist in a fragmented population structure with lower than expected genetic diversity. Three population groups were identified, between which low to moderate levels of gene flow were observed (Nm 0.5 to 3.6). One subpopulation exhibited low genetic differentiation, suggesting a continuous population structure, while the remaining two appear to be less connected, with low emigration and immigration between these populations. Therefore, genetic barriers are present between the subpopulations, and while leopards in the study region may function as a metapopulation, anthropogenic activities threaten to decrease habitat and movement further. Our results indicate that the leopard population may become isolated within a few generations and suggest that management actions should aim to increase habitat connectivity and reduce human-carnivore conflict. Understanding genetic diversity and connectivity of populations has important conservation implications that can highlight management of priority populations to reverse the effects of human-caused extinctions. PMID:25691961

  5. 3D Structures: Microfluidic Stamping on Sheath Flow (Small 24/2016).

    PubMed

    Yoon, Dong Hyun; Tanaka, Daiki; Sekiguchi, Tetsushi; Shoji, Shuichi

    2016-06-01

    A microfluidic stamping method to form functional shapes on a cross section in fibre-shaped flow is presented by D. H. Yoon and co-workers on page 3224. Microfluidic stamping and overstamping allowed various cross sectional shapes on the three-dimensional flow. Dimension of the flows is controlled via a change in combination of 3D structures and fluidic conditions, which correspond to stamp type and stamping force. PMID:27306739

  6. Large-scale flows and coherent structure phenomena in flute turbulence

    SciTech Connect

    Sandberg, I.; Andrushchenko, Zh.N.; Pavlenko, V.P.

    2005-04-15

    The properties of zonal and streamer flows in the flute mode turbulence are investigated. The stability criteria and the frequency of these flows are determined in terms of the spectra of turbulent fluctuations. Furthermore, it is shown that zonal flows can undergo a further nonlinear evolution leading to the formation of long-lived coherent structures which consist of self-bound wave packets supporting stationary shear layers, and thus can be characterized as regions with a reduced level of anomalous transport.

  7. Improved Flow-Field Structures for Direct Methanol Fuel Cells

    SciTech Connect

    Gurau, Bogdan

    2013-05-31

    The direct methanol fuel cell (DMFC) is ideal if high energy-density liquid fuels are required. Liquid fuels have advantages over compressed hydrogen including higher energy density and ease of handling. Although state-of-the-art DMFCs exhibit manageable degradation rates, excessive fuel crossover diminishes system energy and power density. Although use of dilute methanol mitigates crossover, the concomitant lowering of the gross fuel energy density (GFED) demands a complex balance-of-plant (BOP) that includes higher flow rates, external exhaust recirculation, etc. An alternative approach is redesign of the fuel delivery system to accommodate concentrated methanol. NuVant Systems Inc. (NuVant) will maximize the GFED by design and assembly of a DMFC that uses near neat methanol. The approach is to tune the diffusion of highly concentrated methanol (to the anode catalytic layer) to the back-diffusion of water formed at the cathode (i.e. in situ generation of dilute methanol at the anode layer). Crossover will be minimized without compromising the GFED by innovative integration of the anode flow-field and the diffusion layer. The integrated flow-field-diffusion-layers (IFDLs) will widen the current and potential DMFC operating ranges and enable the use of cathodes optimized for hydrogen-air fuel cells.

  8. Simulated measurement of power flow in structures near to simple sources and simple boundaries

    NASA Technical Reports Server (NTRS)

    Mcgary, Michael C.

    1988-01-01

    Advances in electronics technology along with the advent of low cost multichannel Fast Fourier analyzers have made it practical to use higher order central difference formulas to measure power flow in 1- and 2-D structures. The method discussed uses five point differencing for the spatial derivatives in 1-D and a thirteen point difference pattern for the spatial derivatives in 2-D plates and shells. It is assumed that the measuring transducers are accelerometers. An analytical study of the higher order differencing method and the conventional two accelerometer method was performed as a preliminary to the application of these methods to actual aircraft structures. Some classical problems were analyzed in order to simulate and compare the performance of the two methods under near field measurement conditions. These near field conditions include examples of power flows near simple sources and simple boundaries. The estimates produced by the two methods were compared to the exact solution in each example. Presented are the theory and selected results of the study, which indicate that the bias errors of the two accelerometer method under near field measurement conditions may be much larger than previous studies have suggested.

  9. Experiments on the multi-roll-structure of thermocapillary flow in side-heated thin liquid layers

    NASA Astrophysics Data System (ADS)

    Schwabe, D.; Cramer, A.; Schneider, J.; Benz, S.; Metzger, J.

    1999-01-01

    The multi-roll-structure (MRS) with convection rolls, all with the same sense of rotation and axes perpendicular to the applied temperature gradient appears in thin layers driven by thermocapillarity prior to time dependent states. Detailed experimental and numerical results are reported. The MRS in large Prandtl-number fluids is dominated by thermocapillarity and separates from the buoyancy driven bulk flow for deep layers. We prepare a microgravity experiment MAGIA to study thermocapillary flow structures without coupling to buoyancy in a 20.0 mm wide annular layer with free surface of variable depth heated by the outer wall and cooled at the inside.

  10. High-speed holocinematographic velocimeter for studying turbulent flow control physics

    NASA Technical Reports Server (NTRS)

    Weinstein, L. M.; Beeler, G. B.; Lindemann, A. M.

    1985-01-01

    Use of a dual view, high speed, holographic movie technique is examined for studying turbulent flow control physics. This approach, which eliminates some of the limitations of previous holographic techniques, is termed a holocinematographic velocimeter (HCV). The data from this system can be used to check theoretical turbulence modeling and numerical simulations, visualize and measure coherent structures in 'non-simple' turbulent flows, and examine the mechanisms operative in various turbulent control/drag reduction concepts. This system shows promise for giving the most complete experimental characterization of turbulent flows yet available.

  11. A novel planar flow cell for studies of biofilm heterogeneity and flow-biofilm interactions

    PubMed Central

    Zhang, Wei; Sileika, Tadas S.; Chen, Cheng; Liu, Yang; Lee, Jisun; Packman, Aaron I.

    2012-01-01

    Biofilms are microbial communities growing on surfaces, and are ubiquitous in nature, in bioreactors, and in human infection. Coupling between physical, chemical, and biological processes is known to regulate the development of biofilms; however, current experimental systems do not provide sufficient control of environmental conditions to enable detailed investigations of these complex interactions. We developed a novel planar flow cell that supports biofilm growth under complex two-dimensional fluid flow conditions. This device provides precise control of flow conditions and can be used to create well-defined physical and chemical gradients that significantly affect biofilm heterogeneity. Moreover, the top and bottom of the flow chamber are transparent, so biofilm growth and flow conditions are fully observable using non-invasive confocal microscopy and high-resolution video imaging. To demonstrate the capability of the device, we observed the growth of Pseudomonas aeruginosa biofilms under imposed flow gradients. We found a positive relationship between patterns of fluid velocity and biofilm biomass because of faster microbial growth under conditions of greater local nutrient influx, but this relationship eventually reversed because high hydrodynamic shear leads to the detachment of cells from the surface. These results reveal that flow gradients play a critical role in the development of biofilm communities. By providing new capability for observing biofilm growth, solute and particle transport, and net chemical transformations under user-specified environmental gradients, this new planar flow cell system has broad utility for studies of environmental biotechnology and basic biofilm microbiology, as well as applications in bioreactor design, environmental engineering, biogeochemistry, geomicrobiology, and biomedical research. PMID:21656713

  12. μPIV methodology using model systems for flow studies in heterogeneous biopolymer gel microstructures.

    PubMed

    Sott, Kristin; Gebäck, Tobias; Pihl, Maria; Lorén, Niklas; Hermansson, Anne-Marie; Heintz, Alexei; Rasmuson, Anders

    2013-05-15

    A methodology for studying flow in heterogeneous soft microstructures has been developed. The methodology includes: (1) model fractal or random heterogeneous microstructures fabricated in PDMS and characterised using CLSM; (2) μPIV measurements; (3) Lattice-Boltzmann simulations of flow. It has been found that the flow behaviour in these model materials is highly dependent on pore size as well as on the connectivity and occurrence of dead ends. The experimental flow results show good agreement with predictions from the Lattice-Boltzmann modelling. These simulations were performed in geometries constructed from 3D CLSM images of the actual PDMS structures. Given these results, mass transport behaviour may be predicted for even more complex structures, like gels or composite material in, e.g., food or biomaterials. This is a step in the direction towards predictive science with regards to tailoring soft biomaterials for specific mass transport properties. PMID:23489610

  13. Study of Near-Stall Flow Behavior in a Modern Transonic Fan with Composite Sweep

    NASA Technical Reports Server (NTRS)

    Hah, Chunill; Shin, Hyoun-Woo

    2011-01-01

    Detailed flow behavior in a modern transonic fan with a composite sweep is investigated in this paper. Both unsteady Reynolds-averaged Navier-Stokes (URANS) and Large Eddy Simulation (LES) methods are applied to investigate the flow field over a wide operating range. The calculated flow fields are compared with the data from an array of high-frequency response pressure transducers embedded in the fan casing. The current study shows that a relatively fine computational grid is required to resolve the flow field adequately and to calculate the pressure rise across the fan correctly. The calculated flow field shows detailed flow structure near the fan rotor tip region. Due to the introduction of composite sweep toward the rotor tip, the flow structure at the rotor tip is much more stable compared to that of the conventional blade design. The passage shock stays very close to the leading edge at the rotor tip even at the throttle limit. On the other hand, the passage shock becomes stronger and detaches earlier from the blade passage at the radius where the blade sweep is in the opposite direction. The interaction between the tip clearance vortex and the passage shock becomes intense as the fan operates toward the stall limit, and tip clearance vortex breakdown occurs at near-stall operation. URANS calculates the time-averaged flow field fairly well. Details of measured RMS static pressure are not calculated with sufficient accuracy with URANS. On the other hand, LES calculates details of the measured unsteady flow features in the current transonic fan with composite sweep fairly well and reveals the flow mechanism behind the measured unsteady flow field.

  14. Numerical studies on the performance of a flow distributor in tank

    SciTech Connect

    Shin, Soo Jai Kim, Young In; Ryu, Seungyeob; Bae, Youngmin; Kim, Keung Koo

    2015-03-10

    Flow distributors are generally observed in several nuclear power plants. During core make-up tank (CMT) injection into the reactor, the condensation and thermal stratification are observed in the CMT, and rapid condensation disturbs the injection operation. To reduce the condensation phenomena in the tank, CMT was equipped with a flow distributor. The optimal design of the flow distributor is very important to ensure the structural integrity the CMT and its safe operation during certain transient or accident conditions. In the present study, we numerically investigated the performance of a flow distributor in tank with different shape factors such as the total number of holes, pitch-to-hole diameter ratios, diameter of the hole, and the area ratios. These data will contribute to a design of the flow distributor.

  15. Nuclear mgnetic resonance study of granular flows. Final report

    SciTech Connect

    1995-03-01

    We have demonstrated the efficacy of NMRI to granular flow studies of objects that yield NMR signals (seeds, pharmaceutical pills) in confined spaces (rotating cylinders, shaking boxes). Excellent results for velocity and concentration of flowing and colliding particles have been obtained non-invasively. We studied flows in geometries that are otherwise impossible to study because of the optical opacity of the materials. In addition, we obtained data for diffusion and collisional losses which must be related to granular temperature. We also measured the global collisional and frictional energy loss for a rotating cylinder containing granular material and compared it to that obtained from the NMRI velocity and acceleration data. We used the same NMR technique to study the interplay between radial and axial segregation of heterogeneous particles in a partially filled rotating cylinder. We also measured flow and diffusion of vibrating particles in the NMRI apparatus to ascertain that such experiments are, indeed, possible. Some theoretical studies were initiated to explain some of the velocity profiles and free surface shapes of rotating drum flow. A direct numerical simulation of the drum flow successfully predicted a number of features, including velocity, concentration, and dissipation profiles in rotating cylinders.

  16. Extension of vibrational power flow techniques to two-dimensional structures

    NASA Technical Reports Server (NTRS)

    Cuschieri, J. M.

    1987-01-01

    In the analysis of the vibration response and structure-borne vibration transmission between elements of a complex structure, statistical energy analysis (SEA) or Finite Element Analysis (FEA) are generally used. However, an alternative method is using vibrational power flow techniques which can be especially useful in the mid- frequencies between the optimum frequency regimes for FEA and SEA. Power flow analysis has in general been used on one-dimensional beam-like structures or between structures with point joints. In this paper, the power flow technique is extended to two-dimensional plate like structures joined along a common edge without frequency or spatial averaging the results, such that the resonant response of the structure is determined. The power flow results are compared to results obtained using FEA at low frequencies and SEA at high frequencies. The agreement with FEA results is good but the power flow technique has an improved computational efficiency. Compared to the SEA results the power flow results show a closer representation of the actual response of the structure.

  17. Extension of vibrational power flow techniques to two-dimensional structures

    NASA Technical Reports Server (NTRS)

    Cuschieri, Joseph M.

    1988-01-01

    In the analysis of the vibration response and structure-borne vibration transmission between elements of a complex structure, statistical energy analysis (SEA) or finite element analysis (FEA) are generally used. However, an alternative method is using vibrational power flow techniques which can be especially useful in the mid frequencies between the optimum frequency regimes for SEA and FEA. Power flow analysis has in general been used on 1-D beam-like structures or between structures with point joints. In this paper, the power flow technique is extended to 2-D plate-like structures joined along a common edge without frequency or spatial averaging the results, such that the resonant response of the structure is determined. The power flow results are compared to results obtained using FEA results at low frequencies and SEA at high frequencies. The agreement with FEA results is good but the power flow technique has an improved computational efficiency. Compared to the SEA results the power flow results show a closer representation of the actual response of the structure.

  18. Computational Studies of Flame Structures

    NASA Astrophysics Data System (ADS)

    Amin, Vaishali

    This thesis is concerned with computational studies of laminar flame structures using detailed and skeletal chemical kinetic mechanisms. Elementary reactions in these mechanisms control the observable combustion properties such as flame speed, autoignition temperature, ignition delay time, and extinction characteristics in nonpremixed and premixed flame phenomena. First part of thesis deals with computational investigations of influence of carbon monoxide and hydrogen addition on methane flames stabilized in counterflow configuration. Computations were performed employing detailed chemical kinetic mechanism---the San Diego mechanism. In case of nonpremixed flames, effect of carbon xvi monoxide addition on structure and critical condition of extinction were examined. Differences between addition on fuel and oxidizer sides were investigated and plausible explanation given for the differences. For premixed flames, effect of addition of hydrogen and carbon monoxide to reactant mixture was studied. Critical conditions of extinction were predicted using computations for various compositions. Rates of production and consumption of various species were calculated and flame structure was analyzed for nonpremixed and premixed flames. It was found that moderate amount of carbon monoxide addition to methane enhances flame reactivity. However, with large amount of carbon monoxide addition, additive chemistry dominates. Addition of increasing amounts of hydrogen in premixed reactant stream enhances methane flame reactivity. In second part of thesis, kinetic modeling was performed to elucidate the structure and mechanism of extinction and autoignition of nonpremixed toluene flames in counterflow configuration. Computations were performed using detailed chemistry to determine flame structure and to obtain values for critical conditions of extinction and autoignition. Sensitivity analysis of rate parameters, reaction pathway analysis, and spatial reaction rate profiles were used to

  19. Anthraquinone with tailored structure for a nonaqueous metal-organic redox flow battery.

    PubMed

    Wang, Wei; Xu, Wu; Cosimbescu, Lelia; Choi, Daiwon; Li, Liyu; Yang, Zhenguo

    2012-07-01

    A nonaqueous, hybrid metal-organic redox flow battery based on tailored anthraquinone structure is demonstrated to have an energy efficiency of ~82% and a specific discharge energy density similar to those of aqueous redox flow batteries, which is due to the significantly improved solubility of anthraquinone in supporting electrolytes. PMID:22641051

  20. Anthraquinone with tailored structure for a nonaqueous metal-organic redox flow battery.

    PubMed

    Wang, Wei; Xu, Wu; Cosimbescu, Lelia; Choi, Daiwon; Li, Liyu; Yang, Zhenguo

    2012-07-01

    A nonaqueous, hybrid metal-organic redox flow battery based on tailored anthraquinone structure is demonstrated to have an energy efficiency of ~82% and a specific discharge energy density similar to those of aqueous redox flow batteries, which is due to the significantly improved solubility of anthraquinone in supporting electrolytes.

  1. Anthraquinone with Tailored Structure for Nonaqueous Metal-Organic Redox Flow Battery

    SciTech Connect

    Wang, Wei; Xu, Wu; Cosimbescu, Lelia; Choi, Daiwon; Li, Liyu; Yang, Zhenguo

    2012-06-08

    A nonaqueous, hybrid metal-organic redox flow battery based on tailored anthraquinone structure is demonstrated to have an energy efficiency of {approx}82% and a specific discharge energy density similar to aqueous redox flow batteries, which is due to the significantly improved solubility of anthraquinone in supporting electrolytes.

  2. A class of unsteady, three-dimensional flow structures in turbulent boundary layers

    NASA Technical Reports Server (NTRS)

    Ash, R. L.

    1981-01-01

    A restricted class of mathematically admissible, unsteady, three dimensional flows was identified which may constitute part of the structure observed in turbulent boundary layers. The development of the model and some general results are discussed. The resulting solution has characteristics which suggest how upwelling low speed flow can trigger a downward jetting of irrotational high speed fluid into the boundary layer.

  3. Flow Liner Slot Edge Replication Feasibility Study

    NASA Technical Reports Server (NTRS)

    Newman, John A.; Willard, Scott A.; Smith, Stephen W.; Piascik, Robert S.

    2006-01-01

    Surface replication has been proposed as a method for crack detection in space shuttle main engine flowliner slots. The results of a feasibility study show that examination of surface replicas with a scanning electron microscope can result in the detection of cracks as small as 0.005 inch, and surface flaws as small as 0.001 inch, for the flowliner material.

  4. Mean Flow and Turbulence Structure in Ice-Covered Channels: Laboratory Experiments and Preliminary Field Observations

    NASA Astrophysics Data System (ADS)

    Robert, A.; Tran, T.

    2009-12-01

    Northern rivers experience freeze-up over the winter, creating asymmetric under-ice flows. Field measurements were conducted along an ice-covered, gravel-bed river in order to investigate average downstream velocity profile characteristics and the spatial variability of under-ice average flow conditions (itself attributed to the areal distribution of sediment and the heterogeneous nature of ice cover roughness). At the reach scale, measured under-ice flows typically exhibit flow asymmetry and its characteristics depend on the presence of roughness elements on the ice cover underside. River flows were subsequently modeled in the flume laboratory based on an average Froude number derived from field data. Extensive experiments were performed for shallower and deeper flows with a simulated ice cover of varying roughness and a gravel bed. Detailed profile measurements of the root-mean square components of turbulence intensity, Reynolds stresses and turbulent kinetic energy indicate that the turbulence structure is strongly influenced by the presence of an ice cover and its roughness characteristics. A central region of faster flow can develop with the addition of a rough cover at the height where average velocity is routinely sampled. For the case of deeper flows, streamwise and vertical turbulence intensities generally increase in the near-bed and outer flow regions when a cover is added. For deeper flows, Reynolds stresses also increase with addition of a cover and its roughening. Spatially-averaged profiles also suggest that flow depth significantly affects the turbulent flow structure of covered flows with similar low Froude numbers. Bed roughness elements appear to exert the greatest influence on near-bed flow distribution. Laboratory experiments also suggest that the addition of a cover - and its roughening - does not significantly alter estimates of near-bed velocity gradients. These results are discussed in the context of the impact of a warming climate on

  5. Expandable and retractable self-rolled structures based on metal/polymer thin film for flow sensing

    NASA Astrophysics Data System (ADS)

    Zhu, Jianzhong; White, Carl; Saadat, Mehdi; Bart-Smith, Hilary

    2015-11-01

    Most aquatic animals such as fish rely heavily on their ability of detect and respond to ambient flows in order to explore and inhabit various habitats or survive predator-prey encounters. Fish utilize neuromasts in their skin surface and lateral lines in their bodies to align themselves while swimming upstream for migration, avoid obstacles, reduce locomotion cost, and detect flow variations caused by potential predators. In this study, a thin film MEMS sensor analogous to a fish neuromast has been designed for flow sensing. Residual stress arises in many thin film materials during processing. Metal and polymer thin film materials with a significant difference in elastic modular were chosen to form a multiple-layer structure. Upon releasing, the structure rolls into a tube due to mechanical property mismatch. The self-rolled tube can expand or retract, depending on the existence of external force such as flow. An embedded strain sensor detects the deformation of the tube and hence senses the ambient flow. Numerical simulations were conducted to optimize the structural design. Experiments were performed in a flow tank to quantify the performance of the sensor. This research is supported by the Office of Naval Research under the MURI Grant N00014-14-1-0533.

  6. An investigation of dentinal fluid flow in dental pulp during food mastication: simulation of fluid-structure interaction.

    PubMed

    Su, Kuo-Chih; Chuang, Shu-Fen; Ng, Eddie Yin-Kwee; Chang, Chih-Han

    2014-06-01

    This study uses fluid-structure interaction (FSI) simulation to investigate the relationship between the dentinal fluid flow in the dental pulp of a tooth and the elastic modulus of masticated food particles and to investigate the effects of chewing rate on fluid flow in the dental pulp. Three-dimensional simulation models of a premolar tooth (enamel, dentine, pulp, periodontal ligament, cortical bone, and cancellous bone) and food particle were created. Food particles with elastic modulus of 2,000 and 10,000 MPa were used, respectively. The external displacement loading (5 μm) was gradually directed to the food particle surface for 1 and 0.1 s, respectively, to simulate the chewing of food particles. The displacement and stress on tooth structure and fluid flow in the dental pulp were selected as evaluation indices. The results show that masticating food with a high elastic modulus results in high stress and deformation in the tooth structure, causing faster dentinal fluid flow in the pulp in comparison with that obtained with soft food. In addition, fast chewing of hard food particles can induce faster fluid flow in the pulp, which may result in dental pain. FSI analysis is shown to be a useful tool for investigating dental biomechanics during food mastication. FSI simulation can be used to predict intrapulpal fluid flow in dental pulp; this information may provide the clinician with important concept in dental biomechanics during food mastication.

  7. The effects of flow on schooling Devario aequipinnatus: school structure, startle response and information transmission

    PubMed Central

    Chicoli, A.; Butail, S.; Lun, Y.; Bak-Coleman, J.; Coombs, S.; Paley, D.A.

    2014-01-01

    To assess how flow affects school structure and threat detection, startle response rates of solitary and small groups of giant danio Devario aequipinnatus were compared to visual looming stimuli in flow and no-flow conditions. The instantaneous position and heading of each D. aequipinnatus were extracted from high-speed videos. Behavioural results indicate that (1) school structure is altered in flow such that D. aequipinnatus orient upstream while spanning out in a crosswise direction, (2) the probability of at least one D. aequipinnatus detecting the visual looming stimulus is higher in flow than no flow for both solitary D. aequipinnatus and groups of eight D. aequipinnatus, however, (3) the probability of three or more individuals responding is higher in no flow than flow. Taken together, these results indicate a higher probability of stimulus detection in flow but a higher probability of internal transmission of information in no flow. Finally, results were well predicted by a computational model of collective fright response that included the probability of direct detection (based on signal detection theory) and indirect detection (i.e. via interactions between group members) of threatening stimuli. This model provides a new theoretical framework for analysing the collective transfer of information among groups of fishes and other organisms. PMID:24773538

  8. Three-dimensional flow structure and patterns of bed shear stress in an evolving compound meander bend

    USGS Publications Warehouse

    Engel, Frank; Rhoads, Bruce L.

    2016-01-01

    Compound meander bends with multiple lobes of maximum curvature are common in actively evolving lowland rivers. Interaction among spatial patterns of mean flow, turbulence, bed morphology, bank failures and channel migration in compound bends is poorly understood. In this paper, acoustic Doppler current profiler (ADCP) measurements of the three-dimensional (3D) flow velocities in a compound bend are examined to evaluate the influence of channel curvature and hydrologic variability on the structure of flow within the bend. Flow structure at various flow stages is related to changes in bed morphology over the study timeframe. Increases in local curvature within the upstream lobe of the bend reduce outer bank velocities at morphologically significant flows, creating a region that protects the bank from high momentum flow and high bed shear stresses. The dimensionless radius of curvature in the upstream lobe is one-third less than that of the downstream lobe, with average bank erosion rates less than half of the erosion rates for the downstream lobe. Higher bank erosion rates within the downstream lobe correspond to the shift in a core of high velocity and bed shear stresses toward the outer bank as flow moves through the two lobes. These erosion patterns provide a mechanism for continued migration of the downstream lobe in the near future. Bed material size distributions within the bend correspond to spatial patterns of bed shear stress magnitudes, indicating that bed material sorting within the bend is governed by bed shear stress. Results suggest that patterns of flow, sediment entrainment, and planform evolution in compound meander bends are more complex than in simple meander bends. Moreover, interactions among local influences on the flow, such as woody debris, local topographic steering, and locally high curvature, tend to cause compound bends to evolve toward increasing planform complexity over time rather than stable configurations.

  9. Experimental measurement of structural power flow on an aircraft fuselage

    NASA Technical Reports Server (NTRS)

    Cuschieri, J. M.

    1991-01-01

    An experimental technique is used to measure structural intensity through an aircraft fuselage with an excitation load applied near one of the wing attachment locations. The fuselage is a relatively large structure, requiring a large number of measurement locations to analyze the whole of the structure. For the measurement of structural intensity, multiple point measurements are necessary at every location of interest. A tradeoff is therefore required between the number of measurement transducers, the mounting of these transducers, and the accuracy of the measurements. Using four transducers mounted on a bakelite platform, structural intensity vectors are measured at locations distributed throughout the fuselage. To minimize the errors associated with using the four transducer technique, the measurement locations are selected to be away from bulkheads and stiffeners. Furthermore, to eliminate phase errors between the four transducer measurements, two sets of data are collected for each position, with the orientation of the platform with the four transducers rotated by 180 degrees and an average taken between the two sets of data. The results of these measurements together with a discussion of the suitability of the approach for measuring structural intensity on a real structure are presented.

  10. Orbital transfer vehicle launch operations study. Processing flows. Volume 3

    NASA Technical Reports Server (NTRS)

    1986-01-01

    The Orbit Transfer Vehicle (OTV) processing flow and Resource Identification Sheets (RISs) for the ground based orbit transfer vehicle and for the space based orbit transfer vehicle are the primary source of information for the rest of the Kennedy Space Center (KSC) OTV Launch Operations Study. Work is presented which identifies KSC facility requirements for the OTV Program, simplifies or automates either flow though the application technology, revises test practices and identifies crew sizes or skills used. These flows were used as the primary point of departure from current operations and practices. Analyses results were documented by revising the appropriate RIS page.

  11. A study of vapor-liquid flow in porous media

    SciTech Connect

    Satik, Cengiz; Yortsos, Yanis C.

    1994-01-20

    We study the heat transfer-driven liquid-to-vapor phase change in single-component systems in porous media by using pore network models and flow visualization experiments. Experiments using glass micromodels were conducted. The flow visualization allowed us to define the rules for the numerical pore network model. A numerical pore network model is developed for vapor-liquid displacement where fluid flow, heat transfer and capillarity are included at the pore level. We examine the growth process at two different boundary conditions.

  12. Concentrated Flow through a Riparian Buffer: A Case Study

    NASA Astrophysics Data System (ADS)

    Young, C. B.; Nogues, J. P.; Hutchinson, S. L.

    2004-05-01

    Riparian buffers are often used for in-situ treatment of agricultural runoff. Although the benefits of riparian buffers are well recongized, concentration of flow can restrict the efficiency of contaminant removal. This study evaluates flow concentration at a agricultural site near Manhattan, Kansas. Manual and automated GIS analyses of a high-resolution digital elevation model were used to determine the fraction of runoff contributing to each buffer segment. Subsequent simulation of the system in WEPP (Water Erosion and Prediction Project) demonstrates the extend to which flow concentration affects buffer efficiency.

  13. Concentrated Flow through a Riparian Buffer: A Case Study

    NASA Astrophysics Data System (ADS)

    Young, C. B.; Nog