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Sample records for air flow channel

  1. Simulation of 3-D Nonequilibrium Seeded Air Flow in the NASA-Ames MHD Channel

    NASA Technical Reports Server (NTRS)

    Gupta, Sumeet; Tannehill, John C.; Mehta, Unmeel B.

    2004-01-01

    The 3-D nonequilibrium seeded air flow in the NASA-Ames experimental MHD channel has been numerically simulated. The channel contains a nozzle section, a center section, and an accelerator section where magnetic and electric fields can be imposed on the flow. In recent tests, velocity increases of up to 40% have been achieved in the accelerator section. The flow in the channel is numerically computed us ing a 3-D parabolized Navier-Stokes (PNS) algorithm that has been developed to efficiently compute MHD flows in the low magnetic Reynolds number regime: The MHD effects are modeled by introducing source terms into the PNS equations which can then be solved in a very efficient manner. The algorithm has been extended in the present study to account for nonequilibrium seeded air flows. The electrical conductivity of the flow is determined using the program of Park. The new algorithm has been used to compute two test cases that match the experimental conditions. In both cases, magnetic and electric fields are applied to the seeded flow. The computed results are in good agreement with the experimental data.

  2. Numerical investigation of interfacial mass transport resistance and two-phase flow in PEM fuel cell air channels

    NASA Astrophysics Data System (ADS)

    Koz, Mustafa

    Proton exchange membrane fuel cells (PEMFCs) are efficient and environmentally friendly electrochemical engines. The performance of a PEMFC is adversely affected by oxygen (O2) concentration loss from the air flow channel to the cathode catalyst layer (CL). Oxygen transport resistance at the gas diffusion layer (GDL) and air channel interface is a non-negligible component of the O2 concentration loss. Simplified PEMFC performance models in the available literature incorporate the O2 resistance at the GDL-channel interface as an input parameter. However, this parameter has been taken as a constant so far in the available literature and does not reflect variable PEMFC operating conditions and the effect of two-phase flow in the channels. This study numerically calculates the O2 transport resistance at the GDL-air channel interface and expresses this resistance through the non-dimensional Sherwood number (Sh). Local Sh is investigated in an air channel with multiple droplets and films inside. These water features are represented as solid obstructions and only air flow is simulated. Local variations of Sh in the flow direction are obtained as a function of superficial air velocity, water feature size, and uniform spacing between water features. These variations are expressed with mathematical expressions for the PEMFC performance models to utilize and save computational resources. The resulting mathematical correlations for Sh can be utilized in PEMFC performance models. These models can predict cell performance more accurately with the help of the results of this work. Moreover, PEMFC performance models do not need to use a look-up table since the results were expressed through correlations. Performance models can be kept simplified although their predictions will become more realistic. Since two-phase flow in channels is experienced mostly at lower temperatures, performance optimization at low temperatures can be done easier.

  3. The effect of different inlet conditions of air in a rectangular channel on convection heat transfer: Turbulence flow

    SciTech Connect

    Kurtbas, Irfan

    2008-10-15

    Theoretical and empirical correlations for duct flow are given for hydrodynamically and thermally developed flow in most of previous studies. However, this is commonly not a realistic inlet configuration for heat exchanger, in which coolant flow generally turns through a serpentine shaped passage before entering heat sinks. Accordingly, an experimental investigation was carried out to determine average heat transfer coefficients in uniformly heated rectangular channel with 45 and 90 turned flow, and with wall mounted a baffle. The channel was heated through bottom side with the baffle. In present work, a detailed study was conducted for three different height of entry channel (named as the ratio of the height of entry channel to the height of test section (anti H{sub c}=h{sub c}/H)) by varying Reynolds number (Re{sub Dh}). Another variable parameter was the ratio of the baffle height to the channel height (anti H{sub b}=h{sub b}/H). Only one baffle was attached on the bottom (heating) surface. The experimental procedure was validated by comparing the data for the straight channel with no baffle. Reynolds number (Re{sub Dh}) was varied from 2800 to 30,000, so the flow was considered as only turbulent regime. All experiments were conduced with air accordingly; Prandtl number (Pr) was approximately fixed at 0.71. The results showed that average Nusselt number for {theta}=45 and {theta}=90 were 9% and 30% higher, respectively, than that of the straight channel without baffle. Likewise, the pressure drop increased up to 4.4 to 5.3 times compare to the straight channel. (author)

  4. 3-Dimensional numerical study of cooling performance of a heat sink with air-water flow through mini-channel

    NASA Astrophysics Data System (ADS)

    Majumder, Sambit; Majumder, Abhik; Bhaumik, Swapan

    2016-07-01

    The present microelectronics market demands devices with high power dissipation capabilities having enhanced cooling per unit area. The drive for miniaturizing the devices to even micro level dimensions is shooting up the applied heat flux on such devices, resulting in complexity in heat transfer and cooling management. In this paper, a method of CPU processor cooling is introduced where active and passive cooling techniques are incorporated simultaneously. A heat sink consisting of fins is designed, where water flows internally through the mini-channel fins and air flows externally. Three dimensional numerical simulations are performed for large set of Reynolds number in laminar region using finite volume method for both developing flows. The dimensions of mini-channel fins are varied for several aspect ratios such as 1, 1.33, 2 and 4. Constant temperature (T) boundary condition is applied at heat sink base. Channel fluid temperature, pressure drop are analyzed to obtain best cooling option in the present study. It has been observed that as the aspect ratio of the channel decreases Nusselt number decreases while pressure drop increases. However, Nusselt number increases with increase in Reynolds number.

  5. Experimental investigation of water droplet-air flow interaction in a non-reacting PEM fuel cell channel

    NASA Astrophysics Data System (ADS)

    Esposito, Angelo; Montello, Aaron D.; Guezennec, Yann G.; Pianese, Cesare

    It has been well documented that water production in PEM fuel cells occurs in discrete locations, resulting in the formation and growth of discrete droplets on the gas diffusion layer (GDL) surface within the gas flow channels (GFCs). This research uses a simulated fuel cell GFC with three transparent walls in conjunction with a high speed fluorescence photometry system to capture videos of dynamically deforming droplets. Such videos clearly show that the droplets undergo oscillatory deformation patterns. Although many authors have previously investigated the air flow induced droplet detachment, none of them have studied these oscillatory modes. The novelty of this work is to process and analyze the recorded videos to gather information on the droplets induced oscillation. Plots are formulated to indicate the dominant horizontal and vertical deformation frequency components over the range of sizes of droplets from formation to detachment. The system is also used to characterize droplet detachment size at a variety of channel air velocities. A simplified model to explain the droplet oscillation mechanism is provided as well.

  6. Experimental assessment of spanwise-oscillating dielectric electroactive surfaces for turbulent drag reduction in an air channel flow

    NASA Astrophysics Data System (ADS)

    Gatti, Davide; Güttler, Andreas; Frohnapfel, Bettina; Tropea, Cameron

    2015-05-01

    In the present work, wall oscillations for turbulent skin friction drag reduction are realized in an air turbulent duct flow by means of spanwise-oscillating active surfaces based on dielectric electroactive polymers. The actuator system produces spanwise wall velocity oscillations of 820 mm/s semi-amplitude at its resonance frequency of 65 Hz while consuming an active power of a few 100 mW. The actuators achieved a maximum integral drag reduction of 2.4 %. The maximum net power saving, budget of the power benefit and cost of the control, was measured for the first time with wall oscillations. Though negative, the net power saving is order of magnitudes higher than what has been estimated in previous studies. Two new direct numerical simulations of turbulent channel flow show that the finite size of the actuator only partially explains the lower values of integral drag reduction typically achieved in laboratory experiments compared to numerical simulations.

  7. An Experimental Investigation of the Flow of Air in a Flat Broadening Channel

    NASA Technical Reports Server (NTRS)

    Vedernikoff, A. N.

    1944-01-01

    The wide use of diffusers, in various fields of technology, has resulted in several experimental projects to study the action and design of diffusers. Most of the projects dealt with steam (steam turbine nozzles). But diffusers have other applications - that is, ventilators, smoke ducts, air coolers, refrigeration, drying, and so forth. At present there is another application for diffusers in wind-tunnel design. Because of higher requirements and increased power of such installations more attention must be paid to the correctness of work and the decrease in losses due to every section of the tunnel. A diffuser, being one of the component parts of a tunnel , can in the event of faulty construction introduce considerable losses. Therefore, in the design of the new CAHI wind tunnel, it was suggested that an experimental study of diffusers be made, with a view to applying the results to wind tunnels. The experiments conducted by K. K. Baulin in the laboratories of CAHI upon models of diffusers of different cross sections, lengths, and angles of divergence, were a valuable source of experimental data. They were of no help, however, in reaching any conclusion regarding the optimum shape because of the complexity and diversity of the factors which all appeared simultaneously, thereby precluding the.study of the effects of any one factor separately. On the suggestion of the director of the CAHI,Prof. B. N. Ureff, it was decided to experiment on a two-dimensional diffuser model and determine the effect, of the angle of divergence. The author is acquainted with two experimental projects of like nature: the first was conducted with water, the other with air. The first of these works, although containing a wealth of experimental data, does not indicate the nature of flow or its relation to the angle of divergence. The second work is limited to four angles - that is, 12 deg, 24 deg, 45 deg, 90 deg. The study of this diffuser did not supply any information about the effect of

  8. Buoyancy effects in steeply inclined air-water bubbly shear flow in a rectangular channel

    NASA Astrophysics Data System (ADS)

    Sanaullah, K.; Arshad, M.; Khan, A.; Chughtai, I. R.

    2015-07-01

    We report measurements of two-dimensional ( B/ D = 5) fully turbulent and developed duct flows (overall length/depth, L/ D = 60; D-based Reynolds number Re > 104) for inclinations to 30° from vertical at low voidages (< 5 % sectional average) representative of disperse regime using tap water bubbles (4-6 mm) and smaller bubbles (2 mm) stabilised in ionic solution. Pitot and static probe instrumentation, primitive but validated, provided adequate (10 % local value) discrimination of main aspects of the mean velocity and voidage profiles at representative streamwise station i.e L/ D = 40. Our results can be divided into three categories of behaviour. For vertical flow (0°) the evidence is inconclusive as to whether bubbles are preferentially trapped within the wall-layer as found in some, may be most earlier experimental works. Thus, the 4-mm bubbles showed indication of voidage retention but the 2-mm bubbles did not. For nearly vertical flow (5°) there was pronounced profiling of voidage especially with 4-mm bubbles but the transverse transport was not suppressed sufficiently to induce any obvious layering. In this context, we also refer to similarities with previous work on one-phase vertical and nearly vertical mixed convection flows displaying buoyancy inhibited mean shear turbulence. However, with inclined flow (10+ degrees) a distinctively layered pattern was invariably manifested in which voidage confinement increased with increasing inclination. In this paper we address flow behavior at near vertical conditions. Eulerian, mixed and VOF models were used to compute voidage and mean velocity profiles.

  9. A new flooding correlation development and its critical heat flux predictions under low air-water flow conditions in Savannah River Site assembly channels

    SciTech Connect

    Lee, S.Y. )

    1993-10-01

    The upper limit to countercurrent flow, namely, flooding, is important to analyze the reactor coolability during an emergency cooling system (ECS) phase as a result of a large-break loss-of-coolant accident (LOCA) such as a double-ended guillotine break in the Savannah River Site (SRS) reactor system. During normal operation, the reactor coolant system utilizes downward flow through concentric heated tubes with ribs, which subdivided each annular channel into four subchannels. In this paper, a new flooding correlation has been developed based on the analytical models and literature data for adiabatic, steady-state, one-dimensional, air-water flow to predict flooding phenomenon in the SRS reactor assembly channel, which may have a counter-current air-water flow pattern during the ECS phase. In addition, the correlation was benchmarked against the experimental data conducted under the Oak Ridge National Laboratory multislit channel, which is close to the SRS assembly geometry. Furthermore, the correlation has also been used as a constitutive relationship in a new two-component two-phase thermal-hydraulics code FLOWTRAN-TF, which has been developed for a detailed analysis of SRS reactor assembly behavior during LOCA scenarios. Finally, the flooding correlation was applied to the predictions of critical heat flux, and the results were compared with the data taken by the SRS heat transfer laboratory under a single annular channel with ribs and a multiannular prototypic test rig.

  10. Natural Flow Air Cooled Photovoltaics

    NASA Astrophysics Data System (ADS)

    Tanagnostopoulos, Y.; Themelis, P.

    2010-01-01

    Our experimental study aims to investigate the improvement in the electrical performance of a photovoltaic installation on buildings through cooling of the photovoltaic panels with natural air flow. Our experimental study aims to investigate the improvement in the electrical performance of a photovoltaic installation on buildings through cooling of the photovoltaic panels with natural air flow. We performed experiments using a prototype based on three silicon photovoltaic modules placed in series to simulate a typical sloping building roof with photovoltaic installation. In this system the air flows through a channel on the rear side of PV panels. The potential for increasing the heat exchange from the photovoltaic panel to the circulating air by the addition of a thin metal sheet (TMS) in the middle of air channel or metal fins (FIN) along the air duct was examined. The operation of the device was studied with the air duct closed tightly to avoid air circulation (CLOSED) and the air duct open (REF), with the thin metal sheet (TMS) and with metal fins (FIN). In each case the experiments were performed under sunlight and the operating parameters of the experimental device determining the electrical and thermal performance of the system were observed and recorded during a whole day and for several days. We collected the data and form PV panels from the comparative diagrams of the experimental results regarding the temperature of solar cells, the electrical efficiency of the installation, the temperature of the back wall of the air duct and the temperature difference in the entrance and exit of the air duct. The comparative results from the measurements determine the improvement in electrical performance of the photovoltaic cells because of the reduction of their temperature, which is achieved by the naturally circulating air.

  11. FAITH Water Channel Flow Visualization

    NASA Video Gallery

    Water channel flow visualization experiments are performed on a three dimensional model of a small hill. This experiment was part of a series of measurements of the complex fluid flow around the hi...

  12. Time-resolved fast-neutron radiography of air-water two-phase flows in a rectangular channel by an improved detection system

    SciTech Connect

    Zboray, Robert; Dangendorf, Volker; Bromberger, Benjamin; Tittelmeier, Kai; Mor, Ilan

    2015-07-15

    In a previous work, we have demonstrated the feasibility of high-frame-rate, fast-neutron radiography of generic air-water two-phase flows in a 1.5 cm thick, rectangular flow channel. The experiments have been carried out at the high-intensity, white-beam facility of the Physikalisch-Technische Bundesanstalt, Germany, using an multi-frame, time-resolved detector developed for fast neutron resonance radiography. The results were however not fully optimal and therefore we have decided to modify the detector and optimize it for the given application, which is described in the present work. Furthermore, we managed to improve the image post-processing methodology and the noise suppression. Using the tailored detector and the improved post-processing, significant increase in the image quality and an order of magnitude lower exposure times, down to 3.33 ms, have been achieved with minimized motion artifacts. Similar to the previous study, different two-phase flow regimes such as bubbly slug and churn flows have been examined. The enhanced imaging quality enables an improved prediction of two-phase flow parameters like the instantaneous volumetric gas fraction, bubble size, and bubble velocities. Instantaneous velocity fields around the gas enclosures can also be more robustly predicted using optical flow methods as previously.

  13. Time-resolved fast-neutron radiography of air-water two-phase flows in a rectangular channel by an improved detection system

    NASA Astrophysics Data System (ADS)

    Zboray, Robert; Dangendorf, Volker; Mor, Ilan; Bromberger, Benjamin; Tittelmeier, Kai

    2015-07-01

    In a previous work, we have demonstrated the feasibility of high-frame-rate, fast-neutron radiography of generic air-water two-phase flows in a 1.5 cm thick, rectangular flow channel. The experiments have been carried out at the high-intensity, white-beam facility of the Physikalisch-Technische Bundesanstalt, Germany, using an multi-frame, time-resolved detector developed for fast neutron resonance radiography. The results were however not fully optimal and therefore we have decided to modify the detector and optimize it for the given application, which is described in the present work. Furthermore, we managed to improve the image post-processing methodology and the noise suppression. Using the tailored detector and the improved post-processing, significant increase in the image quality and an order of magnitude lower exposure times, down to 3.33 ms, have been achieved with minimized motion artifacts. Similar to the previous study, different two-phase flow regimes such as bubbly slug and churn flows have been examined. The enhanced imaging quality enables an improved prediction of two-phase flow parameters like the instantaneous volumetric gas fraction, bubble size, and bubble velocities. Instantaneous velocity fields around the gas enclosures can also be more robustly predicted using optical flow methods as previously.

  14. Time-resolved fast-neutron radiography of air-water two-phase flows in a rectangular channel by an improved detection system.

    PubMed

    Zboray, Robert; Dangendorf, Volker; Mor, Ilan; Bromberger, Benjamin; Tittelmeier, Kai

    2015-07-01

    In a previous work, we have demonstrated the feasibility of high-frame-rate, fast-neutron radiography of generic air-water two-phase flows in a 1.5 cm thick, rectangular flow channel. The experiments have been carried out at the high-intensity, white-beam facility of the Physikalisch-Technische Bundesanstalt, Germany, using an multi-frame, time-resolved detector developed for fast neutron resonance radiography. The results were however not fully optimal and therefore we have decided to modify the detector and optimize it for the given application, which is described in the present work. Furthermore, we managed to improve the image post-processing methodology and the noise suppression. Using the tailored detector and the improved post-processing, significant increase in the image quality and an order of magnitude lower exposure times, down to 3.33 ms, have been achieved with minimized motion artifacts. Similar to the previous study, different two-phase flow regimes such as bubbly slug and churn flows have been examined. The enhanced imaging quality enables an improved prediction of two-phase flow parameters like the instantaneous volumetric gas fraction, bubble size, and bubble velocities. Instantaneous velocity fields around the gas enclosures can also be more robustly predicted using optical flow methods as previously. PMID:26233413

  15. Mirrored serpentine flow channels for fuel cell

    DOEpatents

    Rock, Jeffrey Allan

    2000-08-08

    A PEM fuel cell having serpentine flow field channels wherein the input/inlet legs of each channel border the input/inlet legs of the next adjacent channels in the same flow field, and the output/exit legs of each channel border the output/exit legs of the next adjacent channels in the same flow field. The serpentine fuel flow channels may be longer, and may contain more medial legs, than the serpentine oxidant flow channels.

  16. Terminal Air Flow Planning

    NASA Technical Reports Server (NTRS)

    Denery, Dallas G.; Erzberger, Heinz; Edwards, Thomas A. (Technical Monitor)

    1998-01-01

    The Center TRACON Automation System (CTAS) will be the basis for air traffic planning and control in the terminal area. The system accepts arriving traffic within an extended terminal area and optimizes the flow based on current traffic and airport conditions. The operational use of CTAS will be presented together with results from current operations.

  17. Oxygen transport resistance at gas diffusion layer - Air channel interface with film flow of water in a proton exchange membrane fuel cell

    NASA Astrophysics Data System (ADS)

    Koz, Mustafa; Kandlikar, Satish G.

    2016-01-01

    Water present as films on the gas diffusion layer-air channel interface in a proton exchange membrane fuel cell (PEMFC) alters the oxygen transport resistance, which is expressed through Sherwood number (Sh). The effect of multiple films along the flow length on Sh is investigated through 3D and stationary simulations. The effects of air Péclet number, non-dimensional film width, length, and spacing are studied. Using the simulation results, non-dimensional correlations are developed for local Sh within a mean absolute percentage error of 9%. These correlations can be used for simulating PEMFC performance over temperature and relative humidity ranges of 20-80 °C and 0-100%, respectively. Sh on the film side can be up to 31% lower than that for a dry channel, while a film may reduce the interfacial width by up to 39%. The corresponding increase in transport resistance results in lowering the voltage by 5 and 8 mV respectively at a current density of 1.5 A cm-2. However, their combined effect leads to a voltage loss of 20 mV due to this additional mass transport resistance. It is therefore important to incorporate the additional resistance introduced by the films while modeling fuel cell performance.

  18. Potential flow through channel constriction.

    USGS Publications Warehouse

    Lee, J.K.

    1984-01-01

    Potential flow through an eccentric, normal constriction of zero thickness in an infinitely long, straight channel of constant width and unit depth is studied by use of a Schwarz-Christoffel transformation. The transformation is integrated by a direct approach. Parametric equations for streamlines are obtained and used to compute an average streamline length for a potential-flow field. -from ASCE Publications Information

  19. Catalytic reaction in confined flow channel

    DOEpatents

    Van Hassel, Bart A.

    2016-03-29

    A chemical reactor comprises a flow channel, a source, and a destination. The flow channel is configured to house at least one catalytic reaction converting at least a portion of a first nanofluid entering the channel into a second nanofluid exiting the channel. The flow channel includes at least one turbulating flow channel element disposed axially along at least a portion of the flow channel. A plurality of catalytic nanoparticles is dispersed in the first nanofluid and configured to catalytically react the at least one first chemical reactant into the at least one second chemical reaction product in the flow channel.

  20. Thermotechnical performance of an air-cooled tuyere with air cooling channels in series

    NASA Astrophysics Data System (ADS)

    Shen, Yuansheng; Zhou, Yuanyuan; Zhu, Tao; Duan, Guangbin

    2016-03-01

    To reduce the cooling air consumption for an air-cooled tuyere, an air-cooled tuyere with air cooling channels in series is developed based on several hypotheses, i.e., a transparent medium in the blast furnace, among others, and the related mathematical models are introduced and developed. Referring to the data from a BF site, the thermotechnical computation for the air-cooled tuyere was performed, and the results show that when the temperature of the inlet cooling air increases, the temperatures for the outlet cooling air, the outer surface of the tuyere, the walls of the air cooling channels and the center channel as well as the heat going into the center channel increase, but the heat absorbed by the cooling air flowing through the air cooling channels decreases. When the cooling air flow rate under the standard state increases, the physical parameters mentioned above change in an opposite directions. Compared to a water-cooled tuyere, the energy savings for an air-cooled tuyere are more than 0.23 kg/min standard coal.

  1. Precipitation patterns during channel flow

    NASA Astrophysics Data System (ADS)

    Jamtveit, B.; Hawkins, C.; Benning, L. G.; Meier, D.; Hammer, O.; Angheluta, L.

    2013-12-01

    Mineral precipitation during channelized fluid flow is widespread in a wide variety of geological systems. It is also a common and costly phenomenon in many industrial processes that involve fluid flow in pipelines. It is often referred to as scale formation and encountered in a large number of industries, including paper production, chemical manufacturing, cement operations, food processing, as well as non-renewable (i.e. oil and gas) and renewable (i.e. geothermal) energy production. We have studied the incipient stages of growth of amorphous silica on steel plates emplaced into the central areas of the ca. 1 meter in diameter sized pipelines used at the hydrothermal power plant at Hellisheidi, Iceland (with a capacity of ca 300 MW electricity and 100 MW hot water). Silica precipitation takes place over a period of ca. 2 months at approximately 120°C and a flow rate around 1 m/s. The growth produces asymmetric ca. 1mm high dendritic structures ';leaning' towards the incoming fluid flow. A novel phase-field model combined with the lattice Boltzmann method is introduced to study how the growth morphologies vary under different hydrodynamic conditions, including non-laminar systems with turbulent mixing. The model accurately predicts the observed morphologies and is directly relevant for understanding the more general problem of precipitation influenced by turbulent mixing during flow in channels with rough walls and even for porous flow. Reference: Hawkins, C., Angheluta, L., Hammer, Ø., and Jamtveit, B., Precipitation dendrites in channel flow. Europhysics Letters, 102, 54001

  2. Continental Lower-crustal Flow: Channel Flow and Laminar Flow

    NASA Astrophysics Data System (ADS)

    LI, Dewei

    Numerous geological, geophysical and geochemical investigations and finite element modeling indicate that crustal flow layers exist in the continental crust. Both channel flow model and laminar flow model have been created to explain the flow laws and flow mechanisms. As revealed by the channel flow model, a low-viscosity channel in middle to lower crust in orogen or plateau with thick crust and high elevation would flow outward from mountain root in response to lateral pressure gradient resulted from topographic loading or to denudation. However, according to the laminar flow model proposed based on investigation of the Qinghai-Tibet plateau, circulative movement of crustal lithologies with different rheological properties between basin and orogen would occur, under the driving forces resulted from dehydration and melting of subduction plate on active continental margin and from thermal energy related to upwelling and diapiring of intercontinental mantle plume or its gravitational interactions. Similarly, when driven by gravity, the softened or melted substances of the lower crust in a basin would flow laterally toward adjacent mountain root, which would result in a thinned basin crust and a thickened orogenic crust. Partially melted magma within the thickened orogenic lower crust would cause vertical movement of metamorphic rocks of lower to middle crust due to density inversion, and the vertical main stress induced by thermal underplating of lower crust would in turn lead to formation of metamorphic core complexes and low-angle detachment fault systems. Lateral spreading of uplifting mountain due to gravitation potential would result in thrust fault systems on the border between mountain and basin. Meanwhile, detritus produced synchronously by intense erosion of uplifting mountain would be transported and deposited along the marginal deep depression in the foreland basin dragged by lower crust flow. Channel flow is similar to laminar flow in a variety of aspects

  3. Annular fuel and air co-flow premixer

    SciTech Connect

    Stevenson, Christian Xavier; Melton, Patrick Benedict; York, William David

    2013-10-15

    Disclosed is a premixer for a combustor including an annular outer shell and an annular inner shell. The inner shell defines an inner flow channel inside of the inner shell and is located to define an outer flow channel between the outer shell and the inner shell. A fuel discharge annulus is located between the outer flow channel and the inner flow channel and is configured to inject a fuel flow into a mixing area in a direction substantially parallel to an outer airflow through the outer flow channel and an inner flow through the inner flow channel. Further disclosed are a combustor including a plurality of premixers and a method of premixing air and fuel in a combustor.

  4. The Flow of Gases in Narrow Channels

    NASA Technical Reports Server (NTRS)

    Rasmussen, R E H

    1951-01-01

    Measurements were made of the flow of gases through various narrow channels a few microns wide at average pressures from 0.00003 to 40 cm. Hg. The flow rate, defined as the product of pressure and volume rate of flow at unit pressure difference, first decreased linearly with decrease in mean pressure in the channel, in agreement with laminar-flow theory, reached a minimum when the mean path length was approximately equal to the channel width, and then increased to a constant value. The product of flow rate and square root of molecular number was approximately the same function of mean path length for all gases for a given channel.

  5. Two-Phase Annular Flow in Helical Coil Flow Channels in a Reduced Gravity Environment

    NASA Technical Reports Server (NTRS)

    Keshock, Edward G.; Lin, Chin S.

    1996-01-01

    A brief review of both single- and two-phase flow studies in curved and coiled flow geometries is first presented. Some of the complexities of two-phase liquid-vapor flow in curved and coiled geometries are discussed, and serve as an introduction to the advantages of observing such flows under a low-gravity environment. The studies proposed -- annular two-phase air-water flow in helical coil flow channels are described. Objectives of the studies are summarized.

  6. Inertial (non-Darcian) channeled seepage flow

    NASA Astrophysics Data System (ADS)

    Foda, Mostafa A.

    1994-10-01

    A slow wave solution is identified for an infinite elastic medium intersected by a two-dimensional fluid channel. Because the wave speed is much slower than the medium's elastic shear wave, the response in the elastic medium is governed by elastostatics. The inertia of the wave is essentially focused in the fluid channel. Furthermore, wave damping is caused by fluid viscous friction on the channel in an elastic solid. It is proposed that these solutions may also be used in the case of a granular porous medium. The seepage channels would then represent a network of preferential flow paths. Therefore we would allow, in this case, the channel porosity to be different from the average granular porosity. For a strongly channel seepage flow or for a low channel porosity the solution is shown to approach that of a single-channel solution, giving rise to a slow propagating wave mode. On the other hand, for weak channeling or nearly `homogeneous' seepage flow the solution is shown to reproduce Biot's (1956) critically damped wave of the second kind. It is proposed that the resonance observed by Foda and Tzang (1994) are in the form of these strongly channeled wave modes.

  7. TS - Dean interactions in curved channel flow

    NASA Technical Reports Server (NTRS)

    Singer, Bart A.; Zang, Thomas A.; Erlebacher, Gordon

    1990-01-01

    A weakly nonlinear theory is developed to study the interaction of TS waves and Dean vortices in curved channel flow. The prediction obtained from the theory agree well with results obtained from direct numerical simulations of curved channel flow, especially for low amplitude disturbances. At low Reynolds numbers the wave interaction is generally stabilizing to both disturbances, though as the Reynolds number increases, many linearly unstable TS waves are further destabilized by the presence of Dean vortices.

  8. Visualization of the air flow behind the automotive benchmark vent

    NASA Astrophysics Data System (ADS)

    Pech, Ondrej; Jedelsky, Jan; Caletka, Petr; Jicha, Miroslav

    2015-05-01

    Passenger comfort in cars depends on appropriate function of the cabin HVAC system. A great attention is therefore paid to the effective function of automotive vents and proper formation of the flow behind the ventilation outlet. The article deals with the visualization of air flow from the automotive benchmark vent. The visualization was made for two different shapes of the inlet channel connected to the benchmark vent. The smoke visualization with the laser knife was used. The influence of the shape of the inlet channel to the airflow direction, its enlargement and position of air flow axis were investigated.

  9. Flow rate limitation in open capillary channel flows.

    PubMed

    Haake, Dennis; Rosendahl, Uwe; Ohlhoff, Antje; Dreyer, Michael E

    2006-09-01

    This paper reports the experimental and theoretical investigations of forced liquid flows through open capillary channels under reduced gravity conditions. An open capillary channel is a structure that establishes a liquid flow path at low Bond numbers, when the capillary pressure caused by the surface tension force dominates in comparison to the hydrostatic pressure induced by gravitational or residual accelerations. In case of steady flow through the channel, the capillary pressure of the free surface balances the pressure difference between the liquid and the surrounding constant-pressure gas phase. Because of convective and viscous momentum transport, the pressure along the flow path decreases and causes the free surface to bend inward. The maximum flow rate is achieved when the free surface collapses and gas ingestion occurs at the outlet. This critical flow rate depends on the geometry of the channel and the properties of the liquid. In this paper we present a comparison of the theoretical and experimental critical flow rates and surface profiles for convective dominated flows. For the prediction of the critical flow rate a one-dimensional theoretical model taking into account the entrance pressure loss and the frictional pressure loss in the channel is developed. PMID:17124140

  10. Rarefied gas flow through nanoscale tungsten channels.

    PubMed

    Ozhgibesov, M S; Leu, T S; Cheng, C H

    2013-05-01

    The aim of this work is to investigate argon flow behaviors through the channels with three types of boundary conditions. Current work deals with numerical simulations of rarefied gas flow through nano-channels using the Molecular Dynamics method. Taking into account that this method is very time consuming, we implemented all the simulations using CUDA capable graphic cards. We found that the well-known and relatively simple Maxwell model of boundary conditions is able to reproduce gas flow through a tungsten channel with irregularities and roughness, while it results in a significant error in the case of a smooth metal surface. We further found that the flow rate through a relatively short channel correlates nonlinearly with the channel's length. This finding is in contrast with the results available in extant literature. Our results are important for both numerical and theoretical analyses of rarefied gas flow in micro- and nano-systems where the choice of boundary conditions significantly influences flow. PMID:23528809

  11. Numerical investigation of turbulent channel flow

    NASA Technical Reports Server (NTRS)

    Moin, P.; Kim, J.

    1981-01-01

    Fully developed turbulent channel flow was simulated numerically at Reynolds number 13800, based on centerline velocity and channel halt width. The large-scale flow field was obtained by directly integrating the filtered, three dimensional, time dependent, Navier-Stokes equations. The small-scale field motions were simulated through an eddy viscosity model. The calculations were carried out on the ILLIAC IV computer with up to 516,096 grid points. The computed flow field was used to study the statistical properties of the flow as well as its time dependent features. The agreement of the computed mean velocity profile, turbulence statistics, and detailed flow structures with experimental data is good. The resolvable portion of the statistical correlations appearing in the Reynolds stress equations are calculated. Particular attention is given to the examination of the flow structure in the vicinity of the wall.

  12. Investigation of supersonic chemically reacting and radiating channel flow

    NASA Technical Reports Server (NTRS)

    Mani, Mortaza; Tiwari, Surendra N.

    1988-01-01

    The 2-D time-dependent Navier-Stokes equations are used to investigate supersonic flows undergoing finite rate chemical reaction and radiation interaction for a hydrogen-air system. The explicit multistage finite volume technique of Jameson is used to advance the governing equations in time until convergence is achieved. The chemistry source term in the species equation is treated implicitly to alleviate the stiffness associated with fast reactions. The multidimensional radiative transfer equations for a nongray model are provided for a general configuration and then reduced for a planar geometry. Both pseudo-gray and nongray models are used to represent the absorption-emission characteristics of the participating species. The supersonic inviscid and viscous, nonreacting flows are solved by employing the finite volume technique of Jameson and the unsplit finite difference scheme of MacCormack. The specified problem considered is of the flow in a channel with a 10 deg compression-expansion ramp. The calculated results are compared with those of an upwind scheme. The problem of chemically reacting and radiating flows are solved for the flow of premixed hydrogen-air through a channel with parallel boundaries, and a channel with a compression corner. Results obtained for specific conditions indicate that the radiative interaction can have a significant influence on the entire flow field.

  13. Sounding rocket experiment on capillary channel flow

    NASA Astrophysics Data System (ADS)

    Rosendahl, U.; Fechtmann, C.; Dreyer, M. E.

    2005-08-01

    This paper is concerned with flow rate limitations in open capillary channels under low-gravity conditions. The channels consist of two parallel plates bounded by free liquid surfaces along the open sides. In the case of steady flow the capillary pressure of the free surface balances the differential pressure between the liquid and the surrounding constant-pressure gas phase. A maximum flow rate is achieved when the adjusted volumetric flow rate exceeds a certain limit leading to a collapse of the free surfaces. In order to investigate this type of flow an experiment aboard the sounding rocket TEXUS-41 was performed. The aim of the investigation was to achieve the profiles of the free liquid surfaces and to determine the maximum flow rate of the steady flow. For this purpose a new approach to the critical flow condition by enlarging the channel length was applied. The paper gives a review of the experimental set-up and the preparation of the flight procedures. Furthermore the experiment performance is described and the typical appearance of the flow indicated by its surface profiles is presented.

  14. Convective dominated flows in open capillary channels

    NASA Astrophysics Data System (ADS)

    Rosendahl, Uwe; Grah, Aleksander; Dreyer, Michael E.

    2010-05-01

    This paper is concerned with convective dominated liquid flows in open capillary channels. The channels consist of two parallel plates bounded by free liquid surfaces along the open sides. In the case of steady flow the capillary pressure of the free surface balances the differential pressure between the liquid and the surrounding constant pressure gas phase. A maximum flow rate is achieved when the adjusted volumetric flow rate exceeds a certain limit leading to a collapse of the free surfaces. The convective dominated flow regime is a special case of open capillary flow, since the viscous forces are negligibly small compared with the convective forces. Flows of this type are of peculiar interest since the free surfaces possess a quasisymmetry in the flow direction. This quasisymmetry enables the application of a new effective method for evaluation of the flow limit. The flow limit is caused by a choking effect. This effect is indicated by the speed index, S, which is defined by the ratio of the flow velocity and the longitudinal capillary wave speed. The speed index is defined analogously to Mach number and tends toward unity in the case of flow limitation, i.e., when the maximum flow rate is reached. Utilizing the quasisymmetry, a new approach for a very precise determination of the speed index is presented. This approach uses a new approximation for the curvature of the surfaces by means of the empirical surface profiles. On the basis of empirical and theoretical data, the paper discusses the typical features of the stable flow. The experiments were performed under microgravity aboard the sounding rockets TEXUS 41 and TEXUS 42. The experiment setup enables the approach to the flow limit through either increase in flow rate or channel length. The theoretical data have been gained from numerical solutions of a one-dimensional flow model. The empirical and theoretical results are in good agreement and both confirm the choking effect as cause of the flow limitation

  15. Asymmetries in an obstructed turbulent channel flow

    NASA Astrophysics Data System (ADS)

    El Khoury, George K.; Pettersen, Bjørnar; Andersson, Helge I.; Barri, Mustafa

    2010-09-01

    The asymmetric flow pattern caused by a single thin-plate obstruction in a plane channel has been explored by means of direct numerical simulations. The blockage ratio was 1:2 and the bulk Reynolds number about 5700. In order to mimic an infinitely long channel section upstream of the obstruction, realistic dynamic inflow conditions were provided by a promising technique proposed by Barri et al. ["Inflow conditions for inhomogeneous turbulent flows," Int. J. Numer. Methods Fluids 60, 227 (2009)]. The fluid downstream of the symmetric obstruction was sucked toward one side where a modestly long region of rather strong recirculating flow was observed. The weaker recirculation bubble formed at the opposite side was 17 times longer than the obstruction height and almost four times the size of the shorter bubble. The overall flow pattern turned out to be rather different from that observed in a similar study of channel flow subjected to periodically repeating obstructions by Makino et al. ["Turbulent structures and statistics in turbulent channel flow with two-dimensional slits," Int. J. Heat Fluid Flow 29, 602 (2008)]. An anomalous variation of the pressure coefficient was observed with an excessively low pressure below the shorter of the bubbles. A locally high pressure occurred where the deflected jet flow impinges on the wall, whereas another pressure minimum could be associated with the flow acceleration caused by the severe blockage due to the major recirculation bubble. The turbulent fluctuations were suppressed due to the acceleration through the obstruction and high levels of streamwise velocity persisted far downstream. Exceptionally high turbulence levels were observed in the mixing-layers emanating from the two sides of the obstruction. The turbulence in these mixing-layers turned out to be qualitatively and quantitatively different on the two sides and exhibited distinctly different anisotropies.

  16. Critical Velocity in Open Capillary Channel Flows

    NASA Technical Reports Server (NTRS)

    Rosendahl, Uwe; Dreyer, Michael E.; Rath, Hans J.; Motil, Brian; Singh, Bhim S. (Technical Monitor)

    2001-01-01

    We investigate forced liquid flows through open capillary channels with free surfaces experimentally. The experiments were performed under low gravity conditions in the Bremen Drop Tower and on board the sounding rocket TEXUS-37. Open capillary channels (vanes) are used in surface tension tanks to transport the propellant and to provide a flow path for the bubble-free liquid supply to the thrusters. Since the free surfaces can only withstand a certain pressure differential between the liquid and ambient, the flow rate in the channel is limited. The maximum flow rate is achieved when the surfaces collapse and gas is ingested into the outlet. Since experimental and theoretical data of this flow rate limitation is lacking, the safety factors for the application of vanes in surface tension tanks must be unnecessary high. The aim of the investigation is to determine the maximum liquid flow rate and the corresponding critical flow velocity. The characteristic nondimensional parameters, OHNESORGE number, and gap ratio, cover a wide range of usual vanes. For the theoretical approach a one-dimensional momentum balance was set up. The numerical solution yields the maximum volume flux and the position of the free surface in good agreement with the experiments.

  17. Optimal feedback control of turbulent channel flow

    NASA Technical Reports Server (NTRS)

    Bewley, Thomas; Choi, Haecheon; Temam, Roger; Moin, Parviz

    1993-01-01

    Feedback control equations were developed and tested for computing wall normal control velocities to control turbulent flow in a channel with the objective of reducing drag. The technique used is the minimization of a 'cost functional' which is constructed to represent some balance of the drag integrated over the wall and the net control effort. A distribution of wall velocities is found which minimizes this cost functional some time shortly in the future based on current observations of the flow near the wall. Preliminary direct numerical simulations of the scheme applied to turbulent channel flow indicates it provides approximately 17 percent drag reduction. The mechanism apparent when the scheme is applied to a simplified flow situation is also discussed.

  18. Patterns in simulated turbulent channel flow

    NASA Technical Reports Server (NTRS)

    Stretch, D.

    1990-01-01

    The surface stress is a key diagnostic in wall bounded turbulent flows. Large fluctuations in the stress are believed to be associated with intermittent 'bursting' events during which a large proportion of the turbulence production takes place. If this is so, then a detailed investigation of the structure of the surface stress and its spatial relationship to events within the flow could have wide application in drag reduction and other aspects of flow control. The initial phase of this project, therefore, concentrated on the surface stress field. The first objective is to carry out a statistical analysis of the instantaneous surface stress in a simulated turbulent channel flow, including comparison with multipoint experimental data from a zero pressure gradient turbulent boundary layer. The second objective is to apply a simple pattern recognition procedure to educe the characteristic spatial structure of various flow diagnostics. The final objective is to extend the pattern recognition analysis to examine the whole three dimensional structure of the flow.

  19. 78. PIPING CHANNEL FOR FUEL LOADING, FUEL TOPPING, COMPRESSED AIR, ...

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

    78. PIPING CHANNEL FOR FUEL LOADING, FUEL TOPPING, COMPRESSED AIR, GASEOUS NITROGEN, AND HELIUM - Vandenberg Air Force Base, Space Launch Complex 3, Launch Pad 3 East, Napa & Alden Roads, Lompoc, Santa Barbara County, CA

  20. Experimental and Numerical Analysis of the air Flow in T-Shape Channel Flow / Eksperymentalna i numeryczna analiza przepływu powietrza przez skrzyżowanie kanałów w kształcie litery T

    NASA Astrophysics Data System (ADS)

    Szmyd, Janusz; Branny, Marian; Karch, Michal; Wodziak, Waldemar; Jaszczur, Marek; Nowak, Remigiusz

    2013-06-01

    This paper presents the results of experimental and numerical investigations of air flow through the crossing of a mining longwall and ventilation gallery. The object investigated consists of airways (headings) arranged in a T-shape. Maintained for technological purposes, the cave is exposed particularly to dangerous accumulations of methane. The laboratory model is a certain simplification of a real longwall and ventilation gallery crossing. Simplifications refer to both the object's geometry and the air flow conditions. The aim of the research is to evaluate the accuracy with which numerical simulations model the real flow. Stereo Particle Image Velocimetry (SPIV) was used to measure all velocity vector components. Three turbulence models were tested: standard k-ɛ, k-ɛ realizable and the Reynolds Stress Model (RSM). The experimental results have been compared against the results of numerical simulations. Good agreement is achieved between all three turbulence model predictions and measurements in the inflow and outflow of the channel. Large differences between the measured and calculated velocity field occur in the cavity zone. Two models, the standard k-ɛ and k-ɛ realizable over-predict the measure value of the streamwise components of velocity. This causes the ventilation intensity to be overestimated in this domain. The RSM model underestimates the measure value of streamwise components of velocity and therefore artificially decreases the intensity of ventilation in this zone. The RSM model provides better predictions than the standard k-ɛ and k-ɛ realizable in the cavity zone. Przedmiotem badań jest walidacja wybranych modeli CFD (Computational Fluid Dynamics) przy przepływie powietrza przez laboratoryjny model skrzyżowania kanałów w kształcie litery T. Stanowisko laboratoryjne przedstawia uproszczony model skrzyżowania ściany z chodnikiem wentylacyjnym. Przyjęto, że przepływ powietrza jest ustalony i izotermiczny. Dla tych warunków z r

  1. Measurements of gravity driven granular channel flows

    NASA Astrophysics Data System (ADS)

    Facto, Kevin

    This dissertation presents experiments that studied two gravity driven granular channel flows. The first experiment used magnetic resonance imaging to measure the density and displacement distributions of poppy seeds flowing in a rough walled channel. Time-averaged measurements of normalized velocity and density showed little flow speed dependence. Instantaneous measurements, however, showed marked velocity dependence in the displacement distributions. There was evidence of aperiodic starting and stopping at lower flow speeds and the onset of density waves on a continuous flow at higher speeds. The second experiment measured forces in all three spatial directions at the boundary of a flow of steel balls. The relationship between the normal and the tangential forces were examined statistically and compared to the Coulomb friction model. For both large and small forces, the tangential and normal forces are unrelated, as there appears to be a strong tendency for the tangential force to maintain a value that will bear the weight the weight of the particles in flow.

  2. Large Rossby number flows in Cozumel Channel

    NASA Astrophysics Data System (ADS)

    Ochoa, J.; Candela, J.; Sheinbaum, J.; Badan, A.

    2003-04-01

    The Caribbean Current flows to the west impinging the Yucatan coast south of Cozumel Island, then, most of its flow turns north, surrounds the island and continues towards the Yucatan Straits. About 4 Sv in the mean pass between the Yucatan coast and the Cozumel Island; through the Cozumel Channel, where subinertial currents exhibit large ageostrophic fluctuations [Chavez et. al. (2003)]. This channel is about 18 km wide, 50 km long, 400 m deep, and 70 km southwest of the Yucatan Straits. The curvature and latitude of the Caribbean Current on its approach to the Yucatan coast vary significantly. Observations with two upward-looking ADCPs, 8.6 km from each other, closely aligned with the mean current at the channel's axis and entrance, allow robust estimations of the current speed (U), direction and curvature (|R|-1). A signed Rossby number (Uf-1R-1), where f is the Coriolis parameter, is readily available as a function of time. The positive/negative curvature is defined by the cyclonic/anticyclonic turn. The currents observations along with pressure measurements at both sides of the channel produce evidence that favor the bend of the current as the cause of the ageostrophic fluctuations. Another possible cause for the ageostrophic fluctuations is the passage of eddies within the channel. We test the gradient wind balance between the currents and pressure observations. A very low frequency component on the seasonal time scale and high frequency fluctuations (superinercial) do not adjust to this balance, only the intermediate frequency variations show a clear equilibrium of centripetal (i.e. due to curvature) plus Coriolis accelerations against the pressure gradient perpendicular to the velocity. The conjecture is that the ageostrophic fluctuations occur when the bend and approach of the Caribbean Current is just south of Cozumel Island, thus influencing all its entrance. When the current impinges the coast further south, the flow, with a longer path to transit

  3. Flag flutter in inviscid channel flow

    NASA Astrophysics Data System (ADS)

    Alben, Silas

    2015-03-01

    Using nonlinear vortex-sheet simulations, we determine the region in parameter space in which a straight flag in a channel-bounded inviscid flow is unstable to flapping motions. We find that for heavier flags, greater confinement increases the size of the region of instability. For lighter flags, confinement has little influence. We then compute the stability boundaries analytically for an infinite flag and find similar results. For the finite flag, we also consider the effect of channel walls on the large-amplitude periodic flapping dynamics. We find that multiple flapping states are possible but rare at a given set of parameters, when periodic flapping occurs. As the channel walls approach the flag, its flapping amplitude decreases roughly in proportion to the near-wall distance, for both symmetric and asymmetric channels. Meanwhile, its dominant flapping frequency and mean number of deflection extrema (or "wavenumber") increase in a nearly stepwise fashion. That is, they remain nearly unchanged over a wide range of channel spacing, but when the channel spacing is decreased below a certain value, they undergo sharp increases corresponding to a higher flapping mode.

  4. Interannual variability in the Yucatan Channel flow

    NASA Astrophysics Data System (ADS)

    Athié, Gabriela; Sheinbaum, Julio; Leben, Robert; Ochoa, José; Shannon, Michael R.; Candela, Julio

    2015-03-01

    Mooring measurements in the Yucatan Channel, from May 2010 to May 2011 and from July 2012 to June 2013 yield a mean transport of 27 and 25 Sv, respectively, with a subinertial standard deviation of 3.5 Sv. These mean transport values are higher than the 23 Sv reported from 21 months of similar measurements (1999-2001). Analysis of low-frequency variations of a transport proxy based on 20 years of altimetry data indicates that during 1999-2001, the flow through Yucatan Channel was anomalously low. This suggests that a sizable compensation through other channels off the Gulf of Mexico is required to match the transport cable measurements of the Florida Current at 27°N.

  5. Epithelial Na(+) channels are regulated by flow.

    PubMed

    Satlin, L M; Sheng, S; Woda, C B; Kleyman, T R

    2001-06-01

    Na(+) absorption in the renal cortical collecting duct (CCD) is mediated by apical epithelial Na(+) channels (ENaCs). The CCD is subject to continuous variations in intraluminal flow rate that we speculate alters hydrostatic pressure, membrane stretch, and shear stress. Although ENaCs share limited sequence homology with putative mechanosensitive ion channels in Caenorhabditis elegans, controversy exists as to whether ENaCs are regulated by biomechanical forces. We examined the effect of varying the rate of fluid flow on whole cell Na(+) currents (I(Na)) in oocytes expressing mouse alpha,beta,gamma-ENaC (mENaC) and on net Na(+) absorption in microperfused rabbit CCDs. Oocytes injected with mENaC but not water responded to the initiation of superfusate flow (to 4-6 ml/min) with a reversible threefold stimulation of I(Na) without a change in reversal potential. The increase in I(Na) was variable among oocytes. CCDs responded to a threefold increase in rate of luminal flow with a twofold increase in the rate of net Na(+) absorption. An increase in luminal viscosity achieved by addition of 5% dextran to the luminal perfusate did not alter the rate of net Na(+) absorption, suggesting that shear stress does not influence Na(+) transport in the CCD. In sum, our data suggest that flow stimulation of ENaC activity and Na(+) absorption is mediated by an increase in hydrostatic pressure and/or membrane stretch. We propose that intraluminal flow rate may be an important regulator of channel activity in the CCD. PMID:11352841

  6. Reality Check: Using Analytic Rectangular Channel Flow Solutions to Interpret and Predict Channelized Lava Flow Behavior on Earth and Mars

    NASA Astrophysics Data System (ADS)

    Gregg, T. K. P.; Sakimoto, S. E. H.

    1999-03-01

    3-D analytic lava channel flow solutions provide more accurate and realistic viscosity and flow rate extimates. This study compares model with data for laboratory channel simulations, active Pu'u O'o and Mauna Loa channels, and MOLA topography of a Mars Elysium channel.

  7. Connecting exact coherent states to turbulent dynamics in channel flow

    NASA Astrophysics Data System (ADS)

    Park, Jae Sung; Graham, Michael D.

    2015-11-01

    The discovery of nonlinear traveling wave solutions to the Navier-Stokes equations or exact coherent states has greatly advanced the understanding of the nature of turbulent shear flows. These solutions are unstable saddle points in state space, while the time evolution of a turbulent flow is a dynamical trajectory wandering around them. In this regard, it is of interest to investigate how closely the turbulent trajectories approach these invariant states. Here, we present connections between turbulent trajectories and one intriguing solution family in channel flow. A state space visualization of turbulent trajectories is presented in a three-dimensional space. The lifetime of the trajectories is well represented by closeness to two distinct solutions resembling in many ways the active and hibernating phases of minimal channel turbulence (Xi & Graham PRL 2010). The connections are then examined by comparing mean profiles and flow structures. More importantly, the connections are confirmed by calculating the L2 distance between the trajectories and the traveling waves. Lastly, paths of an intermittent bursting phenomenon are identified in state space and the relationship between bursting paths and the traveling waves or hibernating turbulence is further discussed. This work was supported by the Air Force Office of Scientific Research through grant FA9550-15-1-0062 (Flow Interactions and Control Program).

  8. Mass conservation: 1-D open channel flow equations

    USGS Publications Warehouse

    DeLong, Lewis L.

    1989-01-01

    Unsteady flow simulation in natural rivers is often complicated by meandering channels of compound section. Hydraulic properties and the length of the wetted channel may vary significantly as a meandering river inundates its adjacent floodplain. The one-dimensional, unsteady, open-channel flow equations can be extended to simulate floods in channels of compound section. It will be shown that equations derived from the addition of differential equations individually describing flow in main and overbank channels do not in general conserve mass when overbank and main channels are of different lengths.

  9. Optimum design of bipolar plates for separate air flow cooling system of PEM fuel cells stacks

    NASA Astrophysics Data System (ADS)

    Franco, Alessandro

    2015-12-01

    The paper discusses about thermal management of PEM fuel cells. The objective is to define criteria and guidelines for the design of the air flow cooling system of fuel cells stacks for different combination of power density, bipolar plates material, air flow rate, operating temperature It is shown that the optimization of the geometry of the channel permits interesting margins for maintaining the use of separate air flow cooling systems for high power density PEM fuel cells.

  10. Numerical Modeling of Surface and Volumetric Cooling using Optimal T- and Y-shaped Flow Channels

    NASA Astrophysics Data System (ADS)

    Kosaraju, Srinivas

    2015-11-01

    The T- and Y-shaped flow channels can be optimized for reduced pressure drop and pumping power. The results of the optimization are in the form of geometric parameters such as length and diameter ratios of the stem and branch sections. While these flow channels are optimized for minimum pressure drop, they can also be used for surface and volumetric cooling applications such as heat exchangers, air conditioning and electronics cooling. In this paper, we studied the heat transfer characteristics of multiple T- and Y-shaped flow channel configurations using numerical simulations. All configurations are subjected to same pumping power and heat generation constraints and their heat transfer performance is studied.

  11. Inception of supraglacial channelization under turbulent flow conditions

    NASA Astrophysics Data System (ADS)

    Mantelli, E.; Camporeale, C.; Ridolfi, L.

    2013-12-01

    Glacier surfaces exhibit an amazing variety of meltwater-induced morphologies, ranging from small scale ripples and dunes on the bed of supraglacial channels to meandering patterns, till to large scale drainage networks. Even though the structure and geometry of these morphologies play a key role in the glacier melting processes, the physical-based modeling of such spatial patterns have attracted less attention than englacial and subglacial channels. In order to partially fill this gap, our work concerns the large scale channelization occurring on the ice slopes and focuses on the role of turbulence on the wavelength selection processes during the channelization inception. In a recent study[1], two of us showed that the morphological instability induced by a laminar film flowing over an ice bed is characterized by transversal length scales of order of centimeters. Being these scales much smaller than the spacing observed in the channelization of supraglacial drainage networks (that are of order of meters) and considering that the water films flowing on glaciers can exhibit Reynolds numbers larger than 104, we investigated the role of turbulence in the inception of channelization. The flow-field is modeled by means of two-dimensional shallow water equations, where Reynolds stresses are also considered. In the depth-averaged heat balance equation an incoming heat flux from air is assumed and forced convection heat exchange with the wall is taken into account, in addition to convection and diffusion in the liquid. The temperature profile in the ice is finally coupled to the liquid through Stefan equation. We then perform a linear stability analysis and, under the assumption of small Stefan number, we solve the differential eigenvalue problem analytically. As main outcome of such an analysis, the morphological instability of the ice-water interface is detected and investigated in a wide range of the independent parameters: longitudinal and transversal wavenumbers

  12. Borders of disorder: in turbulent channel flow

    NASA Astrophysics Data System (ADS)

    Malkus, Willem V. R.

    2003-08-01

    A quantitative theory of the average features of turbulent flow in a channel is described without the introduction of empirical parameters. The qualitative problem consists of maximizing the dissipation rate of the mean flow subject to the Rayleigh condition that the mean flow has no inflections. The quantitative features result from a boundary stability study which determines a smallest scale of motion in the transport of momentum. The velocity fields satisfying these conditions, the averaged equations and the boundary conditions uniquely determine an entire mean velocity profile at all Reynolds numbers within ten per cent of the data. The maximizing condition for the reproducibility of averages emerges from the Navier Stokes equations as a consequence of a novel definition of nonlinear instability. The smallest scale of motion results from a theory for a time-dependent re-stabilization of the boundary layer following a disruptive instability. Computer reassessment of the several asymptotic estimates of the critical boundary eigenstructure can establish the limits of validity of the quantitative results.

  13. Lattice Boltzmann method and channel flow

    NASA Astrophysics Data System (ADS)

    Stensholt, Sigvat; Mongstad Hope, Sigmund

    2016-07-01

    Lattice Boltzmann methods are presented at an introductory level with a focus on fairly simple simulations that can be used to test and illustrate the model’s capabilities. Two scenarios are presented. The first is a simple laminar flow in a straight channel driven by a pressure gradient (Poiseuille flow). The second is a more complex, including a wedge where Moffatt vortices may be induced if the wedge is deep enough. Simulations of the Poiseuille flow scenario accurately capture the theoretical velocity profile. The experiment shows the location of the fluid-wall boundary and the effects viscosity has on the velocity and convergence time. The numerical capabilities of the lattice Boltzmann model are tested further by simulating the more complex Moffatt vortex scenario. The method reproduces with high accuracy the theoretical predction that Moffat vortices will not form in a wedge if the vertex angle exceeds 146°. Practical issues limitations of the lattice Boltzmann method are discussed. In particular the accuracy of the bounce-back boundary condition is first order dependent on the grid resolution.

  14. Simulator Of Rain In Flowing Air

    NASA Technical Reports Server (NTRS)

    Clayton, Richard M.; Cho, Young I.; Shakkottai, Parthasarathy; Back, Lloyd H.

    1989-01-01

    Report describes relatively inexpensive apparatus that creates simulated precipitation from drizzle to heavy rain in flowing air. Small, positive-displacement pump and water-injecting device positioned at low-airspeed end of converging section of wind tunnel 10 in. in diameter. Drops injected by array entrained in flow of air as it accelerates toward narrower outlet, 15 in. downstream. Outlet 5 in. in diameter.

  15. Landscape predictors of channel wetted width at baseflow using air photos

    NASA Astrophysics Data System (ADS)

    Rawlins, Barry; Clark, Liam; Boyd, Doreen

    2013-04-01

    Evasion of carbon dioxide from the surface of freshwater channels accounts for a substantial proportion of its flux from the terrestrial biosphere to the atmosphere; accurate estimates of channel wetted width (WW) are required to improve predictions of this flux. We investigated which landscape and climate-related data were statistically significant predictors of WW at baseflow across a large region (2200 km2) of north Wales and western England (UK) where habitat surveys suggest the majority of channels are in a near natural state. We used 25 cm pixel resolution air photos to measure channel WW at baseflow, and quantified the magnitude of the errors in these measurements. We used flow information from local gauging stations to ensure that channels were at or close to baseflow for the days on which the air photos were captured. The root mean squared difference between the field-based and air photo measurements of WW (n=28 sites) was small (0.14 m) in comparison to the median channel WW (3.07 m), and there was very little bias between the two sets of measurements (0.026 m). We created a set of points along those sections of channels which were visible in air photos and used a digital terrain model to create the drainage catchments for the points and computed their catchment area (CA). We removed points with CA

  16. Evaluation of correlations of flow boiling heat transfer of R22 in horizontal channels.

    PubMed

    Zhou, Zhanru; Fang, Xiande; Li, Dingkun

    2013-01-01

    The calculation of two-phase flow boiling heat transfer of R22 in channels is required in a variety of applications, such as chemical process cooling systems, refrigeration, and air conditioning. A number of correlations for flow boiling heat transfer in channels have been proposed. This work evaluates the existing correlations for flow boiling heat transfer coefficient with 1669 experimental data points of flow boiling heat transfer of R22 collected from 18 published papers. The top two correlations for R22 are those of Liu and Winterton (1991) and Fang (2013), with the mean absolute deviation of 32.7% and 32.8%, respectively. More studies should be carried out to develop better ones. Effects of channel dimension and vapor quality on heat transfer are analyzed, and the results provide valuable information for further research in the correlation of two-phase flow boiling heat transfer of R22 in channels. PMID:23956695

  17. Evaluation of Correlations of Flow Boiling Heat Transfer of R22 in Horizontal Channels

    PubMed Central

    Fang, Xiande; Li, Dingkun

    2013-01-01

    The calculation of two-phase flow boiling heat transfer of R22 in channels is required in a variety of applications, such as chemical process cooling systems, refrigeration, and air conditioning. A number of correlations for flow boiling heat transfer in channels have been proposed. This work evaluates the existing correlations for flow boiling heat transfer coefficient with 1669 experimental data points of flow boiling heat transfer of R22 collected from 18 published papers. The top two correlations for R22 are those of Liu and Winterton (1991) and Fang (2013), with the mean absolute deviation of 32.7% and 32.8%, respectively. More studies should be carried out to develop better ones. Effects of channel dimension and vapor quality on heat transfer are analyzed, and the results provide valuable information for further research in the correlation of two-phase flow boiling heat transfer of R22 in channels. PMID:23956695

  18. Magnetohydrodynamic channel flows with weak transverse magnetic fields.

    PubMed

    Rothmayer, A P

    2014-07-28

    Magnetohydrodynamic flow of an incompressible fluid through a plane channel with slowly varying walls and a magnetic field applied transverse to the channel is investigated in the high Reynolds number limit. It is found that the magnetic field can first influence the hydrodynamic flow when the Hartmann number reaches a sufficiently large value. The magnetic field is found to suppress the steady and unsteady viscous flow near the channel walls unless the wall shapes become large. PMID:24936018

  19. Air flow cued spatial learning in mice.

    PubMed

    Bouchekioua, Youcef; Mimura, Masaru; Watanabe, Shigeru

    2015-01-01

    Spatial learning experiments in rodents typically employ visual cues that are associated with a goal place, even though it is now well established that they have poor visual acuity. We assessed here the possibility of spatial learning in mice based on an air flow cue in a dry version of the Morris water maze task. A miniature fan was placed at each of the four cardinal points of the circular maze, but only one blew air towards the centre of the maze. The three other fans were blowing towards their own box. The mice were able to learn the task only if the spatial relationship between the air flow cue and the position of the goal place was kept constant across trials. A change of this spatial relationship resulted in an increase in the time to find the goal place. We report here the first evidence of spatial learning relying on an air flow cue. PMID:25257773

  20. Transition to turbulence in plane channel flow

    NASA Technical Reports Server (NTRS)

    Biringen, S.; Goglia, G. L.

    1983-01-01

    A numerical simulation of the final stages of transition to turbulence in plane channel flow is reported. Three dimensional, incompressible Navier-Stokes equations are numerically integrated to obtain the time-evolution of two and three dimensional finite amplitude disturbances. Computations are performed on the CYBER-203 vector processor for a 32x51x32 grid. Results are presented for no-slip boundary conditions at the solid walls as well as for periodic suction-blowing to simulate active control of transition by mass transfer. Solutions indicate that the method is capable of simulating the complex character of vorticity dynamics during the various stages of transition and final breakdown. In particular, evidence points to the formation of a lambda-shape vortex and the subsequent system of horseshoe vortices inclined to the main flow direction as the main elements of transition. Calculations involving suction-blowing indicate that interference with a wave of suitable phase and amplitude reduces the disturbance growth rates.

  1. Transition to turbulence in plane channel flows

    NASA Technical Reports Server (NTRS)

    Biringen, S.

    1984-01-01

    Results obtained from a numerical simulation of the final stages of transition to turbulence in plane channel flow are described. Three dimensional, incompressible Navier-Stokes equations are numerically integrated to obtain the time evolution of two and three dimensional finite amplitude disturbances. Computations are performed on CYBER-203 vector processor for a 32x51x32 grid. Results are presented for no-slip boundary conditions at the solid walls as well as for periodic suction blowing to simulate active control of transition by mass transfer. Solutions indicate that the method is capable of simulating the complex character of vorticity dynamics during the various stages of transition and final breakdown. In particular, evidence points to the formation of a lambda-shape vortex and the subsequent system of horseshoe vortices inclined to the main flow direction as the main elements of transition. Calculations involving periodic suction-blowing indicate that interference with a wave of suitable phase and amplitude reduces the disturbance growth rates.

  2. Transition to turbulence in plane channel flows

    NASA Astrophysics Data System (ADS)

    Biringen, S.

    1984-02-01

    Results obtained from a numerical simulation of the final stages of transition to turbulence in plane channel flow are described. Three dimensional, incompressible Navier-Stokes equations are numerically integrated to obtain the time evolution of two and three dimensional finite amplitude disturbances. Computations are performed on CYBER-203 vector processor for a 32x51x32 grid. Results are presented for no-slip boundary conditions at the solid walls as well as for periodic suction blowing to simulate active control of transition by mass transfer. Solutions indicate that the method is capable of simulating the complex character of vorticity dynamics during the various stages of transition and final breakdown. In particular, evidence points to the formation of a lambda-shape vortex and the subsequent system of horseshoe vortices inclined to the main flow direction as the main elements of transition. Calculations involving periodic suction-blowing indicate that interference with a wave of suitable phase and amplitude reduces the disturbance growth rates.

  3. Transition to turbulence in plane channel flow

    NASA Astrophysics Data System (ADS)

    Biringen, S.; Goglia, G. L.

    1983-12-01

    A numerical simulation of the final stages of transition to turbulence in plane channel flow is reported. Three dimensional, incompressible Navier-Stokes equations are numerically integrated to obtain the time-evolution of two and three dimensional finite amplitude disturbances. Computations are performed on the CYBER-203 vector processor for a 32x51x32 grid. Results are presented for no-slip boundary conditions at the solid walls as well as for periodic suction-blowing to simulate active control of transition by mass transfer. Solutions indicate that the method is capable of simulating the complex character of vorticity dynamics during the various stages of transition and final breakdown. In particular, evidence points to the formation of a lambda-shape vortex and the subsequent system of horseshoe vortices inclined to the main flow direction as the main elements of transition. Calculations involving suction-blowing indicate that interference with a wave of suitable phase and amplitude reduces the disturbance growth rates.

  4. Air flow through poppet valves

    NASA Technical Reports Server (NTRS)

    Lewis, G W; Nutting, E M

    1920-01-01

    Report discusses the comparative continuous flow characteristics of single and double poppet valves. The experimental data presented affords a direct comparison of valves, single and in pairs of different sizes, tested in a cylinder designed in accordance with current practice in aviation engines.

  5. Surface Flow and Turbulence in an Estuarine River Channel (Invited)

    NASA Astrophysics Data System (ADS)

    Chickadel, C.; Talke, S. A.; Horner-Devine, A. R.; Jessup, A. T.

    2010-12-01

    Open channel flow, as in rivers and estuaries, produces turbulence at a range of scales and is due to flow over bathymetric features, obstructions, and rough bottoms, or from strongly sheared flow. This turbulence is often visible at the surface as eddies, boils, and surface deflections. Measurement and analysis of open channel turbulence including turbulent kinetic energy, Reynolds stress, and dissipation is critical to understanding mixing and transport, and is important for testing and constraining hydrodynamic models. In situ measurements of turbulence using current meters and scalar tracers are difficult to make and often lack the spatial resolution needed to assess complex flow patterns. A new generation of remote measurements based on thermal infrared (IR) imaging of the water surface is presented here, and has the benefits of high temporal and spatial resolution. Turbulence measurements are explored in a recent experiment in the Snohomish River estuary which has documented turbulent features in IR images of the surface flow. Specifically, the images show a range of rapidly evolving turbulent structures (boils, vortices and fronts) made evident by disruption of the thin skin layer of cool water by turbulent straining and upwelling. We examine thermal imaging data of surface turbulence collected from a nested set of cameras covering scales from millimeters to tens of meters. We show that infrared remote sensing reveals significant turbulent dissipation at the air-water interface. Results reveal that the spatial thermal patterns follow the expected Kolmogorov cascade of turbulent energy below O(1 m) scales even at the water surface, where vertical turbulent length scales are suppressed. Furthermore, application of particle imaging velocimetry (PIV) to IR video show variable surface flow patterns associated with individual coherent features such as erupting boils and eddies. We groundtruth both the spatial and velocity patterns from IR imagery against time

  6. 40 CFR 91.416 - Intake air flow measurement specifications.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 40 Protection of Environment 20 2010-07-01 2010-07-01 false Intake air flow measurement... Procedures § 91.416 Intake air flow measurement specifications. (a) If used, the engine intake air flow measurement method used must have a range large enough to accurately measure the air flow over the...

  7. Communication Channels and Information Flow among Ethnics.

    ERIC Educational Resources Information Center

    Jeffres, Leo W.; Hur, K. Kyoon

    The questionnaire responses of 768 people from a variety of ethnic groups were analyzed to determine what communication channels were used to link ethnics to their native countries and to provide news of the ethnic community. The relationships between channel preferences and demographics, ethnicity, and communication channel patterns were also…

  8. Characterization and Control of Separated Entrance Flow in a Branched Channel

    NASA Astrophysics Data System (ADS)

    Peterson, C. J.; Vukasinovic, B.; Glezer, A.

    2015-11-01

    The evolution of the flow downstream of the inlet of a rectangular channel that is branched along the entire span of the side wall of a primary channel of the same height is investigated experimentally in an air facility. Of particular interest is the formation and scaling of a separated flow domain downstream of the entrance plane into the secondary channel and its interaction with the flow surfaces at speeds up to M = 0 . 4 . The separation is actively controlled using a spanwise array of fluidic actuators on the primary channel's surface upstream of the inlet plane of the secondary duct. The effects of the actuation on the evolution of the separation and attachment of the vorticity layer between upstream surface of the primary duct and the surface of the secondary duct downstream of the branched inlet in the presence of a strong confined adverse pressure gradient are investigated using particle image velocimetry coupled with detailed static surface pressure distributions. The effects of the controlled separation within the secondary channel on the global flow within the primary duct and on flow split between primary and secondary channels are assessed, and it is demonstrated that actuation can effect significant changes in the flow fractions between the channels. Copyright 2015 Boeing. All rights reserved.

  9. Capillary-Driven Flow in Liquid Filaments Connecting Orthogonal Channels

    NASA Technical Reports Server (NTRS)

    Allen, Jeffrey S.

    2005-01-01

    Capillary phenomena plays an important role in the management of product water in PEM fuel cells because of the length scales associated with the porous layers and the gas flow channels. The distribution of liquid water within the network of gas flow channels can be dramatically altered by capillary flow. We experimentally demonstrate the rapid movement of significant volumes of liquid via capillarity through thin liquid films which connect orthogonal channels. The microfluidic experiments discussed provide a good benchmark against which the proper modeling of capillarity by computational models may be tested. The effect of surface wettability, as expressed through the contact angle, on capillary flow will also be discussed.

  10. Numerical Simulation of Two-phase Flow in a Microchannel with Air Gap

    NASA Astrophysics Data System (ADS)

    Liu, Xiaojun; Meinhart, Carl D.

    2001-11-01

    Fluid transport in nano- and micro-scale devices becomes more and more important. The potential advantages of micro-channel with air gap are studied. A simple one-dimensional model of air-water two-phase flow is investigated theoretically. The flow of water is driven by pressure drop. The air in the gap is driven by surface tension and friction forces that exist at the interface between the water and air. With the limitation that air flow rate is zero, the theoretical results are obtained based on continuity and Navier-Stokes equations. Because the viscosity of air is much less than that of water, under same pressure drop, the flow rate of water can be increased to as 4.76 times as that of normal channel without air gap. The theoretical results are tested by numerical simulation with three different software package (CFD2000, FEMLab and CFDRC) using a two-dimensional model. The interface shape, interface velocity, water flow rate and optimum height ratio are studied. Thenumerical results for different package match each other very well. The numerical results show that increasing water flow rate by adding air gap in the micro channel is practicable.

  11. Interaction of droplet and sidewalls with modified surfaces in a PEMFC gas flow channel

    NASA Astrophysics Data System (ADS)

    Shah, Mihir M.

    A Proton Exchange Membrane Fuel Cell (PEMFC) is a clean and highly efficient way of power generation used primarily for transportation applications. Hydrogen and air are supplied to the fuel cell through gas channels, which also remove liquid water generated in the fuel cell. The clogged channels prevent reactant transport to the electrochemically active sites which comprise one of the channel walls and thus, degrading the performance of the cell. Proper management of the product water is a current topic of research interest in commercialization of fuel cell vehicles. Liquid water, produced as by-product of the fuel cell reaction, can clog the gas channels easily since surface tension of water is significant at this length scale. In a PEMFC channel cross-section, water is assumed to be produced in the channel at the center along the flow axis. This assumption is primarily valid and extensively used for experimental purposes. However in a real PEMFC, the water entry is not constrained at the channel center. Hence, more investigations are made using water entry at channel corner (land region) which resulted in contradicting prior results for the water feature behavior for all relevant PEMFC operating conditions, leading to adverse two-phase flow behavior- including slug blockage and fluctuations at channel end. Very limited research is available to study the effect of gas channel surface modifications on the two-phase flow behavior and local PEMFC performance. In this study, the droplet--sidewall dynamic interactions and two--phase local pressure drop across the water droplet present in a PEMFC channel with trapezoidal geometries with surface modifications are studied. These surface modifications include micro-grooves that possess a hybrid wetting regime that will initiate and guide the water feature at channel ends to eject with general ease. Slugs are reduced to films after ejection and thus channel blockage is avoided overcoming the problems caused by water influx

  12. Numerical computation of pulsatile flow through a locally constricted channel

    NASA Astrophysics Data System (ADS)

    Bandyopadhyay, S.; Layek, G. C.

    2011-01-01

    This paper deals with the numerical solution of a pulsatile laminar flow through a locally constricted channel. A finite difference technique has been employed to solve the governing equations. The effects of the flow parameters such as Reynolds number, flow pulsation in terms of Strouhal number, constriction height and length on the flow behaviour have been studied. It is found that the peak value of the wall shear stress has significantly changed with the variation of Reynolds numbers and constriction heights. It is also noted that the Strouhal number and constriction length have little effect on the peak value of the wall shear stress. The flow computation reveals that the peak value of the wall shear stress at maximum flow rate time in pulsatile flow situation is much larger than that due to steady flow. The constriction and the flow pulsation produce flow disturbances at the vicinity of the constriction of the channel in the downstream direction.

  13. 47 CFR 22.805 - Channels for general aviation air-ground service.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 47 Telecommunication 2 2012-10-01 2012-10-01 false Channels for general aviation air-ground... CARRIER SERVICES PUBLIC MOBILE SERVICES Air-Ground Radiotelephone Service General Aviation Air-Ground Stations § 22.805 Channels for general aviation air-ground service. The following channels are...

  14. 47 CFR 22.805 - Channels for general aviation air-ground service.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 47 Telecommunication 2 2014-10-01 2014-10-01 false Channels for general aviation air-ground... CARRIER SERVICES PUBLIC MOBILE SERVICES Air-Ground Radiotelephone Service General Aviation Air-Ground Stations § 22.805 Channels for general aviation air-ground service. The following channels are...

  15. 47 CFR 22.805 - Channels for general aviation air-ground service.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 47 Telecommunication 2 2010-10-01 2010-10-01 false Channels for general aviation air-ground... CARRIER SERVICES PUBLIC MOBILE SERVICES Air-Ground Radiotelephone Service General Aviation Air-Ground Stations § 22.805 Channels for general aviation air-ground service. The following channels are...

  16. 47 CFR 22.805 - Channels for general aviation air-ground service.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 47 Telecommunication 2 2013-10-01 2013-10-01 false Channels for general aviation air-ground... CARRIER SERVICES PUBLIC MOBILE SERVICES Air-Ground Radiotelephone Service General Aviation Air-Ground Stations § 22.805 Channels for general aviation air-ground service. The following channels are...

  17. 47 CFR 22.805 - Channels for general aviation air-ground service.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 47 Telecommunication 2 2011-10-01 2011-10-01 false Channels for general aviation air-ground... CARRIER SERVICES PUBLIC MOBILE SERVICES Air-Ground Radiotelephone Service General Aviation Air-Ground Stations § 22.805 Channels for general aviation air-ground service. The following channels are...

  18. Flow of Slurry in the Inclined Closed Channel

    NASA Astrophysics Data System (ADS)

    Ashrafi Khorasani, Nariman; Piroozram, Parastoo

    2015-11-01

    The flow of slurry in a closed inclined circular channel is examined. The viscoelastic fluid is modeled as a derivative of typical Oldroyd-B relation of stress and velocity gradient. First, gravity is considered as the driving force for the fluid flow to simulate the existing sewage system. The complete flow field is evaluated for this case. Next, a pressure gradient is introduced to observe its effects on the flow. Velocity profile as well as stress distributions are given for different scenarios of the nonlinear fluid flowing in a closed channel with and without pressure gradient.

  19. Nitric oxide flow tagging in unseeded air.

    PubMed

    Dam, N; Klein-Douwel, R J; Sijtsema, N M; Meulen, J J

    2001-01-01

    A scheme for molecular tagging velocimetry is presented that can be used in air flows without any kind of seeding. The method is based on the local and instantaneous creation of nitric oxide (NO) molecules from N(2) and O(2) in the waist region of a focused ArF excimer laser beam. This NO distribution is advected by the flow and can be visualized any time later by laser-induced fluorescence in the gamma bands. The creation of NO is confirmed by use of an excitation spectrum. Two examples of the application of the new scheme for air-flow velocimetry are given in which single laser pulses are used for creation and visualization of NO. PMID:18033499

  20. Substorm Bulge/Surge Controlled by Polar Cap Flow Channels

    NASA Astrophysics Data System (ADS)

    Lyons, L. R.; Nishimura, T.; Zou, Y.; Gallardo-Lacourt, B.; Donovan, E.; Shiokawa, K.; Nicolls, M. J.; Chen, S.; Ruohoniemi, J. M.; Nishitani, N.; McWilliams, K. A.

    2015-12-01

    Previous studies have provided evidence that localized channels of enhanced polar cap flow drive plasma sheet/auroral oval flow channels, auroral poleward boundary intensifications and streamers, and substorm onset. Evidence has also indicated that a persistence of such flow channels after substorm onset may enhance post-onset auroral poleward expansion and activity. Here, we combine auroral imager and radar observations to show evidence that polar-cap flow channels can directly feed the substorm bulge westward motion, i.e., the westward traveling surge, and its poleward expansion well into the pre-existing polar cap. By taking advantage of the capability of tracing polar cap arcs and patches over long distances with red line imaging, we are able to trace flow features that strongly affect the substorm bulge across the polar cap for up to ~1-1.5 hr prior to their impacting and affecting the substorm bulge.

  1. Lessons Learned from AIRS: Improved Determination of Surface and Atmospheric Temperatures Using Only Shortwave AIRS Channels

    NASA Technical Reports Server (NTRS)

    Susskind, Joel

    2011-01-01

    This slide presentation reviews the use of shortwave channels available to the Atmospheric Infrared Sounder (AIRS) to improve the determination of surface and atmospheric temperatures. The AIRS instrument is compared with the Infrared Atmospheric Sounding Interferometer (IASI) on-board the MetOp-A satellite. The objectives of the AIRS/AMSU were to (1) provide real time observations to improve numerical weather prediction via data assimilation, (2) Provide observations to measure and explain interannual variability and trends and (3) Use of AIRS product error estimates allows for QC optimized for each application. Successive versions in the AIRS retrieval methodology have shown significant improvement.

  2. 40 CFR 89.414 - Air flow measurement specifications.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 40 Protection of Environment 20 2011-07-01 2011-07-01 false Air flow measurement specifications. 89.414 Section 89.414 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) AIR... Emission Test Procedures § 89.414 Air flow measurement specifications. (a) The air flow measurement...

  3. 40 CFR 89.414 - Air flow measurement specifications.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 40 Protection of Environment 20 2010-07-01 2010-07-01 false Air flow measurement specifications. 89.414 Section 89.414 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) AIR... Emission Test Procedures § 89.414 Air flow measurement specifications. (a) The air flow measurement...

  4. Transport Of Passive Scalars In A Turbulent Channel Flow

    NASA Technical Reports Server (NTRS)

    Kim, John; Moin, Parviz

    1990-01-01

    Computer simulation of transport of passive scalars in turbulent channel flow described in report. Shows flow structures and statistical properties. As used here, "passive scalars" means scalar quantities like fluctuations in temperature or concentrations of contaminants that do not disturb flow appreciably. Examples include transport of heat in heat exchangers, gas turbines, and nuclear reactors and dispersal of pollution in atmosphere.

  5. Flow characteristics and heat transfer in wavy walled channels

    NASA Astrophysics Data System (ADS)

    Mills, Zachary; Shah, Tapan; Monts, Vontravis; Warey, Alok; Balestrino, Sandro; Alexeev, Alexander

    2013-11-01

    Using lattice Boltzmann simulations, we investigated the effects of wavy channel geometry on the flow and heat transfer within a parallel plate heat exchanger. We observed three distinct flow regimes that include steady flow with and without recirculation and unsteady time-periodic flow. We determined the critical Reynolds numbers at which the flow transitions between different flow regimes. To validate our computational results, we compared the simulated flow structures with the structures observed in a flowing soap film. Furthermore, we examine the effects of the wavy channel geometry on the heat transfer. We find that the unsteady flow regime drastically enhances the rate of heat transfer and show that heat exchangers with wavy walls outperform currently used heat exchangers with similar volume and power characteristics. Results from our study point to a simple and efficient method for increasing performance in compact heat exchangers.

  6. Direct numerical simulation of turbulent channel flow with permeable walls

    NASA Astrophysics Data System (ADS)

    Hahn, Seonghyeon; Je, Jongdoo; Choi, Haecheon

    2002-01-01

    The main objectives of this study are to suggest a proper boundary condition at the interface between a permeable block and turbulent channel flow and to investigate the characteristics of turbulent channel flow with permeable walls. The boundary condition suggested is an extended version of that applied to laminar channel flow by Beavers & Joseph (1967) and describes the behaviour of slip velocities in the streamwise and spanwise directions at the interface between the permeable block and turbulent channel flow. With the proposed boundary condition, direct numerical simulations of turbulent channel flow that is bounded by the permeable wall are performed and significant skin-friction reductions at the permeable wall are obtained with modification of overall flow structures. The viscous sublayer thickness is decreased and the near-wall vortical structures are significantly weakened by the permeable wall. The permeable wall also reduces the turbulence intensities, Reynolds shear stress, and pressure and vorticity fluctuations throughout the channel except very near the wall. The increase of some turbulence quantities there is due to the slip-velocity fluctuations at the wall. The boundary condition proposed for the permeable wall is validated by comparing solutions with those obtained from a separate direct numerical simulation using both the Brinkman equation for the interior of a permeable block and the Navier Stokes equation for the main channel bounded by a permeable block.

  7. Production and study of megawatt air-nitrogen plasmatron with divergent channel of an output electrode

    NASA Astrophysics Data System (ADS)

    Isakaev, E. H.; Chinnov, V. F.; Tyuftyaev, A. S.; Gadzhiev, M. Kh; Sargsyan, M. A.; Konovalov, P. V.

    2015-11-01

    Megawatt generator of high-enthalpy air plasma jet (H ≥ 30 kJ/g) is constructed. Plasmatron belongs to the class of plasma torches with thermionic cathode, tangential swirl flow and divergent channel of an output electrode-anode. Plasma torch ensures the formation of the slightly divergent (2α = 12°) air plasma jet with the diameter D = 50 mm. The current-voltage characteristics of the plasma torch has virtually unchanged voltage relative to its current with enhanced (compared with arcs in cylindrical channels) stable combustion zone. Preliminary analysis of the obtained air plasma spectra shows that at a current of 1500 A near-axis zone of the plasma jet is characterized by a temperature of up to 15000 K, and the peripheral radiating area has a temperature of 8000-9000 K.

  8. Effect of asymmetrical flow field-flow fractionation channel geometry on separation efficiency.

    PubMed

    Ahn, Ji Yeon; Kim, Ki Hun; Lee, Ju Yong; Williams, P Stephen; Moon, Myeong Hee

    2010-06-11

    The separation efficiencies of three different asymmetrical flow field-flow fractionation (AF4) channel designs were evaluated using polystyrene latex standards. Channel breadth was held constant for one channel (rectangular profile), and was reduced either linearly (trapezoidal profile) or exponentially (exponential profile) along the length for the other two. The effective void volumes of the three channel types were designed to be equivalent. Theoretically, under certain flow conditions, the mean channel flow velocity of the exponential channel could be arranged to remain constant along the channel length, thereby improving separation in AF4. Particle separation obtained with the exponential channel was compared with particle separation obtained with the trapezoidal and rectangular channels. We demonstrated that at a certain flow rate condition (outflow/inflow rate=0.2), the exponential channel design indeed provided better performance with respect to the separation of polystyrene nanoparticles in terms of reducing band broadening. While the trapezoidal channel exhibited a little poorer performance than the exponential, the strongly decreasing mean flow velocity in the rectangular channel resulted in serious band broadening, a delay in retention time, and even failure of larger particles to elute. PMID:20439106

  9. Two-phase flow instabilities in a vertical annular channel

    SciTech Connect

    Babelli, I.; Nair, S.; Ishii, M.

    1995-09-01

    An experimental test facility was built to study two-phase flow instabilities in vertical annular channel with emphasis on downward flow under low pressure and low flow conditions. The specific geometry of the test section is similar to the fuel-target sub-channel of the Savannah River Site (SRS) Mark 22 fuel assembly. Critical Heat Flux (CHF) was observed following flow excursion and flow reversal in the test section. Density wave instability was not recorded in this series of experimental runs. The results of this experimental study show that flow excursion is the dominant instability mode under low flow, low pressure, and down flow conditions. The onset of instability data are plotted on the subcooling-Zuber (phase change) numbers stability plane.

  10. Evaporation from flowing channels ( mass-transfer formulas).

    USGS Publications Warehouse

    Fulford, J.M.; Sturm, T.W.

    1984-01-01

    Stability-dependent and Dalton-type mass transfer formulas are determined from experimental evaporation data in ambient and heated channels and are shown to have similar performance in prediction of evaporation. The formulas developed are compared with those proposed by other investigators for lakes and flowing channels. -from ASCE Publications Information

  11. Erosional processes in channelized water flows on Mars

    NASA Technical Reports Server (NTRS)

    Baker, V. R.

    1979-01-01

    A hypothesis is investigated according to which the Martian outflow channels were formed by high-velocity flows of water or dynamically similar liquid. It is suggested that the outflow channels are largely the result of several interacting erosional mechanisms, including fluvial processes involving ice covers, macroturbulence, streamlining, and cavitation.

  12. 6. VIEW OF DAM 83, SHOWING OUTLET CHANNEL FLOWING INTO ...

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

    6. VIEW OF DAM 83, SHOWING OUTLET CHANNEL FLOWING INTO POND A WITH DIVERSION GATES LONG EAST (LEFT) SIDE OF OUTLET CHANNEL, LOOKING SOUTH FROM DOWNSTREAM FACE OF THE DAM - Upper Souris National Wildlife Refuge, Dam 83, Souris River Basin, Foxholm, Surrey (England), ND

  13. Unsteady compressible flows in channel with varying walls

    NASA Astrophysics Data System (ADS)

    Pořízková, P.; Kozel, K.; Horáček, J.

    2014-03-01

    This study deals with numerical solution of a 2D and 3D unsteady flows of a compressible viscous fluid in 2D and 3D channel for low inlet airflow velocity. The unsteadiness of the flow is caused by a prescribed periodic motion of a part of the channel wall, nearly closing the channel during oscillations. The channels shape is a simplified geometry of the glottal space in the human vocal tract. Goal is numerical simulation of flow in the channels which involves attributes of real flow causing acoustic perturbations. The system of Navier-Stokes equations closed with static pressure expression for ideal gas describes the unsteady laminar flow of compressible viscous fluid. The numerical solution is implemented using the finite volume method and the predictor-corrector MacCormack scheme with artificial viscosity using a grid of quadrilateral cells. The unsteady grid of quadrilateral cells is considered in the form of conservation laws using Arbitrary Lagrangian-Eulerian method. The application of developed method for numerical simulations of flow fields in the 2D and 3D channels, acquired from a developed program, are presented for inlet velocity u=4.12 m/s, inlet Reynolds number Re=4481 and the wall motion frequency 100 Hz.

  14. Fracture Flow Channel Imaging Using Cross-Polarized GPR Signals

    NASA Astrophysics Data System (ADS)

    Tsoflias, G. P.; Perll, C.; Baker, M.; Becker, M.

    2014-12-01

    Fractures control the flow of fluids in rocks with important implications for groundwater resources, contaminant transport, geothermal resources, sequestration of carbon dioxide, and the development of unconventional hydrocarbon resources. Ground penetrating radar (GPR) can be used to image fractured rock and monitor the flow of fluids in the subsurface. Conventional GPR imaging uses single-polarization, co-polarized signals. Changes in reflected signal amplitude result from changes in fracture aperture and changes in fluid electrical properties introduced by tracers or contaminants. Recent research has also shown changes in radar reflected signal phase resulting from changes in fluid electrical conductivity. However, the radar response is dependent on the polarization of EM waves. This study investigates the use of cross-polarized GPR signals for imaging flow channeling at a discrete horizontal fracture. Numerical modeling demonstrated that cross-polarized GPR data are able to image fracture channels when the axis of the channel is oriented obliquely to the EM wavefield orientation. Summation of the cross-polarized and co-polarized components results in an accurate representation of the total scattered energy from the channel. Multipolarization, time-lapse 3D GPR field data were used investigate GPR imaging of flow channeling in a discrete subhorizontal fracture. The GPR surveys were conducted during background fresh fracture water conditions and during six varying orientation dipole flow saline tracer tests. The cross-polarized data revealed flow channeling which is in agreement with the co-polarized GPR data and with independent hydraulic tests. In addition, the cross-polarized components showed changes in flow channeling as a result of changing dipole flow orientation and position. This study demonstrates that cross-polarized GPR signals can be used to enhance imaging of flow in fractured rock.

  15. Review of air flow measurement techniques

    SciTech Connect

    McWilliams, Jennifer

    2002-12-01

    Airflow measurement techniques are necessary to determine the most basic of indoor air quality questions: ''Is there enough fresh air to provide a healthy environment for the occupants of the building?'' This paper outlines airflow measurement techniques, but it does not make recommendations for techniques that should be used. The airflows that will be discussed are those within a room or zone, those between rooms or zones, such as through doorways (open or closed) or passive vents, those between the building and outdoors, and those through mechanical air distribution systems. Techniques that are highlighted include particle streak velocimetry, hot wire anemometry, fan pressurization (measuring flow at a given pressure), tracer gas, acoustic methods for leak size determination, the Delta Q test to determine duct leakage flows, and flow hood measurements. Because tracer gas techniques are widely used to measure airflow, this topic is broken down into sections as follows: decay, pulse injection, constant injection, constant concentration, passive sampling, and single and multiple gas measurements for multiple zones.

  16. Optical Air Flow Measurements for Flight Tests and Flight Testing Optical Air Flow Meters

    NASA Technical Reports Server (NTRS)

    Jentink, Henk W.; Bogue, Rodney K.

    2005-01-01

    Optical air flow measurements can support the testing of aircraft and can be instrumental to in-flight investigations of the atmosphere or atmospheric phenomena. Furthermore, optical air flow meters potentially contribute as avionics systems to flight safety and as air data systems. The qualification of these instruments for the flight environment is where we encounter the systems in flight testing. An overview is presented of different optical air flow measurement techniques applied in flight and what can be achieved with the techniques for flight test purposes is reviewed. All in-flight optical airflow velocity measurements use light scattering. Light is scattered on both air molecules and aerosols entrained in the air. Basic principles of making optical measurements in flight, some basic optical concepts, electronic concepts, optoelectronic interfaces, and some atmospheric processes associated with natural aerosols are reviewed. Safety aspects in applying the technique are shortly addressed. The different applications of the technique are listed and some typical examples are presented. Recently NASA acquired new data on mountain rotors, mountain induced turbulence, with the ACLAIM system. Rotor position was identified using the lidar system and the potentially hazardous air flow profile was monitored by the ACLAIM system.

  17. Flow and heat transfer in a curved channel

    NASA Technical Reports Server (NTRS)

    Brinich, P. F.; Graham, R. W.

    1977-01-01

    Flow and heat transfer in a curved channel of aspect ratio 6 and inner- to outer-wall radius ratio 0.96 were studied. Secondary currents and large longitudinal vortices were found. The heat-transfer rates of the outer and inner walls were independently controlled to maintain a constant wall temperature. Heating the inner wall increased the pressure drop along the channel length, whereas heating the outer wall had little effect. Outer-wall heat transfer was as much as 40 percent greater than the straight-channel correlation, and inner-wall heat transfer was 22 percent greater than the straight-channel correlation.

  18. Pulsating laminar fully developed channel and pipe flows.

    PubMed

    Haddad, Kais; Ertunç, Ozgür; Mishra, Manoranjan; Delgado, Antonio

    2010-01-01

    Analytical investigations are carried out on pulsating laminar incompressible fully developed channel and pipe flows. An analytical solution of the velocity profile for arbitrary time-periodic pulsations is derived by approximating the pulsating flow variables by a Fourier series. The explicit interdependence between pulsations of velocity, mass-flow rate, pressure gradient, and wall shear stress are shown by using the proper dimensionless parameters that govern the flow. Utilizing the analytical results, the scaling laws for dimensionless pulsation amplitudes of the velocity, mass-flow rate, pressure gradient, and wall shear stress are analyzed as functions of the dimensionless pulsation frequency. Special attention has been given to the scaling laws describing the flow reversal phenomenon occurring in pulsating flows, such as the condition for flow reversal, the dependency of the reversal duration, and the amplitude. It is shown that two reversal locations away from the wall can occur in pulsating flows in pipes and channels and the reversed amount of mass per period reaches a maximum at a certain dimensionless frequency for a given amplitude of mass-flow rate fluctuations. These analyses are numerically conducted for pipe and channel flows over a large frequency range in a comparative manner. PMID:20365456

  19. CFD modeling of turbulent duct flows for coolant channel analysis

    NASA Astrophysics Data System (ADS)

    Ungewitter, Ronald J.; Chan, Daniel C.

    1993-07-01

    The design of modern liquid rocket engines requires the analysis of chamber coolant channels to maximize the heat transfer while minimizing the coolant flow. Coolant channels often do not remain at a constant cross section or at uniform curvature. New designs require higher aspect ratio coolant channels than previously used. To broaden the analysis capability and to complement standard analysis tools an investigation on the accuracy of CFD predictions for coolant channel flow has been initiated. Validation of CFD capabilities for coolant channel analysis will enhance the capabilities for optimizing design parameters without resorting to extensive experimental testing. The eventual goal is to use CFD to determine the flow fields of unique coolant channel designs and therefore determine critical heat transfer coefficients. In this presentation the accuracy of a particular CFD code is evaluated for turbulent flows. The first part of the presentation is a comparison of numerical results to existing cold flow data for square curved ducts (NASA CR-3367, 'Measurements of Laminar and Turbulent Flow in a Curved Duct with Thin Inlet Boundary Layers'). The results of this comparison show good agreement with the relatively coarse experimental data. The second part of the presentation compares two cases of higher aspect ratio channels (AR=2.5,10) to show changes in axial and secondary flow strength. These cases match experimental work presently in progress and will be used for future validation. The comparison shows increased secondary flow strength of the higher aspect ratio case due to the change in radius of curvature. The presentation includes a test case with a heated wall to demonstrate the program's capability. The presentation concludes with an outline of the procedure used to validate the CFD code for future design analysis.

  20. Numerical investigation of interfacial transport resistance due to water droplets in proton exchange membrane fuel cell air channels

    NASA Astrophysics Data System (ADS)

    Koz, Mustafa; Kandlikar, Satish G.

    2013-12-01

    Oxygen transport resistance at the air flow channel and gas diffusion layer (GDL) interface is needed in modelling the performance of a proton exchange membrane fuel cell (PEMFC). This resistance is expressed through the non-dimensional Sherwood number (Sh). The effect of the presence of a droplet on Sh is studied numerically in an isolated air flow channel using a commercially available package, COMSOL Multiphysics®. A droplet is represented as a solid obstruction placed on the GDL-channel interface and centred along the channel width. The effect of a single droplet is first studied for a range of superficial mean air velocities and droplet sizes. Secondly, the effect of droplet spacing on Sh is studied through simulations of two consecutive droplets. Lastly, multiple droplets in a row are studied as a more representative case of a PEMFC air flow channel. The results show that the droplets significantly increase Sh above the fully developed value in the wake region. This enhancement increases with the number of droplets, droplet size, and superficial mean air velocity. Moreover, the analogy between mass and heat transfer is investigated by comparing Sh to the equivalent Nusselt number.

  1. Analysis and comparison between rough channel and pipe flows

    NASA Astrophysics Data System (ADS)

    Sassun, David; Flores, Oscar; Orlandi, Paolo

    2016-04-01

    Direct numerical simulations of turbulent channel and pipe flows are presented to highlight the effect of roughness at low Reynolds number (Reτ = 180 ‑ 360). Several surfaces are reproduced with the immersed boundaries method, allowing a one-to-one comparison of the two canonical flows. In general, all rough surfaces produce the same effect on the flow in pipes and channels, with small differences in the roughness function, RMS velocities and spectral energy density of pipes and channels. The only exception is for the rough surfaces made of longitudinal bars. In particular, the triangular bars (riblets) show drag reduction in the channel and drag increase in the pipe. This behaviour is linked to the development of spanwise rollers and wide u-structures near the plane of the crest of the pipe.

  2. 40 CFR 89.414 - Air flow measurement specifications.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 40 Protection of Environment 20 2014-07-01 2013-07-01 true Air flow measurement specifications. 89... Test Procedures § 89.414 Air flow measurement specifications. (a) The air flow measurement method used... during the test. Overall measurement accuracy must be ± 2 percent of the maximum engine value for...

  3. 40 CFR 89.414 - Air flow measurement specifications.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 40 Protection of Environment 21 2013-07-01 2013-07-01 false Air flow measurement specifications... Emission Test Procedures § 89.414 Air flow measurement specifications. (a) The air flow measurement method... during the test. Overall measurement accuracy must be ± 2 percent of the maximum engine value for...

  4. 40 CFR 89.414 - Air flow measurement specifications.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 40 Protection of Environment 21 2012-07-01 2012-07-01 false Air flow measurement specifications... Emission Test Procedures § 89.414 Air flow measurement specifications. (a) The air flow measurement method... during the test. Overall measurement accuracy must be ± 2 percent of the maximum engine value for...

  5. 40 CFR 90.416 - Intake air flow measurement specifications.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 40 Protection of Environment 20 2010-07-01 2010-07-01 false Intake air flow measurement... Gaseous Exhaust Test Procedures § 90.416 Intake air flow measurement specifications. (a) If used, the engine intake air flow measurement method used must have a range large enough to accurately measure...

  6. ABSORBING BOUNDARY TECHNIQUE FOR OPEN CHANNEL FLOWS. (R825200)

    EPA Science Inventory

    An absorbing boundary condition is formulated and applied to the one-dimensional open channel flow equations in conjunction with an explicit MacCormack scheme. The physical flow domain has been truncated by introducing an artificial pseudo-boundary. By using an appropriate bounda...

  7. Piecewise uniform conduction-like flow channels and method therefor

    DOEpatents

    Cummings, Eric B.; Fiechtner, Gregory J.

    2006-02-28

    A low-dispersion methodology for designing microfabricated conduction channels for on-chip electrokinetic-based systems is presented. The technique relies on trigonometric relations that apply for ideal electrokinetic flows, allowing faceted channels to be designed on chips using common drafting software and a hand calculator. Flows are rotated and stretched along the abrupt interface between adjacent regions with differing permeability. Regions bounded by interfaces form flow "prisms" that can be combined with other designed prisms to obtain a wide range of turning angles and expansion ratios while minimizing dispersion. Designs are demonstrated using two-dimensional numerical solutions of the Laplace equation.

  8. Experimental and Numerical Investigation of Flows in Expanding Channels

    SciTech Connect

    Vorobieff, Peter; Putkaradze, Vakhtang

    2008-10-24

    We present an experimental realization of the classical Jeffery-Hamel flows inside a wedge-shaped channel. We compare the measured velocity fields with the predictions of Jeffery-Hamel theory. A detailed experimental study of bifurcation diagrams for the solutions reveals the absolute stability of the pure outflow solution and an interesting hysteretic structure for bifurcations. We also observe a multiple vortex flow regime predicted earlier numerically and analytically. Experimental studies of the stability of the flow to perturbations at the channel exit are also conducted.

  9. Subsonic flow in the channel of a diagonal MHD generator

    SciTech Connect

    Isakova, N.P.; Medin, S.A.

    1981-05-01

    A numerical study has been made of the local and integral characteristics of the planar subsonic flow in the channel of an MHD generator with diagonal electrode connection. It is shown that the inhomogeneity in the parameter distribution is dependent on the electrical loading, and the largest deviations from homogeneous flow occur on open circuit and short circuit. A comparison is made with a channel of Faraday type as regards the main integral characteristics. The data from two-dimensional analysis are compared with those from a one-dimensional flow model.

  10. 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.

  11. Flow field induced particle accumulation inside droplets in rectangular channels.

    PubMed

    Hein, Michael; Moskopp, Michael; Seemann, Ralf

    2015-07-01

    Particle concentration is a basic operation needed to perform washing steps or to improve subsequent analysis in many (bio)-chemical assays. In this article we present field free, hydrodynamic accumulation of particles and cells in droplets flowing within rectangular micro-channels. Depending on droplet velocity, particles either accumulate at the rear of the droplet or are dispersed over the entire droplet cross-section. We show that the observed particle accumulation behavior can be understood by a coupling of particle sedimentation to the internal flow field of the droplet. The changing accumulation patterns are explained by a qualitative change of the internal flow field. The topological change of the internal flow field, however, is explained by the evolution of the droplet shape with increasing droplet velocity altering the friction with the channel walls. In addition, we demonstrate that accumulated particles can be concentrated, removing excess dispersed phase by splitting the droplet at a simple channel junction. PMID:26032835

  12. Flows and mixing in channels with misaligned superhydrophobic walls

    NASA Astrophysics Data System (ADS)

    Nizkaya, Tatiana V.; Asmolov, Evgeny S.; Zhou, Jiajia; Schmid, Friederike; Vinogradova, Olga I.

    2015-03-01

    Aligned superhydrophobic surfaces with the same texture orientation reduce drag in the channel and generate secondary flows transverse to the direction of the applied pressure gradient. Here we show that a transverse shear can be easily generated by using superhydrophobic channels with misaligned textured surfaces. We propose a general theoretical approach to quantify this transverse flow by introducing the concept of an effective shear tensor. To illustrate its use, we present approximate theoretical solutions and Dissipative Particle Dynamics simulations for striped superhydrophobic channels. Our results demonstrate that the transverse shear leads to complex flow patterns, which provide a new mechanism of a passive vertical mixing at the scale of a texture period. Depending on the value of Reynolds number two different scenarios occur. At relatively low Reynolds number the flow represents a transverse shear superimposed with two corotating vortices. For larger Reynolds number these vortices become isolated, by suppressing fluid transport in the transverse direction.

  13. Surface drifter trajectories highlight flow pathways in the Mozambique Channel

    NASA Astrophysics Data System (ADS)

    Hancke, L.; Roberts, M. J.; Ternon, J. F.

    2014-02-01

    The pattern of surface circulation in the Mozambique Channel was elucidated from the trajectories of 82 satellite-tracked drifters over the period 2000-2010 and complementary satellite-derived altimetry. Overall, the trajectories indicated that anticyclonic activity was mostly observed on the western side of the Channel, with cyclonic activity being more prevalent in the east. A lack of eddy activity was noted in the southeast corner of the Channel (i.e. SW of Madagascar). Drifter behaviour illustrated that surface water from the Comoros Basin, entrained into anticyclonic eddies during formation, can be retained and isolated for months whilst being transported southwards through the Channel. During a tropical cyclone weather event, a drifter was observed to switch between counter-rotating eddies indicating that horizontal mixing of the Ekman layer does occur. The drifters also illustrated and emphasised the flow field and transport between eddies (i.e. the interstitial flow) in the Mozambique Channel. Despite the dominance of southward propagating anticyclones, drifters were able to move north and south through the Channel in the frontal flow field between eddies within periods of 51-207 days. Cross-channel transport in both directions between the Madagascan and Mozambique shelf regions was similarly observed, with time spans of 19-30 days. Surprisingly, drifters from the southern limb of the East Madagascar Current were transported westward across the channel to the Mozambique shelf. This transport was similarly facilitated by the frontal flow field between eddies. It is hypothesised that the frontal zones between eddies and interstitial waters play an important role in distributing biota in the Mozambique Channel.

  14. Thermal Drawdown-Induced Flow Channeling in Fractured Geothermal Reservoirs

    NASA Astrophysics Data System (ADS)

    Fu, Pengcheng; Hao, Yue; Walsh, Stuart D. C.; Carrigan, Charles R.

    2016-03-01

    We investigate the flow-channeling phenomenon caused by thermal drawdown in fractured geothermal reservoirs. A discrete fracture network-based, fully coupled thermal-hydrological-mechanical simulator is used to study the interactions between fluid flow, temperature change, and the associated rock deformation. The responses of a number of randomly generated 2D fracture networks that represent a variety of reservoir characteristics are simulated with various injection-production well distances. We find that flow channeling, namely flow concentration in cooled zones, is the inevitable fate of all the scenarios evaluated. We also identify a secondary geomechanical mechanism caused by the anisotropy in thermal stress that counteracts the primary mechanism of flow channeling. This new mechanism tends, to some extent, to result in a more diffuse flow distribution, although it is generally not strong enough to completely reverse flow channeling. We find that fracture intensity substantially affects the overall hydraulic impedance of the reservoir but increasing fracture intensity generally does not improve heat production performance. Increasing the injection-production well separation appears to be an effective means to prolong the production life of a reservoir.

  15. 47 CFR 22.857 - Channel plan for commercial aviation air-ground systems.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 47 Telecommunication 2 2014-10-01 2014-10-01 false Channel plan for commercial aviation air-ground... CARRIER SERVICES PUBLIC MOBILE SERVICES Air-Ground Radiotelephone Service Commercial Aviation Air-Ground Systems § 22.857 Channel plan for commercial aviation air-ground systems. The 849-851 MHz and 894-896...

  16. 47 CFR 22.857 - Channel plan for commercial aviation air-ground systems.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 47 Telecommunication 2 2013-10-01 2013-10-01 false Channel plan for commercial aviation air-ground... CARRIER SERVICES PUBLIC MOBILE SERVICES Air-Ground Radiotelephone Service Commercial Aviation Air-Ground Systems § 22.857 Channel plan for commercial aviation air-ground systems. The 849-851 MHz and 894-896...

  17. 47 CFR 22.857 - Channel plan for commercial aviation air-ground systems.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 47 Telecommunication 2 2011-10-01 2011-10-01 false Channel plan for commercial aviation air-ground... CARRIER SERVICES PUBLIC MOBILE SERVICES Air-Ground Radiotelephone Service Commercial Aviation Air-Ground Systems § 22.857 Channel plan for commercial aviation air-ground systems. The 849-851 MHz and 894-896...

  18. 47 CFR 22.857 - Channel plan for commercial aviation air-ground systems.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 47 Telecommunication 2 2012-10-01 2012-10-01 false Channel plan for commercial aviation air-ground... CARRIER SERVICES PUBLIC MOBILE SERVICES Air-Ground Radiotelephone Service Commercial Aviation Air-Ground Systems § 22.857 Channel plan for commercial aviation air-ground systems. The 849-851 MHz and 894-896...

  19. Flow and heat transfer characteristics of orthogonally rotating channel

    NASA Astrophysics Data System (ADS)

    Tamura, Hiroshi; Ishigaki, Hiroshi

    1991-12-01

    Numerical analysis was conducted to predict the centripetal buoyant effect on flow and heat transfer characteristics in a channel rotating about a perpendicular axis. The conditions were assumed to be laminar, fully developed, and uniform heat flux. Calculation were conducted both for radially outward flow from the rotating axis and radially inward flow. The calculated results indicated that for radially outward flow buoyancy decreases the suction side friction and heat transfer while increasing pressure side friction and heat transfer. This trends were reversed for radially inward flow.

  20. Determination of air side heat transfer coefficient in a mini-channel heat exchanger using Wilson Plot method

    NASA Astrophysics Data System (ADS)

    Thoo, K. K.; Chin, W. M.; Heikal, M. R.

    2013-12-01

    In this study, the air side heat transfer coefficient of an aluminium mini-channel heat exchanger was investigated for single-phase flow in the mini-channel, with water in the tubes and air on the outside. Research methods included hydraulic tests on a single mini-channel tube, Wilson Plot experiments and experiment validation. Results obtained from the hydraulic test showed that turbulent flow occurred in the tube at a Reynolds number of 830. Wilson Plot experiments were conducted to determine air side heat transfer coefficient of the heat exchanger. The tube side Reynolds number was maintained above 1000 to ensure turbulent flow and tube side heat transfer coefficient was calculated using Gnielinski equation for turbulent flow. The air side heat transfer coefficients obtained from the Wilson Plot experiments were in good agreement with known correlations. The outcome of this study is to use the air side heat transfer coefficient to calculate the performance of refrigerant condensers for different tube pass ratios and flow pass configurations.

  1. Decentralized and Tactical Air Traffic Flow Management

    NASA Technical Reports Server (NTRS)

    Bertsimas, Dimitris; Odoni, Amedeo R.

    1997-01-01

    This project dealt with the following topics: 1. Review and description of the existing air traffic flow management system (ATFM) and identification of aspects with potential for improvement. 2. Identification and review of existing models and simulations dealing with all system segments (enroute, terminal area, ground) 3. Formulation of concepts for overall decentralization of the ATFM system, ranging from moderate decentralization to full decentralization 4. Specification of the modifications to the ATFM system required to accommodate each of the alternative concepts. 5. Identification of issues that need to be addressed with regard to: determination of the way the ATFM system would be operating; types of flow management strategies that would be used; and estimation of the effectiveness of ATFM with regard to reducing delay and re-routing costs. 6. Concept evaluation through identification of criteria and methodologies for accommodating the interests of stakeholders and of approaches to optimization of operational procedures for all segments of the ATFM system.

  2. Dynamics of premixed hydrogen/air flames in mesoscale channels

    SciTech Connect

    Pizza, Gianmarco; Frouzakis, Christos E.; Boulouchos, Konstantinos; Mantzaras, John; Tomboulides, Ananias G.

    2008-10-15

    Direct numerical simulation with detailed chemistry and transport is used to study the stabilization and dynamics of lean ({phi}=0.5) premixed hydrogen/air atmospheric pressure flames in mesoscale planar channels. Channel heights of h=2, 4, and 7 mm, and inflow velocities in the range 0.3{<=}U{sub IN}{<=}1100cm/ s are investigated. Six different burning modes are identified: mild combustion, ignition/extinction, closed steady symmetric flames, open steady symmetric flames, oscillating and, finally, asymmetric flames. Chaotic behavior of cellular flame structures is observed for certain values of U{sub IN}. Stability maps delineating the regions of the different flame types are finally constructed. (author)

  3. A universal transition to turbulence in channel flow

    NASA Astrophysics Data System (ADS)

    Sano, Masaki; Tamai, Keiichi

    2016-03-01

    Transition from laminar to turbulent flow drastically changes the mixing, transport, and drag properties of fluids, yet when and how turbulence emerges is elusive even for simple flow within pipes and rectangular channels. Unlike the onset of temporal disorder, which is identified as the universal route to chaos in confined flows, characterization of the onset of spatiotemporal disorder has been an outstanding challenge because turbulent domains irregularly decay or spread as they propagate downstream. Here, through extensive experimental investigation of channel flow, we identify a distinctive transition with critical behaviour. Turbulent domains continuously injected from an inlet ultimately decayed, or in contrast, spread depending on flow rates. Near a transition point, critical behaviour was observed. We investigate both spatial and temporal dynamics of turbulent clusters, measuring four critical exponents, a universal scaling function and a scaling relation, all in agreement with the (2 + 1)-dimensional directed percolation universality class.

  4. A Numerical simulation of transition in plane channel flow

    NASA Astrophysics Data System (ADS)

    Goglia, G.; Biringen, S.

    1982-08-01

    A numerical simulation of the final stages of transition to turbulence in plane channel flow at a Reynolds number of 7500 is described. Three dimensional, incompressible Navier-Stokes equations are numerically integrated to obtain the time evolution of two and three dimensional finite amplitude disturbances. Computations are performed on the CYBER-203 vector processor for a 32 by 33 by 32 grid. Solutions indicate the existence of structures similar to those observed in the laboratory and which are characteristic of various stages of transition that lead to final breakdown. Details of the resulting flow field after breakdown indicate the evolution of streak-like formations found in turbulent flows. Although the flow field does approach a steady state (turbulent channel flow), implementation of subgrid-scale terms are necessary to obtain proper turbulent statistics.

  5. A numerical simulation of transition in plane channel flow

    NASA Astrophysics Data System (ADS)

    Biringen, S.

    1983-01-01

    This paper involves a numerical simulation of the final stages of transition to turbulence in plane channel flow at a Reynolds number of 7500. Three-dimensional, incompressible Navier-Stokes equations are numerically integrated to obtain the time-evolution of two- and three-dimensional finite-amplitude disturbances. Computations are performed on the CYBER-203 vector processor for a 32 x 33 x 32 grid. Solutions indicate the existence of structures similar to those observed in the laboratory and which are characteristic of various stages of transition that lead to final breakdown. Details of the resulting flow field after breakdown indicate the evolution of streak-like formations found in turbulent flows. Although the flow field does approach a steady-state (turbulent channel flow), implementation of subgrid-scale terms are necesary to obtain proper turbulent statistics.

  6. A Numerical simulation of transition in plane channel flow

    NASA Technical Reports Server (NTRS)

    Goglia, G.; Biringen, S.

    1982-01-01

    A numerical simulation of the final stages of transition to turbulence in plane channel flow at a Reynolds number of 7500 is described. Three dimensional, incompressible Navier-Stokes equations are numerically integrated to obtain the time evolution of two and three dimensional finite amplitude disturbances. Computations are performed on the CYBER-203 vector processor for a 32 by 33 by 32 grid. Solutions indicate the existence of structures similar to those observed in the laboratory and which are characteristic of various stages of transition that lead to final breakdown. Details of the resulting flow field after breakdown indicate the evolution of streak-like formations found in turbulent flows. Although the flow field does approach a steady state (turbulent channel flow), implementation of subgrid-scale terms are necessary to obtain proper turbulent statistics.

  7. Combustor air flow control method for fuel cell apparatus

    DOEpatents

    Clingerman, Bruce J.; Mowery, Kenneth D.; Ripley, Eugene V.

    2001-01-01

    A method for controlling the heat output of a combustor in a fuel cell apparatus to a fuel processor where the combustor has dual air inlet streams including atmospheric air and fuel cell cathode effluent containing oxygen depleted air. In all operating modes, an enthalpy balance is provided by regulating the quantity of the air flow stream to the combustor to support fuel cell processor heat requirements. A control provides a quick fast forward change in an air valve orifice cross section in response to a calculated predetermined air flow, the molar constituents of the air stream to the combustor, the pressure drop across the air valve, and a look up table of the orifice cross sectional area and valve steps. A feedback loop fine tunes any error between the measured air flow to the combustor and the predetermined air flow.

  8. Flow rate limitation in open wedge channel under microgravity

    NASA Astrophysics Data System (ADS)

    Wei, YueXing; Chen, XiaoQian; Huang, YiYong

    2013-08-01

    A study of flow rate limitation in an open wedge channel is reported in this paper. Under microgravity condition, the flow is controlled by the convection and the viscosity in the channel as well as the curvature of the liquid free surface. A maximum flow rate is achieved when the curvature cannot balance the pressure difference leading to a collapse of the free surface. A 1-dimensional theoretical model is used to predict the critical flow rate and calculate the shape of the free surface. Computational Fluid Dynamics tool is also used to simulate the phenomenon. Results show that the 1-dimensional model overestimates the critical flow rate because extra pressure loss is not included in the governing equation. Good agreement is found in 3-dimensional simulation results. Parametric study with different wedge angles and channel lengths show that the critical flow rate increases with increasing the cross section area; and decreases with increasing the channel length. The work in this paper can help understand the surface collapsing without gravity and for the design in propellant management devices in satellite tanks.

  9. Separation of Particles in Swirling Flow in Coaxial Channel

    NASA Astrophysics Data System (ADS)

    Vasilevsky, Michail; Zyatikov, Pavel; Deeva, Vera; Kozyrev, Ilya

    2016-02-01

    Cyclones are widely used devices to separate a dispersed phase (e.g. particles or droplets) from a continuous phase. The separation of particles in coaxial channels with different length is considered in paper. In this study we show that as coaxial channels length grows, the efficiency increases. In addition we demonstrate that as a gap between cylinder components is reduced, the aerosol spray efficiency is reduced also in turbulent flow.

  10. Dean flow-coupled inertial focusing in curved channels

    PubMed Central

    Ramachandraiah, Harisha; Ardabili, Sahar; Faridi, Asim M.; Gantelius, Jesper; Kowalewski, Jacob M.; Mårtensson, Gustaf; Russom, Aman

    2014-01-01

    Passive particle focusing based on inertial microfluidics was recently introduced as a high-throughput alternative to active focusing methods that require an external force field to manipulate particles. In inertial microfluidics, dominant inertial forces cause particles to move across streamlines and occupy equilibrium positions along the faces of walls in flows through straight micro channels. In this study, we systematically analyzed the addition of secondary Dean forces by introducing curvature and show how randomly distributed particles entering a simple u-shaped curved channel are focused to a fixed lateral position exiting the curvature. We found the lateral particle focusing position to be fixed and largely independent of radius of curvature and whether particles entering the curvature are pre-focused (at equilibrium) or randomly distributed. Unlike focusing in straight channels, where focusing typically is limited to channel cross-sections in the range of particle size to create single focusing point, we report here particle focusing in a large cross-section area (channel aspect ratio 1:10). Furthermore, we describe a simple u-shaped curved channel, with single inlet and four outlets, for filtration applications. We demonstrate continuous focusing and filtration of 10 μm particles (with >90% filtration efficiency) from a suspension mixture at throughputs several orders of magnitude higher than flow through straight channels (volume flow rate of 4.25 ml/min). Finally, as an example of high throughput cell processing application, white blood cells were continuously processed with a filtration efficiency of 78% with maintained high viability. We expect the study will aid in the fundamental understanding of flow through curved channels and open the door for the development of a whole set of bio-analytical applications. PMID:25379077

  11. Plasma channel localisation during multiple filamentation in air

    SciTech Connect

    Panov, N A; Kosareva, O G; Kandidov, V P; Akoezbek, N; Scalora, M; Chin, S L

    2007-12-31

    It is shown by numerical simulations that multiple filamentation of a femtosecond laser pulse with a negative initial phase modulation in air leads to an increase in the density of self-induced laser plasma compared to the case when a transform-limited laser pulse of the same duration is used. Simultaneous control of the duration of the chirped pulse and the beam diameter results in an increase in the distance over which the first filament is formed, the length of the plasma channel, and its linear density. (nonlinear optical phenomena)

  12. Observations of the flow in the Mozambique Channel

    NASA Astrophysics Data System (ADS)

    de Ruijter, Wilhelmus P. M.; Ridderinkhof, Herman; Lutjeharms, Johann R. E.; Schouten, Mathijs W.; Veth, Cornelis

    2002-05-01

    During a recent research cruise to investigate the nature and continuity of the Mozambique Current, we observed that the flow in the Mozambique Channel is dominated by a train of large anti-cyclonic eddies (diameters >300 km) that reach to the channel bottom and propagate southward. At a frequency of 4 per year they cause a net poleward transport of about 15 Sv (1 Sv = 106 m3/s). In the deep sea, a Mozambique Undercurrent flows equatorward along the continental slope. Using a lowered acoustic Doppler current profiler maximum observed velocities are about 0.2 m/s around 2400 m with another current core around 1000 m. It carries about 5 Sv of intermediate (AAIW) and deep waters (NADW) of Atlantic origin into the Channel. Subsequently, the equatorward flowing AAIW is largely entrained by the eddies and, while mixing with intermediate water from the North Indian Ocean in the eddy core, returned to the Agulhas Retroflection region.

  13. Stability of stratified two-phase flows in inclined channels

    NASA Astrophysics Data System (ADS)

    Barmak, I.; Gelfgat, A. Yu.; Ullmann, A.; Brauner, N.

    2016-08-01

    Linear stability of the stratified gas-liquid and liquid-liquid plane-parallel flows in the inclined channels is studied with respect to all wavenumber perturbations. The main objective is to predict the parameter regions in which the stable stratified configuration in inclined channels exists. Up to three distinct base states with different holdups exist in the inclined flows, so that the stability analysis has to be carried out for each branch separately. Special attention is paid to the multiple solution regions to reveal the feasibility of the non-unique stable stratified configurations in inclined channels. The stability boundaries of each branch of the steady state solutions are presented on the flow pattern map and are accompanied by the critical wavenumbers and the spatial profiles of the most unstable perturbations. Instabilities of different nature are visualized by the streamlines of the neutrally stable perturbed flows, consisting of the critical perturbation superimposed on the base flow. The present analysis confirms the existence of two stable stratified flow configurations in a region of low flow rates in the countercurrent liquid-liquid flows. These configurations become unstable with respect to the shear mode of instability. It was revealed that in slightly upward inclined flows the lower and middle solutions for the holdup are stable in the part of the triple solution region, while the upper solution is always unstable. In the case of downward flows, in the triple solution region, none of the solutions are stable with respect to the short-wave perturbations. These flows are stable only in the single solution region at low flow rates of the heavy phase, and the long-wave perturbations are the most unstable ones.

  14. Ultrasound Doppler Velocimetry Measurements in Turbulent Liquid Metal Channel Flow

    NASA Astrophysics Data System (ADS)

    Rivero, Michel; Jian, Dandan; Karcher, Christian; Cuevas, Sergio

    2010-11-01

    Control of molten metal flow using magnetic fields is important in industrial applications. The Electromagnetic Flow Control Channel (EFCO) is an experimental test facility, located at Ilmenau University of Technology, for the development of such kind of control systems. The working fluid is the low-melting liquid metal alloy GaInSn in eutectic composition. In this channel, flow control is realized by combining and coupling the non-contact flow driving technology of electromagnetic pumps based on rotating permanent magnets and the non-contact flow rate measurement technology termed Lorentz Force Velocimetry (LFV). The flow rate is adjusted by controlling the rotation rate of the permanent magnet system. Physically, LFV is based on measuring the force acting on a magnet system. This force is induced by the melt flow passing through the static magnetic field generated by the system and is proportional to the flow. To calibrate such flow meters, we apply UDV technique to measure and analyse both turbulent hydrodynamic and MHD flow profiles in EFCO at various Reynolds numbers.

  15. Dynamic Flow Management Problems in Air Transportation

    NASA Technical Reports Server (NTRS)

    Patterson, Sarah Stock

    1997-01-01

    In 1995, over six hundred thousand licensed pilots flew nearly thirty-five million flights into over eighteen thousand U.S. airports, logging more than 519 billion passenger miles. Since demand for air travel has increased by more than 50% in the last decade while capacity has stagnated, congestion is a problem of undeniable practical significance. In this thesis, we will develop optimization techniques that reduce the impact of congestion on the national airspace. We start by determining the optimal release times for flights into the airspace and the optimal speed adjustment while airborne taking into account the capacitated airspace. This is called the Air Traffic Flow Management Problem (TFMP). We address the complexity, showing that it is NP-hard. We build an integer programming formulation that is quite strong as some of the proposed inequalities are facet defining for the convex hull of solutions. For practical problems, the solutions of the LP relaxation of the TFMP are very often integral. In essence, we reduce the problem to efficiently solving large scale linear programming problems. Thus, the computation times are reasonably small for large scale, practical problems involving thousands of flights. Next, we address the problem of determining how to reroute aircraft in the airspace system when faced with dynamically changing weather conditions. This is called the Air Traffic Flow Management Rerouting Problem (TFMRP) We present an integrated mathematical programming approach for the TFMRP, which utilizes several methodologies, in order to minimize delay costs. In order to address the high dimensionality, we present an aggregate model, in which we formulate the TFMRP as a multicommodity, integer, dynamic network flow problem with certain side constraints. Using Lagrangian relaxation, we generate aggregate flows that are decomposed into a collection of flight paths using a randomized rounding heuristic. This collection of paths is used in a packing integer

  16. Supersonic flow in an expanding MHD channel of diagonal type

    SciTech Connect

    Likhachev, A.P.; Medin, S.A.

    1983-03-01

    A quasi-two-dimensional numerical analysis of the supersonic flow of a nonviscous, non-heat-conducting gas in an expanding (with respect to the insulation walls) MHD channel of diagonal type is performed. The induced magnetic fields are neglected. The influence of the conditions of channel loading and the commutation angle of the short-circuited, ideally sectioned electrodes on the flow structure, the distribution of the electrodynamic parameters, and the integral characteristics of the generator is considered. The results of quasi-two-dimensional and quasi-one-dimensional calculations are compared.

  17. Fluctuating supply and emplacement dynamic of channelized lava flows

    NASA Astrophysics Data System (ADS)

    Tarquini, Simone; de'Michieli Vitturi, Mattia

    2014-05-01

    The evolution of lava flows emplaced on Mount Etna (Italy) in September 2004 is examined in detail through the analysis of morphometric measurements of flow units. The growth of the main channelized flow is consistent with a layering of lava blankets which maintains the initial geometry of the channel (although levees are widened and raised), and is here explicitly related to the repeated overflow of lava pulses. A simple analytical model is introduced describing the evolution of the flow level in a channelized flow unit fed by a fluctuating supply. The model, named FLOWPULSE, shows that a fluctuation in the velocity of lava extrusion at the vent triggers the formation of pulses which become increasingly high the farther they are from the vent, and are invariably destined to overflow within a given distance. The FLOWPULSE simulations are in accordance with the observed morphology, characterized by a very flat initial profile followed by a massive increase in flow unit cross-section area between 600 and 700 m downflow. The modeled emplacement dynamics provides also an explanation for the observed substantial "loss" of the original flowing mass with increasing distance from the vent.

  18. Bifurcations in Flow through a Wavy Walled Channel

    NASA Astrophysics Data System (ADS)

    Mills, Zachary; Sup Song, Won; Alexeev, Alexander

    2015-11-01

    Using computational modeling, we examine the bifurcations that occur in laminar flow of a Newtonian fluid in a channel with sinusoidal walls, driven by a constant pressure gradient. The lattice Boltzmann method was used as our computational model. Our simulations revealed that for a set of geometric parameters the flow in the channel undergoes multiple bifurcations across the range of flow rates investigated. These bifurcations take the form of an initial Hopf bifurcation where the flow transitions from steady to unsteady. The subsequent bifurcations in the flow take the form of additional Hopf, and period-doubling bifurcations. The type and pressure drop at which these bifurcations occur is highly dependent on the geometry of the channel. By performing simulations to determine the critical pressure drops where bifurcations occur and the type for various geometries we developed a flow regime map. The results are important for designing laminar heat/mass exchangers utilizing unsteady flows for enhancing transport processes. This work is supported by General Motors Corporation.

  19. Local dynamic subgrid-scale models in channel flow

    NASA Technical Reports Server (NTRS)

    Cabot, William H.

    1994-01-01

    The dynamic subgrid-scale (SGS) model has given good results in the large-eddy simulation (LES) of homogeneous isotropic or shear flow, and in the LES of channel flow, using averaging in two or three homogeneous directions (the DA model). In order to simulate flows in general, complex geometries (with few or no homogeneous directions), the dynamic SGS model needs to be applied at a local level in a numerically stable way. Channel flow, which is inhomogeneous and wall-bounded flow in only one direction, provides a good initial test for local SGS models. Tests of the dynamic localization model were performed previously in channel flow using a pseudospectral code and good results were obtained. Numerical instability due to persistently negative eddy viscosity was avoided by either constraining the eddy viscosity to be positive or by limiting the time that eddy viscosities could remain negative by co-evolving the SGS kinetic energy (the DLk model). The DLk model, however, was too expensive to run in the pseudospectral code due to a large near-wall term in the auxiliary SGS kinetic energy (k) equation. One objective was then to implement the DLk model in a second-order central finite difference channel code, in which the auxiliary k equation could be integrated implicitly in time at great reduction in cost, and to assess its performance in comparison with the plane-averaged dynamic model or with no model at all, and with direct numerical simulation (DNS) and/or experimental data. Other local dynamic SGS models have been proposed recently, e.g., constrained dynamic models with random backscatter, and with eddy viscosity terms that are averaged in time over material path lines rather than in space. Another objective was to incorporate and test these models in channel flow.

  20. Local dynamic subgrid-scale models in channel flow

    NASA Astrophysics Data System (ADS)

    Cabot, William H.

    1994-12-01

    The dynamic subgrid-scale (SGS) model has given good results in the large-eddy simulation (LES) of homogeneous isotropic or shear flow, and in the LES of channel flow, using averaging in two or three homogeneous directions (the DA model). In order to simulate flows in general, complex geometries (with few or no homogeneous directions), the dynamic SGS model needs to be applied at a local level in a numerically stable way. Channel flow, which is inhomogeneous and wall-bounded flow in only one direction, provides a good initial test for local SGS models. Tests of the dynamic localization model were performed previously in channel flow using a pseudospectral code and good results were obtained. Numerical instability due to persistently negative eddy viscosity was avoided by either constraining the eddy viscosity to be positive or by limiting the time that eddy viscosities could remain negative by co-evolving the SGS kinetic energy (the DLk model). The DLk model, however, was too expensive to run in the pseudospectral code due to a large near-wall term in the auxiliary SGS kinetic energy (k) equation. One objective was then to implement the DLk model in a second-order central finite difference channel code, in which the auxiliary k equation could be integrated implicitly in time at great reduction in cost, and to assess its performance in comparison with the plane-averaged dynamic model or with no model at all, and with direct numerical simulation (DNS) and/or experimental data. Other local dynamic SGS models have been proposed recently, e.g., constrained dynamic models with random backscatter, and with eddy viscosity terms that are averaged in time over material path lines rather than in space. Another objective was to incorporate and test these models in channel flow.

  1. Yield Hardening of Electrorheological Fluids in Channel Flow

    NASA Astrophysics Data System (ADS)

    Helal, Ahmed; Qian, Bian; McKinley, Gareth H.; Hosoi, A. E.

    2016-06-01

    Electrorheological fluids offer potential for developing rapidly actuated hydraulic devices where shear forces or pressure-driven flow are present. In this study, the Bingham yield stress of electrorheological fluids with different particle volume fractions is investigated experimentally in wall-driven and pressure-driven flow modes using measurements in a parallel-plate rheometer and a microfluidic channel, respectively. A modified Krieger-Dougherty model can be used to describe the effects of the particle volume fraction on the yield stress and is in good agreement with the viscometric data. However, significant yield hardening in pressure-driven channel flow is observed and attributed to an increase and eventual saturation of the particle volume fraction in the channel. A phenomenological physical model linking the densification and consequent microstructure to the ratio of the particle aggregation time scale compared to the convective time scale is presented and used to predict the enhancement in yield stress in channel flow, enabling us to reconcile discrepancies in the literature between wall-driven and pressure-driven flows.

  2. Determination of the functioning parameters in asymmetrical flow field-flow fractionation with an exponential channel.

    PubMed

    Déjardin, P

    2013-08-30

    The flow conditions in normal mode asymmetric flow field-flow fractionation are determined to approach the high retention limit with the requirement d≪l≪w, where d is the particle diameter, l the characteristic length of the sample exponential distribution and w the channel height. The optimal entrance velocity is determined from the solute characteristics, the channel geometry (exponential to rectangular) and the membrane properties, according to a model providing the velocity fields all over the cell length. In addition, a method is proposed for in situ determination of the channel height. PMID:23885667

  3. Transitional Flows in Imperfect Millimeter-Scale Channels

    NASA Astrophysics Data System (ADS)

    Lissandrello, Charles; Li, Le; Ekinci, Kamil L.; Yakhot, Victor

    2015-11-01

    The majority of workers studying transition to turbulence in pipes have been interested in the flow response to perturbations in otherwise perfect pipes. Conversely, the ``fuzzy'' problem involving inlet disturbances, pipe imperfections, and pipe roughness has not attracted as much attention. Here, we investigate both experimentally and theoretically the transition to turbulence in imperfect millimeter-scale channels. For probing the flows, we use microcantilever sensors embedded in the channel walls. We perform experiments in two nominally identical channels. We quantify growing perturbations near the channel wall by their spectra and statistical properties, including probability densities and low- and high-order moments. The different sets of imperfections in the two channels result in two random flows in which the high-order moments of the near-wall fluctuations differ by orders of magnitude. Surprisingly, however, the lowest-order statistics in both cases appear to be qualitatively similar and can be described by a proposed noisy Landau equation for a slow mode. The noise, regardless of its origin, regularizes the Landau singularity of the relaxation time and makes transitions driven by different noise sources appear similar.

  4. Surface-directed boundary flow in microfluidic channels.

    PubMed

    Huang, Tom T; Taylor, David G; Lim, Kwan Seop; Sedlak, Miroslav; Bashir, Rashid; Mosier, Nathan S; Ladisch, Michael R

    2006-07-01

    Channel geometry combined with surface chemistry enables a stable liquid boundary flow to be attained along the surfaces of a 12 microm diameter hydrophilic glass fiber in a closed semi-elliptical channel. Surface free energies and triangular corners formed by PDMS/glass fiber or OTS/glass fiber surfaces are shown to be responsible for the experimentally observed wetting phenomena and formation of liquid boundary layers that are 20-50 microm wide and 12 microm high. Viewing this stream through a 20 microm slit results in a virtual optical window with a 5 pL liquid volume suitable for cell counting and pathogen detection. The geometry that leads to the boundary layer is a closed channel that forms triangular corners where glass fiber and the OTS coated glass slide or PDMS touch. The contact angles and surfaces direct positioning of the fluid next to the fiber. Preferential wetting of corner regions initiates the boundary flow, while the elliptical cross-section of the channel stabilizes the microfluidic flow. The Young-Laplace equation, solved using fluid dynamic simulation software, shows contact angles that exceed 105 degrees will direct the aqueous fluid to a boundary layer next to a hydrophilic fiber with a contact angle of 5 degrees. We believe this is the first time that an explanation has been offered for the case of a boundary layer formation in a closed channel directed by a triangular geometry with two hydrophobic wetting edges adjacent to a hydrophilic surface. PMID:16800710

  5. Changes in air flow patterns using surfactants and thickeners during air sparging: Bench-scale experiments

    NASA Astrophysics Data System (ADS)

    Kim, Juyoung; Kim, Heonki; Annable, Michael D.

    2015-01-01

    Air injected into an aquifer during air sparging normally flows upward according to the pressure gradients and buoyancy, and the direction of air flow depends on the natural hydrogeologic setting. In this study, a new method for controlling air flow paths in the saturated zone during air sparging processes is presented. Two hydrodynamic parameters, viscosity and surface tension of the aqueous phase in the aquifer, were altered using appropriate water-soluble reagents distributed before initiating air sparging. Increased viscosity retarded the travel velocity of the air front during air sparging by modifying the viscosity ratio. Using a one-dimensional column packed with water-saturated sand, the velocity of air intrusion into the saturated region under a constant pressure gradient was inversely proportional to the viscosity of the aqueous solution. The air flow direction, and thus the air flux distribution was measured using gaseous flux meters placed at the sand surface during air sparging experiments using both two-, and three-dimensional physical models. Air flow was found to be influenced by the presence of an aqueous patch of high viscosity or suppressed surface tension in the aquifer. Air flow was selective through the low-surface tension (46.5 dyn/cm) region, whereas an aqueous patch of high viscosity (2.77 cP) was as an effective air flow barrier. Formation of a low-surface tension region in the target contaminated zone in the aquifer, before the air sparging process is inaugurated, may induce air flow through the target zone maximizing the contaminant removal efficiency of the injected air. In contrast, a region with high viscosity in the air sparging influence zone may minimize air flow through the region prohibiting the region from de-saturating.

  6. Using DNS and Statistical Learning to Model Bubbly Channel Flow

    NASA Astrophysics Data System (ADS)

    Ma, Ming; Lu, Jiacai; Tryggvason, Gretar

    2015-11-01

    The transient evolution of laminar bubbly flow in a vertical channel is examined by direct numerical simulation (DNS). Nearly spherical bubbles, initially distributed evenly in a fully developed parabolic flow, are driven relatively quickly to the walls, where they increase the drag and reduce the flow rate on a longer time scale. Once the flow rate has been decreased significantly, some of the bubbles move back into the channel interior and the void fraction there approaches the value needed to balance the weight of the mixture and the imposed pressure gradient. A database generated by averaging the DNS results is used to model the closure terms in a simple model of the average flow. Those terms relate the averaged lateral flux of the bubbles, the velocity fluctuations and the averaged surface tension force to the fluid shear, the void fraction and its gradient, as well as the distance to the nearest wall. An aggregated neural network is used for the statistically leaning of unknown closures, and closure relationships are tested by following the evolution of bubbly channel flow with different initial conditions. It is found that the model predictions are in reasonably good agreement with DNS results. Supported by NSF.

  7. Basic hydraulic principles of open-channel flow

    USGS Publications Warehouse

    Jobson, Harvey E.; Froehlich, David C.

    1988-01-01

    The three basic principles of open-channel-flow analysis--the conservation of mass, energy, and momentum--are derived, explained, and applied to solve problems of open-channel flow. These principles are introduced at a level that can be comprehended by a person with an understanding of the principles of physics and mechanics equivalent to that presented in the first college level course of the subject. The reader is assumed to have a working knowledge of algebra and plane geometry as well as some knowledge of calculus. Once the principles have been derived, a number of example applications are presented that illustrate the computation of flow through culverts and bridges, and over structures, such as dams and weirs. Because resistance to flow is a major obstacle to the successful application of the energy principle to open-channel flow, procedures are outlined for the rational selection of flow resistance coefficients. The principle of specific energy is shown to be useful in the prediction of water-surface profiles both in the qualitative and quantitative sense. (USGS)

  8. 47 CFR 22.857 - Channel plan for commercial aviation air-ground systems.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 47 Telecommunication 2 2010-10-01 2010-10-01 false Channel plan for commercial aviation air-ground systems. 22.857 Section 22.857 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) COMMON CARRIER SERVICES PUBLIC MOBILE SERVICES Air-Ground Radiotelephone Service Commercial Aviation Air-Ground Systems § 22.857 Channel plan...

  9. Investigation of Turbulent Flow in a Two-Dimensional Channel

    NASA Technical Reports Server (NTRS)

    Laufer, John

    1951-01-01

    A detailed exploration of the field of mean and fluctuating quantities in a two-dimensional turbulent channel flow is presented. The measurements were repeated at three Reynolds numbers, 12,300, 30,800, and 61,600, based on the half width of the channel and the maximum mean velocity. A channel of 5-inch width and 12:1 aspect ratio was used for the investigation. Mean-speed and axial-fluctuation measurements were made well within the laminar sublayer. The semitheoretical predictions concerning the extent of the laminar sublayer were confirmed. The distribution of the velocity fluctuations in the direction of mean flow u' shows that the influence of the viscosity extends farther from the wall than indicated by the mean velocity profile, the region of influence being approximately four times as wide.

  10. Urban Infrastructure, Channel-Floodplain Morphology and Flood Flow Patterns

    NASA Astrophysics Data System (ADS)

    Miller, A. J.; Smith, J. A.; Nelson, C. B.

    2006-12-01

    The relationship between the channel and the floodplain in urban settings is heavily influenced by (1) altered watershed hydrologic response and frequency distribution of flows, (2) channel enlargement resulting from altered hydrology under conditions of limited sediment supply, (3) direct modification of channels and floodplains for purposes of erosion mitigation, flood protection, commercial development and creation of public amenities, (4) valley constrictions and flow obstructions associated with bridges, culverts, road embankments and other types of floodplain encroachment causing fragmentation or longitudinal segmentation of the riparian corridor. Field observation of inundation patterns associated with recurring floods in the Baltimore metropolitan area is used in combination with 2-dimensional hydraulic modeling to simulate patterns of floodplain inundation and to explore the relationships between magnitude and shape of the flood hydrograph, morphology of the urban channel-floodplain system, and the frequency and extent of floodplain inundation. Case studies include a July 2004 flood associated with a 300-year 2-hour rainfall in a small (14.2 km2) urban watershed, as well as several other events caused by summer thunderstorms with shorter recurrence intervals that generated an extraordinary flood response. The influence of urban infrastructure on flood inundation and flow patterns is expressed in terms of altered (and hysteretic) stage-discharge relationships, stepped flood profiles, rapid longitudinal attenuation of flood waves, and transient flow reversals at confluences and constrictions. Given the current level of interest in restoration measures these patterns merit consideration in planning future development and mitigation efforts.

  11. Morphology of Cryogenic Flows and Channels on Dwarf Planet Ceres

    NASA Astrophysics Data System (ADS)

    Krohn, Katrin; Jaumann, Ralf; Otto, Katharina A.; von der Gathen, Isabel; Matz, Klaus-Dieter; Buczkowski, Debra L.; Williams, David A.; Pieters, Carle M.; Preusker, Frank; Roatsch, Thomas; Stephan, Katrin; Wagner, Roland J.; Russell, Christopher T.; Raymond, Carol A.

    2016-04-01

    Cereś surface is affected by numerous impact craters and some of them show features such as channels or multiple flow events forming a smooth, less cratered surface, indicating possible post-impact resurfacing [1,2]. Flow features occur on several craters on Ceres such as Haulani, Ikapati, Occator, Jarimba and Kondos in combination with smooth crater floors [3,4], appearing as extended plains, ponded material, lobate flow fronts and in the case of Haulani lobate flows originating from the crest of the central ridge [3] partly overwhelming the mass wasting deposits from the rim. Haulanís crater flanks are also affected by multiple flow events radiating out from the crater and partly forming breakages. Flows occur as fine-grained lobes with well-defined margins and as smooth undifferentiated streaky flows covering the adjacent surface. Thus, adjacent craters are covered by flow material. Occator also exhibits multiple flows but in contrast to Haulani, the flows originating from the center overwhelm the mass wasting deposits from the rim [4]. The flows have a "bluish" signature in the FC color filters ratio. Channels occur at relatively fresh craters. They also show the "bluish" signature like the flows and plains. Only few channels occur at older "reddish" craters. They are relatively fresh incised into flow features or crater ejecta. Most are small, narrow and have lobated lobes with predominant distinctive flow margins. The widths vary between a few tens of meters to about 3 km. The channels are found on crater flanks as well as on the crater floors. The occurrence of flow features indicates viscous material on the surface. Those features could be formed by impact melt. However, impact melt is produced during the impact, assuming similar material properties as the ejecta it is expected to have nearly the same age as the impact itself, but the flows and plains are almost free of craters, thus, they seem to be much younger than the impact itself. In addition, the

  12. Nonsteady flow of a vapor-drop flow in a heated channel

    SciTech Connect

    Kroshilin, V.E.; Khodzhaev, Y.D.

    1992-06-01

    Flow of a vapor-drop mixture in a heated channel is studied under steady and non-steady conditions using a model which considers direct thermal interaction of drops with the heating surface. 10 refs., 4 figs.

  13. Power formula for open-channel flow resistance

    USGS Publications Warehouse

    Chen, Cheng-lung

    1988-01-01

    This paper evaluates various power formulas for flow resistance in open channels. Unlike the logarithmic resistance equation that can be theoretically derived either from Prandtl's mixing-length hypothesis or von Karman's similarity hypothesis, the power formula has long had an appearance of empiricism. Nevertheless, the simplicity in the form of the power formula has made it popular among the many possible forms of flow resistance formulas. This paper reexamines the concept and rationale of the power formulation, thereby addressing some critical issues in the modeling of flow resistance.

  14. Turbulent flow and heat transfer in rotating channels and tubes

    NASA Astrophysics Data System (ADS)

    Mitiakov, V. Y.; Petropavlovskii, R. R.; Ris, V. V.; Smirnov, E. M.; Smirnov, S. A.

    This document is a reduction of the author's experimental results on turbulent flow characteristics and heat transfer in rotating channels whose axes are parallel to the plane of rotation. Substantial dissimilarities of longitudinal velocity field profile and pulsational characteristics are caused by effects of stabilization and destabilization and secondary flow production. Local heat transfer coefficients vary over the perimeter of the tube section connecting detected flow peculiarities. It is shown that the increase in rotational intensity caused an increase in the relative dissimilarity of the local heat transfer coefficients and increased their mean value.

  15. Flow regimes, bed morphology, and flow resistance in self-formed step-pool channels

    NASA Astrophysics Data System (ADS)

    Comiti, F.; Cadol, D.; Wohl, E.

    2009-04-01

    We used a mobile bed flume with scaled grain size distribution, channel geometry, and flow to examine morphology and hydraulics of stepped channels. We hypothesized that (1) step geometry and flow resistance differs significantly as a function of the range of grain sizes present, (2) a transition from nappe to skimming flow occurs in stepped channels with mobile beds for conditions similar to stepped spillways, and (3) the partitioning of flow resistance changes significantly when flow passes from nappe to skimming conditions. Results support each of these hypotheses and help to illuminate the complexity of V-Q relationships in stepped channels, in which a dramatic decrease in flow resistance and increase in velocity accompany the transition from nappe to skimming flow near step-forming events. Therefore, a single flow resistance equation applicable to both ordinary and large floods may not be ideal in stepped channels. Nonetheless, models based on dimensionless velocity and unit discharge appear more robust compared to those based on the Darcy-Weisbach friction factor.

  16. Statistics of polymer extensions in turbulent channel flow.

    PubMed

    Bagheri, Faranggis; Mitra, Dhrubaditya; Perlekar, Prasad; Brandt, Luca

    2012-11-01

    We present direct numerical simulations of turbulent channel flow with passive Lagrangian polymers. To understand the polymer behavior we investigate the behavior of infinitesimal line elements and calculate the probability distribution function (PDF) of finite-time Lyapunov exponents and from them the corresponding Cramer's function for the channel flow. We study the statistics of polymer elongation for both the Oldroyd-B model (for Weissenberg number Wi<1) and the FENE model. We use the location of the minima of the Cramer's function to define the Weissenberg number precisely such that we observe coil-stretch transition at Wi ≈1. We find agreement with earlier analytical predictions for PDF of polymer extensions made by Balkovsky, Fouxon, and Lebedev [Phys. Rev. Lett. 84, 4765 (2000)] for linear polymers (Oldroyd-B model) with Wi <1 and by Chertkov [Phys. Rev. Lett. 84, 4761 (2000)] for nonlinear FENE-P model of polymers. For Wi >1 (FENE model) the polymer are significantly more stretched near the wall than at the center of the channel where the flow is closer to homogenous isotropic turbulence. Furthermore near the wall the polymers show a strong tendency to orient along the streamwise direction of the flow, but near the center line the statistics of orientation of the polymers is consistent with analogous results obtained recently in homogeneous and isotropic flows. PMID:23214883

  17. Statistics of polymer extensions in turbulent channel flow

    NASA Astrophysics Data System (ADS)

    Bagheri, Faranggis; Mitra, Dhrubaditya; Perlekar, Prasad; Brandt, Luca

    2012-11-01

    We present direct numerical simulations of turbulent channel flow with passive Lagrangian polymers. To understand the polymer behavior we investigate the behavior of infinitesimal line elements and calculate the probability distribution function (PDF) of finite-time Lyapunov exponents and from them the corresponding Cramer's function for the channel flow. We study the statistics of polymer elongation for both the Oldroyd-B model (for Weissenberg number Wi<1) and the FENE model. We use the location of the minima of the Cramer's function to define the Weissenberg number precisely such that we observe coil-stretch transition at Wi ≈1. We find agreement with earlier analytical predictions for PDF of polymer extensions made by Balkovsky, Fouxon, and Lebedev [Phys. Rev. Lett.PRLTAO0031-900710.1103/PhysRevLett.84.4765 84, 4765 (2000)] for linear polymers (Oldroyd-B model) with Wi <1 and by Chertkov [Phys. Rev. Lett.PRLTAO0031-900710.1103/PhysRevLett.84.4761 84, 4761 (2000)] for nonlinear FENE-P model of polymers. For Wi >1 (FENE model) the polymer are significantly more stretched near the wall than at the center of the channel where the flow is closer to homogenous isotropic turbulence. Furthermore near the wall the polymers show a strong tendency to orient along the streamwise direction of the flow, but near the center line the statistics of orientation of the polymers is consistent with analogous results obtained recently in homogeneous and isotropic flows.

  18. The Effects of Wall Roughness on Particle Velocities in a Turbulent Channel Flow

    NASA Astrophysics Data System (ADS)

    Benson, Michael; Eaton, John

    2003-11-01

    Previous experiments on particle-laden turbulent channel flows have shown lower than expected particle mean velocities. This research examined wall roughness effects on particle velocity distributions. Experiments were conducted in an existing vertical, fully developed channel air flow apparatus. Particle-board walls in the flow development section were replaced with smooth acrylic walls. The final 1.7 m of the development section was either a smooth section made of acrylic or a second section roughened by attaching mesh screen made of 0.25 mm diameter wire. The channel operated at a Reynolds number of 13,800 and was seeded with 150 im diameter spherical glass particles at 15loading. The wall roughness had little effect on the mean fluid velocity profile, but the particle velocity profiles and PDF's showed substantial dependence on the wall roughness. Particle mean velocities were higher than the gas velocity for the smooth wall flow, but substantially lagged the gas phase in the rough wall case, except near the wall. The particle streamwise rms velocity was nearly uniform across the channel width for the rough wall case.

  19. 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.

  20. Capillary channel flow experiments aboard the International Space Station

    NASA Astrophysics Data System (ADS)

    Conrath, M.; Canfield, P. J.; Bronowicki, P. M.; Dreyer, M. E.; Weislogel, M. M.; Grah, A.

    2013-12-01

    In the near-weightless environment of orbiting spacecraft capillary forces dominate interfacial flow phenomena over unearthly large length scales. In current experiments aboard the International Space Station, partially open channels are being investigated to determine critical flow rate-limiting conditions above which the free surface collapses ingesting bubbles. Without the natural passive phase separating qualities of buoyancy, such ingested bubbles can in turn wreak havoc on the fluid transport systems of spacecraft. The flow channels under investigation represent geometric families of conduits with applications to liquid propellant acquisition, thermal fluids circulation, and water processing for life support. Present and near future experiments focus on transient phenomena and conduit asymmetries allowing capillary forces to replace the role of gravity to perform passive phase separations. Terrestrial applications are noted where enhanced transport via direct liquid-gas contact is desired.

  1. Capillary channel flow experiments aboard the International Space Station.

    PubMed

    Conrath, M; Canfield, P J; Bronowicki, P M; Dreyer, M E; Weislogel, M M; Grah, A

    2013-12-01

    In the near-weightless environment of orbiting spacecraft capillary forces dominate interfacial flow phenomena over unearthly large length scales. In current experiments aboard the International Space Station, partially open channels are being investigated to determine critical flow rate-limiting conditions above which the free surface collapses ingesting bubbles. Without the natural passive phase separating qualities of buoyancy, such ingested bubbles can in turn wreak havoc on the fluid transport systems of spacecraft. The flow channels under investigation represent geometric families of conduits with applications to liquid propellant acquisition, thermal fluids circulation, and water processing for life support. Present and near future experiments focus on transient phenomena and conduit asymmetries allowing capillary forces to replace the role of gravity to perform passive phase separations. Terrestrial applications are noted where enhanced transport via direct liquid-gas contact is desired. PMID:24483559

  2. The pulsating laminar flow in a rectangular channel

    NASA Astrophysics Data System (ADS)

    Valueva, E. P.; Purdin, M. S.

    2015-11-01

    The finite difference method is used to solve the task of the developed pulsating laminar flow in a rectangular channel. The optimum of the difference scheme parameters was determined. Data on the amplitude and phase of the longitudinal velocity oscillations, the hydraulic and friction drag coefficients, the shear stress on the wall have been obtained. Using the dimensionless value of the frequency pulsations two characteristic regimes — the quasisteady-state regime and the high-frequency regime have been identified. In the quasi-steady-state regime, the values of all hydrodynamic quantities at each instant of time correspond to the velocity value averaged over the cross section at a given moment of time. It is shown that in the high-frequency regime, the dependences on the dimensionless oscillation frequency of oscillating components of hydrodynamic quantities are identical for rectilinear channels with a different cross-sectional form (round pipe, flat and a rectangular channels). The effect of the aspect ratio of the rectangular channel sides channel on the pulsating flow dynamics has been analyzed.

  3. Passive scalars in turbulent channel flow at high Reynolds number

    NASA Astrophysics Data System (ADS)

    Pirozzoli, Sergio; Bernardini, Matteo; Orlandi, Paolo

    2015-11-01

    We study passive scalars in turbulent plane channels at computationally high Reynolds number, which allows to observe previously unnoticed effects. The mean scalar profiles are found to obey a generalized logarithmic law which includes a linear correction term in the whole lower half-channel, and they follow a universal parabolic defect profile in the core region. This is consistent with recent findings regarding the mean velocity profiles in channel flow. The scalar variances also exhibit a near universal parabolic distribution in the core flow, and hints of a sizeable log layer, unlike the velocity variances. The energy spectra highlight the formation of large scalar-bearing eddies spanning each half-channel, which are caused by production excess over dissipation, and which are clearly visible in the flow visualizations. Close correspondence of the velocity and scalar eddies is observed, the main difference being that the latter have more convoluted interfaces, which translates into higher scalar dissipation. Another notable Reynolds number effect is the decreased correlation of the scalar field with the vertical velocity field, which is traced to the reduced effectiveness of ejection events. We acknowledge that the results reported in this paper have been achieved using the PRACE Research Infrastructure resource FERMI based at CINECA, Casalecchio di Reno, Italy.

  4. The Impact of the AIRS Spatial Response on Channel-to-Channel and Multi-Instrument Data Analyses

    NASA Technical Reports Server (NTRS)

    Elliott, Denis A.; Pagano, Thomas S.; Aumann, H. H.

    2006-01-01

    The Atmospheric Infrared Sounder (AIRS) measures the infrared spectrum in 2378 channels between 3.7 and 15.4 microns with a very high spectral resolution of approximately 1200. AIRS footprints are approximately 1.1 by 0.6 degrees. Because AIRS is a grating spectrometer, each channel has a unique spatial response. Image rotation due to the scan mirror causes these spatial responses to rotate. In effect, each channel has 90 spatial responses, one for each scene footprint in the scan line. Although the spatial response for most channels is symmetric and nearly uniform, some channels have significantly asymmetric response. This paper reviews and describes the prelaunch measurements that characterized the spatial response functions. Next, it describes the conversion of the ground-based results into footprint-specific response functions valid in flight. Then we describe the postlaunch validation of the measurements, including centroid location, axes orientations, and a check on the full two-dimensional response functions. This latter check involves comparison of AIRS data with that of the Moderate Resolution Imaging Spectrometer (MODIS), which flies on the same platform as AIRS. An important result is that AIRS/MODIS brightness temperature comparisons are significantly improved (scatter reduced) when the AIRS spatial response is explicitly taken into account. Finally, a status report is given on attempts to fully verify the prelaunch measurements by deriving the AIRS spatial response from flight data alone.

  5. Femtosecond laser flow tagging in non-air flows

    NASA Astrophysics Data System (ADS)

    Zhang, Yibin; Calvert, Nathan

    2015-11-01

    The Femtosecond Laser Electronic Excitation Tagging (FLEET) [Michael, J. B. et al., Applied optics, 50(26), 2011] method is studied in nitrogen-containing gaseous flows. The underlying mechanism behind the FLEET process is the dissociation of molecular nitrogen into atomic nitrogen, which produces long-lived florescence as the nitrogen atoms recombine. Spectra and images of the resulting tagged line provide insight into the effects of different atmospheric gases on the FLEET process. The ionization cross-section, conductivity and energy states of the gaseous particles are each brought into consideration. These experiments demonstrate the feasibility for long-lived flow tagging on the order of hundreds of microseconds in non-air environments. Of particular interest are the enhancement of the FLEET signal with the addition of argon gas, and the non-monotonic quenching effect of oxygen on the length, duration and intensity of the resulting signal and spectra. FLEET is characterized in number of different atmospheric gases, including that simulating Mar's atmospheric composition.

  6. Predicting equilibrium states with Reynolds stress closures in channel flow and homogeneous shear flow

    NASA Technical Reports Server (NTRS)

    Abid, R.; Speziale, C. G.

    1993-01-01

    Turbulent channel flow and homogeneous shear flow have served as basic building block flows for the testing and calibration of Reynolds stress models. A direct theoretical connection is made between homogeneous shear flow in equilibrium and the log-layer of fully-developed turbulent channel flow. It is shown that if a second-order closure model is calibrated to yield good equilibrium values for homogeneous shear flow it will also yield good results for the log-layer of channel flow provided that the Rotta coefficient is not too far removed from one. Most of the commonly used second-order closure models introduce an ad hoc wall reflection term in order to mask deficient predictions for the log-layer of channel flow that arise either from an inaccurate calibration of homogeneous shear flow or from the use of a Rotta coefficient that is too large. Illustrative model calculations are presented to demonstrate this point which has important implications for turbulence modeling.

  7. Predicting equilibrium states with Reynolds stress closures in channel flow and homogeneous shear flow

    NASA Technical Reports Server (NTRS)

    Abid, R.; Speziale, C. G.

    1992-01-01

    Turbulent channel flow and homogeneous shear flow have served as basic building block flows for the testing and calibration of Reynolds stress models. A direct theoretical connection is made between homogeneous shear flow in equilibrium and the log-layer of fully-developed turbulent channel flow. It is shown that if a second-order closure model is calibrated to yield good equilibrium values for homogeneous shear flow it will also yield good results for the log-layer of channel flow provided that the Rotta coefficient is not too far removed from one. Most of the commonly used second-order closure models introduce an ad hoc wall reflection term in order to mask deficient predictions for the log-layer of channel flow that arise either from an inaccurate calibration of homogeneous shear flow or from the use of a Rotta coefficient that is too large. Illustrative model calculations are presented to demonstrate this point which has important implications for turbulence modeling.

  8. Overland flow erosion inferred from Martian channel network geometry

    NASA Astrophysics Data System (ADS)

    Seybold, Hansjörg; Kirchner, James

    2016-04-01

    The controversy about the origin of Mars' channel networks is almost as old as their discovery 150 years ago. Over the last few decades, new Mars probes have revealed more detailed structures in Martian The controversy about the origin of Mars' channel networks is almost as old as their discovery 150 years ago. Over the last few decades, new Mars probes have revealed more detailed structures in Martian drainage networks, and new studies suggest that Mars once had large volumes of surface water. But how this water flowed, and how it could have carved the channels, remains unclear. Simple scaling arguments show that networks formed by similar mechanisms should have similar branching angles on Earth and Mars, suggesting that Earth analogues can be informative here. A recent analysis of high-resolution data for the continental United States shows that climate leaves a characteristic imprint in the branching geometry of stream networks. Networks growing in humid regions have an average branching angle of α = 2π/5 = 72° [1], which is characteristic of network growth by groundwater sapping [2]. Networks in arid regions, where overland flow erosion is more dominant, show much smaller branching angles. Here we show that the channel networks on Mars have branching angles that resemble those created by surficial flows on Earth. This result implies that the growth of Martian channel networks was dominated by near-surface flow, and suggests that deeper infiltration was inhibited, potentially by permafrost or by impermeable weathered soils. [1] Climate's Watermark in the Geometry of River Networks, Seybold et al.; under review [2] Ramification of stream networks, Devauchelle et al.; PNAS (2012)

  9. Proper horizontal photospheric flows in a filament channel

    NASA Astrophysics Data System (ADS)

    Schmieder, B.; Roudier, T.; Mein, N.; Mein, P.; Malherbe, J. M.; Chandra, R.

    2014-04-01

    Context. An extended filament in the central part of the active region NOAA 11106 crossed the central meridian on Sept. 17, 2010 in the southern hemisphere. It has been observed in Hα with the THEMIS telescope in the Canary Islands and in 304 Å with the EUV imager (AIA) onboard the Solar Dynamic Observatory (SDO). Counterstreaming along the Hα threads and bright moving blobs (jets) along the 304 Å filament channel were observed during 10 h before the filament erupted at 17:03 UT. Aims: The aim of the paper is to understand the coupling between magnetic field and convection in filament channels and relate the horizontal photospheric motions to the activity of the filament. Methods: An analysis of the proper photospheric motions using SDO/HMI continuum images with the new version of the coherent structure tracking (CST) algorithm developed to track granules, as well as the large scale photospheric flows, was performed for three hours. Using corks, we derived the passive scalar points and produced a map of the cork distribution in the filament channel. Averaging the velocity vectors in the southern hemisphere in each latitude in steps of 3.5 arcsec, we defined a profile of the differential rotation. Results: Supergranules are clearly identified in the filament channel. Diverging flows inside the supergranules are similar in and out of the filament channel. Converging flows corresponding to the accumulation of corks are identified well around the Hα filament feet and at the edges of the EUV filament channel. At these convergence points, the horizontal photospheric velocity may reach 1 km s-1, but with a mean velocity of 0.35 km s-1. In some locations, horizontal flows crossing the channel are detected, indicating eventually large scale vorticity. Conclusions: The coupling between convection and magnetic field in the photosphere is relatively strong. The filament experienced the convection motions through its anchorage points with the photosphere, which are

  10. A Study on the Air flow outside Ambient Vaporizer Fin

    NASA Astrophysics Data System (ADS)

    Oh, G.; Lee, T.; Jeong, H.; Chung, H.

    2015-09-01

    In this study, we interpreted Fog's Fluid that appear in the Ambient Vaporizer and predict the point of change Air to Fog. We interpreted using Analysis working fluid was applied to LNG and Air. We predict air flow when there is chill of LNG in the air Temperature and that makes fog. Also, we interpreted based on Summer and Winter criteria in the air temperature respectively. Finally, we can check the speed of the fog when fog excreted.

  11. Soil flushing with EDTA solutions: A model for channeled flow

    SciTech Connect

    Garcia-Delgado, R.A.; Rodriguez-Maroto, J.M.; Gomez-Lahoz, C.; Vereda-Alonso, C.; Garcia-Herruzo, F.

    1998-04-01

    A 1-D model for the flushing of metal contaminated soils with extracting aqueous solutions is presented. Previous experimental results of the flushing of carbonatic soil contaminated with lead with EDTA solutions showed the formation of channels of preferential flow as well as substantial rebounds in effluent lead concentration after periods of no pumping, indicating an important kinetic limitation for lead removal. This limitation is associated with the presence of a stagnant aqueous phase in addition to the mobile aqueous phase running through the channels. The model assumes an initial homogeneous distribution of lead in the soil, mainly present as small spheres of a solid carbonate which must dissolve. If the spheres are far from the channels, after solution the lead must diffuse through the stagnant aqueous phase until it reaches the channels and is washed out of the column. The model is able to simulate the rebound curves as well as the effluent concentration during the course of the operation. The importance of the way the channels arise is established by sensitivity studies performed for different mechanisms of the solution circulation and the formation of channels. More experimental results are needed to discriminate which of the alternatives studied is operative.

  12. Erosive dynamics of channels incised by subsurface water flow

    NASA Astrophysics Data System (ADS)

    Lobkovsky, Alexander E.; Smith, Braunen E.; Kudrolli, Arshad; Mohrig, David C.; Rothman, Daniel H.

    2007-09-01

    We propose a dynamical model for channels incised into an erodible bed by subsurface water flow. The model is validated by the time-resolved topographic measurements of channel growth in a laboratory-scale experiment. Surface heights in the experiment are measured via a novel laser-aided imaging technique. The erosion rate in the model is composed of diffusive and advective components as well as a simple driving term due to the seeping water. Steady driving conditions may exist whenever channels are incised into a flat and level erodible bed by a water table replenished via steady (on average) rainfall. Under such steady driving conditions, the model predicts an asymptotically self-similar growing shape for the channel transects. Conversely, given a transect shape that evolved under steady driving conditions and an estimate of the erosion rate at the bottom of the channel, granular transport coefficients can be inferred from the static channel shape. We report an estimate of these transport coefficients for a system of ravines incised into unconsolidated sand in the Apalachicola River basin, Florida.

  13. Model reduction and feedback control of transitional channel flow

    NASA Astrophysics Data System (ADS)

    Ilak, Milos

    This dissertation examines the use of reduced-order models for design of linear feedback controllers for fluid flows. The focus is on transitional channel flow, a canonical shear flow case with a simple geometry yet complex dynamics. Reduced-order models of the linearized Navier-Stokes equations, which describe the evolution of perturbations in transitional channel flow, are computed using two methods for snapshot-based balanced truncation, Balanced Proper Orthogonal Decomposition (BPOD) and Eigensystem Realization Algorithm (ERA). The performance of these models in feedback control is evaluated in both linearized and nonlinear Direct Numerical Simulations (DNS) of channel flow. The first part of the dissertation describes the application of BPOD to very large systems, and the detailed evaluation of the resulting reduced-order models. Exact balanced truncation, a standard method from control theory, is not computationally tractable for very large systems, such as those typically encountered in fluid flow simulations. The BPOD method, introduced by Rowley (2005), provides a close approximation. We first show that the approximation is indeed close by applying the method to a 1-D linear perturbation to channel flow at a single spatial wavenumber pair, for which exact balanced truncation is tractable. Next, as the first application of BPOD to a very high-dimensional linear system, we show that reduced-order BPOD models of a localized 3-D perturbation capture the dynamics very well. Moreover, the BPOD models significantly outperform standard Proper Orthogonal Decomposition (POD) models, as illustrated by a striking example where models using the POD modes that capture most of the perturbation energy fail to capture the perturbation dynamics. Next, reduced-order models of a complete control system for linearized channel flow are obtained using ERA, a computationally efficient method that results in the same reduced-order models as BPOD. Linear Quadratic Gaussian (LQG

  14. Modeling of gas flow in the cylindrical channels of high-voltage plasma torches with rod electrodes

    NASA Astrophysics Data System (ADS)

    Borovskoy, A. M.; Popov, S. D.; Surov, A. V.

    2013-08-01

    The article is devoted to the calculation of gas dynamic parameters of gas flow in various areas of low-temperature plasma generator, therefore, target area's grid was built for the simulation of plasma gas flow in channels of studied high-voltage AC plasma torches and calculations of three-dimensional gas flow was made using GAMBIT and FLUENT soft-ware and Spalart-Allmares turbulence model, air flow was simulated in the tangential feed's areas, in the cylindrical channel, in the tapering nozzle chamber and in the mixing chamber of plasma torches and outside (in the environment); thus, 3D-modelling of the cold plasma-forming gas flow was performed in cylindrical channels of studied high-voltage AC plasma torches with rod electrodes for the first time.

  15. Numerical modeling of turbulent flow in a channel

    NASA Technical Reports Server (NTRS)

    Dai, Y. W.; Ghoniem, A. F.; Sherman, F. S.; Oppenheim, A. K.

    1983-01-01

    Two-dimensional incompressible turbulent flow in a channel with a backward-facing step was studied numerically by Chorin's Random Vortex Method (RVM), an algorithm capable of tracing the action of elementary turbulent eddies and their cumulative effects without imposing any restrictions upon their motions. The step occurs in one side of a channel with otherwise flat, parallel walls; its height equals 1/3, 1/4 or 1/5 the width of the channel downstream. The main objective was to investigate the behavior of the large-scale turbulent eddies in a flow and the flow characteristics in the separated shear layer, the reattached zone, and the rebuilding boundary layer after reattachment. The unsteady vorticity field and the distribution of time-averaged turbulent statistics were obtained. The effects of expansion step height and initial boundary layer state were also studied. Comparisons were made with the available experimental results. The agreement is satisfactory in the velocity profiles and in the reattachment length, and fairly good in the turbulence profiles. Also a mechanism of the development of the reattaching turbulent flow was suggested by the numerical results.

  16. Statistics of polymer extensions in turbulent channel flow

    NASA Astrophysics Data System (ADS)

    Bagheri, F.; Mitra, D.; Perlekar, P.; Brandt, L.

    2010-11-01

    We carry out direct numerical simulations of three dimensional channel flow with passive polymer additives. We also calculate, for the first time, the PDF of finite-time Lyapunov exponents and from them the corresponding Cramer's function for the channel flow. We study the statistics of polymer elongation for both the Oldroyd-B model (for Wi less than 1) and the FENE model. We use the location of the minima of the Cramer's function to define the Weissenberg number precisely such that we observe coil-stretch transition at Wi approximately 1. For the Oldroyd-B model we find that the PDF of polymer extensions shows power-law behavior irrespective of the wall-normal coordinate of the polymer molecule, but the range of scaling does depend on the wall-normal coordinate. The exponent of this power-law matches with the earlier theoretical results within error bars. In addition we also find the dependence of the PDF of polymer extension on the wall-normal coordinate, v.i.z, the polymer are more stretched near the wall than at the center of the flow. We further study the orientation of the polymers with respect the channel geometry. Our results show that the polymers close to the wall have a very high probability of being oriented along the stream-wise direction of the flow.

  17. Computational heat transfer analysis for oscillatory channel flows

    NASA Technical Reports Server (NTRS)

    Ibrahim, Mounir; Kannapareddy, Mohan

    1993-01-01

    An accurate finite-difference scheme has been utilized to investigate oscillatory, laminar and incompressible flow between two-parallel-plates and in circular tubes. The two-parallel-plates simulate the regenerator of a free-piston Stirling engine (foil type regenerator) and the channel wall was included in the analysis (conjugate heat transfer problem). The circular tubes simulate the cooler and heater of the engine with an isothermal wall. The study conducted covered a wide range for the maximum Reynolds number (from 75 to 60,000), Valensi number (from 2.5 to 700), and relative amplitude of fluid displacement (0.714 and 1.34). The computational results indicate a complex nature of the heat flux distribution with time and axial location in the channel. At the channel mid-plane we observed two thermal cycles (out of phase with the flow) per each flow cycle. At this axial location the wall heat flux mean value, amplitude and phase shift with the flow are dependent upon the maximum Reynolds number, Valensi number and relative amplitude of fluid displacement. At other axial locations, the wall heat flux distribution is more complex.

  18. Instability of streamwise vortices in plane channel flows

    NASA Technical Reports Server (NTRS)

    Coughlin, K.; Jimenez, J.; Moser, R. D.

    1994-01-01

    We present analysis and numerical experiments on the instability of streamwise vortices in 'minimal channel' flows and argue that this instability is a key feature in the observed intermittent cycle of formation, break-up, and re-formation of these structures. The base flow is a three-component, two-dimensional pair of counter-rotating rolls with axes aligned along the direction of the mean shear. While it is not a steady solution to the Navier-Stokes equations, we show numerically that this flow is unstable on a fast time scale to a secondary, three-dimensional Floquet mode. The growth of the secondary instability does not saturate in a new equilibrium, but continues until highly unstable local shear layers form and the entire flow breaks down into turbulence. Our analysis is motivated in part by the strong similarities between the intermittent turbulent cycle in minimal channel flows and one studied, both experimentally and in computations, in Couette-Taylor flow.

  19. Final stages of transition to turbulence in plane channel flow

    NASA Technical Reports Server (NTRS)

    Biringen, S.

    1984-01-01

    This paper involves a numerical simulation of the final stages of transition to turbulence in plane channel flow at a Reynolds number of 1500. Three-dimensional incompressible Navier-Stokes equations are numerically integrated to obtain the time evolution of two- and three-dimensional finite-amplitude disturbances. Computations are performed on the CYBER-203 vector processor for a 32 x 51 x 32 grid. Solutions indicate the existence of structures similar to those observed in the laboratory and characteristics of the various stages of transition that lead to final breakdown. In particular, evidence points to the formation of a upside-down-V-shaped vortex and the subsequent system of horseshoe vortices inclined to the main flow direction as the primary elements of transition. Details of the resulting flow field after breakdown indicate the evolution of streaklike formations found in turbulent flows. Although the flow field does approach a steady state (turbulent channel flow), the introduction of subgrid-scale terms seems necessary to obtain fully developed turbulence statistics.

  20. Final stages of transition to turbulence in plane channel flow

    NASA Astrophysics Data System (ADS)

    Biringen, S.

    1984-11-01

    This paper involves a numerical simulation of the final stages of transition to turbulence in plane channel flow at a Reynolds number of 1500. Three-dimensional incompressible Navier-Stokes equations are numerically integrated to obtain the time evolution of two- and three-dimensional finite-amplitude disturbances. Computations are performed on the CYBER-203 vector processor for a 32 x 51 x 32 grid. Solutions indicate the existence of structures similar to those observed in the laboratory and characteristics of the various stages of transition that lead to final breakdown. In particular, evidence points to the formation of a upside-down-V-shaped vortex and the subsequent system of horseshoe vortices inclined to the main flow direction as the primary elements of transition. Details of the resulting flow field after breakdown indicate the evolution of streaklike formations found in turbulent flows. Although the flow field does approach a steady state (turbulent channel flow), the introduction of subgrid-scale terms seems necessary to obtain fully developed turbulence statistics.

  1. Superelevation and overspill control secondary flow dynamics in submarine channels

    NASA Astrophysics Data System (ADS)

    Dorrell, R. M.; Darby, S. E.; Peakall, J.; Sumner, E. J.; Parsons, D. R.; Wynn, R. B.

    2013-08-01

    In subaerial and submarine meander bends, fluid flow travels downstream in a helical spiral, the structure of which is determined by centrifugal, hydrostatic, baroclinic, and Coriolis forces that together balance frictional stresses generated by the flow. The sense of rotation of this helical flow, and in particular, whether the near bed flow is directed toward the inner bank, e.g., "river-normal," or outer bank, e.g., "river-reversed," is crucial to the morphodynamic evolution of the channel. However, in recent years, there has been a debate over the river-normal or river-reversed nature of submarine flows. Herein, we develop a novel three-dimensional closure of secondary flow dynamics, incorporating downstream convective material transport, to cast new light on this debate. Specifically, we show that the presence of net radial material transport, arising from flow superelevation and overspill, exerts a key control on the near bed orientation of secondary flow in submarine meanders. Our analysis implies that river-reversed flows are likely to be much more prevalent throughout submarine-canyon fan systems than prior studies have indicated.

  2. Rivulet Flow In Vertical Parallel-Wall Channel

    SciTech Connect

    D. M. McEligot; G. E. Mc Creery; P. Meakin

    2006-04-01

    In comparison with studies of rivulet flow over external surfaces, rivulet flow confined by two surfaces has received almost no attention. Fully-developed rivulet flow in vertical parallel-wall channels was characterized, both experimentally and analytically for flows intermediate between a lower flow limit of drop flow and an upper limit where the rivulets meander. Although this regime is the most simple rivulet flow regime, it does not appear to have been previously investigated in detail. Experiments were performed that measured rivulet widths for aperture spacing ranging from 0.152 mm to 0.914 mm. The results were compared with a simple steadystate analytical model for laminar flow. The model divides the rivulet cross-section into an inner region, which is dominated by viscous and gravitational forces and where essentially all flow is assumed to occur, and an outer region, dominated by capillary forces, where the geometry is determined by the contact angle between the fluid and the wall. Calculations using the model provided excellent agreement with data for inner rivulet widths and good agreement with measurements of outer rivulet widths.

  3. Groundwater cleanup by in-situ sparging. VIII. Effect of air channeling on dissolved volatile organic compounds removal efficiency

    SciTech Connect

    Wilson, D.J.; Gomez-Lahoz, C.; Rodriguez-Maroto, J.M. )

    1994-12-01

    A mathematical model for removal of dissolved volatile organic compounds (VOCs) from contaminated aquifers by in-situ air sparging is described. The model assumes that the sparging air moves through persistent channels in the aquifer, and that VOC transport to the sparging air is by diffusion/dispersion and air-induced circulation of the water in the vicinity of the sparging well. The dependence of model results on the parameters of the model is explored. The use of pulsed air flow in sparging as a means to increase VOC transport by dispersion is suggested. An extension and modification of the Sellers-Schreiber preliminary screening model for in-situ air sparging is also described. The revised model includes an improved method for calculating bubble residence times in the aquifer, and also permits the modeling of nonaqueous phase liquid (NAPL) removal.

  4. A simple analytical model of coupled single flow channel over porous electrode in vanadium redox flow battery with serpentine flow channel

    NASA Astrophysics Data System (ADS)

    Ke, Xinyou; Alexander, J. Iwan D.; Prahl, Joseph M.; Savinell, Robert F.

    2015-08-01

    A simple analytical model of a layered system comprised of a single passage of a serpentine flow channel and a parallel underlying porous electrode (or porous layer) is proposed. This analytical model is derived from Navier-Stokes motion in the flow channel and Darcy-Brinkman model in the porous layer. The continuities of flow velocity and normal stress are applied at the interface between the flow channel and the porous layer. The effects of the inlet volumetric flow rate, thickness of the flow channel and thickness of a typical carbon fiber paper porous layer on the volumetric flow rate within this porous layer are studied. The maximum current density based on the electrolyte volumetric flow rate is predicted, and found to be consistent with reported numerical simulation. It is found that, for a mean inlet flow velocity of 33.3 cm s-1, the analytical maximum current density is estimated to be 377 mA cm-2, which compares favorably with experimental result reported by others of ∼400 mA cm-2.

  5. Numerical study of a novel micro-diaphragm flow channel with piezoelectric device for proton exchange membrane fuel cells

    NASA Astrophysics Data System (ADS)

    Ma, H. K.; Huang, S. H.; Chen, B. R.; Cheng, L. W.

    Previous studies have shown that the amplitude of the vibration of a piezoelectric (PZT) device produces an oscillating flow that changes the chamber volume along with a curvature variation of the diaphragm. In this study, an actuating micro-diaphragm with piezoelectric effects is utilized as an air-flow channel in proton exchange membrane fuel cell (PEMFC) systems, called PZT-PEMFC. This newly designed gas pump, with a piezoelectric actuation structure, can feed air into the system of an air-breathing PEMFC. When the actuator moves outward to increase the cathode channel volume, the air is sucked into the chamber; moving inward decreases the channel's volume and thereby compresses air into the catalyst layer and enhancing the chemical reaction. The air-standard PZT-PEMFC cycle is proposed to describe an air-breathing PZT-PEMFC. A novel design for PZT-PEMFCs has been proposed and a three-dimensional, transitional model has been successfully built to account for its major phenomena and performance. Moreover, at high frequencies, PZT actuation leads to a more stable current output, more drained water, higher sucked air, higher hydrogen consumption, and also overcomes concentration losses.

  6. Two-phase Flow Characteristics in a Gas-Flow Channel of Polymer Electrolyte Membrane Fuel Cells

    NASA Astrophysics Data System (ADS)

    Cho, Sung Chan

    Fuel cells, converting chemical energy of fuels directly into electricity, have become an integral part of alternative energy and energy efficiency. They provide a power source of high energy-conversion efficiency and zero emission, meeting the critical demands of a rapidly growing society. The proton exchange membrane (PEM) fuel cells, also called polymer electrolyte fuel cells (PEFCs), are the major type of fuel cells for transportation, portable and small-scale stationary applications. They provide high-power capability, work quietly at low temperatures, produce only water byproduct and no emission, and can be compactly assembled, making them one of the leading candidates for the next generation of power sources. Water management is one of the key issues in PEM fuel cells: appropriate humidification is critical for the ionic conductivity of membrane while excessive water causes flooding and consequently reduces cell performance. For efficient liquid water removal from gas flow channels of PEM fuel cells, in-depth understanding on droplet dynamics and two-phase flow characteristics is required. In this dissertation, theoretical analysis, numerical simulation, and experimental testing with visualization are carried out to understand the two-phase flow characteristics in PEM fuel cell channels. Two aspects of two-phase phenomena will be targeted: one is the droplet dynamics at the GDL surface; the other is the two-phase flow phenomena in gas flow channels. In the former, forces over a droplet, droplet deformation, and detachment are studied. Analytical solutions of droplet deformation and droplet detachment velocity are obtained. Both experiments and numerical simulation are conducted to validate analytical results. The effects of contact angle, channel geometry, superficial air velocity, properties of gas phase fluids are examined and criteria for the detachment velocity are derived to relate the Reynolds number to the Weber number. In the latter, two-phase flow

  7. 40 CFR 1065.225 - Intake-air flow meter.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 40 Protection of Environment 34 2013-07-01 2013-07-01 false Intake-air flow meter. 1065.225 Section 1065.225 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) AIR POLLUTION CONTROLS ENGINE-TESTING PROCEDURES Measurement Instruments Flow-Related Measurements § 1065.225...

  8. 40 CFR 1065.225 - Intake-air flow meter.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 40 Protection of Environment 33 2011-07-01 2011-07-01 false Intake-air flow meter. 1065.225 Section 1065.225 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) AIR POLLUTION CONTROLS ENGINE-TESTING PROCEDURES Measurement Instruments Flow-Related Measurements § 1065.225...

  9. 40 CFR 1065.225 - Intake-air flow meter.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 40 Protection of Environment 34 2012-07-01 2012-07-01 false Intake-air flow meter. 1065.225 Section 1065.225 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) AIR POLLUTION CONTROLS ENGINE-TESTING PROCEDURES Measurement Instruments Flow-Related Measurements § 1065.225...

  10. 40 CFR 1065.225 - Intake-air flow meter.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 40 Protection of Environment 33 2014-07-01 2014-07-01 false Intake-air flow meter. 1065.225 Section 1065.225 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) AIR POLLUTION CONTROLS ENGINE-TESTING PROCEDURES Measurement Instruments Flow-Related Measurements § 1065.225...

  11. 40 CFR 1065.225 - Intake-air flow meter.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 40 Protection of Environment 32 2010-07-01 2010-07-01 false Intake-air flow meter. 1065.225 Section 1065.225 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) AIR POLLUTION CONTROLS ENGINE-TESTING PROCEDURES Measurement Instruments Flow-Related Measurements § 1065.225...

  12. Particle displacement tracking applied to air flows

    NASA Technical Reports Server (NTRS)

    Wernet, Mark P.

    1991-01-01

    Electronic Particle Image Velocimeter (PIV) techniques offer many advantages over conventional photographic PIV methods such as fast turn around times and simplified data reduction. A new all electronic PIV technique was developed which can measure high speed gas velocities. The Particle Displacement Tracking (PDT) technique employs a single cw laser, small seed particles (1 micron), and a single intensified, gated CCD array frame camera to provide a simple and fast method of obtaining two-dimensional velocity vector maps with unambiguous direction determination. Use of a single CCD camera eliminates registration difficulties encountered when multiple cameras are used to obtain velocity magnitude and direction information. An 80386 PC equipped with a large memory buffer frame-grabber board provides all of the data acquisition and data reduction operations. No array processors of other numerical processing hardware are required. Full video resolution (640x480 pixel) is maintained in the acquired images, providing high resolution video frames of the recorded particle images. The time between data acquisition to display of the velocity vector map is less than 40 sec. The new electronic PDT technique is demonstrated on an air nozzle flow with velocities less than 150 m/s.

  13. Coherent vorticity extraction in turbulent channel flow using anisotropic wavelets

    NASA Astrophysics Data System (ADS)

    Yoshimatsu, Katsunori; Sakurai, Teluo; Schneider, Kai; Farge, Marie; Morishita, Koji; Ishihara, Takashi

    2014-11-01

    We examine the role of coherent vorticity in a turbulent channel flow. DNS data computed at friction-velocity based Reynolds number 320 is analyzed. The vorticity is decomposed using three-dimensional anisotropic orthogonal wavelets. Thresholding of the wavelet coefficients allows to extract the coherent vorticity, corresponding to few strong wavelet coefficients. It retains the vortex tubes of the turbulent flow. Turbulent statistics, e.g., energy, enstrophy and energy spectra, are close to those of the total flow. The nonlinear energy budgets are also found to be well preserved. The remaining incoherent part, represented by the large majority of the weak coefficients, corresponds to a structureless, i.e., a noise-like background flow.

  14. An improved near-wall treatment for turbulent channel flows

    NASA Astrophysics Data System (ADS)

    El Gharbi, Najla; Absi, Rafik; Benzaoui, Ahmed; Bennacer, Rachid

    2011-01-01

    The success of predictions of wall-bounded turbulent flows requires an accurate description of the flow in the near-wall region. This article presents a comparative study between different near-wall treatments and presents an improved method. The study is applied to fully developed plane channel flow (i.e. the flow between two infinitely large plates). Simulations were performed using Fluent. Near-wall treatments available in Fluent were tested: standard wall functions, non-equilibrium wall function and enhanced wall treatment. A user defined function (UDF), based on an analytical profile for the turbulent kinetic energy (Absi, R., 2008. Analytical solutions for the modeled k-equation. ASME Journal of Applied Mechanics, 75 (4), 044501), is developed and implemented. Predicted turbulent kinetic energy profiles are presented and validated by DNS data.

  15. Nonlinear dispersion of a pollutant ejected into a channel flow

    NASA Astrophysics Data System (ADS)

    Van Gorder, Robert A.; Vajravelu, Kuppalapalle

    2011-10-01

    In this paper, we study the nonlinear coupled boundary value problem arising from the nonlinear dispersion of a pollutant ejected by an external source into a channel flow. We obtain exact solutions for the steady flow for some special cases and an implicit exact solution for the unsteady flow. Additionally, we obtain analytical solutions for the transient flow. From the obtained solutions, we are able to deduce the qualitative influence of the model parameters on the solutions. Furthermore, we are able to give both exact and analytical expressions for the skin friction and wall mass transfer rate as functions of the model parameters. The model considered can be useful for understanding the polluting situations of an improper discharge incident and evaluating the effects of decontaminating measures for the water bodies.

  16. Aerodynamic investigation of the flow field in a 180 deg turn channel with sharp bend

    NASA Astrophysics Data System (ADS)

    Rau, Guido; Arts, Tony

    1994-07-01

    The internal cooling of gas turbine blades is generally ensured by secondary air flowing through narrow passages existing inside the airfoils. These internal channels are usually connected by 180 deg turns with sharp bends. The aerodynamic and associated convective heat transfer characteristics observed in this type of geometry are significantly influenced by strong secondary flows and flow separations. The purpose of the present experimental effort is to give a detailed description of some aerodynamic aspects of this particular flow pattern. Detailed measurements of the three-dimensional velocity field were performed by means of a two-component Laser Doppler Velocimeter. The third velocity component was obtained by repeating the measurements at two different orientations of the emitting optics with respect to the test section.

  17. Ion channel networks in the control of cerebral blood flow.

    PubMed

    Longden, Thomas A; Hill-Eubanks, David C; Nelson, Mark T

    2016-03-01

    One hundred and twenty five years ago, Roy and Sherrington made the seminal observation that neuronal stimulation evokes an increase in cerebral blood flow.(1) Since this discovery, researchers have attempted to uncover how the cells of the neurovascular unit-neurons, astrocytes, vascular smooth muscle cells, vascular endothelial cells and pericytes-coordinate their activity to control this phenomenon. Recent work has revealed that ionic fluxes through a diverse array of ion channel species allow the cells of the neurovascular unit to engage in multicellular signaling processes that dictate local hemodynamics.In this review we center our discussion on two major themes: (1) the roles of ion channels in the dynamic modulation of parenchymal arteriole smooth muscle membrane potential, which is central to the control of arteriolar diameter and therefore must be harnessed to permit changes in downstream cerebral blood flow, and (2) the striking similarities in the ion channel complements employed in astrocytic endfeet and endothelial cells, enabling dual control of smooth muscle from either side of the blood-brain barrier. We conclude with a discussion of the emerging roles of pericyte and capillary endothelial cell ion channels in neurovascular coupling, which will provide fertile ground for future breakthroughs in the field. PMID:26661232

  18. Application of large eddy interaction model to channel flow

    NASA Technical Reports Server (NTRS)

    Hong, S. K.; Rubesin, M. W.

    1985-01-01

    A procedure utilizing an expansion of proper orthogonal functions (or modes) to predict a fully developed flow in channel is derived. To examine numerical and conceptual difficulties, preliminary computations are performed with assigned mean velocity, and turbulence is expressed with only the first mode. The nonlinear interactions of the components of the first mode are treated specifically, with the influence of higher modes neglected; this treatment required adjustment of the skewness and effective Reynolds number to assure energy equilibrium of the first mode. Computational results show that the first mode possesses the structural character similar to that of the entire flow.

  19. Distribution of incompressible flow within interdigitated channels and porous electrodes

    NASA Astrophysics Data System (ADS)

    Kee, Robert J.; Zhu, Huayang

    2015-12-01

    This paper develops a general model with which to evaluate flow uniformity and pressure drop within interdigitated-channel structures, especially in the context of redox flow batteries. The governing equations are cast in dimensionless variables, leading to a set of characteristic dimensionless parameter groups. The systems of governing equations are solved computationally, with the results presented graphically. Because the results are general, the underlying model itself is not needed to apply the quantitative design guidelines. However, the paper presents and discusses all the information required to recreate the model as needed.

  20. River flow mass exponents with fractal channel networks and rainfall

    USGS Publications Warehouse

    Troutman, B.M.; Over, T.M.

    2001-01-01

    An important problem in hydrologic science is understanding how river flow is influenced by rainfall properties and drainage basin characteristics. In this paper we consider one approach, the use of mass exponents, in examining the relation of river flow to rainfall and the channel network, which provides the primary conduit for transport of water to the outlet in a large basin. Mass exponents, which characterize the power-law behavior of moments as a function of scale, are ideally suited for defining scaling behavior of processes that exhibit a high degree of variability or intermittency. The main result in this paper is an expression relating the mass exponent of flow resulting from an instantaneous burst of rainfall to the mass exponents of spatial rainfall and that of the network width function. Spatial rainfall is modeled as a random multiplicative cascade and the channel network as a recursive replacement tree; these fractal models reproduce certain types of self-similar behavior seen in actual rainfall and networks. It is shown that under these modeling assumptions the scaling behavior of flow mirrors that of rainfall if rainfall is highly variable in space, and on the other hand flow mirrors the structure of the network if rainfall is not so highly variable. ?? 2001 Elsevier Science Ltd. All rights reserved.

  1. Experimental study on heat transfer and flow resistance in improved latticework cooling channels

    NASA Astrophysics Data System (ADS)

    Deng, Hongwu; Wang, Kai; Zhu, Jianqin; Pan, Wenyan

    2013-06-01

    Characteristics of heat transfer and flow resistance of the latticework (vortex) cooling channel with ribs truncated at their two ends were theoretically and experimentally studied compared with regular and smooth channels of the same configuration. The results showed: the heat transfer efficiency of the latticework channel with two slots was better than those of regular and smooth channels of the same configuration, its flow resistance situation in the slotted channel becomes quite complex; The flow resistances of 2 mm- and 4 mm-slotted channels were obviously lower than that of the regular channel, but they are still much higher than that of the smooth channel; Compared with the regular channel, the total heat transfer efficiencies of the slotted channels were pretty improved, among them the 4-mm slotted channel has the biggest enhancement. From the experimental results, it is obvious that the latticework channel with proper slots has a great prospect in the design of the inner cooling channels of turbine blades.

  2. Integrated turbine-compressor provides air flow for cooling

    NASA Technical Reports Server (NTRS)

    Ferri, A.

    1970-01-01

    Modified supersonic turbine cycle provides cooling air to surrounding structures. Simplified mechanical design assures correct balance of air flow, allows direct issue of cool air to the structure, and assists in matching turbine work output to work input required by the compressor.

  3. Research on Air Flow Measurement and Optimization of Control Algorithm in Air Disinfection System

    NASA Astrophysics Data System (ADS)

    Bing-jie, Li; Jia-hong, Zhao; Xu, Wang; Amuer, Mohamode; Zhi-liang, Wang

    2013-01-01

    As the air flow control system has the characteristics of delay and uncertainty, this research designed and achieved a practical air flow control system by using the hydrodynamic theory and the modern control theory. Firstly, the mathematical model of the air flow distribution of the system is analyzed from the hydrodynamics perspective. Then the model of the system is transformed into a lumped parameter state space expression by using the Galerkin method. Finally, the air flow is distributed more evenly through the estimation of the system state and optimal control. The simulation results show that this algorithm has good robustness and anti-interference ability

  4. Flow interaction between multiple cross-flow inlets in a horizontal pipe or channel

    NASA Astrophysics Data System (ADS)

    Jha, Pranab N.; Smith, Chuck; Metcalfe, Ralph W.

    2013-11-01

    Incompressible flow in horizontal channels and pipes with multiple cross-flow inlets was studied numerically. Flow interference among the inlets was studied using an axisymmetric pipe flow model with five cross-flow inlets. Three basic flow regimes - trickle flow, partially blocked flow and fully blocked flow - were identified with respect to the blocking of upstream inlets by the downstream ones. The effects of inlet pressure and inlet size on the flow regimes under steady state conditions were studied. The presence of these regimes was supported by field data obtained from a horizontal natural gas well at two different times in the production cycle. Using a hydrostatic pressure model of reservoirs as the inlet boundary condition that drained fluid into the channel, the dynamic interaction of the inlets was studied. The transient behavior of the flow regimes was simulated and the key time-scales involved were identified. This is supported by field data where a similar behavior can be observed over time. Initially, the upstream inlets were in a blocked state, but opened up at a later time, leading to a trickle flow regime. Supported in Part by Apache Corporation.

  5. Three-dimensional freezing of flowing water in a tube cooled by air flow

    NASA Astrophysics Data System (ADS)

    Sugawara, M.; Komatsu, Y.; Beer, H.

    2015-05-01

    The 3-D freezing of flowing water in a copper tube cooled by air flow is investigated by means of a numerical analysis. The air flows normal to the tube axis. Several parameters as inlet water mean velocity w m , inlet water temperature T iℓ t , air flow temperature T a and air flow velocity u a are selected in the calculations to adapt it to a winter season actually encountered. The numerical results present the development of the ice layer mean thickness and its 3-D morphologies as well as the critical ice layer thickness in the tube choked by the ice layer.

  6. Air-flow regulation system for a coal gasifier

    DOEpatents

    Fasching, George E.

    1984-01-01

    An improved air-flow regulator for a fixed-bed coal gasifier is provided which allows close air-flow regulation from a compressor source even though the pressure variations are too rapid for a single primary control loop to respond. The improved system includes a primary controller to control a valve in the main (large) air supply line to regulate large slow changes in flow. A secondary controller is used to control a smaller, faster acting valve in a secondary (small) air supply line parallel to the main line valve to regulate rapid cyclic deviations in air flow. A low-pass filter with a time constant of from 20 to 50 seconds couples the output of the secondary controller to the input of the primary controller so that the primary controller only responds to slow changes in the air-flow rate, the faster, cyclic deviations in flow rate sensed and corrected by the secondary controller loop do not reach the primary controller due to the high frequency rejection provided by the filter. This control arrangement provides at least a factor of 5 improvement in air-flow regulation for a coal gasifier in which air is supplied by a reciprocating compressor through a surge tank.

  7. Rain and channel flow supplements to subsurface water beneath hyper-arid ephemeral stream channels

    NASA Astrophysics Data System (ADS)

    Kampf, Stephanie K.; Faulconer, Joshua; Shaw, Jeremy R.; Sutfin, Nicholas A.; Cooper, David J.

    2016-05-01

    In hyper-arid regions, ephemeral stream channels are important sources of subsurface recharge and water supply for riparian vegetation, but few studies have documented the subsurface water content dynamics of these systems. This study examines ephemeral channels in the hyper-arid western Sonoran Desert, USA to determine how frequently water recharges the alluvial fill and identify variables that affect the depth and persistence of recharge. Precipitation, stream stage, and subsurface water content measurements were collected over a three-year study at six channels with varying contributing areas and thicknesses of alluvial fill. All channels contain coarse alluvium composed primarily of sands and gravels, and some locations also have localized layers of fine sediment at 2-3 m depth. Rain alone contributed 300-400 mm of water input to these channels over three years, but water content responses were only detected for 36% of the rain events at 10 cm depth, indicating that much of the rain water was either quickly evaporated or taken up by plants. Pulses of water from rain events were detected only in the top meter of alluvium. The sites each experienced ⩽5 brief flow events, which caused transient saturation that usually lasted only a few hours longer than flow. These events were the only apparent source of water to depths >1 m, and water from flow events quickly percolated past the deepest measurement depths (0.5-3 m). Sustained saturation in the shallow subsurface only developed where there was a near-surface layer of finer consolidated sediments that impeded deep percolation.

  8. A correlation for nucleate flow boiling in small channels

    SciTech Connect

    Tran, T.N. |; Wambsganss, M.W.; Chyu, M.C.; France, D.M.

    1997-08-01

    Compact heat exchangers are becoming more attractive for applications in which energy conservation, space saving, and cost are important considerations. Applications exist in the process industries where phase-change heat transfer realizes more compact designs and improved performance compared to single-phase heat transfer. However, there have been only a few studies in the literature reporting on phase-change heat transfer and two-phase flow in compact heat exchangers, and validated design correlations are lacking. Recent data from experiments on flow boiling of refrigerants in small channels have led researchers to conclude that nucleation is the dominant heat transfer mechanism over a broad range of heat flux and wall superheats. Local heat transfer coefficients and overall two-phase pressure drops were measured for three different refrigerants with circular and non-circular channels in a range of pressures. This data base supports the nucleate boiling mechanism, and it was used to develop a new correlation for heat transfer in nucleate flow boiling. The correlation is based on the Rohsenow boiling model, introducing a confinement number defined by Kew and Cornwell. The new correlation predicts the experimental data for nucleate flow boiling of three refrigerants within {+-}15%.

  9. Direct numerical simulation of curved turbulent channel flow

    NASA Technical Reports Server (NTRS)

    Moser, R. D.; Moin, P.

    1984-01-01

    Low Reynolds number, mildly curved, turbulent channel flow has been simulated numerically without subgrid scale models. A new spectral numerical method developed for this problem was used, and the computations were performed with 2 million degrees of freedom. A variety of statistical and structural information has been extracted from the computed flow fields. These include mean velocity, turbulence stresses, velocity skewness, and flatness factors, space time correlations and spectra, all the terms in the Reynolds stress balance equations, and contour and vector plots of instantaneous velocity fields. The effects of curvature on this flow were determined by comparing the concave and convex sides of the channel. The observed effects are consistent with experimental observations for mild curvature. The most significant difference in the turbulence statistics between the concave and convex sides was in the Reynolds shear stress. This was accompanied by significant differences in the terms of the Reynolds shear stress balance equations. In addition, it was found that stationary Taylor-Gortler vortices were present and that they had a significant effect on the flow by contributing to the mean Reynolds shear stress, and by affecting the underlying turbulence.

  10. Strongly coupled turbulent gas-particle flows in vertical channels

    NASA Astrophysics Data System (ADS)

    Fox, Rodney O.; Capecelatro, Jesse; Desjardins, Olivier

    2015-11-01

    Eulerian-Lagrangian (EL) simulations of strongly coupled (high mass loading) gas-particle flows in vertical channels are performed with the purpose of exploring the fundamental physics of fully developed, wall-bounded multiphase turbulence. An adaptive spatial filter is developed that accurately decomposes the total granular energy of the particles into correlated and uncorrelated components at each location in the wall-normal direction of the flow. In this manner, Reynolds- and phase-averaged (PA) two-phase turbulence statistics up to second order are reported for both phases and for three values of the PA mean fluid velocity. As expected due to the high mass loading, in all cases the turbulence production due to mean drag dominates production due to mean shear. A multiphase LRR-IP Reynolds-stress turbulence model is developed to predict the turbulent flow statistics as a function of the wall-normal distance. Using a correlation for the vertical drift velocity developed from the EL data, the turbulence model predictions agree satisfactorily with all of one-point EL statistics for the vertical channel flows, as well as for the homogeneous cluster-induced turbulence (CIT) statistics reported previously. Funded by U.S. National Science Foundation (CBET-1437865).

  11. On the Analysis of Flows in Vibrating Channels

    NASA Astrophysics Data System (ADS)

    Zandi, Sahab; Mohammadi, Alireza; Floryan, Jerzy Maciej

    2015-11-01

    Pressure losses in channels with vibrating walls have been analyzed. Surface vibrations were assumed to have the form of travelling waves. The waves can have arbitrary profiles. The spectrally accurate immersed boundary conditions (IBC) method based on the Fourier expansions in the flow direction and the Chebyshev expansions in the transverse direction has been developed. The results show dependence of the pressure losses on the phase speed of the waves, with the waves propagating in the downstream direction reducing the pressure gradient required to maintain a fixed flow rate. A drag increase is observed when the waves propagate with a phase speed similar to the flow velocity. Analytical solution demonstrates that the drag changes result from the nonlinear interactions and vary proportionally to A2 for small enough A, where A stands for the wave amplitude. This work has been carried out with support from the Natural Sciences and Engineering Research Council (NSERC) of Canada.

  12. Large eddy simulation of turbulent channel flow: ILLIAC 4 calculation

    NASA Technical Reports Server (NTRS)

    Kim, J.; Moin, P.

    1979-01-01

    The three-dimensional time dependent equations of motion were numerically integrated for fully-developed turbulent channel flow. A large scale flow field was obtained directly from the solution of these equations, and small scale field motions were simulated through an eddy viscosity model. The calculations were carried out on the ILLIAC 4 computer. The computed flow patterns show that the wall layer consists of coherent structures of low speed and high speed streaks alternating in the spanwise direction. These structures were absent in the regions away from the wall. Hot spots, small localized regions of very large turbulent shear stress, were frequently observed. The profiles of the pressure velocity-gradient correlations show a significant transfer of energy from the normal to the spanwise component of turbulent kinetic energy in the immediate neighborhood of the wall ('the splatting effect').

  13. Pressure-driven flow in a channel with porous walls

    NASA Astrophysics Data System (ADS)

    Liu, Qianlong; Prosperetti, Andrea

    2010-11-01

    The finite-Reynolds-number three-dimensional flow in a channel bounded by one and two parallel porous walls is studied numerically. The porous medium is modelled by spheres in a simple cubic arrangement. The results for the slip velocity at the surface of the porous layers are compared with the phenomenological Beavers-Joseph model. It is found that the value of the slip coefficient is different for pressure-driven and shear-driven flow. A modification of the relation is suggested to deal with this feature. Furthermore, detailed results on the flow structure and the hydrodynamic forces and couple acting on the sphere layer bounding the porous medium are reported and their dependence on the Reynolds number illustrated. It is shown that, at finite Reynolds numbers, a lift force acts on the spheres, which may be expected to contribute to the the mobilization of bottom sediments.

  14. Flows and hypoxic blackwater events in managed ephemeral river channels

    NASA Astrophysics Data System (ADS)

    Hladyz, Sally; Watkins, Susanne C.; Whitworth, Kerry L.; Baldwin, Darren S.

    2011-04-01

    SummaryAs pressure increases on the availability of water resources worldwide, especially in the face of climatic change, it is probable that the likelihood of streams undergoing at least some periods of drying will increase in arid and semi-arid regions. This has implications for the ongoing management of waterways in these areas. One area of concern is the potential occurrence of hypoxic blackwater events upon re-instatement of flows in creek and river channels following periods of drying. Hypoxic blackwater events are characterised by high levels of dissolved organic carbon (DOC), the metabolism of which results in low dissolved oxygen (DO) in the water column, which can cause fish and crustacean mortality. Therefore, understanding hypoxic blackwater events is important in order to reduce the potential for fish mortalities and other water quality impacts from both managed and natural flows. In this study, we set out to determine the factors that influenced the occurrence of a hypoxic blackwater event in the Edward-Wakool river system, in southern NSW, Australia during the previous austral summer (2008-2009). Standing stocks of plant litter, emergent macrophytes and river red gum saplings ( Eucalyptus camaldulensis Dehn.), as well as rates of litterfall, were determined in dry and inundated channels. A series of mesocosm experiments were undertaken to determine which carbon source was the greatest contributor to DOC and to DO depletion, and what loadings could result in hypoxia. These experiments were then used to create a simple algorithm relating carbon loading in a dry channel to DOC in the overlying water column following inundation. Results revealed that plant litter was the main contributor to water column DOC and to DO depletion. Litter loadings equal to or greater than 370 g m -2 were found to cause DO in a shallow (20 cm) water column at 20 °C to fall to zero within two days. This loading was approximately half of that found in dry channels in the

  15. Experimental study on corrugated cross-flow air-cooled plate heat exchangers

    SciTech Connect

    Kim, Minsung; Baik, Young-Jin; Park, Seong-Ryong; Ra, Ho-Sang; Lim, Hyug

    2010-11-15

    Experimental study on cross-flow air-cooled plate heat exchangers (PHEs) was performed. The two prototype PHEs were manufactured in a stack of single-wave plates and double-wave plates in parallel. Cooling air flows through the PHEs in a crosswise direction against internal cooling water. The heat exchanger aims to substitute open-loop cooling towers with closed-loop water circulation, which guarantees cleanliness and compactness. In this study, the prototype PHEs were tested in a laboratory scale experiments. From the tests, double-wave PHE shows approximately 50% enhanced heat transfer performance compared to single-wave PHE. However, double-wave PHE costs 30% additional pressure drop. For commercialization, a wide channel design for air flow would be essential for reliable performance. (author)

  16. Sensitivity analysis of vegetation-induced flow steering in channels

    NASA Astrophysics Data System (ADS)

    Bywater-Reyes, S.; Wilcox, A. C.; Lightbody, A.; Stella, J. C.

    2014-12-01

    Morphodynamic feedbacks result in alternating bars within channels, and the resulting convective accelerations dictate the cross-stream force balance of channels and in turn influence morphology. Pioneer woody riparian trees recruit on river bars and may steer flow and alter this force balance. This study uses two-dimensional hydraulic modeling to test the sensitivity of the flow field to riparian vegetation at the reach scale. We use two test systems with different width-to-depth ratios, substrate sizes, and vegetation structure: the gravel-bed Bitterroot River, MT and the sand-bed Santa Maria River, AZ. We model vegetation explicitly as a drag force by spatially specifying vegetation density, height, and drag coefficient, across varying hydraulic (e.g., discharge, eddy viscosity) conditions and compare velocity vectors between runs. We test variations in vegetation configurations, including the present-day configuration of vegetation in our field systems (extracted from LiDAR), removal of vegetation (e.g., from floods or management actions), and expansion of vegetation. Preliminary model runs suggest that the sensitivity of convective accelerations to vegetation reflects a balance between the extent and density of vegetation inundated and other sources of channel roughness. This research quantifies how vegetation alters hydraulics at the reach scale, a fundamental step to understanding vegetation-morphodynamic interactions.

  17. Turbulent flow statistics of vegetative channel with seepage

    NASA Astrophysics Data System (ADS)

    Devi, Thokchom Bebina; Kumar, Bimlesh

    2015-12-01

    The present study is carried out for studying the impact of submerged, flexible vegetation in a channel where downward seepage occurs. Laboratory experiments on artificial vegetation of two different heights, 8 cm and 6 cm, were conducted for no-seepage, 10% seepage and 15% seepage cases. Vegetation height is an important parameter in influencing the flow characteristics in a vegetated channel, where velocity is reduced near the top of the vegetation. Results show that velocity measured at upstream vegetation section is always higher than the downstream section even with the application of downward seepage. The maximum value of Reynolds stress occurs near the top of the vegetation. When the flow enters the vegetation section, the local effect of the presence of vegetation on sediment transport is more at the upstream vegetation section and then decreases which is shown by higher Reynolds stress at the upstream as compared to downstream vegetation section highlighting the importance of vegetation in providing as an erosion control. The maximum Reynolds stress at no seepage is increased by a percentage of 17% for 10% seepage and average of 30.5% for 15% seepage. The turbulence intensities at no seepage are increased by an average value of 15% for 10% seepage and 25% for 15% seepage. The reduction of Reynolds stress and turbulent intensities along the longitudinal direction implies the importance of using vegetation as a river restoration measure providing considerable stability to channels. Third order moments highlight that downward seepage increases the streamwise flux and decreases the upward flux.

  18. Numerical simulation of droplets deposition in a horizontal turbulent channel flow

    NASA Astrophysics Data System (ADS)

    Shwaish, Ibraheem K.

    1999-11-01

    In this dissertation, a two-phase, air-droplets, dilute, turbulent, and steady state flow in a horizontal rectangular channel, is modeled and numerically simulated using a modified KIVA-3V code. The deposition of different sizes of droplets on the walls of the channel is also studied. In this model, the interaction effects between the phases (two-way coupling) are considered by source terms in the momentum and energy equations for the continuous phase and by the instantaneous local velocity of the air in the droplet equation of motion, which includes the aerodynamic and gravitational forces. The turbulence is modeled by a k-ɛ model. The interaction effects between the turbulence and the dispersed droplets are also taken into account. The effects of the turbulence on the droplets are modeled by a fluctuating component added to the local air velocity in the droplet equation of motion. The effects of the droplets on the turbulence are modeled by two extra terms in the equation of motion for k and for ɛ. A stochastic model, which includes the spray equation, the droplet equation of motion, and a computational particle technique, is utilized. The flow variables in this simulation are consistent with theory and with experimental correlations. The large droplet behaviors are consistent with theory and experiments. The small droplet behavior agrees with some studies and contradicts others.

  19. Relationship between surface velocity divergence and gas transfer in open-channel flows with submerged simulated vegetation

    NASA Astrophysics Data System (ADS)

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

    2016-05-01

    Velocity and gas concentration measurements were carried out to reveal gas transfer phenomena in open-channel turbulent flows with flat bottom and submerged vegetation bottom conditions. A large-scale coherent vortex appears near the vegetation top due to shear instability, and the submerged vegetation was found to promote gas transfer beneath the air- water interface. Furthermore, we revealed a great dependency of gas transfer on vegetation density. The present measurement results propose a new surface divergence model with wide generality, connecting reasonably the gas transfer velocity and the surface divergence intensity in open-channel flows, irrespective of bottom roughness conditions.

  20. A Flow-Channel Analysis for the Mars Hopper

    SciTech Connect

    W. Spencer Cooley

    2013-02-01

    The Mars Hopper is an exploratory vehicle designed to fly on Mars using carbon dioxide from the Martian atmosphere as a rocket propellant. The propellent gasses are thermally heated while traversing a radioisotope ther- mal rocket (RTR) engine’s core. This core is comprised of a radioisotope surrounded by a heat capacitive material interspersed with tubes for the propellant to travel through. These tubes, or flow channels, can be manu- factured in various cross-sectional shapes such as a special four-point star or the traditional circle. Analytical heat transfer and computational fluid dynamics (CFD) anal- yses were performed using flow channels with either a circle or a star cross- sectional shape. The nominal total inlet pressure was specified at 2,805,000 Pa; and the outlet pressure was set to 2,785,000 Pa. The CO2 inlet tem- perature was 300 K; and the channel wall was 1200 K. The steady-state CFD simulations computed the smooth-walled star shape’s outlet temper- ature to be 959 K on the finest mesh. The smooth-walled circle’s outlet temperature was 902 K. A circle with a surface roughness specification at 0.01 mm gave 946 K and at 0.1 mm yielded 989 K. The The effects of a slightly varied inlet pressure were also examined. The analytical calculations were based on the mass flow rates computed in the CFD simulations and provided significantly higher outlet temperature results while displaying the same comparison trends. Research relating to the flow channel heat transfer studies was also done. Mathematical methods to geometrically match the cross-sectional areas of the circle and star, along with a square and equilateral triangle, were derived. A Wolfram Mathematica 8 module was programmed to analyze CFD results using Richardson Extrapolation and calculate the grid convergence index (GCI). A Mathematica notebook, also composed, computes and graphs the bulk mean temperature along a flow channel’s length while the user dynam- ically provides the input

  1. Combustion wave propagation regimes in a channel equipped with an array of cross-flow cylindrical obstacles

    NASA Astrophysics Data System (ADS)

    Pinos, Thomas Arthur Richard

    Flame propagation through a channel equipped with obstacles was studied experimentally. Two types of obstacle geometries were investigated, i.e., wall-mounted cross-flow cylinders and fence-type obstacles mounted on the top and bottom channel surfaces. The motivation for this research is its applications to both high-speed propulsion and industrial explosion safety. The effect of obstacle distribution and blockage ratio on flame acceleration was investigated in a 2.54cm x 7.6cm "narrow" channel with wall-mounted cross-flow cylindrical obstacles. The cylinders were arranged in a "staggered" or "inline" pattern, with blockage ratios of 0.5 and 0.67. Schlieren images were used to study the flame shape and its leading edge velocity for a range of fuel-air mixtures compositions. It was determined that initial flame propagation occurs faster in higher blockage ratios due to the higher frequency perturbation to the flow. Flame acceleration led to different quasi-steady flame and detonation propagation regimes. In general, higher final steady flame velocities were reached in the lower blockage ratios, and detonation limits were found to be influenced by the geometry. The influence of channel width on flame acceleration was also determined using fence-type obstacles with a single blockage ratio. Experiments were performed in a 2.54cm x 7.6cm and 7.6cm x 7.6cm channel. Schlieren images were again used to study the flame shape and to obtain leading edge velocity. The flame tip was found to have a parabolic profile across the channel width for the narrower channel and flatter profile in the wider channel. It was determined that the channel width has a weak effect on the flame velocity down the channel length. As such, flame acceleration was initially only slightly more pronounced in the narrow channel before the reverse became true later in the wide channel.

  2. Microscopic origin of channeled flow in lamellar titanium aluminide.

    PubMed

    Katzarov, Ivaylo H; Paxton, Anthony T

    2010-06-01

    We employ a quantum mechanical bond order potential in an atomistic simulation of channeled flow. We show that the original hypothesis that this is achieved by a cooperative deployment of slip and twinning is correct, first because a twin is able to "protect" a 60° ordinary dislocation from becoming sessile, and second because the two processes are found to be activated by Peierls stresses of similar magnitude. In addition we show an explicit demonstration of the lateral growth of a twin, again at a similar level of stress. Thus these simultaneous processes are shown to be capable of channeling deformation into the observed state of plane strain in so-called "A"-oriented mechanical testing of titanium aluminide superalloy. PMID:20867180

  3. Study on airflow characteristics in the semi-closed irregular narrow flow channel

    NASA Astrophysics Data System (ADS)

    Jin, Yuzhen; Hu, Xiaodong; Zhu, Linhang; Hu, Xudong; Jin, Yingzi

    2016-04-01

    The air-jet loom is widely used in the textile industry. The interaction mechanism of airflow and yarn is not clear in such a narrow flow channel, the gas consumption is relatively large, the yarn motion is unstable and the weft insertion is often interrupted during the operation. In order to study the characteristics of the semi-closed flow field in profiled dents, the momentum conservation equation is modified and the model parameters and boundary conditions are set. Compared with the different r, the ratio of profiled dent's thickness and gap, the results show that the smaller the r is, the smaller the velocity fluctuations of the airflow is. When the angle of profiled dents α is close to zero, the diffusion of the airflow will be less. The experiment is also conducted to verify the result of the simulation with a high-speed camera and pressure sensor in profiled dents. The airflow characteristics in the semi-closed irregular narrow flow channel in the paper would provide the theoretical basis for optimizing the weft insertion process of the air-jet loom.

  4. Position paper -- Tank ventilation system design air flow rates

    SciTech Connect

    Goolsby, G.K.

    1995-01-04

    The purpose of this paper is to document a project position on required ventilation system design air flow rates for the waste storage tanks currently being designed by project W-236A, the Multi-Function Waste Tank Facility (MWTF). The Title 1 design primary tank heat removal system consists of two systems: a primary tank vapor space ventilation system; and an annulus ventilation system. At the conclusion of Title 1 design, air flow rates for the primary and annulus ventilation systems were 960 scfm and 4,400 scfm, respectively, per tank. These design flow rates were capable of removing 1,250,000 Btu/hr from each tank. However, recently completed and ongoing studies have resulted in a design change to reduce the extreme case heat load to 700,000 Btu/hr. This revision of the extreme case heat load, coupled with results of scale model evaporative testing performed by WHC Thermal Hydraulics, allow for a reduction of the design air flow rates for both primary and annulus ventilation systems. Based on the preceding discussion, ICF Kaiser Hanford Co. concludes that the design should incorporate the following design air flow rates: Primary ventilation system--500 scfm maximum and Annulus ventilation system--1,100 scfm maximum. In addition, the minimum air flow rates in the primary and annulus ventilation systems will be investigated during Title 2 design. The results of the Title 2 investigation will determine the range of available temperature control using variable air flows to both ventilation systems.

  5. Stability of stratified two-phase flows in horizontal channels

    NASA Astrophysics Data System (ADS)

    Barmak, I.; Gelfgat, A.; Vitoshkin, H.; Ullmann, A.; Brauner, N.

    2016-04-01

    Linear stability of stratified two-phase flows in horizontal channels to arbitrary wavenumber disturbances is studied. The problem is reduced to Orr-Sommerfeld equations for the stream function disturbances, defined in each sublayer and coupled via boundary conditions that account also for possible interface deformation and capillary forces. Applying the Chebyshev collocation method, the equations and interface boundary conditions are reduced to the generalized eigenvalue problems solved by standard means of numerical linear algebra for the entire spectrum of eigenvalues and the associated eigenvectors. Some additional conclusions concerning the instability nature are derived from the most unstable perturbation patterns. The results are summarized in the form of stability maps showing the operational conditions at which a stratified-smooth flow pattern is stable. It is found that for gas-liquid and liquid-liquid systems, the stratified flow with a smooth interface is stable only in confined zone of relatively low flow rates, which is in agreement with experiments, but is not predicted by long-wave analysis. Depending on the flow conditions, the critical perturbations can originate mainly at the interface (so-called "interfacial modes of instability") or in the bulk of one of the phases (i.e., "shear modes"). The present analysis revealed that there is no definite correlation between the type of instability and the perturbation wavelength.

  6. Instability of a cantilevered flexible plate in viscous channel flow

    NASA Astrophysics Data System (ADS)

    Balint, T. S.; Lucey, A. D.

    2005-10-01

    The stability of a flexible cantilevered plate in viscous channel flow is studied as a representation of the dynamics of the human upper airway. The focus is on instability mechanisms of the soft palate (flexible plate) that cause airway blockage during sleep. We solve the Navier Stokes equations for flow with Reynolds numbers up to 1500 fully coupled with the dynamics of the plate motion solved using finite-differences. The study is 2-D and based upon linearized plate mechanics. When both upper and lower airways are open, the plate is found to lose its stability through a flutter mechanism and a critical Reynolds number exists. When one airway is closed, the plate principally loses its stability through a divergence mechanism and a critical flow speed exists. However, below the divergence-onset flow speed, flutter can exist for low levels of structural damping in the flexible plate. Our results serve to extend understanding of flow-induced instability of cantilevered flexible plates and will ultimately improve the diagnosis and treatment of upper-airway disorders.

  7. Parallel, open-channel lateral flow (immuno) assay substrate based on capillary-channeled polymer films.

    PubMed

    Zhang, Lynn X; Jiang, Liuwei; Willett, Daniel R; Marcus, R Kenneth

    2016-02-01

    Presented here is a novel implementation of polypropylene capillary-channeled polymer (C-CP) films, functionalized for bioaffinity separations and implemented as a platform for lateral flow (immuno) assays. The parallel ∼80 μm × 80 μm channels pass test solutions down the 30 mm film length via spontaneous wicking action, setting up the possibility for immobilizing different capture agents in the respective channels. The base-film modification process is divided into two steps: ultraviolet light treatment to improve hydrophillicity of the polypropylene substrate and the physical adsorption of a functionalized lipid tethered ligand (LTL) as a selective capture agent. The entire modification procedure is performed under ambient conditions in an aqueous solution without extreme pH conditions. In this demonstration, physical adsorption of a biotinylated-LTL onto the UV-treated PP surface selectively captures Texas Red-labeled streptavidin (SAv-TR) in the presence of enhanced green fluorescence protein (EGFP), which passes without retention in less than 5 s. In addition to the fluorescence imaging of the protein solutes, matrix assisted laser desorption/ionization-mass spectrometry (MALDI-MS) was used to confirm the formation of the LTL-SAv conjugates on the channel surface as well as to demonstrate an alternative means of probing the capture step. The present effort sets the groundwork for further development of C-CP films as a parallel, multi-analyte LFA platform; a format that to-date has not been described. PMID:26646022

  8. Flow and Diffusion in Channel-Guided Cell Migration

    PubMed Central

    Marel, Anna-Kristina; Zorn, Matthias; Klingner, Christoph; Wedlich-Söldner, Roland; Frey, Erwin; Rädler, Joachim O.

    2014-01-01

    Collective migration of mechanically coupled cell layers is a notable feature of wound healing, embryonic development, and cancer progression. In confluent epithelial sheets, the dynamics have been found to be highly heterogeneous, exhibiting spontaneous formation of swirls, long-range correlations, and glass-like dynamic arrest as a function of cell density. In contrast, the flow-like properties of one-sided cell-sheet expansion in confining geometries are not well understood. Here, we studied the short- and long-term flow of Madin-Darby canine kidney (MDCK) cells as they moved through microchannels. Using single-cell tracking and particle image velocimetry (PIV), we found that a defined averaged stationary cell current emerged that exhibited a velocity gradient in the direction of migration and a plug-flow-like profile across the advancing sheet. The observed flow velocity can be decomposed into a constant term of directed cell migration and a diffusion-like contribution that increases with density gradient. The diffusive component is consistent with the cell-density profile and front propagation speed predicted by the Fisher-Kolmogorov equation. To connect diffusion-mediated transport to underlying cellular motility, we studied single-cell trajectories and occurrence of vorticity. We discovered that the directed large-scale cell flow altered fluctuations in cellular motion at short length scales: vorticity maps showed a reduced frequency of swirl formation in channel flow compared with resting sheets of equal cell density. Furthermore, under flow, single-cell trajectories showed persistent long-range, random-walk behavior superimposed on drift, whereas cells in resting tissue did not show significant displacements with respect to neighboring cells. Our work thus suggests that active cell migration manifests itself in an underlying, spatially uniform drift as well as in randomized bursts of short-range correlated motion that lead to a diffusion-mediated transport

  9. Effects of Longitudinal Grooves on the Stability of Channel Flow

    NASA Astrophysics Data System (ADS)

    Moradi, H. Vafadar; Floryan, Jerzy M.

    2014-11-01

    The travelling wave instability in a channel with small-amplitude longitudinal grooves of arbitrary shape has been studied. The disturbance velocity field is always three-dimensional with disturbances which connect to the two-dimensional waves in the limit of zero groove amplitude playing the critical role. The presence of grooves destabilizes the flow if the groove wave number β is larger than βtran ~ 4 . 22 , but stabilizes the flow for smaller β. It has been found that βtran does not depend on the groove amplitude. The dependence of the critical Reynolds number on the groove amplitude and wave number has been determined. Special attention has been paid to the drag-reducing long wavelength grooves, including the optimal grooves. It has been demonstrated that such grooves slightly increase the critical Reynolds number, i.e., such grooves do not cause an early breakdown into turbulence.

  10. Principles of transverse flow fractionation of microparticles in superhydrophobic channels.

    PubMed

    Asmolov, Evgeny S; Dubov, Alexander L; Nizkaya, Tatiana V; Kuehne, Alexander J C; Vinogradova, Olga I

    2015-07-01

    We propose a concept of fractionation of micron-sized particles in a microfluidic device with a bottom wall decorated by superhydrophobic stripes. The stripes are oriented at an angle α to the direction of a driving force, G, which generally includes an applied pressure gradient and gravity. Separation relies on the initial sedimentation of particles under gravity in the main forward flow, and their subsequent lateral deflection near a superhydrophobic wall due to generation of a secondary flow transverse to G. We provide some theoretical arguments allowing us to quantify the transverse displacement of particles in the microfluidic channel, and confirm the validity of theoretical predictions in test experiments with monodisperse fractions of microparticles. Our results can guide the design of superhydrophobic microfluidic devices for efficient sorting of microparticles with a relatively small difference in size and density. PMID:26016651

  11. Fluid flow over arbitrary bottom topography in a channel

    NASA Astrophysics Data System (ADS)

    Panda, Srikumar

    2016-05-01

    In this paper, two-dimensional free surface potential flow over an arbitrary bottom in a channel is considered to analyze the behavior of the free surface profile using linear theory. It is assumed that the fluid is inviscid, incompressible and flow is irrotational. Perturbation analysis in conjunction with Fourier transform technique is employed to determine the first order corrections of some important physical quantities such as free surface profile, velocity potential, etc. From the practical point of view, one arbitrary bottom topography is considered to determine the free surface profile since the free surface profile depends on the bottom topography. It is found that the free surface profile is oscillatory in nature, representing a wave propagating downstream and no wave upstream.

  12. Conservation-form equations of unsteady open-channel flow

    USGS Publications Warehouse

    Lai, C.; Baltzer, R.A.; Schaffranek, R.W.

    2002-01-01

    The unsteady open-channel flow equations are typically expressed in a variety of forms due to the imposition of differing assumptions, use of varied dependent variables, and inclusion of different source/sink terms. Questions often arise as to whether a particular equation set is expressed in a form consistent with the conservation-law definition. The concept of conservation form is developed to clarify the meaning mathematically. Six sets of unsteady-flow equations typically used in engineering practice are presented and their conservation properties are identified and discussed. Results of the theoretical development and analysis of the equations are substantiated in a set of numerical experiments conducted using alternate equation forms. Findings of these analytical and numerical efforts demonstrate that the choice of dependent variable is the fundamental factor determining the nature of the conservation properties of any particular equation form.

  13. Large eddy interactions in a turbulent channel flow

    NASA Technical Reports Server (NTRS)

    Hong, S. K.

    1985-01-01

    The dynamic processes of large eddies in a turbulent channel flow have been examined by utilizing an orthogonal expansion of the velocity fluctuation, known in the literature as the Proper Orthogonal Decomposition Theorem. The mathematical form of these functions is unknown in contrast to the Fourier analysis. Attention is focused on the nonlinear, turbulence-turbulence interaction process in the dynamical equation for large eddies (the first term in the expansion). The nonlinear interactions of the components of the first mode are treated exactly, but influences of higher modes are modeled. This requires adjustment of both the skewness and the effective Reynolds number so that the energy equilibrium of the large eddies is ensured when the mean velocity distribution is assumed known for experiments. Computational results show that the first mode contributes significantly to turbulent intensities and possesses a structural and statistical character similar to that of the entire flow.

  14. Ignition of hydrocarbon-air supersonic flow by volumetric ionization

    NASA Astrophysics Data System (ADS)

    Goldfeld, Marat A.; Pozdnyakov, George A.

    2015-11-01

    The paper describes the results of the electron-beam initiation of the combustion in the mixtures of hydrogen, natural gas or kerosene vapors with air. Electron beam characteristics were studied in closed volume with immobile gas. The researches included definition of an integrated current of an electronic beam, distribution of a current density and an estimation of average energy of electrons. Possibility of fuel mixtures ignition by means of this approach in the combustor at high velocity at the entrance was demonstrated. Experiments were carried out at Mach numbers of 4 and 5. Process of ignition and combustion under electron beam action was researched. It was revealed that ignition of mixture occurs after completion of electron gun operation. Data obtained have confirmed effectiveness of electron beam application for ignition of hydrogen and natural gas. The numerical simulation of the combustion of mixture in channel was carried out by means of ANSYS CFD 12.0 instrumentation on the basis of Reynolds averaged Navier-Stokes equation using SST/k-ω turbulence model. For combustion modeling, a detailed kinetic scheme with 38 reactions of 8 species was implemented taking into account finite rate chemistry. Computations have shown that the developed model allow to predict ignition of a mixture and flame propagation even at low flow temperatures.

  15. Effect of air flow on tubular solar still efficiency

    PubMed Central

    2013-01-01

    Background An experimental work was reported to estimate the increase in distillate yield for a compound parabolic concentrator-concentric tubular solar still (CPC-CTSS). The CPC dramatically increases the heating of the saline water. A novel idea was proposed to study the characteristic features of CPC for desalination to produce a large quantity of distillate yield. A rectangular basin of dimension 2 m × 0.025 m × 0.02 m was fabricated of copper and was placed at the focus of the CPC. This basin is covered by two cylindrical glass tubes of length 2 m with two different diameters of 0.02 m and 0.03 m. The experimental study was operated with two modes: without and with air flow between inner and outer tubes. The rate of air flow was fixed throughout the experiment at 4.5 m/s. On the basis of performance results, the water collection rate was 1445 ml/day without air flow and 2020 ml/day with air flow and the efficiencies were 16.2% and 18.9%, respectively. Findings The experimental study was operated with two modes: without and with air flow between inner and outer tubes. The rate of air flow was fixed throughout the experiment at 4.5 m/s. Conclusions On the basis of performance results, the water collection rate was 1445 ml/day without air flow and 2020 ml/day with air flow and the efficiencies were 16.2% and 18.9%, respectively. PMID:23587020

  16. Elasto-Aerodynamics-Driven Triboelectric Nanogenerator for Scavenging Air-Flow Energy.

    PubMed

    Wang, Shuhua; Mu, Xiaojing; Wang, Xue; Gu, Alex Yuandong; Wang, Zhong Lin; Yang, Ya

    2015-10-27

    Efficient scavenging the kinetic energy from air-flow represents a promising approach for obtaining clean, sustainable electricity. Here, we report an elasto-aerodynamics-driven triboelectric nanogenerator (TENG) based on contact electrification. The reported TENG consists of a Kapton film with two Cu electrodes at each side, fixed on two ends in an acrylic fluid channel. The relationship between the TENG output power density and its fluid channel dimensions is systematically studied. TENG with a fluid channel size of 125 × 10 × 1.6 mm(3) delivers the maximum output power density of about 9 kW/m(3) under a loading resistance of 2.3 MΩ. Aero-elastic flutter effect explains the air-flow induced vibration of Kapton film well. The output power scales nearly linearly with parallel wiring of multiple TENGs. Connecting 10 TENGs in parallel gives an output power of 25 mW, which allows direct powering of a globe light. The TENG is also utilized to scavenge human breath induced air-flow energy to sustainably power a human body temperature sensor. PMID:26343789

  17. Computational fluid dynamics for modeling the turbulent natural convection in a double air-channel solar chimney system

    NASA Astrophysics Data System (ADS)

    Zavala-Guillén, I.; Xamán, J.; Álvarez, G.; Arce, J.; Hernández-Pérez, I.; Gijón-Rivera, M.

    2016-03-01

    This study reports the modeling of the turbulent natural convection in a double air-channel solar chimney (SC-DC) and its comparison with a single air-channel solar chimney (SC-C). Prediction of the mass flow and the thermal behavior of the SC-DC were obtained under three different climates of Mexico during one summer day. The climates correspond to: tropical savannah (Mérida), arid desert (Hermosillo) and temperate with warm summer (Mexico City). A code based on the Finite Volume Method was developed and a k‑ω turbulence model has been used to model air turbulence in the solar chimney (SC). The code was validated against experimental data. The results indicate that during the day the SC-DC extracts about 50% more mass flow than the SC-C. When the SC-DC is located in Mérida, Hermosillo and Mexico City, the air-changes extracted along the day were 60, 63 and 52, respectively. The air temperature at the outlet of the chimney increased up to 33%, 38% and 61% with respect to the temperature it has at the inlet for Mérida, Hermosillo and Mexico City, respectively.

  18. Interaction of a turbulent channel flow with a compliant tensegrity fabric

    NASA Astrophysics Data System (ADS)

    Luo, Haoxiang; Bewley, Thomas

    2004-11-01

    A non-trivial influence of the compliant surface on the statistics of near-wall turbulence has been found by direct numerical simulations of a channel flow at Re_τ=150 passing over a ``tensegrity fabric'' surface. Inspired from nature, this compliant surface model is special truss system having tensile members distinguished from the compressive members, as we have presented at previous APS meetings. Validated by a variety of flows, a pseudospectral/finite-difference flow solver with a 3D coordinate transformation is coupled with a C++ code calculating the dynamics of the tensegrity fabric to simulate the flow/structure interaction. Simulation results show that, when the structure has high stiffness and damping, the flow acts as if the interface were a solid flat wall. When the structure's stiffness and damping are reduced, it may resonate under the excitation of the flow disturbances. The resonating flow/structure interface forms a streamwise wave reminiscent of air-water interface but traveling at a much faster phase speed, a few times of the viscous velocity u_τ. Although the wave's amplitude is small, y_w^+≈ 2, it changes the near-wall turbulence significantly. Drag on the compliant surface is increased by about 17% where form drag accounts for only one third of the drag increase due to the small wall deformation. Various domain sizes have been tried in order to make sure that the structure's vibration mode is correct.

  19. Atlas chamber, power flow channel, and diagnostic interface design

    SciTech Connect

    Wurden, G.A.; Davis, H.A.; Taylor, A.; Bowman, D.; Ballard, E.; Ney, S.; Scudder, D.; Trainor, J.

    1997-09-01

    The Atlas pulsed-power machine, presently being designed at Los Alamos, will deliver a pulse of {approximately} 45 MA, in 4--5 {micro}sec, with energies of up to 6 MJ (from a bank of 36 MJ maximum) to a load assembly, located in vacuum. Design considerations for the vacuum vessel, power flow channel from the vessel inward, are presented. In contrast to Sandia`s PBFA II-Z, where 20 MA currents and 2--2.5 MJ of energy are delivered to ({approximately} 15 mg) loads in {approximately} 100 nsec, the Atlas structures will have to be designed for longer timescales and higher energies to drive heavy lines ({approximately} 70 g). Design issues for the chamber include materials stresses, formation of (and protection from) debris and molten jets, impulse loading, and survivability and ease of replacement of internal structures. For the power flow channel designs, issues are minimizing inductance, preventing movement of conductors during and after firing, damage mitigation, reducing the cost of materials and installation, and electrical insulation. A key issue for damage mitigation is the radius within which total destruction of material objects occurs. Choices of vessel size, insulator materials, cost and ease of manufacturing, and mechanical stability issues are presently in the conceptual design phase. Typical access requirements for diagnostics (including radial and axial X-ray backlighting, flux loops, spectroscopy, interferometry, bolometry, etc.) are provided for in the design.

  20. Structural organization of uniform momentum core in turbulent channel flow

    NASA Astrophysics Data System (ADS)

    Yang, Jongmin; Hwang, Jinyul; Sung, Hyung Jin

    2015-11-01

    The coherent structures across the boundary of the quiescent core region are explored using the direct numerical simulation data of a turbulent channel flow at Reτ = 930. The quiescent core is the region where the streamwise momentum is relatively uniform with low-level turbulence in channel flow. Across the boundary of this region, the turbulence intensity and the Reynolds shear stress decrease suddenly. The mean velocity profile shows a significant jump which indicates a strong mean shear layer at the boundary of the uniform core region. Due to the strong mean shear, the prograde vortices are dominantly distributed along the boundary with the retrograde vortices below them. The prograde and retrograde vortices are distributed in a pair with a uniform wall-normal distance. Large-scale low- and high-speed structures are characterized by the positions of the core boundary, revealing that the core boundary is modulated by the large-scale structures. This work was supported by the Creative Research Initiatives (No. 2015-001828) program of the National Research Foundation of Korea (MSIP) and supported by the Supercomputing Center (KISTI).

  1. Longitudinal dispersion in open channel flow with suspended canopies.

    PubMed

    Huai, Wenxin; Li, Chengguang

    2016-01-01

    Suspended canopies can cause flow disturbances such as reducing velocities within the canopy, and increasing flow beneath the canopy. Flow modifications by canopies dramatically affect the fate and transport of sediment, nutrients, contaminants, dissolved oxygen, and fauna in aquatic systems. A three-zone model is presented here to predict the longitudinal dispersion coefficient by simplifying Chikwendu's N-zone model. To validate the model, both flow field and tracer experiments were conducted using a straight rectangular Plexiglas flume, with rigid circular rods as the modeled suspended canopies. The result shows that velocities increased above the flume bed and maximized at a point between the canopies and flume bed. Above that point, streamwise velocities decreased into and within the canopies. Reynolds shear stresses were largest at the canopy interface and smallest (zero) at the velocity maximum point. Good agreement between the modeled results and experimental data shows that the model can effectively predict the longitudinal dispersion coefficient in open channels with suspended canopies. PMID:27508377

  2. DNS and modeling of bubbly flows in vertical channels

    NASA Astrophysics Data System (ADS)

    Ma, Ming; Lu, Jiacai; Tryggvason, Gretar

    2014-11-01

    The transient motion of bubbly flow, in a vertical channel is studied, using direct numerical simulations (DNS) where every continuum length and time scale is resolved. Nearly spherical bubbles of the same size, injected into laminar upflow, are quickly pushed to the walls due to lift. The velocity then slows down, eventually resulting in some of the bubbles returning to the core forming a mixture where the weight matches the imposed pressure gradient and the void fraction is easily predicted. Unlike the statistically steady state, where the flow structure is relatively simple and in some cases depends only on the sign of the lift coefficient, the transient evolution is more sensitive to the governing parameters. The DNS results are used to provide values for the unresolved closure terms in a simple average model for the flow, found by mining the data, using various techniques such as regression and neural networks. Results for a large number of bubbles of several different sizes in turbulent upflow are also presented and the prospects of using a similar approach for LES-like simulations of more complex flows are discussed, including the simplification of the interface structure resulting from filtering. Research supported by DOE (CASL) and NSF Grant CBET 1335913.

  3. Nanofluid Flow and Heat Transfer in Channel Entrance Region

    NASA Astrophysics Data System (ADS)

    Liu, Joseph T. C.; Puliti, Gianluca

    2014-11-01

    The present work uses the continuum description of nanofluid flow to study the flow, heat and mass transfer in the entrance and developing region of channels or tubes, where the viscous and heat conduction layers are thin and the heat transfer is much more intense than fully developed flow. Instead of supplementing the formulation with thermodynamic properties based on mixture calculations, use is made of recent molecular dynamical computations of such properties, specifically, the density and heat capacity of gold-water nanofluids. The more general formulation results, within the Rayleigh-Stokes (plug flow) approximation and perturbation for small volume fraction, show that the nanofluid density-heat capacity has an enormous effect in the inertia mechanism in causing the nanofluid temperature profile to steepen. The nanofluid thermal conductivity though has an explicit enhancement of the surface heat transfer rate has the almost hidden effect of stretching the nanofluid temperature profile thus giving the opposite effect of enhancement. Quantitative results for Gold-Water nanofluid is presented.

  4. Per-channel basis normalization methods for flow cytometry data

    PubMed Central

    Hahne, Florian; Khodabakhshi, Alireza Hadj; Bashashati, Ali; Wong, Chao-Jen; Gascoyne, Randy D.; Weng, Andrew P.; Seifert-Margolis, Vicky; Bourcier, Katarzyna; Asare, Adam; Lumley, Thomas; Gentleman, Robert; Brinkman, Ryan R.

    2013-01-01

    Between-sample variation in high throughput flow cytometry data poses a significant challenge for analysis of large scale data sets, such as those derived from multi-center clinical trials. It is often hard to match biologically relevant cell populations across samples due to technical variation in sample acquisition and instrumentation differences. Thus normalization of data is a critical step prior to analysis, particularly in large-scale data sets from clinical trials, where group specific differences may be subtle and patient-to-patient variation common. We have developed two normalization methods that remove technical between-sample variation by aligning prominent features (landmarks) in the raw data on a per-channel basis. These algorithms were tested on two independent flow cytometry data sets by comparing manually gated data, either individually for each sample or using static gating templates, before and after normalization. Our results show a marked improvement in the overlap between manual and static gating when the data are normalized, thereby facilitating the use of automated analyses on large flow cytometry data sets. Such automated analyses are essential for high throughput flow cytometry. PMID:19899135

  5. Compressible Turbulent Channel Flows: DNS Results and Modeling

    NASA Technical Reports Server (NTRS)

    Huang, P. G.; Coleman, G. N.; Bradshaw, P.; Rai, Man Mohan (Technical Monitor)

    1994-01-01

    The present paper addresses some topical issues in modeling compressible turbulent shear flows. The work is based on direct numerical simulation of two supersonic fully developed channel flows between very cold isothermal walls. Detailed decomposition and analysis of terms appearing in the momentum and energy equations are presented. The simulation results are used to provide insights into differences between conventional time-and Favre-averaging of the mean-flow and turbulent quantities. Study of the turbulence energy budget for the two cases shows that the compressibility effects due to turbulent density and pressure fluctuations are insignificant. In particular, the dilatational dissipation and the mean product of the pressure and dilatation fluctuations are very small, contrary to the results of simulations for sheared homogeneous compressible turbulence and to recent proposals for models for general compressible turbulent flows. This provides a possible explanation of why the Van Driest density-weighted transformation is so successful in correlating compressible boundary layer data. Finally, it is found that the DNS data do not support the strong Reynolds analogy. A more general representation of the analogy is analysed and shown to match the DNS data very well.

  6. Thermal characteristics of air flow cooling in the lithium ion batteries experimental chamber

    SciTech Connect

    Lukhanin A.; Rohatgi U.; Belyaev, A.; Fedorchenko, D.; Khazhmuradov, M.; Lukhanin, O; Rudychev, I.

    2012-07-08

    A battery pack prototype has been designed and built to evaluate various air cooling concepts for the thermal management of Li-ion batteries. The heat generation from the Li-Ion batteries was simulated with electrical heat generation devices with the same dimensions as the Li-Ion battery (200 mm x 150 mm x 12 mm). Each battery simulator generates up to 15W of heat. There are 20 temperature probes placed uniformly on the surface of the battery simulator, which can measure temperatures in the range from -40 C to +120 C. The prototype for the pack has up to 100 battery simulators and temperature probes are recorder using a PC based DAQ system. We can measure the average surface temperature of the simulator, temperature distribution on each surface and temperature distributions in the pack. The pack which holds the battery simulators is built as a crate, with adjustable gap (varies from 2mm to 5mm) between the simulators for air flow channel studies. The total system flow rate and the inlet flow temperature are controlled during the test. The cooling channel with various heat transfer enhancing devices can be installed between the simulators to investigate the cooling performance. The prototype was designed to configure the number of cooling channels from one to hundred Li-ion battery simulators. The pack is thermally isolated which prevents heat transfer from the pack to the surroundings. The flow device can provide the air flow rate in the gap of up to 5m/s velocity and air temperature in the range from -30 C to +50 C. Test results are compared with computational modeling of the test configurations. The present test set up will be used for future tests for developing and validating new cooling concepts such as surface conditions or heat pipes.

  7. Modeling of Multi-Scale Channeling Phenomena in Porous Flow

    NASA Astrophysics Data System (ADS)

    Räss, Ludovic; Omlin, Samuel; Yarushina, Viktoriya; Simon, Nina; Podladchikov, Yuri

    2015-04-01

    Predictive modeling of fluid percolation through tight porous rocks is critical to evaluate environmental risks associated with waste storage and reservoir operations. To understand the evolution of two-phase mixtures of fluid and solid it is insufficient to only combine single-phase fluid flow methods and solid mechanics. A proper coupling of these two different multi-scales physical processes is required to describe the complex evolution of permeability and porosity in space and in time. We conduct numerical modeling experiments in geometrically simple but physically complex systems of stressed rocks containing self-focusing porous flow. Our model is physically and thermodynamically consistent and describes the formation and evolution of fluid pathways. The model consists of a system of coupled equations describing poro-elasto-viscous deformation and flow. Nonlinearity of the solid rheology is also taken into account. We have developed a numerical application based on an iterative finite difference scheme that runs on mutli-GPUs cluster in parallel. In order to validate these models, we consider the largest CO2 sequestration project in operation at the Sleipner field in the Norwegian North Sea. Attempts to match the observations at Sleipner using conventional reservoir simulations fail to capture first order observations, such as the seemingly effortless vertical flow of CO2 through low permeability shale layers and the formation of focused flow channels or chimneys. Conducted high-resolution three-dimensional numerical simulations predict the formation of dynamically evolving high porosity and permeability pathways as a natural outcome of porous flow nonlinearly coupled with rock deformation, which may trigger leakage through low permeability barriers.

  8. Ramification of Channel Networks Incised by Groundwater Flow

    NASA Astrophysics Data System (ADS)

    Yi, R. S.; Seybold, H. F.; Petroff, A. P.; Devauchelle, O.; Rothman, D.

    2011-12-01

    The geometry of channel networks has been a source of fascination since at least Leonardo da Vinci's time. Yet a comprehensive understanding of ramification---the mechanism of branching by which a stream network acquires its geometric complexity---remains elusive. To investigate the mechanisms of ramification and network growth, we consider channel growth driven by groundwater flow as a model system, analogous to a medical scientist's laboratory rat. We test our theoretical predictions through analysis of a particularly compelling example found on the Florida Panhandle north of Bristol. As our ultimate goal is to understand ramification and growth dynamics of the entire network, we build a computational model based on the following growth hypothesis: Channels grow in the direction that captures the maximum water flux. When there are two such directions, tips bifurcate. The direction of growth can be determined from the expansion of the ground water field around each tip, where each coefficient in this expansion has a physical interpretation. The first coefficient in the expansion determines the ground water discharge, leading to a straight growth of the channel. The second term describes the asymmetry in the water field leading to a bending of the stream in the direction of maximal water flux. The ratio between the first and the third coefficient determines a critical distance rc over which the tip feels inhomogeneities in the ground water table. This initiates then the splitting of the tip. In order to test our growth hypothesis and to determine rc, we grow the Florida network backward. At each time step we calculate the solution of the ground water field and determine the appropriate expansion coefficients around each tip. Comparing this simulation result to the predicted values provides us with a stringent measure for rc and the significance of our growth hypothesis.

  9. Supersonic Air Flow due to Solid-Liquid Impact

    NASA Astrophysics Data System (ADS)

    Gekle, Stephan; Peters, Ivo R.; Gordillo, José Manuel; van der Meer, Devaraj; Lohse, Detlef

    2010-01-01

    A solid object impacting on liquid creates a liquid jet due to the collapse of the impact cavity. Using visualization experiments with smoke particles and multiscale simulations, we show that in addition, a high-speed air jet is pushed out of the cavity. Despite an impact velocity of only 1m/s, this air jet attains supersonic speeds already when the cavity is slightly larger than 1 mm in diameter. The structure of the air flow closely resembles that of compressible flow through a nozzle—with the key difference that here the “nozzle” is a liquid cavity shrinking rapidly in time.

  10. Computational and experimental study of spin coater air flow

    NASA Astrophysics Data System (ADS)

    Zhu, Xiaoguang; Liang, Faqiu; Haji-Sheikh, A.; Ghariban, N.

    1998-06-01

    An extensive 2- and 3-D analysis of air flow in a POLARISTM 2200 Microlithography Cluster spin coater was conducted using FLUENTTM Computational Fluid Dynamics (CFD) software. To supplement this analysis, direct measurement of air flow velocity was also performed using a DantecTM Hot Wire Anemometer. Velocity measurements were made along two major planes across the entire flow field in the spin coater at various operating conditions. It was found that the flow velocity at the spin coater inlet is much lower than previously assumed and quite nonuniform. Based on this observation, a pressure boundary condition rather than a velocity boundary condition was used for subsequent CFD analysis. A comparison between calculated results and experimental data shows that the 3D model accurately predicts the air flow field in the spin coater. An added advantage of this approach is that the CFD model can be easily generated from the mechanical design database and used to analyze the effect of design changes. The modeled and measured results show that the flow pattern in the spin bowl is affected by interactions between the spinning wafer, exhaust flow, and the gap between the spin head and surrounding baffle. Different operating conditions such as spin speed, inlet pressure, and exhaust pressure were found to generate substantially different flow patterns. It was also found that backflow of air could be generated under certain conditions.

  11. Low-noise flow valve for air ducts

    NASA Technical Reports Server (NTRS)

    Gallo, E. A.

    1970-01-01

    Valve assembly controls air flow from feeder into main duct, with minimum of turbulence, friction, pressure differential, and noise. Valve consists of damper, deflector, and spring. Streamlining of damper and deflector merges flow smoothly, while spring keeps damper and deflector in contact and eliminates valve chatter and damping vibrations.

  12. Localized reconnection in the magnetotail driven by lobe flow channels: Global MHD simulation

    NASA Astrophysics Data System (ADS)

    Nishimura, Y.; Lyons, L. R.

    2016-02-01

    Recent ionospheric measurements suggest polar cap flow channels often trigger nightside auroral brightening. However, measurements were limited to the ionosphere, and it was not understood if such flow channels can exist in the lobe and can trigger magnetotail reconnection in a localized cross-tail extent. We examined if localized flow channels can form self-consistently in a global MHD regime, and if so, how such flow channels originate and relate to localized magnetotail reconnection. We show that lobe convection became nonuniform with azimuthally narrow flow channels (enhanced dawn-dusk electric fields) of ~3 RE cross-tail width. The flow channels propagated from the dayside toward the plasma sheet as an interplanetary magnetic field (IMF) discontinuity swept tailward. The plasma sheet around the lobe flow channels became thinner with a similar cross-tail extent and then localized reconnection occurred. These results suggest that localized flow channels can propagate tailward across the lobe and drive localized magnetotail reconnection, that the cross-tail width of reconnection and resulting plasma sheet flow channels and dipolarization fronts are related to the width of inflow from the lobe, and that IMF discontinuities drive lobe flow channels.

  13. Flow distribution and maximum current density studies in redox flow batteries with a single passage of the serpentine flow channel

    NASA Astrophysics Data System (ADS)

    Ke, Xinyou; Alexander, J. Iwan D.; Prahl, Joseph M.; Savinell, Robert F.

    2014-12-01

    Flow batteries show promise for very large-scale stationary energy storage such as needed for the grid and renewable energy implementation. In recent years, researchers and developers of redox flow batteries (RFBs) have found that electrode and flow field designs of PEM fuel cell (PEMFC) technology can increase the power density and consequently push down the cost of flow battery stacks. In this paper we present a macroscopic model of a typical PEMFC-like RFB electrode-flow field design. The model is a layered system comprised of a single passage of a serpentine flow channel and a parallel underlying porous electrode (or porous layer). The effects of the inlet volumetric flow rate, permeability of the porous layer, thickness of the porous layer and thickness of the flow channel on the flow penetration into the porous layer are investigated. The maximum current density corresponding to stoichiometry is estimated to be 377 mA cm-2 and 724 mA cm-2, which compares favorably with experiments of ∼400 mA cm-2 and ∼750 mA cm-2, for a single layer and three layers of the carbon fiber paper, respectively.

  14. Low power, constant-flow air pump systems

    SciTech Connect

    Polito, M.D.; Albert, B.

    1994-01-01

    A rugged, yet small and lightweight constant-flow air pump system has been designed. Flow control is achieved using a novel approach which is three times more power efficient than previous designs. The resultant savings in battery size and weight makes these pumps ideal for sampling air on balloon platforms. The pump package includes meteorological sensors and an onboard computer that stores time and sensor data and turns the constant-flow pump circuit on/off. Some applications of these systems are also presented in this report.

  15. Evaporation of stationary alcohol layer in minichannel under air flow

    NASA Astrophysics Data System (ADS)

    Afanasyev, Ilya; Orlova, Evgenija; Feoktistov, Dmitriy

    2015-01-01

    This paper presents experimental investigation of effect of the gas flow rate moving parallel to the stationary liquid layer on the evaporation rate under the conditions of formation of a stable plane "liquid-gas" interface. The average evaporation flow rate of liquid layer (ethanol) by the gas flow (air) has been calculated using two independent methods. Obtained results have been compared with previously published data.

  16. The effect of passive mixing on pressure drop and oxygen mass fraction using opposing channel flow field design in a Proton Exchange Membrane Fuel Cell

    NASA Astrophysics Data System (ADS)

    Singh, Anant Bir

    This study investigates a flow field with opposing channel design. Previous studies on flow field designs have been focused on improving fuel utilization which often leads to increased pressure drop. This increased pressure drop is typical because standard designs employ either a single flow channel to clear blockages or dead end condition to force the flow through the gas diffusion layer. The disadvantage with these designs is the increased resistance to the flow which requires higher pressure, which becomes a parasitic loss that lowers the system efficiency. For this study the focus was to reduce the pressure drop by providing a less resistive path to the flow. To achieve a less resistive path, the inlet channel was split into two opposing channels. These channels are then recombined only to be split again for the next leg. Therefore, the split channel design should reduce the pressure drop which reduces the parasitic load and ultimately contributes to higher system efficiency. In addition the recombining of the streams at each leg should induce mixing. Having opposing channels should also increase cross flow under the lands to reduce mass transfer loses. The cathode side of the fuel cell is especially sensitive to the mass transport losses since air (oxygen mixed with nitrogen) is used for supplying oxygen unlike the anode side which uses pure hydrogen. To test the hypothesis of having benefits from an opposing channel design, both an experimental and analytical approach was taken. For the experiment, a serpentine flow field and opposing channel flow field plates were compared over several flow rates with compressed air. To test the hypothesis of increased mass transfer, the two flow fields were modeled using a CFD software package, COMSOL. It was found that the opposing channel configuration for high flow rate with multiple entry and exit conditions exhibited significant improvement over the single serpentine channel. Pressure drop was ⅓ less than the

  17. Wave-induced topographic formstress in baroclinic channel flow

    NASA Astrophysics Data System (ADS)

    Olbers, Dirk; Lettmann, Karsten; Wolff, Jörg-Olaf

    2007-12-01

    Large-scale zonal flow driven across submarine topography establishes standing Rossby waves. In the presence of stratification, the wave pattern can be represented by barotropic and baroclinic Rossby waves of mixed planetary topographic nature, which are locked to the topography. In the balance of momentum, the wave pattern manifests itself as topographic formstress. This wave-induced formstress has the net effect of braking the flow and reducing the zonal transport. Locally, it may lead to acceleration, and the parts induced by the barotropic and baroclinic waves may have opposing effects. This flow regime occurs in the circumpolar flow around Antarctica. The different roles that the wave-induced formstress plays in homogeneous and stratified flows through a zonal channel are analyzed with the BARBI (BARotropic-Baroclinic-Interaction ocean model, Olbers and Eden, J Phys Oceanogr 33:2719-2737, 2003) model. It is used in complete form and in a low-order version to clarify the different regimes. It is shown that the barotropic formstress arises by topographic locking due to viscous friction and the baroclinic one due to eddy-induced density advection. For the sinusoidal topography used in this study, the transport obeys a law in which friction and wave-induced formstress act as additive resistances, and windstress, the effect of Ekman pumping on the density stratification, and the buoyancy forcing (diapycnal mixing of the stratified water column) of the potential energy stored in the stratification act as additive forcing functions. The dependence of the resistance on the system parameters (lateral viscosity ɛ, lateral diffusivity κ of eddy density advection, Rossby radius λ, and topography height δ) as well as the dependence of transport on the forcing functions are determined. While the current intensity in a channel with homogeneous density decreases from the viscous flat bottom case in an inverse quadratic law ~ δ -2 with increasing

  18. Bedrock erosion by sliding wear in channelized granular flow

    NASA Astrophysics Data System (ADS)

    Hung, C. Y.; Stark, C. P.; Capart, H.; Smith, B.; Maia, H. T.; Li, L.; Reitz, M. D.

    2014-12-01

    Boundary forces generated by debris flows can be powerful enough to erode bedrock and cause considerable damage to infrastructure during runout. Bedrock wear can be separated into impact and sliding wear processes. Here we focus on sliding wear. We have conducted experiments with a 40-cm-diameter grainflow-generating rotating drum designed to simulate dry channelized debris flows. To generate sliding erosion, we placed a 20-cm-diameter bedrock plate axially on the back wall of the drum. The rotating drum was half filled with 2.3-mm-diameter grains, which formed a thin grain-avalanching layer with peak flow speed and depth close to the drum axis. The whole experimental apparatus was placed on a 100g-ton geotechnical centrifuge and, in order to scale up the stress level, spun to a range of effective gravity levels. Rates and patterns of erosion of the bedrock plate were mapped after each experiment using 3d micro-photogrammetry. High-speed video and particle tracking were employed to measure granular flow dynamics. The resulting data for granular velocities and flow geometry were used to estimate impulse exchanges and forces on the bedrock plate. To address some of the complexities of granular flow under variable gravity levels, we developed a continuum model framed around a GDR MiDi rheology. This model allowed us to scale up boundary forcing while maintaining the same granular flow regime, and helped us to understand important aspects of the flow dynamics including e.g. fluxes of momentum and kinetic energy. In order to understand the detailed processes of boundary forcing, we performed numerical simulations with a new contact dynamics model. This model confirmed key aspects of our continuum model and provided information on second-order behavior such as fluctuations in the forces acting on the wall. By combining these measurements and theoretical analyses, we have developed and calibrated a constitutive model for sliding wear that is a threshold function of

  19. Numerical Study on a Detailed Air Flows in an Urban Area Using a CFD model

    NASA Astrophysics Data System (ADS)

    Kwon, A.

    2014-12-01

    In this study, detailed air flows in an urban area were analyzed using a computational fluid dynamics (CFD) model. For this model buildings used as the surface boundary in the model were constructed using Los Angeles Region Imagery Acquisition Consortium 2 Geographic Information System (LARIAC2 GIS) data. Three target areas centered at the cross roads of Broadway & 7th St., Olive & 12th St., and Wilshire blvd. & Carondelet, Los Angeles, California were considered. The size of each numerical domain is 400 m, 400 m, and 200 m in the x‒, y‒, and z‒directions, respectively. The grid sizes in the x‒, y‒, and z‒directions are 2 m, 2 m, and 2 m, respectively. Based on the inflow wind data provided by California Air Resources Board, detailed flow characteristics were investigated for each target area. Descending air flow were developed at the leeward area of tall building and ascending air current were occurred on the windward area of tall building. Vertically rotating vortices were formed in spaces between buildings, so-called, street canyons and horizontally rotating vortices appeared near cross roads. When flows came into narrow street canyon from wide street canyon, channeling effects appeared and flow speed increased for satisfying mass continuity.

  20. The Hydrodynamic Stability of Channel Flow with Compliant Boundaries

    NASA Astrophysics Data System (ADS)

    Gajjar, J. S. B.; Sibanda, P.

    1996-03-01

    An asymptotic theory is developed for the hydrodynamic stability of an incompressible fluid flowing in a channel in which one wall is rigid and the other is compliant. We exploit the multideck structure of the flow to investigate theoretically the development of disturbances to the flow in the limit of large Reynolds numbers. A simple spring-plate model is used to describe the motion of the compliant wall, and this study considers the effect of the various wall parameters, such as tension, inertia, and damping, on the stability properties. An amplitude equation for a modulated wavetrain is derived and the properties of this equation are studied for a number of cases including linear and nonlinear theory. It is shown that in general the effect of viscoelastic damping is destabilizing. In particular, for large damping, the analysis points to a fast travelling wave, short-scale instability, which may be related to a flutter instability observed in some experiments. This work also demonstrates that the conclusions obtained by previous investigators in which the effect of tension, inertia, and other parameters is neglected, may be misleading. Finally it is shown that a set of compliant-wall parameters exists for which the Haberman type of critical layer analysis leads to stable equilibrium amplitudes, in contrast to many other stability problems where such equilibrium amplitudes are unstable.

  1. The initial-value problem for viscous channel flows

    NASA Technical Reports Server (NTRS)

    Criminale, W. O.; Jackson, T. L.; Lasseigne, D. G.

    1995-01-01

    Plane viscous channel flows are perturbed and the ensuing initial-value problems are investigated in detail. Unlike traditional methods where traveling wave normal modes are assumed for solution, this works offers a means whereby completely arbitrary initial input can be specified without having to resort to eigenfunction expansions. The full temporal behavior, including both early time transients and the long time asymptotics, can be determined for any initial disturbance. Effects of three-dimensionality can be assessed. The bases for the analysis are: (a) linearization of the governing equations; (b) Fourier decomposition in the spanwise and streamwise directions of the flow; and (c) direct numerical integration of the resulting partial differential equations. All of the stability data that are known for such flows can be reproduced. Also, the optimal initial condition can be determined in a straight forward manner and such optimal conditions clearly reflect transient growth data that is easily determined by a rational choice of a basis for the initial conditions. Although there can be significant transient growth for subcritical values of the Reynolds number using this approach it does not appear possible that arbitrary initial conditions will lead to the exceptionally large transient amplitudes that have been determined by optimization of normal modes. The approach is general and can be applied to other classes of problems where only a finite discrete spectrum exists, such as the boundary layer for example.

  2. Analysis of turbulent cavitating flow in a micro channel

    NASA Astrophysics Data System (ADS)

    Egerer, Christian; Hickel, Stefan; Schmidt, Steffen; Adams, Nikolaus

    2013-11-01

    Associated with the collapse of vapor cavities is the formation of shock waves and liquid micro-jets, which can lead to the damage of material (cavitation erosion) or even failure of engineering devices, e.g. fuel injectors. We performed Large-Eddy Simulations of the turbulent cavitating flow through a micro channel, resembling a throttle valve commonly found in fuel injectors, at two different operating points with the aim of indentifying such erosion sensitive areas. The underlying numerical method of our flow solver INCA solves the compressible Navier-Stokes equations on a Cartesian adaptive grid for a homogeneous mixture of liquid and vapor in order to account for all relevent physical effects, i.e., compressibility of the liquid-vapor mixture as well as transitional flow and turbulence. The effect of non-represented scales on the represented ones is accounted for by the Adaptive Local Deconvolution Method, a non-linear finite volume scheme for the convective fluxes. We will present a comparison of numerical results with experiments as well as a detailed analysis of the interplay between vortical and cavitation structures. Furthermore, tools enabling the automatic detection of erosion sensitive areas will be discussed and applied.

  3. Similarity flow in interaction of a shock wave with an inclined heated channel

    SciTech Connect

    Artemiev, V.I.; Medvedyuk, S.A.; Rybakov, V.A.

    1993-11-01

    A study is made of gasdynamic flow that initiates when a shock wave propagates along a thin heated channel. Analytical conditions of the onset of an unsteady flow precursor are obtained. The flow similarity is proved experimentally; precursor characteristics vs shock wave and heated channel parameters are analyzed.

  4. Computation of flow and heat transfer in rotating cavities with peripheral flow of cooling air.

    PubMed

    Kiliç, M

    2001-05-01

    Numerical solutions of the Navier-Stokes equations have been used to model the flow and the heat transfer that occurs in the internal cooling-air systems of gas turbines. Computations are performed to study the effect of gap ratio, Reynolds number and the mass flow rate on the flow and the heat transfer structure inside isothermal and heated rotating cavities with peripheral flow of cooling air. Computations are compared with some of the recent experimental work on flow and heat transfer in rotating-cavities. The agreement between the computed and the available experimental data is reasonably good. PMID:11460668

  5. Analysis of flood-flow frequency, flow duration, and channel-forming flow for the James River in South Dakota

    USGS Publications Warehouse

    Benson, R.D.

    1988-01-01

    The James River, which originates in North Dakota and joins the Missouri River near Yankton, South Dakota, is about 747 miles long, with about 474 river miles located in South Dakota. The James River basin includes 21,116 sq mi, with 14,428 sq mi located in South Dakota. Bankfull capacity of the James River in South Dakota ranges from a minimum of about 200 cu ft/sec near the mouth. Discharges that produce bankfull conditions on much of the river in South Dakota occur on an average of once in about 2 years. The 10-year flood flows, which range from 1,620 cu ft/sec (at the gage near Stratford) to 8,870 cu ft/sec (at the gage near Scotland), cause major flooding on most of the river in South Dakota. The river also has potential for extending periods of low or zero flow, especially in the northern portion within South Dakota. Generally, low flows occur from late summer until spring snowmelt. The James River at Columbia had zero flow for 623 consecutive days from July 13, 1958, through March 26, 1960. The channel pattern (channel alignment) has changed little since 1922. This channel stability indicates that channel formation is approaching a state of equilibrium. It does not appear that velocities in the river are sufficient to carry the sediment being delivered by the tributaries. (Author 's abstract)

  6. Flow of a reactive fluid through partially saturated fractures: Experimental observations of the influence of entrapped phase geometry on evolving flow channels

    NASA Astrophysics Data System (ADS)

    Detwiler, R. L.; Fisher, S.

    2008-12-01

    Reactive fluids cause dissolution and precipitation along mineral surfaces that can lead to the development of flow channels in porous and fractured media. In fully saturated fractures, dissolution of fracture surfaces leads to different behaviors depending on the relative magnitudes of advective and diffusive transport of dissolved minerals and surface reaction rates. The resulting alterations of the fracture pore space (apertures) range from relatively uniform dissolution of the fracture surfaces to the formation of distinct dissolution channels that dominate flow through the fracture. These processes are further complicated in many subsurface systems, where multiple fluids/phases interact within pore spaces (e.g., CO2 sequestration, groundwater contamination by organic solvents, oil and gas production). We present experimental results that explore the additional influence of an entrapped nonwetting phase on the formation of dissolution channels in fractures. We fabricated analog fractures by mating a 10x15-cm, smooth, reactive surface (KH2PO4) with a rough, non-reactive surface (glass). The resulting fractures were transparent allowing direct measurement of evolving fracture apertures and fluid phase distribution using established quantitative visualization techniques. Experiments were initiated by slowly injecting (negligible viscous forces) air into a fully saturated fracture followed by slow reinvasion of water. The resulting initial condition for the fracture dissolution experiments was a complex distribution of immobile air bubbles entrapped predominantly within large aperture regions. These bubbles were completely surrounded by flowing water (under-saturated with respect to KH2PO4) within smaller aperture regions. During experiments, mineral dissolution led to localized fracture aperture growth, which in turn caused gradual redistribution of the entrapped air within the fracture. The resulting evolution of dissolution channels differed significantly from

  7. 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.

  8. Modeling of Gas-Liquid Flow Through An Interconnected Channel Matrix

    SciTech Connect

    Crandall, Dustin; Ahmadi, Goodarz; Smith, Duane.H

    2009-01-01

    The motion of a less viscous, non-wetting gas into a liquid-saturated porous medium is known as drainage. Drainage is an important process in environmental applications, such as enhanced oil recovery and geologic CO2 sequestration. Understanding what conditions will increase the volume of gas that can saturate an initially water-saturated porous medium is of importance for predictions of the total CO2 volume that can be sequestered in known geologic formations. To further the understanding of how drainage flow properties are related to different injection flow-rates, a porous medium consisting of interconnected channels and pores was manufactured to perform bench-top experiments of drainage. Additionally, a finite-volume model of this interconnected channel matrix was constructed. Numerical simulations of constant-rate injection into the model porous medium are first shown to compare favorably to the bench-top experiments. The fluid and injection properties of the drainage process were then varied to evaluate the flow conditions which would maximize the volume of gas trapped within the porous medium. In particular, CO2 displacing brine within the porous medium was modeled, with representative subsurface temperatures and fluid properties. It was shown with these fluid conditions a higher final saturation of the invading less-viscous CO2 was obtained, as compared to air into water experiments at similar injection rates.

  9. Floating particle trapping and diffusion in vegetated open channel flow

    NASA Astrophysics Data System (ADS)

    Defina, Andrea; Peruzzo, Paolo

    2010-11-01

    In this paper we present early results of laboratory experiments to investigate the transport and diffusion of floating particles (e.g., buoyant seeds) in open channel flow with emergent vegetation. The experiments are aimed at providing a better understanding of the relevant particle-vegetation interaction mechanisms responsible for the observed diffusion processes. Qualitative observational data are then used to set up a stochastic model for floating particle transport and diffusion. Quantitative observations, such as the distribution of distances travelled by a particle before it is permanently captured by a plant and the arrival-time distributions at prescribed cross sections along the vegetated test section, are instead used to calibrate and validate the model. The comparison between theoretical predictions and experimental results is quite satisfactory and suggests that the observed relevant aspects of the particle-vegetation interaction processes are properly described in the model.

  10. Spool Valve for Switching Air Flows Between Two Beds

    NASA Technical Reports Server (NTRS)

    Dean, W. Clark

    2005-01-01

    U.S. Patent 6,142,151 describes a dual-bed ventilation system for a space suit, with emphasis on a multiport spool valve that switches air flows between two chemical beds that adsorb carbon dioxide and water vapor. The valve is used to alternately make the air flow through one bed while exposing the other bed to the outer-space environment to regenerate that bed through vacuum desorption of CO2 and H2O. Oxygen flowing from a supply tank is routed through a pair of periodically switched solenoid valves to drive the spool valve in a reciprocating motion. The spool valve equalizes the pressures of air in the beds and the volumes of air flowing into and out of the beds during the alternations between the adsorption and desorption phases, in such a manner that the volume of air that must be vented to outer space is half of what it would be in the absence of pressure equalization. Oxygen that has been used to actuate the spool valve in its reciprocating motion is released into the ventilation loop to replenish air lost to vacuum during the previous desorption phase of the operating cycle.

  11. Cold air outbreaks along a non-frozen sea channel: effects of wind on snow bands

    NASA Astrophysics Data System (ADS)

    Savijärvi, Hannu

    2015-08-01

    Wintertime cold air outbreaks along a non-frozen sea channel or a long lake can become destructive if the related bands of heavy snowfall hit onto land. The forcing for such bands is studied with a 2D numerical model set across an east-west sea channel at 60oN (`Gulf of Finland'), varying the basic geostrophic wind V g. Without any V g opposite coastal land breezes emerge with convergence. This results in a quasi-steady rising motion w max ~ 7.5 cm/s at 600 m in the middle of the gulf, which can force a snow band. During weak V g, the rising motion is reduced but least so for winds from 60o to 80o (~ENE), when modest alongshore bands could exist near the downstream (Estonian) coast. During V g of 4-6 m/s from any direction, the land breezes and rising motions are reduced more effectively, so snow bands are not expected during moderate basic flow. In contrast, during a strong V g of 20-25 m/s from 110o to 120o (~ESE) the land breeze perturbations are intense with w max up to 15-18 cm/s. The induced alongshore bands of heavy snowfall are located in these cases at the sea but quite close to the downstream (Finnish) coast. They can suddenly make a landfall if the basic wind turns clockwise.

  12. Equipment for Measuring Air Flow, Air Temperature, Relative Humidity, and Carbon Dioxide in Schools. Technical Bulletin.

    ERIC Educational Resources Information Center

    Jacobs, Bruce W.

    Information on equipment and techniques that school facility personnel may use to evaluate IAQ conditions are discussed. Focus is placed on the IAQ parameters of air flow, air temperature, relative humidity, as well as carbon dioxide and the equipment used to measure these factors. Reasons for measurement and for when the measurement of these…

  13. Cross-flow versus counterflow air-stripping towers

    SciTech Connect

    Little, J.C.; Marinas, B.J.

    1997-07-01

    Mass-transfer and pressure-drop packing performance correlations are used together with tower design equations and detailed cost models to compare the effectiveness of cross-flow and counterflow air stripping towers over a wide range of contaminant volatility. Cross-flow towers are shown to offer a significant economic advantage over counterflow towers when stripping low volatility organic contaminants primarily due to savings in energy costs. These savings increase as contaminant volatility decreases and as water flow rate increases. A further advantage of the cross-flow configuration is that it extends the feasible operating range for air stripping as cross-flow towers can accommodate higher air-to-water flow ratios than conventional counterflow towers. Finally it is shown that the optimized least-cost design for both counterflow and cross-flow towers varies with Henry`s law constant, water flow rate, and percent removal, but that the optimum is virtually insensitive to other cost and operating variables. This greatly simplifies the tower design procedure.

  14. Direct numerical simulation of sediment entrainment in turbulent channel flow

    NASA Astrophysics Data System (ADS)

    Ji, C.; Munjiza, A.; Avital, E.; Ma, J.; Williams, J. J. R.

    2013-05-01

    In this paper, the entrainment and movement of coarse particles on the bed of an open channel is numerically investigated. Rather than model the sediment transport using a concentration concept, this study treats the sediment as individual particles and investigates the interaction between turbulent coherent structures and particle entrainment. The applied methodology is a combination of the direct numerical simulation of turbulent flow, the combined finite-discrete element modeling of particle motion and collision, and the immersed boundary method for the fluid-solid interaction. In this study, flow over a water-worked rough-bed consisting of 2-3 layers of densely packed spheres is adopted and the Shields function is 0.065 which is just above the entrainment threshold to give a bed-load regime. Numerical results for turbulent flow, sediment entrainment statistics, hydrodynamic forces acting on the particles, and the interaction between turbulence coherent structures and particle entrainment are presented. It is shown that the presence of entrained particles significantly modifies the mean velocity and turbulence quantity profiles in the vicinity of a rough-bed and that the instantaneous lift force can be larger than a particle's submerged weight in a narrow region above the effective bed location, although the mean lift force is always smaller than the submerged weight. This, from a hydrodynamic point of view, presents strong evidence for a close cause-and-effect relationship between coherent structures and sediment entrainment. Furthermore, instantaneous numerical results on particle entrainment and the surrounding turbulent flow are reported which show a strong correlation between sediment entrainment and sweep events and the underlying mechanisms are discussed.

  15. Natural laminar flow hits smoother air

    NASA Technical Reports Server (NTRS)

    Holmes, B. J.

    1985-01-01

    Natural laminar flow (NLF) may be attained in aircraft with lower cost, weight, and maintenance penalties than active flow laminarization by means of a slot suction system. A high performance general aviation jet aircraft possessing a moderate degree of NLF over wing, fuselage, empennage and engine nacelles will accrue a 24 percent reduction in total aircraft drag in the cruise regime. NASA-Langley has conducted NLF research centered on the use of novel airfoil profiles as well as composite and milled aluminum alloy construction methods which minimize three-dimensional aerodynamic surface roughness and waviness. It is noted that higher flight altitudes intrinsically reduce unit Reynolds numbers, thereby minimizing turbulence for a given cruise speed.

  16. Air flow analysis in the upper Río Negro Valley (Argentina)

    NASA Astrophysics Data System (ADS)

    Cogliati, M. G.; Mazzeo, N. A.

    2006-06-01

    The so called Upper Río Negro Valley in Argentina is one of the most important fruit and vegetable production regions of the country. It comprises the lower valleys of the Limay and Neuquén rivers and the upper Negro river valley. Out of the 41,671 cultivated hectares, 84.6% are cultivated with fruit trees, especially apple, pear and stone fruit trees. Late frosts occurring when trees are sensitive to low temperatures have a significant impact on the regional production. This study presents an analysis of air flow characteristics in the Upper Río Negro Valley and its relationship with ambient air flow. To such effect, observations made when synoptic-scale weather patterns were favorable for radiative frosts (light wind and clear sky) or nocturnal temperature inversion in the lower layer were used. In the Negro river valley, both wind channeling and downward horizontal momentum transport from ambient wind were observed; in nighttime, very light wind events occurred, possibly associated with drainage winds from the nearby higher levels of the barda. In the Neuquén river valley, the prevailing effect appeared to be forced channeling, consistent with the results obtained in valleys where the synoptic scale wind crossed the axis of the valley. In the Limay river valley, the flow was observed to blow parallel to the longitudinal valley axis, possibly influenced by pressure gradient and forced channeling.

  17. Cooling channels design analysis with chaotic laminar trajectory for closed cathode air-cooled PEM fuel cells using non-reacting numerical approach

    NASA Astrophysics Data System (ADS)

    N, W. Mohamed W. A.

    2015-09-01

    The thermal management of Polymer Electrolyte Membrane (PEM) fuel cells contributes directly to the overall power output of the system. For a closed cathode PEM fuel cell design, the use of air as a cooling agent is a non-conventional method due to the large heat load involved, but it offers a great advantage for minimizing the system size. Geometrical aspects of the cooling channels have been identified as the basic parameter for improved cooling performance. Numerical investigation using STAR-CCM computational fluid dynamics platform was applied for non-reacting cooling effectiveness study of various channel geometries for fuel cell application. The aspect ratio of channels and the flow trajectory are the parametric variations. A single cooling plate domain was selected with an applied heat flux of 2400 W/m2 while the cooling air are simulated at Reynolds number of 400 that corresponds to normal air flow velocities using standard 6W fans. Three channel designs of similar number of channels (20 channels) are presented here to analyze the effects of having chaotic laminar flow trajectory compared to the usual straight path trajectory. The total heat transfer between the cooling channel walls and coolant were translated into temperature distribution, maximum temperature gradient, average plate temperature and overall cooling effectiveness analyses. The numerical analysis shows that the chaotic flow promotes a 5% to 10% improvement in cooling effectiveness, depending on the single-axis or multi-axis flow paths applied. Plate temperature uniformity is also more realizable using the chaotic flow designs.

  18. Kelvin-Helmholtz Unstable Magnetotail Flow Channels: Deceleration and Radiation of MHD Waves

    NASA Astrophysics Data System (ADS)

    Turkakin, H.; Mann, I. R.; Rankin, R.

    2014-12-01

    The Kelvin-Helmholtz instability (KHI) of magnetotail flow channels associated with burstybulk flows (BBFs) is investigated. MHD oscillations of the channel in both kink and sausage modes areinvestigated for KHI, and both the primary and secondary KHIs are found that drive MHD waves. Theseinstabilities are likely to be important for flow channel braking where the KHI removes energy from the flow.At flow speeds above the peak growth rate, the MHD modes excited by KHI develop from surface modesinto propagating modes leading to the radiation of MHD waves from the flow channel. The coupling ofBBF-driven shear flow instabilities to MHD waves presented here represents a new paradigm to explain BBFexcitation of tail flapping. Our model can also explain, for the first time, the generation mechanism for theobservations of waves propagating toward both flanks and emitted from BBF channels in the magnetotail.

  19. Kelvin-Helmholtz unstable magnetotail flow channels: Deceleration and radiation of MHD waves

    NASA Astrophysics Data System (ADS)

    Turkakin, H.; Mann, I. R.; Rankin, R.

    2014-06-01

    The Kelvin-Helmholtz instability (KHI) of magnetotail flow channels associated with bursty bulk flows (BBFs) is investigated. MHD oscillations of the channel in both kink and sausage modes are investigated for KHI, and both the primary and secondary KHIs are found that drive MHD waves. These instabilities are likely to be important for flow channel braking where the KHI removes energy from the flow. At flow speeds above the peak growth rate, the MHD modes excited by KHI develop from surface modes into propagating modes leading to the radiation of MHD waves from the flow channel. The coupling of BBF-driven shear flow instabilities to MHD waves presented here represents a new paradigm to explain BBF excitation of tail flapping. Our model can also explain, for the first time, the generation mechanism for the observations of waves propagating toward both flanks and emitted from BBF channels in the magnetotail.

  20. Partial flow compensation by transverse bypass configuration in multi-channel cryogenic compact heat exchanger

    NASA Astrophysics Data System (ADS)

    Jung, Jeheon; Hwang, Gyuwan; Baek, Seungwhan; Jeong, Sangkwon; Rowe, Andrew M.

    2012-01-01

    High-performance multi-channel heat exchangers are vulnerable to small defects such as ill-manufacture or contamination in flow channels. Even slight flow mal-distribution may result in drastic reduction of their thermal performance. In order to accommodate such performance reduction in multi-channel heat exchangers, transverse bypass structure among the channels of hot stream or cold stream is proposed. Since transverse bypass structure enables voluntary flow re-distribution among the channels, detrimental effect of flow defects can be partially reduced and flow mal-distribution can be locally relieved. The lower the flow resistance of transverse bypass is, the more substantial the flow re-distribution is and the larger its effect can be. Quantitative analysis and experimental verification on the effect of transverse bypass is carried out, and the results are presented in this paper.

  1. Optical Air Flow Measurements in Flight

    NASA Technical Reports Server (NTRS)

    Bogue, Rodney K.; Jentink, Henk W.

    2004-01-01

    This document has been written to assist the flight-test engineer and researcher in using optical flow measurements in flight applications. The emphasis is on describing tradeoffs in system design to provide desired measurement performance as currently understood. Optical system components are discussed with examples that illustrate the issues. The document concludes with descriptions of optical measurement systems designed for a variety of applications including aeronautics research, airspeed measurement, and turbulence hazard detection. Theoretical discussion is minimized, but numerous references are provided to supply ample opportunity for the reader to understand the theoretical underpinning of optical concepts.

  2. Channel Geometry and Flood Flows: Quantifying over-bank flow dynamics during high-flow events in North Carolina's floodplains

    NASA Astrophysics Data System (ADS)

    Lovette, J. P.; Duncan, J. M.; Vimal, S.; Band, L. E.

    2015-12-01

    Natural riparian areas play numerous roles in the maintenance and improvement of stream water quality. Both restoration of riparian areas and improvement of hydrologic connectivity to the stream are often key goals of river restoration projects. These management actions are designed to improve nutrient removal by slowing and treating overland flow delivered from uplands and by storing, treating, and slowly releasing streamwater from overbank inundation during flood events. A major question is how effective this storage of overbank flow is at treating streamwater based on the cumulative time stream discharge at a downstream location has spent in shallower, slower overbank flow. The North Carolina Floodplain Mapping Program maintains a detailed statewide Flood Risk Information System (FRIS) using HEC-RAS modeling, lidar, and detailed surveyed river cross-sections. FRIS provides extensive information regarding channel geometry on approximately 39,000 stream reaches (a slightly coarser spatial resolution than the NHD+v2 dataset) with tens of cross-sections for each reach. We use this FRIS data to calculate volume and discharge from floodplain riparian areas separately from in-channel flow during overbank events. Preliminary results suggest that a small percentage of total annual discharge interacts with the full floodplain extent along a stream reach due to the infrequency of overbank flow events. However, with the significantly different physical characteristics of the riparian area when compared to the channel itself, this overbank flow can provide unique services to water quality. Our project aims to use this information in conjunction with data from the USGS SPARROW program to target non-point source hotspots of Nitrogen and Phosphorus addition and removal. By better understanding the flow dynamics within riparian areas during high flow events, riparian restoration projects can be carried out with improved efficacy.

  3. Compressible turbulent channel flow with impedance boundary conditions

    NASA Astrophysics Data System (ADS)

    Scalo, Carlo; Bodart, Julien; Lele, Sanjiva

    2014-11-01

    We have performed large-eddy simulations of compressible turbulent channel flow at one bulk Reynolds number, Reb = 6900, for bulk Mach numbers Mb = 0.05, 0.2, 0.5, with linear acoustic impedance boundary conditions (IBCs). The IBCs are formulated in the time domain following Fung and Ju (2004) and coupled with a Navier-Stokes solver. The impedance model adopted is a three-parameter Helmholtz oscillator with resonant frequency tuned to the outer layer eddies. The IBC's resistance, R, has been varied in the range, R = 0.01, 0.10, 1.00. Tuned IBCs result in a noticeable drag increase for sufficiently high Mb and/or low R, exceeding 300% for Mb = 0.5 and R = 0.01, and thus represents a promising passive control technique for delaying boundary layer separation and/or enhancing wall heat transfer. Alterations to the turbulent flow structure are confined to the first 15% of the boundary layer thickness where the classical buffer-layer coherent vortical structures are replaced by an array of Kelvin-Helmholtz-like rollers. The non-zero asymptotic value of the Reynolds shear stress gradient at the wall results in the disappearance of the viscous sublayer and very early departure of the mean velocity profiles from the law of the wall.

  4. Coalescence and breakup of large droplets in turbulent channel flow

    NASA Astrophysics Data System (ADS)

    Scarbolo, Luca; Bianco, Federico; Soldati, Alfredo

    2015-07-01

    Coalescence and breakup of large deformable droplets dispersed in a wall-bounded turbulent flow are investigated. Droplets much larger than the Kolmogorov length scale and characterized by a broad range of surface tension values are considered. The turbulent field is a channel flow computed with pseudo-spectral direct numerical simulations, while phase interactions are described with a phase field model. Within this physically consistent framework, the motion of the interfaces, the capillary effects, and the complex topological changes experienced by the droplets are simulated in detail. An oil-water emulsion is mimicked: the fluids are considered of same density and viscosity for a range of plausible values of surface tension, resulting in a simplified system that sets a benchmark for further analysis. In the present conditions, the Weber number (We), that is, the ratio between inertia and surface tension, is a primary factor for determining the droplets coalescence rate and the occurrence of breakups. Depending on the value of We, two different regimes are observed: when We is smaller than a threshold value (We < 1 in our simulations), coalescence dominates until droplet-droplet interactions are prevented by geometric separation; when We is larger than the threshold value (We > 1), a permanent dynamic equilibrium between coalescence and breakup events is established.

  5. Large eddy simulation of incompressible turbulent channel flow

    NASA Technical Reports Server (NTRS)

    Moin, P.; Reynolds, W. C.; Ferziger, J. H.

    1978-01-01

    The three-dimensional, time-dependent primitive equations of motion were numerically integrated for the case of turbulent channel flow. A partially implicit numerical method was developed. An important feature of this scheme is that the equation of continuity is solved directly. The residual field motions were simulated through an eddy viscosity model, while the large-scale field was obtained directly from the solution of the governing equations. An important portion of the initial velocity field was obtained from the solution of the linearized Navier-Stokes equations. The pseudospectral method was used for numerical differentiation in the horizontal directions, and second-order finite-difference schemes were used in the direction normal to the walls. The large eddy simulation technique is capable of reproducing some of the important features of wall-bounded turbulent flows. The resolvable portions of the root-mean square wall pressure fluctuations, pressure velocity-gradient correlations, and velocity pressure-gradient correlations are documented.

  6. Flow and transport in channels with submerged vegetation

    NASA Astrophysics Data System (ADS)

    Nepf, Heidi; Ghisalberti, Marco

    2008-09-01

    This paper reviews recent work on flow and transport in channels with submerged vegetation, including discussions of turbulence structure, mean velocity profiles, and dispersion. For submerged canopies of sufficient density, the dominant characteristic of the flow is the generation of a shear-layer at the top of the canopy. The shear-layer generates coherent vortices by Kelvin-Helmholtz (KH) instability. These vortices control the vertical exchange of mass and momentum, influencing both the mean velocity profile, as well as the turbulent diffusivity. For flexible canopies, the passage of the KH vortices generates a progressive wave along the canopy interface, termed monami. The KH vortices formed at the top of the canopy penetrate a distance δ e into the canopy. This penetration scale segregates the canopy into an upper layer of rapid transport and a lower layer of slow transport. Flushing of the upper canopy is enhanced by the energetic shear-scale vortices. In the lower layer turbulence is limited to length-scales set by the stem geometry, and the resulting transport is significantly slower than that of the upper layer.

  7. Numerical investigation of transition critical Reynolds number of channel flow.

    NASA Astrophysics Data System (ADS)

    Zhang, Yongming

    2015-11-01

    Two critical Reynolds numbers are mentioned in investigation of laminar-turbulent transition. One is instability critical Reynolds number from linear stability theory (LST). The other is transition critical Reynolds number at which transition occurs in reality, which is significantly lower than the former in general. The determination of transition critical Reynolds number is of important practical significance in some engineering problems. Theoretical method has not been proposed for its determination, so it has to depend on experiments. However, for some flows with important practical significance, such as hypersonic boundary layer, transition critical Reynolds number cannot be determined by experiments in current situation. In this paper, transition critical Reynolds number of incompressible channel flow is determined by direct numerical simulations (DNS). It is found as Re =1114, which agrees with experimental data. In subsequent paper, transition critical Reynolds number of boundary layer will be investigation by the similar method. Project supported by the National Natural Science Foundation of China (Nos. 11202147, 11332007, 11172203, and 91216111) and the Specialized Research Fund (New Teacher Class) for the Doctoral Program of Higher Education (No. 20120032120007).

  8. Compressible turbulent channel flow with impedance boundary conditions

    NASA Astrophysics Data System (ADS)

    Scalo, Carlo; Bodart, Julien; Lele, Sanjiva K.

    2015-03-01

    We have performed large-eddy simulations of isothermal-wall compressible turbulent channel flow with linear acoustic impedance boundary conditions (IBCs) for the wall-normal velocity component and no-slip conditions for the tangential velocity components. Three bulk Mach numbers, Mb = 0.05, 0.2, 0.5, with a fixed bulk Reynolds number, Reb = 6900, have been investigated. For each Mb, nine different combinations of IBC settings were tested, in addition to a reference case with impermeable walls, resulting in a total of 30 simulations. The adopted numerical coupling strategy allows for a spatially and temporally consistent imposition of physically realizable IBCs in a fully explicit compressible Navier-Stokes solver. The IBCs are formulated in the time domain according to Fung and Ju ["Time-domain impedance boundary conditions for computational acoustics and aeroacoustics," Int. J. Comput. Fluid Dyn. 18(6), 503-511 (2004)]. The impedance adopted is a three-parameter damped Helmholtz oscillator with resonant angular frequency, ωr, tuned to the characteristic time scale of the large energy-containing eddies. The tuning condition, which reads ωr = 2πMb (normalized with the speed of sound and channel half-width), reduces the IBCs' free parameters to two: the damping ratio, ζ, and the resistance, R, which have been varied independently with values, ζ = 0.5, 0.7, 0.9, and R = 0.01, 0.10, 1.00, for each Mb. The application of the tuned IBCs results in a drag increase up to 300% for Mb = 0.5 and R = 0.01. It is shown that for tuned IBCs, the resistance, R, acts as the inverse of the wall-permeability and that varying the damping ratio, ζ, has a secondary effect on the flow response. Typical buffer-layer turbulent structures are completely suppressed by the application of tuned IBCs. A new resonance buffer layer is established characterized by large spanwise-coherent Kelvin-Helmholtz rollers, with a well-defined streamwise wavelength λx, traveling downstream with

  9. Velocity Vector Field Visualization of Flow in Liquid Acquisition Device Channel

    NASA Technical Reports Server (NTRS)

    McQuillen, John B.; Chao, David F.; Hall, Nancy R.; Zhang, Nengli

    2012-01-01

    A capillary flow liquid acquisition device (LAD) for cryogenic propellants has been developed and tested in NASA Glenn Research Center to meet the requirements of transferring cryogenic liquid propellants from storage tanks to an engine in reduced gravity environments. The prototypical mesh screen channel LAD was fabricated with a mesh screen, covering a rectangular flow channel with a cylindrical outlet tube, and was tested with liquid oxygen (LOX). In order to better understand the performance in various gravity environments and orientations at different liquid submersion depths of the screen channel LAD, a series of computational fluid dynamics (CFD) simulations of LOX flow through the LAD screen channel was undertaken. The resulting velocity vector field visualization for the flow in the channel has been used to reveal the gravity effects on the flow in the screen channel.

  10. Flow field simulation of gas-water two phase flow in annular channel

    NASA Astrophysics Data System (ADS)

    Ji, Pengcheng; Dong, Feng

    2014-04-01

    The gas-water two-phase flow is very common in the industrial processes. the deep understanding of the two-phase flow state is to achieve the production equipment design and safe operation. In the measurement of gas-water two-phase flow, the differential pressure sensor is widely used, and some measurement model of multiphase flow have been concluded. The differential pressure is generated when fluid flowing through the throttling components to calculate flow rate. This paper mainly focuses on two points: 1. The change rule of the parameters include velocity, pressure, phase fraction as the change of time, when the phase inlet velocity is given. 2. Analysis the distribution of the parameters above-mentioned at a certain moment under the condition of different water inlet velocity. Three-dimensional computational fluid dynamics (CFD) approach was used to simulate gas-water two-phase flow fluid in the annular channel, which is composed of horizontal pipe and long- waist cone sensor. The simulation results were obtained from FLUENT software.

  11. Numerical simulations of non-homogeneous viscoelastic turbulent channel flow

    NASA Astrophysics Data System (ADS)

    Housiadas, Kostas; Beris, Antony

    2004-11-01

    The effect of the polymer mixing in turbulent channel flow is studied through numerical simulations, using a spectral technique. In particular, we simulate injection of polymeric material through a slit very close to the wall and parallel to it in pre-established Newtonian turbulent flow. The governing equations consist of the mass conservation, the modified Navier-Stokes equation (in order to take into account the polymer extra-stress), the evolution equation for the conformation tensor and an advection-diffusion equation for the polymer concentration. The injection process is simulated by dividing the computational domain in three different regions: (a) the entrance region where the polymer is introduced (b) the developing region where the polymer is allowed to convect freely interacting/modifying the turbulent flow and (c) the recovering region where we use a reacting sink to force the removal of the polymer from the solvent in order to re-establish the inlet conditions. A fully spectral method is used in order to solve the set of governing equations similar to that developed for homogenous viscoelastic turbulent DNS (Housiadas & Beris, Phys. Fluids, 15, (2003)). Although a significantly improved numerical algorithm has been successfully used before (Housiadas & Beris, to appear in J. Non-Newt. Fluid Mech. (2004)) a further improved version of that algorithm is presented in this work. The new algorithm has enabled us to extend the simulations for much wider range of viscoelasticity parameter values as well as for many viscoelastic models like the FENE-P, Giesekus, Oldroyd-B and the modified Giesekus/FENE-P model. Results for illustrative sets of parameter values are going to be presented.

  12. Air flow management in an internal combustion engine through the use of electronically controlled air jets

    SciTech Connect

    Swain, M.R.

    1988-12-27

    This patent describes a means for producing an air/fuel mixture in the valve pocket and means for directing the air/fuel mixture past the intake valve into the combustion chamber, the improvement comprising a device for generating a swirling flow of the air/fuel mixture in the combustion chamber to thereby obtain greater combustion stability. The device has a nozzle positioned within the valve pocket and directed at an acute angle toward the intake valve comprising at least one opening for receiving air, connected to a first pathway, and at least one opening for expelling air, connected, to a second pathway joined to the first pathway and extending to the expulsion opening. The device also includes a means for controlling the flow of air through the pathway and out the expulsion opening comprising: (i) a stopper having sides complementary in shape to the pair of opposed arcuate walls movable from an open position allowing air through the pathway to a closed position, wherein the sides of the stopper are in a sealed relationship with the opposed arcaute sides of the junction thereby preventing the flow of air through the second pathway and out of the expulsion opening; and (ii) an electronic computer which determines the size and duration of the pathway opening.

  13. Correlations of Surface Deformation and 3D Flow Field in a Compliant Wall Turbulent Channel Flow.

    NASA Astrophysics Data System (ADS)

    Wang, Jin; Zhang, Cao; Katz, Joseph

    2015-11-01

    This study focuses on the correlations between surface deformation and flow features, including velocity, vorticity and pressure, in a turbulent channel flow over a flat, compliant Polydimethylsiloxane (PDMS) wall. The channel centerline velocity is 2.5 m/s, and the friction Reynolds number is 2.3x103. Analysis is based on simultaneous measurements of the time resolved 3D velocity and surface deformation using tomographic PIV and Mach-Zehnder Interferometry. The volumetric pressure distribution is calculated plane by plane by spatially integrating the material acceleration using virtual boundary, omni-directional method. Conditional sampling based on local high/low pressure and deformation events reveals the primary flow structures causing the deformation. High pressure peaks appear at the interface between sweep and ejection, whereas the negative deformations peaks (dent) appear upstream, under the sweeps. The persistent phase lag between flow and deformations are presumably caused by internal damping within the PDMS. Some of the low pressure peaks and strong ejections are located under the head of hairpin vortices, and accordingly, are associated with positive deformation (bump). Others bumps and dents are correlated with some spanwise offset large inclined quasi-streamwise vortices that are not necessarily associated with hairpins. Sponsored by ONR.

  14. Flow behaviour analysis and experimental investigation for emitter micro-channels

    NASA Astrophysics Data System (ADS)

    Wei, Zhengying; Cao, Meng; Liu, Xia; Tang, Yiping; Lu, Bingheng

    2012-07-01

    The existing research of the flow behavior in emitter micro-channels mainly focuses on the single-phase flow behavior. And the recent micro-particle image velocimetry (PIV) experimental research on the flow characteristics in various micro-channels mainly focuses on the single-phase fluid flow. However, using an original-size emitter prototype to perform the experiments on the two-phase flow characteristics of the labyrinth channels is seldom reported. In this paper, the practical flow of water, mixed with sand escaped from filtering, in the labyrinth channel, is investigated. And some research work on the clogging mechanism of the labyrinth channel's structure is conducted. Computational fluid dynamics(CFD) analysis has been performed on liquid-solid two-phase flow in labyrinthchannel emitters. Based on flow visualization technology—micro-PIV, the flow in labyrinth channel has been photographed and recorded. The path line graph and velocity vector graph are obtained through the post-treatment of experimental results. The graphs agree well with CFD analysis results, so CFD analysis can be used in optimal design of labyrinth-channel emitters. And the optimized anti-clogging structures of the rectangular channel and zigzag channel have been designed here. The CFD numerical simulation and the micro-PIV experiments analysis on labyrinth-channel emitter, make the "black box" of the flow behavior in the emitter channel broken. Furthermore, the proposed research promotes an advanced method to evaluate the emitter's performance and can be used to conducting the optimal design of the labyrinth-channel emitters.

  15. Comparisons of the hydraulics of water flows in Martian outflow channels with flows of similar scale on earth

    NASA Technical Reports Server (NTRS)

    Komar, P. D.

    1979-01-01

    The hydraulics of channelized water flows on Mars and the resulting sediment transport rates are calculated, and similar computations are performed for such terrestrial analogs as the Mississippi River and the catastrophic Lake Missoula floods that formed the Channeled Scabland in eastern Washington State. The morphologies of deep-sea channels formed by catastrophic turbidity currents are compared with the Martian channels, many similarities are pointed out, and the hydraulics of the various flows are compared. The results indicate that the velocities, discharges, bottom shear stresses, and sediment-transport capacity of water flows along the Martian channels would be comparable to those of the oceanic turbidity currents and the Lake Missoula floods. It is suggested that the submarine canyons from which turbidity currents originate are the terrestrial counterparts to the chaotic-terrain areas or craters that serve as sources for many of the Martian channels.

  16. Heat transfer performance comparison of steam and air in gas turbine cooling channels with different rib angles

    NASA Astrophysics Data System (ADS)

    Shi, Xiaojun; Gao, Jianmin; Xu, Liang; Li, Fajin

    2013-11-01

    Using steam as working fluid to replace compressed air is a promising cooling technology for internal cooling passages of blades and vanes. The local heat transfer characteristics and the thermal performance of steam flow in wide aspect ratio channels ( W/ H = 2) with different angled ribs on two opposite walls have been experimentally investigated in this paper. The averaged Nusselt number ratios and the friction factor ratios of steam and air in four ribbed channels were also measured under the same test conditions for comparison. The Reynolds number range is 6,000-70,000. The rib angles are 90°, 60°, 45°, and 30°, respectively. The rib height to hydraulic diameter ratio is 0.047. The pitch-to-rib height ratio is 10. The results show that the Nusselt number ratios of steam are 1.19-1.32 times greater than those of air over the range of Reynolds numbers studied. For wide aspect ratio channels using steam as the coolant, the 60° angled ribs has the best heat transfer performance and is recommended for cooling design.

  17. Airway blood flow response to dry air hyperventilation in sheep

    SciTech Connect

    Parsons, G.H.; Baile, E.M.; Pare, P.D.

    1986-03-01

    Airway blood flow (Qaw) may be important in conditioning inspired air. To determine the effect of eucapneic dry air hyperventilation (hv) on Qaw in sheep the authors studied 7 anesthetized open-chest sheep after 25 min. of warm dry air hv. During each period of hv the authors have recorded vascular pressures, cardiac output (CO), and tracheal mucosal and inspired air temperature. Using a modification of the reference flow technique radiolabelled microspheres were injected into the left atrium to make separate measurements after humid air and dry air hv. In 4 animals a snare around the left main pulmonary artery was used following microsphere injection to prevent recirculation (entry into L lung of microspheres from the pulmonary artery). Qaw to the trachea and L lung as measured and Qaw for the R lung was estimated. After the final injection the sheep were killed and bronchi (Br) and lungs removed. Qaw (trachea plus L lung plus R lung) in 4 sheep increased from a mean of 30.8 to 67.0 ml/min. Airway mucosal temp. decreased from 39/sup 0/ to 33/sup 0/C. The authors conclude that dry air hv cools airway mucosa and increases Qaw in sheep.

  18. Air flow phenomena in the model of the blind drift

    NASA Astrophysics Data System (ADS)

    Jaszczur, Marek; Karch, Michał; Zych, Marcin; Hanus, Robert; Petryka, Leszek; Świsulski, Dariusz

    2016-03-01

    In the presented paper, Particle Image Velocimetry (PIV) has been used to investigate flow pattern and turbulent structure in the model of blind drift. The presented model exist in mining, and has been analyzed to resolve ventilation issues. Blind region is particularly susceptible to unsafe methane accumulation. The measurement system allows us to evaluate all components of the velocity vector in channel cross-section simultaneously. First order and second order statistic of the velocity fields from different channel cross-section are computed and analyzed.

  19. Liquid plug flow in a vertical two-dimensional channel

    NASA Astrophysics Data System (ADS)

    Bull, Joseph; Halpern, David; Grotberg, James

    2001-11-01

    Gravity and pressure driven liquid plug flow in a two-dimensional vertical channel is investigated as a model of instilled liquid transport in the lungs. There are a number of clinical situations in which liquids are instilled into the lungs. Of particular interest is liquid ventilation where perfluorocarbon liquids are delivered to the lung and subsequently used for ventilation in place of gas. Additionally the perfuorocarbon can be used as a carrier for drugs or genetic material. Some other examples of liquid instillation into the lungs include surfactant replacement therapy, lung lavage, and cardio-pulmonary resuscitation. The desired distribution of liquid depends on the application. Our model is developed using the Stokes equation subject to interfacial and wall boundary conditions, and is solved using the boundary element method. We obtain steady-state and time-dependent solutions. As the plug propagates along the thin-film-lined channel, it takes up liquid from the leading film and deposit liquid in the trailing film. The trailing film thickness, interface shapes and plug speed are determined as functions of the parameters of the problem, Bond number, driving pressure, and leading film thickness and initial plug length for the time-dependent problem. These results are important clinically since the trailing film thickness determines when the plug ruptures affecting the ultimate liquid distribution, and thicker films can result in airway closure. This research was supported by NIH grants HL41126, HL64373, and HL54224-04S1. J.L. Bull is a Parker B. Francis Fellow in Pulmonary Research.

  20. The significance of micro-topography in generating flow structures in open channel flow

    NASA Astrophysics Data System (ADS)

    Hardy, R. J.

    2011-12-01

    This poster investigates the effect of micro-topographic roughness on the generation, evolution and dissipation of turbulent flow structures in open channel flow. Primarily, a series of flume experiment were undertaken where natural fluvial gravel was placed in a flume and water worked until a stable bed with no sediment transport was obtained. The surface topography was measured to create a digital elevation model (DEM) enabling particle size characteristics to be measured and roughness lengths to be calculated. Flow was measured, at flow Reynolds numbers over two orders of magnitude, using Particle Imaging Velocimetry at data frequencies up to 100 Hz at a spatial resolution of 2×10-3 m. The flume conditions also provided the necessary boundary conditions for Large Eddy Simulation of flow over these heterogeneous surfaces. The data generated by these two separate methodologies was analyzed through a series of approaches, and included: i) standard Reynolds decomposition to the flow fields; ii) Eulerian coherent structure detection methods based on the invariants of the velocity gradient tensor; iii) Lagrangian coherent structure identification methods based upon direct Lyapunov exponents (DLE) and; iv) Proper Orthogonal Decomposition (POD) analysis to obtain a full understanding of the turbulent flow structures. Once the LES scheme had been fully validated against the PIV data, scales of topography were removed from the DEM. The LES simulations were then recalculated to assess the influence of topography on the generation of turbulent flow structures. The results demonstrate that the generative mechanism for these bed-generated coherent flow structures are merging hairpin-type vortices that form around bed clasts and generate larger-scale roller-type structures. This mechanism of generation appears consistent over the range of Reynolds numbers but the spatial and temporal length scales appear dependent upon the bed roughness.

  1. Distribution of air-water mixtures in parallel vertical channels as an effect of the header geometry

    SciTech Connect

    Marchitto, Annalisa; Fossa, Marco; Guglielmini, Giovanni

    2009-07-15

    Uneven phase distribution in heat exchangers is a cause of severe reductions in thermal performances of refrigeration equipment. To date, no general design rules are available to avoid phase separation in manifolds with several outlet channels, and even predicting the phase and mass distribution in parallel channels is a demanding task. In the present paper, measurements of two-phase air-water distributions are reported with reference to a horizontal header supplying 16 vertical upward channels. The effects of the operating conditions, the header geometry and the inlet port nozzle were investigated in the ranges of liquid and gas superficial velocities of 0.2-1.2 and 1.5-16.5 m/s, respectively. Among the fitting devices used, the insertion of a co-axial, multi-hole distributor inside the header confirmed the possibility of greatly improving the liquid and gas flow distribution by the proper selection of position, diameter and number of the flow openings between the supplying distributor and the system of parallel channels connected to the header. (author)

  2. Long-wave linear stability theory for two-fluid channel flow including compressibility effects

    NASA Astrophysics Data System (ADS)

    Segin, Tetyana M.; Kondic, Lou; Tilley, Burt S.

    2006-10-01

    We present the linear stability of the laminar flow of an immiscible system of a compressible gas and incompressible liquid separated by an interface with large surface tension in a thin inclined channel. The flow is driven by an applied pressure drop and gravity. Following the air-water case, which is found in a variety of engineering systems, the ratio of the characteristic values of the gas and liquid densities and viscosities are assumed to be disparate. Under the lubrication approximation, and assuming ideal gas behaviour and isothermal conditions, this approach leads to a coupled non-linear system of partial differential equations describing the evolution of the interface between the gas and the liquid and the streamwise density distribution of the gas. This system also includes the effects of viscosity stratification, inertia, shear and capillarity. A linear stability analysis that allows for physically relevant non-zero pressure-drop base state is then performed. In contrast to the zero-pressure drop case which is amenable to the classical normal-mode approach, this configuration requires numerically solving a boundary-value problem for the gas density and interfacial deviations from the base state in the streamwise coordinate. We find that the effect of the gas compressibility on the interfacial stability in the limit of vanishingly small wavenumber is destabilizing, even for Stokes flow in the liquid. However, for finite wavenumber disturbances, compressibility may have stabilizing effects. In this regime, sufficient shear is required to destabilize the flow.

  3. An experimental and analytical study of flow through a supersonic open channel with contoured floor

    NASA Technical Reports Server (NTRS)

    Saheli, F. P.; Dunn, B.; Marrs, K.; Kumar, A.; Peery, K. M.

    1984-01-01

    A wind tunnel experiment was performed to study the characteristics of supersonic airflow (M(infinity) = 2.5-3.86) through an open channel with a contoured floor. The measured static pressures along the centerline of the channel floor exhibited an unexpected rise at the end of the channel. Complex three-dimensional interactions of compression and expansion waves within the channel coupled with external flow perturbations caused by model/tunnel wall interference were the suspected sources of this flow behavior. Three-dimensional inviscid flow analysis procedures were used to investigate and explain this phenomenon. The results of the computations and the experiment are presented and discussed.

  4. Heat transfer, pressure drop, and mass flow rate in pin fin channels with long and short trailing edge ejection holes

    NASA Astrophysics Data System (ADS)

    Lau, S. C.; Han, J. C.; Batten, T.

    1988-06-01

    The turbulent heat transfer and friction characteristics in the pin fin channels with small trailing edge ejection holes found in internally-cooled turbine airfoils have been experimentally investigated. It is found that the overall heat transfer increases when the length of the trailing edge ejection holes is increased and when the trailing edge ejection holes are configured such that much of the cooling air is forced to flow further downstream in the radial flow direction prior to exiting. The increase in the overall heat transfer is shown to be accompanied by an increase in the overall pressure drop.

  5. Transport of self-propelling bacteria in micro-channel flow

    NASA Astrophysics Data System (ADS)

    Costanzo, A.; Di Leonardo, R.; Ruocco, G.; Angelani, L.

    2012-02-01

    Understanding the collective motion of self-propelling organisms in confined geometries, such as that of narrow channels, is of great theoretical and practical importance. By means of numerical simulations we study the motion of model bacteria in 2D channels under different flow conditions: fluid at rest, steady and unsteady flow. We find aggregation of bacteria near channel walls and, in the presence of external flow, also upstream swimming, which turns out to be a very robust result. Detailed analysis of bacterial velocity and orientation fields allows us to quantify the phenomenon by varying cell density, channel width and fluid velocity. The tumbling mechanism turns out to have strong influence on velocity profiles and particle flow, resulting in a net upstream flow in the case of non-tumbling organisms. Finally we demonstrate that upstream flow can be enhanced by a suitable choice of an unsteady flow pattern.

  6. Evolutionary Concepts for Decentralized Air Traffic Flow Management

    NASA Technical Reports Server (NTRS)

    Adams, Milton; Kolitz, Stephan; Milner, Joseph; Odoni, Amedeo

    1997-01-01

    Alternative concepts for modifying the policies and procedures under which the air traffic flow management system operates are described, and an approach to the evaluation of those concepts is discussed. Here, air traffic flow management includes all activities related to the management of the flow of aircraft and related system resources from 'block to block.' The alternative concepts represent stages in the evolution from the current system, in which air traffic management decision making is largely centralized within the FAA, to a more decentralized approach wherein the airlines and other airspace users collaborate in air traffic management decision making with the FAA. The emphasis in the discussion is on a viable medium-term partially decentralized scenario representing a phase of this evolution that is consistent with the decision-making approaches embodied in proposed Free Flight concepts for air traffic management. System-level metrics for analyzing and evaluating the various alternatives are defined, and a simulation testbed developed to generate values for those metrics is described. The fundamental issue of modeling airline behavior in decentralized environments is also raised, and an example of such a model, which deals with the preservation of flight bank integrity in hub airports, is presented.

  7. A weakly nonlinear theory for wave-vortex interactions in curved channel flow

    NASA Technical Reports Server (NTRS)

    Singer, Bart A.; Erlebacher, Gordon; Zang, Thomas A.

    1992-01-01

    A weakly nonlinear theory is developed to study the interaction of Tollmien-Schlichting (TS) waves and Dean vortices in curved channel flow. The predictions obtained from the theory agree well with results obtained from direct numerical simulations of curved channel flow, especially for low amplitude disturbances. Some discrepancies in the results of a previous theory with direct numerical simulations are resolved.

  8. Glow Discharge Characteristics in Transverse Supersonic Air Flow

    NASA Astrophysics Data System (ADS)

    Timerkaev, B. A.; Zalyaliev, B. R.; Saifutdinov, A. I.

    2014-11-01

    A low pressure glow discharge in a transverse supersonic gas flow of air at pressures of the order 1 torr has been experimentally studied for the case where the flow only partially fills the inter electrode gap. It is shown that the space region with supersonic gas flow has a higher concentration of gas particles and, therefore, works as a charged particle generator. The near electrode regions of glow discharge are concentrated specifically in this region. This structure of glow discharge is promising for plasma deposition of coatings under ultralow pressures

  9. Split-flow regeneration in absorptive air separation

    DOEpatents

    Weimer, Robert F.

    1987-01-01

    A chemical absorptive separation of air in multiple stage of absorption and desorption is performed with partial recycle of absorbent between stages of desorption necessary to match equilibrium conditions in the various stages of absorption. This allows reduced absorbent flow, reduced energy demand and reduced capital costs.

  10. The Wells turbine in an oscillating air flow

    SciTech Connect

    Raghunathan, S.; Ombaka,

    1984-08-01

    An experimental study of the performance of a 0.2 m diameter Wells self rectifying air turbine with NACA 0021 blades is presented. Experiments were conducted in an oscillating flowrig. The effects of Reynolds number and Strouhal number on the performance of the turbine were investigated. Finally comparison between the results with the predictions from uni-directional flow tests are made.

  11. Split-flow regeneration in absorptive air separation

    DOEpatents

    Weimer, R.F.

    1987-11-24

    A chemical absorptive separation of air in multiple stage of absorption and desorption is performed with partial recycle of absorbent between stages of desorption necessary to match equilibrium conditions in the various stages of absorption. This allows reduced absorbent flow, reduced energy demand and reduced capital costs. 4 figs.

  12. 30 CFR 57.22213 - Air flow (III mines).

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 30 Mineral Resources 1 2013-07-01 2013-07-01 false Air flow (III mines). 57.22213 Section 57.22213 Mineral Resources MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR METAL AND NONMETAL MINE SAFETY AND HEALTH SAFETY AND HEALTH STANDARDS-UNDERGROUND METAL AND NONMETAL MINES Safety Standards...

  13. 30 CFR 57.22213 - Air flow (III mines).

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 30 Mineral Resources 1 2010-07-01 2010-07-01 false Air flow (III mines). 57.22213 Section 57.22213 Mineral Resources MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR METAL AND NONMETAL MINE SAFETY AND HEALTH SAFETY AND HEALTH STANDARDS-UNDERGROUND METAL AND NONMETAL MINES Safety Standards...

  14. 30 CFR 57.22213 - Air flow (III mines).

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 30 Mineral Resources 1 2014-07-01 2014-07-01 false Air flow (III mines). 57.22213 Section 57.22213 Mineral Resources MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR METAL AND NONMETAL MINE SAFETY AND HEALTH SAFETY AND HEALTH STANDARDS-UNDERGROUND METAL AND NONMETAL MINES Safety Standards...

  15. 30 CFR 57.22213 - Air flow (III mines).

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 30 Mineral Resources 1 2011-07-01 2011-07-01 false Air flow (III mines). 57.22213 Section 57.22213 Mineral Resources MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR METAL AND NONMETAL MINE SAFETY AND HEALTH SAFETY AND HEALTH STANDARDS-UNDERGROUND METAL AND NONMETAL MINES Safety Standards...

  16. 30 CFR 57.22213 - Air flow (III mines).

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 30 Mineral Resources 1 2012-07-01 2012-07-01 false Air flow (III mines). 57.22213 Section 57.22213 Mineral Resources MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR METAL AND NONMETAL MINE SAFETY AND HEALTH SAFETY AND HEALTH STANDARDS-UNDERGROUND METAL AND NONMETAL MINES Safety Standards...

  17. Analyzing low frequency waves associated with plasma sheet flow channels

    NASA Astrophysics Data System (ADS)

    Xing, X.; Liang, J.; Wang, C. P.; Lyons, L. R.; Angelopoulos, V.

    2014-12-01

    Low frequency (0.006~0.02 Hz) magnetic oscillations are frequently observed to be associated with the substorm-related dipolarization in the near-Earth plasma sheet. It has been suggested that these oscillations are possibly triggered by ballooning instability in the transition region. However, our multi-point observations using THEMIS spacecraft have shown that similar oscillations are observed to be associated with the earthward moving flow channels as they penetrate from middle tail to the transition region. Linear MHD wave analysis suggested that these oscillations ahead of the dipolarization front are magnetosonic waves. For most of the cases, the thermal pressure and magnetic pressures variations are anti-phase, indicating slow mode waves. However, by taking advantage of the spacecraft located very close in X-Y plane and slightly away from the central plasma sheet, we found that for many events the phase relation between the thermal and magnetic pressure variations is Z-dependent, which suggests that the observational evidence for slow mode may not be applicable. In order to further examine these waves, we performed a MHD analysis in inhomogeneous plasma sheet. The calculation shows that for Harris Sheet configuration, the thermal and magnetic pressures variations can be anti-phase for any wave other than slow mode waves where the vertical velocity disturbance reaches its maximum, thus this phase relation may not be used as an identifier of magnetosonic wave modes. We will show the dispersion relation and wave generated disturbances obtained from the numerical calculations.

  18. Behavior of Heavy Particles in Turbulent Channel Flow

    NASA Astrophysics Data System (ADS)

    Lee, Junghoon; Lee, Changhoon

    2010-11-01

    The motion of heavy particles in turbulent channel flow was investigated by using direct numerical simulation. We assumed that Stokes drag, Saffman lift and Magnus lift act on the motion of heavy spherical particles in turbulence. In this study, Stokes number is defined as the particle response time normalized by the wall units. The range of the Stokes number is 0.1˜50 and the diameter of a particle is 0.06˜0.3 in wall unit. Collision of particles with the wall is modelled by an elastic collision. Relevant velocity and acceleration statistics of heavy particles for the given range of Stokes number were investigated to interpret the particle accumulation near the wall. Particle accumulation at the wall is maximized when the Stokes number is around 15. And we found that Saffman lift force has a great effect on particle acceleration in the wall-normal direction near the wall. Detailed statistics including probability density function and autocorrelation of particle velocity and acceleration will be presented in the meeting.

  19. Morphological impacts of flow events of varying magnitude on ephemeral channels in a semiarid region

    NASA Astrophysics Data System (ADS)

    Hooke, J. M.

    2016-01-01

    Flows in ephemeral channels in semiarid areas are only occasional, and channel changes are episodic; but the flash floods can be devastating and have major geomorphological impacts. Data on morphological impacts of flows in semiarid areas are needed to increase understanding of the dynamics and variability of geomorphic responses in such channels. For this purpose nine reaches of river channel in three catchments in SE Spain - the Nogalte, Torrealvilla, and Salada - have been sites for measurement of flows and their effects over the period 1997-2012. The sites encompass a range of channel size, channel morphology, substrate, vegetation, and position within the catchments. A major difference is between schist and marl bedrock areas. Peak flow stage has been recorded and topography surveyed at frequent intervals and after major flow events. Over the 16-year period, an average of 0.5 flow events per year has been recorded at the schist sites, and an average of one per year at the marl sites; but occurrence has been highly variable from year to year. Threshold daily rainfall for channel flow is mostly 15-20 mm, but higher rainfalls do not always produce flow. One to two major floods have occurred in each of the catchments in the period, including the extreme flood event of September 2012 in the Nogalte catchment. Measured morphological changes have occurred between 2 and 10 times at the monitored sites. The same size flow can have differing effects depending on the state of the system. Low flow can mobilise sediment without producing much morphological change. The long-term trajectory of the reaches and the sediment substrate has a major influence on response to events. Channel change is governed by threshold values of hydraulic conditions. The measurements provide an indication of the scale of maximum erosion and deposition that occurs within the channels and on the floodplains over a range of flow magnitudes and the flow impacts that need to be considered in

  20. A stagnation pressure probe for droplet-laden air flow

    NASA Technical Reports Server (NTRS)

    Murthy, S. N. B.; Leonardo, M.; Ehresman, C. M.

    1985-01-01

    It is often of interest in a droplet-laden gas flow to obtain the stagnation pressure of both the gas phase and the mixture. A flow-decelerating probe (TPF), with separate, purged ports for the gas phase and the mixture and with a bleed for accumulating liquid at the closed end, has been developed. Measurements obtained utilizing the TPF in a nearly isothermal air-water droplet mixture flow in a smooth circular pipe under various conditions of flow velocity, pressure, liquid concentration and droplet size are presented and compared with data obtained under identical conditions with a conventional, gas phase stagnation pressure probe (CSP). The data obtained with the CSP and TPF probes are analyzed to determine the applicability of the two probes in relation to the multi-phase characteristics of the flow and the geometry of the probe.

  1. Channelized fluid flow in oceanic crust reconciles heat-flow and permeability data

    PubMed

    Fisher; Becker

    2000-01-01

    Hydrothermal fluid circulation within the sea floor profoundly influences the physical, chemical and biological state of the crust and the oceans. Circulation within ridge flanks (in crust more than 1 Myr old) results in greater heat loss and fluid flux than that at ridge crests and persists for millions of years, thereby altering the composition of the crust and overlying ocean. Fluid flow in oceanic crust is, however, limited by the extent and nature of the rock's permeability. Here we demonstrate that the global data set of borehole permeability measurements in uppermost oceanic crust defines a trend with age that is consistent with changes in seismic velocity. This trend-which indicates that fluid flow should be greatly reduced in crust older than a few million years-would appear to be inconsistent with heat-flow observations, which on average indicate significant advective heat loss in crust up to 65 Myr old. But our calculations, based on a lateral flow model, suggest that regional-scale permeabilities are much higher than have been measured in boreholes. These results can be reconciled if most of the fluid flow in the upper crust is channelized through a small volume of rock, influencing the geometry of convection and the nature of fluid-rock interaction. PMID:10638753

  2. Evolution of the Detached Westward Flow Channel as Observed by the Unwin HF Radar

    NASA Astrophysics Data System (ADS)

    Makarevich, R. A.; Dyson, P. L.

    2005-12-01

    We examine the spatial and temporal evolution of latitudinally narrow regions with enhanced Doppler velocity observed by the Unwin TIGER HF radar equatorward of Auroral Westward Flow Channels. AWFCs were detected by both the Bruny Island and New Zealand (Unwin) TIGER radars as regions with enhanced westward convection, at about -62 deg MLAT. A second, more equatorward (~ -60 deg MLAT) channel with enhanced westward convection was detected only by the Unwin radar. The spatio-temporal behaviour of the second channel and its characteristics were found to be significantly different from those of AWFCs, e.g. both the channel and flow directions were significantly non-L-shell-aligned. We also investigate the relationship between the flow speeds within the two types of flow channels. In all cases, the second channel appeared to originate within or close to the AWFC, with the flow deviation from the magnetic L-shell direction and latitudinal separation between channels increasing with time. In sharp contrast to the AWFC that persisted for 2-3 hours, the second channel was recognizable only for 30-50 min. A relation between multiple flow channels and other subauroral phenomena such as subauroral ion drifts (SAID) and subauroral polarization streams (SAPS), and the implications of observations for models of SAID and SAPS formation are discussed.

  3. Parametric Studies of Flow Separation using Air Injection

    NASA Technical Reports Server (NTRS)

    Zhang, Wei

    2004-01-01

    Boundary Layer separation causes the airfoil to stall and therefore imposes dramatic performance degradation on the airfoil. In recent years, flow separation control has been one of the active research areas in the field of aerodynamics due to its promising performance improvements on the lifting device. These active flow separation control techniques include steady and unsteady air injection as well as suction on the airfoil surface etc. This paper will be focusing on the steady and unsteady air injection on the airfoil. Although wind tunnel experiments revealed that the performance improvements on the airfoil using injection techniques, the details of how the key variables such as air injection slot geometry and air injection angle etc impact the effectiveness of flow separation control via air injection has not been studied. A parametric study of both steady and unsteady air injection active flow control will be the main objective for this summer. For steady injection, the key variables include the slot geometry, orientation, spacing, air injection velocity as well as the injection angle. For unsteady injection, the injection frequency will also be investigated. Key metrics such as lift coefficient, drag coefficient, total pressure loss and total injection mass will be used to measure the effectiveness of the control technique. A design of experiments using the Box-Behnken Design is set up in order to determine how each of the variables affects each of the key metrics. Design of experiment is used so that the number of experimental runs will be at minimum and still be able to predict which variables are the key contributors to the responses. The experiments will then be conducted in the 1ft by 1ft wind tunnel according to the design of experiment settings. The data obtained from the experiments will be imported into JMP, statistical software, to generate sets of response surface equations which represent the statistical empirical model for each of the metrics as

  4. Measurement of the Shear Lift Force on a Bubble in a Channel Flow

    NASA Technical Reports Server (NTRS)

    Nahra, Henry K.; Motil, Brian; Skor, Mark

    2005-01-01

    Two-phase flow systems play vital roles in the design of some current and anticipated space applications of two-phase systems which include: thermal management systems, transfer line flow in cryogenic storage, space nuclear power facilities, design and operation of thermal bus, life support systems, propulsion systems, In Situ Resource Utilization (ISRU), and space processes for pharmaceutical applications. The design of two-phase flow systems for space applications requires a clear knowledge of the behaviors of the dispersed phase (bubble), its interaction with the continuous phase (liquid) and its effect on heat and mass transfer processes, The need to understand the bubble generation process arises from the fact that for all space applications, the size and distribution of bubbles are extremely crucial for heat and mass transfer control. One important force in two-phase flow systems is the lift force on a bubble or particle in a liquid shear flow. The shear lift is usually overwhelmed by buoyancy in normal gravity, but it becomes an important force in reduced gravity. Since the liquid flow is usually sheared because of the confining wall, the trajectories of bubbles and particles injected into the liquid flow are affected by the shear lift in reduced gravity. A series of experiments are performed to investigate the lift force on a bubble in a liquid shear flow and its effect on the detachment of a bubble from a wall under low gravity conditions. Experiments are executed in a Poiseuille flow in a channel. An air-water system is used in these experiments that are performed in the 2.2 second drop tower. A bubble is injected into the shear flow from a small injector and the shear lift is measured while the bubble is held stationary relative to the fluid. The trajectory of the bubble prior, during and after its detachment from the injector is investigated. The measured shear lift force is calculated from the trajectory of the bubble at the detachment point. These

  5. Factors affecting measurement of channel thickness in asymmetrical flow field-flow fractionation.

    PubMed

    Dou, Haiyang; Jung, Euo Chang; Lee, Seungho

    2015-05-01

    Asymmetrical flow field-flow fractionation (AF4) has been considered to be a useful tool for simultaneous separation and characterization of polydisperse macromolecules or colloidal nanoparticles. AF4 analysis requires the knowledge of the channel thickness (w), which is usually measured by injecting a standard with known diffusion coefficient (D) or hydrodynamic diameter (dh). An accurate w determination is a challenge due to its uncertainties arising from the membrane's compressibility, which may vary with experimental condition. In the present study, influence of factors including the size and type of the standard on the measurement of w was systematically investigated. The results revealed that steric effect and the particles-membrane interaction by van der Waals or electrostatic force may result in an error in w measurement. PMID:25817708

  6. Flow-induced channel formation in the cytoplasm of motile cells

    NASA Astrophysics Data System (ADS)

    Guy, Robert D.; Nakagaki, Toshiyuki; Wright, Grady B.

    2011-07-01

    A model is presented to explain the development of flow channels within the cytoplasm of the plasmodium of the giant amoeba Physarum polycephalum. The formation of channels is related to the development of a self-organizing tubular network in large cells. Experiments indicate that the flow of cytoplasm is involved in the development and organization of these networks, and the mathematical model proposed here is motivated by recent experiments involving the observation of development of flow channel in small cells. A model of pressure-driven flow through a polymer network is presented in which the rate of flow increases the rate of depolymerization. Numerical solutions and asymptotic analysis of the model in one spatial dimension show that under very general assumptions this model predicts the formation of channels in response to flow.

  7. The impact of mass flow and masking on the pressure drop of air filter in heavy-duty diesel engine

    NASA Astrophysics Data System (ADS)

    Hoseeinzadeh, Sepideh; Gorji-Bandpy, Mofid

    2012-04-01

    This paper presents a computational fluid dynamics (CFD) calculation approach to predict and evaluate the impact of the mass-flow inlet on the pressure drop of turbocharger`s air filtfer in heavy-duty diesel engine. The numerical computations were carried out using a commercial CFD program whereas the inlet area of the air filter consisted of several holes connected to a channel. After entering through the channel, the air passes among the holes and enters the air filter. The effect of masking holes and hydraulic diameter is studied and investigated on pressure drop. The results indicate that pressure drop increase with decreasing of hydraulic diameter and masking of the holes has considerable affect on the pressure drop.

  8. Flow over a Modern Ram-Air Parachute Canopy

    NASA Astrophysics Data System (ADS)

    Mohammadi, Mohammad; Johari, Hamid

    2010-11-01

    The flow field on the central section of a modern ram-air parachute canopy was examined numerically using a finite-volume flow solver coupled with the one equation Spalart-Allmaras turbulence model. Ram-air parachutes are used for guided airdrop applications, and the canopy resembles a wing with an open leading edge for inflation. The canopy surfaces were assumed to be impermeable and rigid. The flow field consisted of a vortex inside the leading edge opening which effectively closed off the canopy and diverted the flow around the leading edge. The flow experienced a rather bluff leading edge in contrast to the smooth leading of an airfoil, leading to a separation bubble on the lower lip of the canopy. The flow inside the canopy was stagnant beyond the halfway point. The section lift coefficient increased linearly with the angle of attack up to 8.5 and the lift curve slope was about 8% smaller than the baseline airfoil. The leading edge opening had a major effect on the drag prior to stall; the drag is at least twice the baseline airfoil drag. The minimum drag of the section occurs over the angle of attack range of 3 -- 7 .

  9. Enhanced laser-induced plasma channels in air

    NASA Astrophysics Data System (ADS)

    Yanlei, Zuo; Xiaofeng, Wei; Kainan, Zhou; Xiaoming, Zeng; Jingqin, Su; Zhihong, Jiao; Na, Xie; Zhaohui, Wu

    2016-03-01

    Plasma is a significant medium in high-energy density physics since it can hardly be damaged. For some applications such as plasma based backward Raman amplification (BRA), uniform high-density and large-scale plasma channels are required. In the previous experiment, the plasma transverse diameter and density are 50-200 μm and 1-2 × 1019 cm-3, here we enhance them to 0.8 mm and 8 × 1019 cm-3, respectively. Moreover, the gradient plasma is investigated in our experiment. A proper plasma gradient can be obtained with suitable pulse energy and delay. The experimental results are useful for plasma physics and nonlinear optics. Project supported by the Development Foundation of the Chinese Academy of Engineering Physics (Grant Nos. 2012A0401019 and 2013A0401019).

  10. Properties of a constricted-tube air-flow levitator

    NASA Technical Reports Server (NTRS)

    Rush, J. E.; Stephens, W. K.; Ethridge, E. C.

    1982-01-01

    The properties of a constricted-tube gas flow levitator first developed by Berge et al. (1981) have been investigated experimentally in order to predict its behavior in a gravity-free environment and at elevated temperatures. The levitator consists of a constricted (quartz) tube fed at one end by a source of heated air or gas. A spherical sample is positioned by the air stream on the downstream side of the constriction, where it can be melted and resolidified without touching the tube. It is shown experimentally that the kinematic viscosity is the important fluid parameter for operation in thermal equilibrium at high temperatures. If air is heated from room temperature to 1200 C, the kinematic viscosity increases by a factor of 14. To maintain a given value of the Reynolds number, the flow rate would have to be increased by the same factor for a specific geometry of tube and sample. Thus, to maintain stable equilibrium, the flow rate should be increased as the air or other gas is heated. The other stability problem discussed is associated with changes in the shape of a cylindrical sample as it melts.

  11. Two-phase flow and transport in the air cathode of proton exchange membrane fuel cells

    SciTech Connect

    WANG,Z.H.; WANG,C.Y.; CHEN,KEN S.

    2000-03-20

    Two-phase flow and transport of reactants and products in the air cathode of proton exchange membrane (PEM) fuel cells is studied analytically and numerically. Four regimes of water distribution and transport are classified by defining three threshold current densities and a maximum current density. They correspond to first appearance of liquid water at the membrane/cathode interface, extension of the gas-liquid two-phase zone to the cathode/channel interface, saturated moist air exiting the gas channel, and complete consumption of oxygen by the electrochemical reaction. When the cell operates above the first threshold current density, liquid water appears and a two-phase zone forms within the porous cathode. A two-phase, multi-component mixture model in conjunction with a finite-volume-based computational fluid dynamics (CFD) technique is applied to simulate the cathode operation in this regime. The model is able to handle the situation where a single-phase region co-exists with a two-phase zone in the air cathode. For the first time, the polarization curve as well as water and oxygen concentration distributions encompassing both single- and two-phase regimes of the air cathode are presented. Capillary action is found to be the dominant mechanism for water transport inside the two-phase zone. The liquid water saturation within the cathode is predicted to reach 6.3% at 1.4 A/cm{sup 2}.

  12. Air Flow and Pressure Drop Measurements Across Porous Oxides

    NASA Technical Reports Server (NTRS)

    Fox, Dennis S.; Cuy, Michael D.; Werner, Roger A.

    2008-01-01

    This report summarizes the results of air flow tests across eight porous, open cell ceramic oxide samples. During ceramic specimen processing, the porosity was formed using the sacrificial template technique, with two different sizes of polystyrene beads used for the template. The samples were initially supplied with thicknesses ranging from 0.14 to 0.20 in. (0.35 to 0.50 cm) and nonuniform backside morphology (some areas dense, some porous). Samples were therefore ground to a thickness of 0.12 to 0.14 in. (0.30 to 0.35 cm) using dry 120 grit SiC paper. Pressure drop versus air flow is reported. Comparisons of samples with thickness variations are made, as are pressure drop estimates. As the density of the ceramic material increases the maximum corrected flow decreases rapidly. Future sample sets should be supplied with samples of similar thickness and having uniform surface morphology. This would allow a more consistent determination of air flow versus processing parameters and the resulting porosity size and distribution.

  13. Air-cooled, hydrogen-air fuel cell

    NASA Technical Reports Server (NTRS)

    Shelekhin, Alexander B. (Inventor); Bushnell, Calvin L. (Inventor); Pien, Michael S. (Inventor)

    1999-01-01

    An air-cooled, hydrogen-air solid polymer electrolyte (SPE) fuel cell with a membrane electrode assembly operatively associated with a fluid flow plate having at least one plate cooling channel extending through the plate and at least one air distribution hole extending from a surface of the cathode flow field into the plate cooling channel.

  14. Distribution and velocity of inertial particles in a turbulent channel flow

    NASA Astrophysics Data System (ADS)

    Coletti, Filippo; Fong, Kee Onn; Nemes, Andras; Sloan, Nicholas

    2015-11-01

    The segregation of inertial particles in specific regions of turbulent fluid flows is a well known phenomenon, but experimental observations of its three-dimensional nature are lacking. Here we are concerned with the transport of small inertial particles in wall-bounded turbulence. In particular we consider a fully developed vertical channel flow. The working fluid is air laden with size-selected glass particles. The volume and mass loading are kept low and the particle diameter is smaller than the viscous length scale, so that the turbulence is unaffected by the dispersed phase. Tomographic particle image velocimetry is used to reconstruct the position and velocity of the inertial particles. In particular, the tendency of the particles to concentrate intermittently (turbulence clustering) and to drift towards the wall (turbophoresis) are quantitatively characterized by the instantaneous and mean concentration fields, respectively. The findings are discussed in relation to the results of previous studies which have used one-way coupled direct numerical simulations, and on which the current understanding of this class of flows is based.

  15. Effects of pulsation on separated flow and heat transfer in enlarged channel

    NASA Astrophysics Data System (ADS)

    Yoshikawa, Hiroyuki; Kai, Tomonori; Munekata, Mizue; Ohba, Hideki

    2011-03-01

    Numerical results of three-dimensional separated flow and heat transfer in an enlarged rectangular channel are presented in this paper. The expansion ratio and aspect ratio of the channel are 2.0 and 16.0, respectively. Reynolds number of the flow is 200 and it is over the critical Reynolds number. Over the critical Reynolds number, the flow in the symmetric channel becomes asymmetric and deflects to one side of the walls. Effects of the pulsating fluctuation at the inlet upon the flow in the channel are investigated. It is clarified that the inlet flow with a pulsating fluctuation of Strouhal number 0.05 and 0.10 strongly affects on the flow in the channel, and heat transfer on the walls is enhanced, especially on the wall surface covered with long separation bubble. On the other hand, the pulsation of St = 0.0125 oscillates the shear layer more weakly than that of St = 0.05, 0.10 and the enhancement of heat transfer is smaller, though some vortices are shed from the vicinity of the side wall near the reattachment region. The oscillation of the main flow calms down gradually as the Strouhal number of the pulsation increases over 0.10. The influence of pulsation of St = 0.20 on the flow is restricted in the near downstream of the step, and heat transfer on the walls is almost similar to that of the steady flow in the channel.

  16. Noise control of subsonic cavity flows using plasma actuated receptive channels

    NASA Astrophysics Data System (ADS)

    Das Gupta, Arnob; Roy, Subrata

    2014-12-01

    We introduce a passive receptive rectangular channel at the trailing edge of an open rectangular cavity to reduce the acoustic tones generated due to coherent shear layer impingement. The channel is numerically tested at Mach 0.3 using an unsteady three-dimensional large eddy simulation. Results show reduction in pressure fluctuations in the cavity due to which sound pressure levels are suppressed. Two linear dielectric barrier discharge plasma actuators are placed inside the channel to enhance the flow through it. Specifically, acoustic suppression of 7 dB was obtained for Mach 0.3 flow with the plasma actuated channel. Also, the drag coefficient for the cavity reduced by over three folds for the channel and over eight folds for the plasma actuated channel. Such a channel can be useful in noise and drag reduction for various applications, including weapons bay, landing gear and branched piping systems.

  17. Performance of a turbulence model for flows in partially vegetated open channels

    NASA Astrophysics Data System (ADS)

    Jahra, Fatima; Kawahara, Yoshihisa; Hasegawa, Fumiaki

    A non-linear k-epsilon model coupled with a vegetation model has been applied to three turbulent flows in partially vegetated open channels to scrutinize its performance. Three test cases include flow in a straight rectangular channel with vegetation belts along both sides of the channel and flows in a compound channel with different emergent vegetation zones over a floodplain, where experimental data have been obtained by the authors. Comparison with the experimental results demonstrates that the non-linear k-epsilon model can reasonably captures secondary flows of the second kind and a row of large vortices along the interface between main channel and vegetated zones, which the standard k-epsilon model fails to produce. The calculated results are found to show fairly good agreement with the measurements in terms of mean streamwise velocity, secondary currents of the second kind and Reynolds shear stresses components.

  18. Does the choice of the forcing term affect flow statistics in DNS of turbulent channel flow?

    NASA Astrophysics Data System (ADS)

    Quadrio, Maurizio; Frohnapfel, Bettina; Hasegawa, Yosuke

    2016-01-01

    We seek possible statistical consequences of the way a forcing term is added to the Navier--Stokes equations in the Direct Numerical Simulation (DNS) of incompressible channel flow. Simulations driven by constant flow rate, constant pressure gradient and constant power input are used to build large databases, and in particular to store the complete temporal trace of the wall-shear stress for later analysis. As these approaches correspond to different dynamical systems, it can in principle be envisaged that these differences are reflect by certain statistics of the turbulent flow field. The instantaneous realizations of the flow in the various simulations are obviously different, but, as expected, the usual one-point, one-time statistics do not show any appreciable difference. However, the PDF for the fluctuations of the streamwise component of wall friction reveals that the simulation with constant flow rate presents lower probabilities for extreme events of large positive friction. The low probability value of such events explains their negligible contribution to the commonly computed statistics; however, the very existence of a difference in the PDF demonstrates that the forcing term is not entirely uninfluential. Other statistics for wall-based quantities (the two components of friction and pressure) are examined; in particular spatio-temporal autocorrelations show small differences at large temporal separations, where unfortunately the residual statistical uncertainty is still of the same order of the observed difference. Hence we suggest that the specific choice of the forcing term does not produce important statistical consequences, unless one is interested in the strongest events of high wall friction, that are underestimated by a simulation run at constant flow rate.

  19. Fuel cell stack with passive air supply

    DOEpatents

    Ren, Xiaoming; Gottesfeld, Shimshon

    2006-01-17

    A fuel cell stack has a plurality of polymer electrolyte fuel cells (PEFCs) where each PEFC includes a rectangular membrane electrode assembly (MEA) having a fuel flow field along a first axis and an air flow field along a second axis perpendicular to the first axis, where the fuel flow field is long relative to the air flow field. A cathode air flow field in each PEFC has air flow channels for air flow parallel to the second axis and that directly open to atmospheric air for air diffusion within the channels into contact with the MEA.

  20. High-frame rate imaging of two-phase flow in a thin rectangular channel using fast neutrons.

    PubMed

    Zboray, R; Mor, I; Dangendorf, V; Stark, M; Tittelmeier, K; Cortesi, M; Adams, R

    2014-08-01

    We have demonstrated the feasibility of performing high-frame-rate, fast neutron radiography of air-water two-phase flows in a thin channel with rectangular cross section. The experiments have been carried out at the accelerator facility of the Physikalisch-Technische Bundesanstalt. A polychromatic, high-intensity fast neutron beam with average energy of 6 MeV was produced by 11.5 MeV deuterons hitting a thick Be target. Image sequences down to 10 ms exposure times were obtained using a fast-neutron imaging detector developed in the context of fast-neutron resonance imaging. Different two-phase flow regimes such as bubbly slug and churn flows have been examined. Two phase flow parameters like the volumetric gas fraction, bubble size and mean bubble velocities have been measured. The first results are promising, improvements for future experiments are also discussed. PMID:24709611

  1. Pressure drop of two-phase plug flow in round mini-channels: Influence of surface wettability

    SciTech Connect

    Lee, Chi Young; Lee, Sang Yong

    2008-09-15

    In the present experimental study, the pressure drop of two-phase plug flows in round mini-channels was investigated for three different tube materials, i.e., glass, polyurethane and Teflon, respectively, with their inner diameters ranging from 1.62 to 2.16 mm. Air and water were used as the test fluids. In the wet-plug flow regime (wet wall condition at the gas portions), the pressure drop was reasonably predicted by the homogeneous flow model or by the correlations of Mishima and Hibiki [K. Mishima, T. Hibiki, Some characteristics of air-water two-phase flow in small diameter vertical tubes, Int. J. Multiphase Flow 22 (1996) 703-712] and Chisholm [D. Chisholm, A theoretical basis for the Lockhart-Martinelli correlation for two-phase flow, Int. J. Heat Mass Transfer 10 (1967) 1767-1778]. On the other hand, in the dry-plug flow regime (dry wall condition at the gas portions), the role of the moving contact lines turned out to be significant. To take into account the effect of the moving contact lines, a modified Lockhart-Martinelli type correlation was proposed, which fitted the measured pressure-drop data within the mean deviation of 6%. (author)

  2. Flow measurement of a two-phase fluid around a cylinder in a channel using particle image velocimetry

    SciTech Connect

    Hassan, Y.A.; Martinez, R.S.; Philip, O.G.; Schmidl, W.D.

    1994-12-31

    The particle image velocimetry (PIV) flow measurement technique was used to study two-phase flow over cylindrical rods inserted in a channel. For the two-phase flow study, a mixture of water and small air bubbles was used. The water flow rate was 378 cm{sup 3}/s and the airflow rate was {approximately}30 cm{sup 3}/s. The water was seeded with fluorescent particle tracers in order to record the position of the particles and the air bubbles independently. Then the data were analyzed to obtain the velocity fields for both experiments. One of the major concerns with steam generator operation is the tube vibration caused by turbulent flow buffeting. The vibration can cause wear on the tube joints that may eventually lead to ruptures and leaks. This repair procedure can be very costly. To help avoid this problem, experimental data are needed to test the empirical correlations that predict the behavior of the turbulent flow around the cylinders. The PIV flow measurement technique can be used to acquire that experimental data.

  3. Liquid water quantification in the cathode side gas channels of a proton exchange membrane fuel cell through two-phase flow visualization

    NASA Astrophysics Data System (ADS)

    Banerjee, Rupak; Kandlikar, Satish G.

    2014-02-01

    Water management is crucial to the performance of PEM fuel cells. Water is generated as part of the electrochemical reaction, and is removed through the reactant channels. This results in two-phase flow in the reactant channels. Increased understanding of the behavior of the liquid water in the channels allows us to devise better strategies for managing the water content inside the fuel cell. Most previous work has been focused on qualitative information regarding flow pattern maps. The current work presents new algorithms developed in MATLAB® to quantify the liquid water and to identify the flow patterns in the cathode side reactant channels. Parallel channels with dimensions matching those of commercial stacks have been used in this study. The liquid water present in the reactant channels is quantified for different temperature, inlet RH and current density conditions, and the results are presented in terms of area coverage ratio. The dominant flow patterns for the different conditions have been mapped, and trends interpreted on the basis of air flow velocities and saturation conditions within the channels.

  4. Width adjustment in experimental gravel-bed channels in response to overbank flows

    NASA Astrophysics Data System (ADS)

    Pitlick, John; Marr, Jeff; Pizzuto, Jim

    2013-06-01

    We conducted a series of flume experiments to investigate the response of self-formed gravel-bed channels to floods of varying magnitude and duration. Floods were generated by increasing the discharge into a channel created in sand- and gravel-sized sediment with a median grain size of 2 mm. Flooding increased the Shields stress along the channel perimeter, causing bank erosion and rapid channel widening. The sediment introduced to the channel by bank erosion was not necessarily deposited on the channel bed, but was rather transported downstream, a process likely facilitated by transient fining of the bed surface. At the end of each experiment, bank sediments were no longer in motion, "partial bed load transport" characterized the flat-bed portion of the channel, and the Shields stress approached a constant value of 0.056, about 1.2 times the critical Shields stress for incipient motion. Furthermore, the discharge was entirely accommodated by flow within the channel: the creation of a stable channel entirely eliminated overbank flows. We speculate that similar processes may occur in nature, but only where bank sediments are non-cohesive and where channel-narrowing processes cannot counteract bank erosion during overbank flows. We also demonstrate that a simple model of lateral bed load transport can reproduce observed channel widening rates, suggesting that simple methods may be appropriate for predicting width increases in channels with non-cohesive, unvegetated banks, even during overbank flows. Last, we present a model for predicting the equilibrium width and depth of a stable gravel-bed channel with a known channel-forming Shields stress.

  5. Flow regime classification in air magnetic fluid two-phase flow

    NASA Astrophysics Data System (ADS)

    Kuwahara, T.; DeVuyst, F.; Yamaguchi, H.

    2008-05-01

    A new experimental/numerical technique of classification of flow regimes (flow patterns) in air-magnetic fluid two-phase flow is proposed in the present paper. The proposed technique utilizes the electromagnetic induction to obtain time-series signals of the electromotive force, allowing us to make a non-contact measurement. Firstly, an experiment is carried out to obtain the time-series signals in a vertical upward air-magnetic fluid two-phase flow. The signals obtained are first treated using two kinds of wavelet transforms. The data sets treated are then used as input vectors for an artificial neural network (ANN) with supervised training. In the present study, flow regimes are classified into bubbly, slug, churn and annular flows, which are generally the main flow regimes. To validate the flow regimes, a visualization experiment is also performed with a glycerin solution that has roughly the same physical properties, i.e., kinetic viscosity and surface tension, as a magnetic fluid used in the present study. The flow regimes from the visualization are used as targets in an ANN and also used in the estimation of the accuracy of the present method. As a result, ANNs using radial basis functions are shown to be the most appropriate for the present classification of flow regimes, leading to small classification errors.

  6. Flow regime classification in air-magnetic fluid two-phase flow.

    PubMed

    Kuwahara, T; De Vuyst, F; Yamaguchi, H

    2008-05-21

    A new experimental/numerical technique of classification of flow regimes (flow patterns) in air-magnetic fluid two-phase flow is proposed in the present paper. The proposed technique utilizes the electromagnetic induction to obtain time-series signals of the electromotive force, allowing us to make a non-contact measurement. Firstly, an experiment is carried out to obtain the time-series signals in a vertical upward air-magnetic fluid two-phase flow. The signals obtained are first treated using two kinds of wavelet transforms. The data sets treated are then used as input vectors for an artificial neural network (ANN) with supervised training. In the present study, flow regimes are classified into bubbly, slug, churn and annular flows, which are generally the main flow regimes. To validate the flow regimes, a visualization experiment is also performed with a glycerin solution that has roughly the same physical properties, i.e., kinetic viscosity and surface tension, as a magnetic fluid used in the present study. The flow regimes from the visualization are used as targets in an ANN and also used in the estimation of the accuracy of the present method. As a result, ANNs using radial basis functions are shown to be the most appropriate for the present classification of flow regimes, leading to small classification errors. PMID:21694270

  7. Interrelationships of petiole air canal architecture, water depth and convective air flow in Nymphaea odorata (Nymphaeaceae)

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Premise of the study--Nymphaea odorata grows in water up to 2 m deep, producing fewer, larger leaves in deeper water. This species has a convective flow system that moves gases from younger leaves through submerged parts to older leaves, aerating submerged parts. Petiole air canals are in the conv...

  8. Micromachined pipettes integrated in a flow channel for single DNA molecule study by optical trapping

    NASA Astrophysics Data System (ADS)

    Rusu, Cristina R.; van't Oever, Ronny; de Boer, Meint J.; Jansen, Henri V.; Berenschot, Erwin; Elwenspoek, Miko C.; Bennink, Martin L.; Kanger, Johannes S.; de Grooth, Bart G.; Greve, Jan; Brugger, Juergen P.; van den Berg, Albert

    2000-03-01

    We have developed a micromachined flow cell consisting of a flow channel integrated with micropipettes. The flow cell is used in combination with an optical trap set-up (optical tweezers) to study mechanical and structural properties of (lambda) -DNA molecules. The flow cell was realized using silicon micromachining including the so-called buried channel technology to fabricate the micropipettes, the wet etching of glass to create the flow channel, and the powder blasting of glass to create the fluid connections. The volume of the flow cell is 2 (mu) l. The pipettes have a length of 130 micrometer, a width of 5 - 10 micrometer, a round opening of 1 micron and can be processed with different shapes. Using this flow cell we stretched single molecules ((lambda) -DNA) showing typical force-extension curves also found with conventional techniques.

  9. Modeling Flow and Vegetation Effects in a Curved Channel

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Channel bank erosion devastates land of agriculture, contributes largely to the sediment yield from watersheds, and deteriorates the downstream channel morphology and water quality. An important part of the bank erosion is due to bank failure known to be related to many factors including properties ...

  10. Character of energy flow in air shower core

    NASA Technical Reports Server (NTRS)

    Mizushima, K.; Asakimori, K.; Maeda, T.; Kameda, T.; Misaki, Y.

    1985-01-01

    Energy per charged particle near the core of air showers was measured by 9 energy flow detectors, which were the combination of Cerenkov counters and scintillators. Energy per particle of each detector was normalized to energy at 2m from the core. The following results were obtained as to the energy flow: (1) integral frequency distribution of mean energy per particle (averaged over 9 detectors) is composed of two groups separated distinctly; and (2) showers contained in one group show an anisotropy of arrival direction.

  11. DEVELOPMENT OF A LOW PRESSURE, AIR ATOMIZED OIL BURNER WITH HIGH ATOMIZER AIR FLOW

    SciTech Connect

    BUTCHER,T.A.

    1998-01-01

    This report describes technical advances made to the concept of a low pressure, air atomized oil burner for home heating applications. Currently all oil burners on the market are of the pressure atomized, retention head type. These burners have a lower firing rate limit of about 0.5 gallons per hour of oil, due to reliability problems related to small flow passage sizes. High pressure air atomized burners have been shown to be one route to avoid this problem but air compressor cost and reliability have practically eliminated this approach. With the low pressure air atomized burner the air required for atomization can be provided by a fan at 5--8 inches of water pressure. A burner using this concept, termed the Fan-Atomized Burner or FAB has been developed and is currently being commercialized. In the head of the FAB, the combustion air is divided into three parts, much like a conventional retention head burner. This report describes development work on a new concept in which 100% of the air from the fan goes through the atomizer. The primary advantage of this approach is a great simplification of the head design. A nozzle specifically sized for this concept was built and is described in the report. Basic flow pressure tests, cold air velocity profiles, and atomization performance have been measured. A burner head/flame tube has been developed which promotes a torroidal recirculation zone near the nozzle for flame stability. The burner head has been tested in several furnace and boiler applications over the tiring rate range 0.2 to 0.28 gallons per hour. In all cases the burner can operate with very low excess air levels (under 10%) without producing smoke. Flue gas NO{sub x} concentration varied from 42 to 62 ppm at 3% 0{sub 2}. The concept is seen as having significant potential and planned development efforts are discussed.

  12. Heat/mass transfer and flow characteristics of pin fin cooling channels in turbine blades

    NASA Astrophysics Data System (ADS)

    Lau, S. C.; Saxena, A.

    Experiments studied the local heat/mass transfer distributions and pressure drops in pin fin channels that modeled internal cooling passages in gas turbine blades. Heat/mass transfer distributions were determined for a straight flow through a pin fin channel (H/D = 1.0, X/D = S/D = 2.5) and a flow through the pin fin channel with trailing edge flow ejection. The overall friction factor and local pressure drop results were obtained for various configurations and lengths of the trailing edge ejection holes. The results show that, when there is trailing edge flow ejection, the main flow stream turns toward the trailing edge ejection holes. The wake regions downstream of the pins and the regions affected by secondary flow shift toward the ejection holes. The local channel wall heat/mass transfer is generally high immediately upstream of a pin, in the wake region downstream of a pin, and in the regions affected by secondary flow. In the case with trailing edge flow ejection, the heat/mass transfer generally decreases in the radial direction as a result of the reducing radial mass flow rate. The overall friction is higher when the trailing edge ejection holes are longer and when they are configured such that more flow is forced further downstream in the pin fin channel before exiting through the ejection holes.

  13. Effects of air flow directions on composting process temperature profile

    SciTech Connect

    Kulcu, Recep; Yaldiz, Osman

    2008-07-01

    In this study, chicken manure mixed with carnation wastes was composted by using three different air flow directions: R1-sucking (downward), R2-blowing (upward) and R3-mixed. The aim was to find out the most appropriate air flow direction type for composting to provide more homogenous temperature distribution in the reactors. The efficiency of each aeration method was evaluated by monitoring the evolution of parameters such as temperature, moisture content, CO{sub 2} and O{sub 2} ratio in the material and dry material losses. Aeration of the reactors was managed by radial fans. The results showed that R3 resulted in a more homogenous temperature distribution and high dry material loss throughout the composting process. The most heterogeneous temperature distribution and the lowest dry material loss were obtained in R2.

  14. Vision and air flow combine to streamline flying honeybees

    PubMed Central

    Taylor, Gavin J.; Luu, Tien; Ball, David; Srinivasan, Mandyam V.

    2013-01-01

    Insects face the challenge of integrating multi-sensory information to control their flight. Here we study a ‘streamlining' response in honeybees, whereby honeybees raise their abdomen to reduce drag. We find that this response, which was recently reported to be mediated by optic flow, is also strongly modulated by the presence of air flow simulating a head wind. The Johnston's organs in the antennae were found to play a role in the measurement of the air speed that is used to control the streamlining response. The response to a combination of visual motion and wind is complex and can be explained by a model that incorporates a non-linear combination of the two stimuli. The use of visual and mechanosensory cues increases the strength of the streamlining response when the stimuli are present concurrently. We propose this multisensory integration will make the response more robust to transient disturbances in either modality. PMID:24019053

  15. Buoyant instabilities in downward flow in a symmetrically heated vertical channel

    SciTech Connect

    Evans, G.; Greif, R.

    1996-07-01

    This study of the downward flow of nitrogen in a tall, partially heated vertical channel (upstream isothermal at T{sub in}*, heated region isothermal at T{sub s}* downstream adiabatic) shows the strong effects of buoyancy even for small temperature differences. Time-dependent oscillations including periodic flow reversals occur along the channel walls. Although the flow and heat transfer are asymmetric, the temperature and axial component of velocity show symmetric reflections at two times that are half a period apart and the lateral component of velocity shows antisymmetric reflections at the two times. There is strong interaction between the downward flow in the central region of the channel and the upward flow along the heated channel walls. At the top of the heated region, the upward buoyant flow turns toward the center of the channel and is incorporated into the downward flow. Along the channel centerline there are nonmonotonic variations of the axial component of velocity and temperature and a large lateral component of velocity that reverses direction periodically. Results are presented for Re = 219.7 and Gr/Re{sup 2} = 1.83, 8.0, and 13.7. The heat transfer and the frequency of the oscillations increases and the flow and temperature fields become more complex as Gr/Re{sup 2} increases. The results have applications to fiber drying, food processing, crystal growth, solar energy collection, cooling of electronic circuits, ventilation, etc.

  16. Impact of Flow Regulation on Channel Morphology Around Tributary Junctions, West and White Rivers, Vermont

    NASA Astrophysics Data System (ADS)

    Renshaw, C.; Curtis, K.; Magilligan, F.; Dade, W.

    2008-12-01

    By resupplying the mainstem with water and sediment, tributaries are a primary mechanism for mitigating the impacts of flow regulation. As a result, morphological and ecological adjustments associated with flow regulation may be particularly pronounced at tributary junctions. Despite the extensive literature on how dams alter channel morphology, few studies have focused specifically on the relationship between flow regulation and consequent changes in bedload sediment transport at tributary junctions. Using historical aerial photographs, modern channel surveys, and flow modeling, we compare temporal changes between regulated and unregulated tributary junction morphology and sediment transport dynamics. In contrast to what has been observed along the Colorado River, where flow regulation has led to a reduction in the number and size of channel bars, we observe significant bar growth post-regulation along the West River in southern Vermont. In some cases exposed bar area increased more than 50 percent in the first three decades after regulation and coincides with a corresponding reduction in channel width. Revegetation of former floodplain surfaces has begun to reduce the exposed bar area. However, flow modeling indicates that the channel remains underfit with respect to the new flow regime, with the current 2- and 50-yr floods lacking sufficient competence to transport the bedload sediment discharged by tributaries. Thus even 50 years post regulation, additional morphological changes are still required for the mainstem channel to fully adjust to the new flow regime.

  17. A TWO-DIMENSIONAL LATTICE MODEL FOR DESCRIBING THE OPEN CHANNEL FLOW WITH VEGETATION

    Technology Transfer Automated Retrieval System (TEKTRAN)

    A 2D lattice Boltzmann model (LBM) is proposed for describing the turbulent shallow water flow in a vegetated channel. The flow turbulence is taken into account by means of the standard Smagorinsky subgrid-scale model. The drag stress exerted by the flow on the vegetation as well as the frictional e...

  18. Numerical characterization of the hydrodynamics and thermal behavior of air flow in flexible air distribution system

    NASA Astrophysics Data System (ADS)

    Gharehdaghi, Samad; Moujaes, Samir

    2013-10-01

    Flexible duct air distribution systems are used in a large percentage of residential and small commercial buildings in the United States . Very few empirical or predictive data are available though to help provide the HVAC design engineer with reliable information . Moreover, because of the ducts flexibility, the shapes of these ducts offer a different set of operating fluid flow and thermal conditions from traditional smooth metal ducts. Hence, both the flow field and heat transfer through this kind of ducts are much more complex and merit to be analyzed from a numerical predictive approach. The aim of this research paper is to compute some of the hydrodynamic and heat transfer characteristics of the air flow inside these ducts over a range of Re numbers commonly used in the flow conditions of these air distribution systems. The information resulting from this CFD simulation, where a κ-ɛ turbulent model is used to predict the flow conditions, provide pressure drop and average convective heat transfer coefficients that exist in these ducts and was compared to previously found data. Circulation zones in the depressions of these ducts are found to exist which are suspected of influencing the pressured drop and heat transfer coefficients as compared to smooth ducts. The results show that fully developed conditions exist much earlier with regard to the inlet for both hydrodynamic and thermal entrance regions than what would be expected in smooth ducts under the same turbulent conditions.

  19. Development of an air flow thermal balance calorimeter

    NASA Technical Reports Server (NTRS)

    Sherfey, J. M.

    1972-01-01

    An air flow calorimeter, based on the idea of balancing an unknown rate of heat evolution with a known rate of heat evolution, was developed. Under restricted conditions, the prototype system is capable of measuring thermal wattages from 10 milliwatts to 1 watt, with an error no greater than 1 percent. Data were obtained which reveal system weaknesses and point to modifications which would effect significant improvements.

  20. Electron concentration distribution in a glow discharge in air flow

    NASA Astrophysics Data System (ADS)

    Mukhamedzianov, R. B.; Gaisin, F. M.; Sabitov, R. A.

    1989-04-01

    Electron concentration distributions in a glow discharge in longitudinal and vortex air flows are determined from the attenuation of the electromagnetic wave passing through the plasma using microwave probes. An analysis of the distribution curves obtained indicates that electron concentration decreases in the direction of the anode. This can be explained by charge diffusion toward the chamber walls and electron recombination and sticking within the discharge.

  1. Methods of Visually Determining the Air Flow Around Airplanes

    NASA Technical Reports Server (NTRS)

    Gough, Melvin N; Johnson, Ernest

    1932-01-01

    This report describes methods used by the National Advisory Committee for Aeronautics to study visually the air flow around airplanes. The use of streamers, oil and exhaust gas streaks, lampblack and kerosene, powdered materials, and kerosene smoke is briefly described. The generation and distribution of smoke from candles and from titanium tetrachloride are described in greater detail because they appear most advantageous for general application. Examples are included showing results of the various methods.

  2. Effect of flow pulsation on mass transport in a cathode channel of polymer electrolyte membrane fuel cell

    NASA Astrophysics Data System (ADS)

    Han, Hun Sik; Kim, Yun Ho; Kim, Seo Young; Hyun, Jae Min

    2012-09-01

    An experimental and theoretical study on the cathode flow pulsation in a polymer electrolyte membrane (PEM) fuel cell is performed. A 10-cell PEM fuel cell stack with open-air cathode channels is employed to investigate the effects of the cathode flow pulsation on the overall performance. The polarization and corresponding power curves obtained show that both the limiting current density and the maximum power density are substantially enhanced when the pulsating component is added to the cathode mainstream flow. The flow pulsation at Re = 77 provides the maximum increment of 40% and 35.5% in the limiting current density and in the maximum power density, respectively. The enhancement of the overall performance is more pronounced at low Reynolds numbers. Also, the theoretical mass transport analysis in the pulsating cathode flow channel is carried out to verify the present experimental results. The momentum and species conservation equations are analytically solved, and the effective time-averaged dispersion coefficient is defined to account for the enhanced mass transport by the flow pulsation. Comprehensive analytical solutions show that the effect of the relevant parameters is in well accordance with the experimental results.

  3. On the impact of entrapped air in infiltration under ponding conditions. Part a: Preferential air flow path effects on infiltration

    NASA Astrophysics Data System (ADS)

    Mizrahi, Guy; Weisbrod, Noam; Furman, Alex

    2015-04-01

    Entrapped air effects on infiltration under ponding conditions could be important for massive infiltration of managed aquifer recharge (MAR) or soil aquifer treatment (SAT) of treated wastewater. Earlier studies found that under ponding conditions, air is being entrapped and compressed until it reaches a pressure which will enable the air to escape (unstable air flow). They also found that entrapped air could reduce infiltration by 70-90%. Most studies have dealt with entrapped air effects when soil surface topography is flat. The objective of this study is to investigate, under ponding conditions, the effects of: (1) irregular surface topography on preferential air flow path development (stable air flow); (2) preferential air flow path on infiltration; and (3) hydraulic head on infiltration when air is trapped. Column experiments were used to investigate these particular effects. A 140 cm deep and 30 cm wide column packed with silica sand was used under two boundary conditions: in the first, air can only escape vertically upward through the soil surface; in the second, air is free to escape through 20 ports installed along the column perimeter. The surface was flooded with 13 liters of water, with ponding depth decreasing with time. Two soil surface conditions were tested: flat surface and irregular surface (high and low surface zones). Additionally, Helle-show experiments were conducted in order to obtain a visual observation of preferential air flow path development. The measurements were carried out using a tension meter, air pressure transducers, TDR and video cameras. It was found that in irregular surfaces, stable air flow through preferential paths was developed in the high altitude zones. Flat surface topography caused unstable air flow through random paths. Comparison between irregular and flat surface topography showed that the entrapped air pressure was lower and the infiltration rate was about 40% higher in the irregular surface topography than in the

  4. Quasi-steady-state air plasma channel produced by a femtosecond laser pulse sequence

    PubMed Central

    Lu, Xin; Chen, Shi-You; Ma, Jing-Long; Hou, Lei; Liao, Guo-Qian; Wang, Jin-Guang; Han, Yu-Jing; Liu, Xiao-Long; Teng, Hao; Han, Hai-Nian; Li, Yu-Tong; Chen, Li-Ming; Wei, Zhi-Yi; Zhang, Jie

    2015-01-01

    A long air plasma channel can be formed by filamentation of intense femtosecond laser pulses. However, the lifetime of the plasma channel produced by a single femtosecond laser pulse is too short (only a few nanoseconds) for many potential applications based on the conductivity of the plasma channel. Therefore, prolonging the lifetime of the plasma channel is one of the key challenges in the research of femtosecond laser filamentation. In this study, a unique femtosecond laser source was developed to produce a high-quality femtosecond laser pulse sequence with an interval of 2.9 ns and a uniformly distributed single-pulse energy. The metre scale quasi-steady-state plasma channel with a 60–80 ns lifetime was formed by such pulse sequences in air. The simulation study for filamentation of dual femtosecond pulses indicated that the plasma channel left by the previous pulse was weakly affected the filamentation of the next pulse in sequence under our experimental conditions. PMID:26493279

  5. Quasi-steady-state air plasma channel produced by a femtosecond laser pulse sequence.

    PubMed

    Lu, Xin; Chen, Shi-You; Ma, Jing-Long; Hou, Lei; Liao, Guo-Qian; Wang, Jin-Guang; Han, Yu-Jing; Liu, Xiao-Long; Teng, Hao; Han, Hai-Nian; Li, Yu-Tong; Chen, Li-Ming; Wei, Zhi-Yi; Zhang, Jie

    2015-01-01

    A long air plasma channel can be formed by filamentation of intense femtosecond laser pulses. However, the lifetime of the plasma channel produced by a single femtosecond laser pulse is too short (only a few nanoseconds) for many potential applications based on the conductivity of the plasma channel. Therefore, prolonging the lifetime of the plasma channel is one of the key challenges in the research of femtosecond laser filamentation. In this study, a unique femtosecond laser source was developed to produce a high-quality femtosecond laser pulse sequence with an interval of 2.9 ns and a uniformly distributed single-pulse energy. The metre scale quasi-steady-state plasma channel with a 60-80 ns lifetime was formed by such pulse sequences in air. The simulation study for filamentation of dual femtosecond pulses indicated that the plasma channel left by the previous pulse was weakly affected the filamentation of the next pulse in sequence under our experimental conditions. PMID:26493279

  6. Monitoring debris flow induced channel morphodynamics with terrestrial laser scanning, Chalk Cliffs, CO (Invited)

    NASA Astrophysics Data System (ADS)

    Wasklewicz, T. A.; Staley, D. M.

    2010-12-01

    Debris flows are important geomorphic agents in alpine drainages. They have been linked with channel initiation in headwater streams, connectivity of organic material and sediment through drainage basins, and as hazards to human development in and adjacent to steep watersheds. Debris flows also significantly alter channel morphometry at a variety of spatial scales. Of particular interest are topographic changes associated with multiple surge fronts within a debris flow as well as between several debris flows. An unnamed tributary stream to Chalk Creek, CO has over the last decade experienced one to four debris flow events annually. Four field sampling campaigns were conducted in the summer and fall of 2009. A Leica ScanStation 2, in conjunction with a robust local control network, were used to capture channel morphodynamics along five stream reaches prior to the debris flow season and after three debris flows. Point cloud data from the scanner permit the generation of two centimeter planimetric resolution digital terrain models (DTM). DTM-of-difference analyses and measures of slope, roughness, sediment transport volumes and channel dimensions were employed to detect spatial and temporal morphometric changes. The first debris flow occurred on unsaturated bed material and resulted in aggradation along 3 of the 5 reaches. One reach, a bedrock step, remained relatively unchanged, while the final reach saw significant erosion along boulder steps in the channel and an associated mass failure adjacent to the stream bank through this section. The second debris flow resulted in net aggradation along all of the reaches. The third and largest debris flow took place on saturated bed materials. The flow produced net erosion along all reaches. Significant channel changes were associated with the headward erosion of debris flow snouts and bank failures associated with undercutting of angle-of-repose slopes during debris flow erosion. Analysis of the potential relationships

  7. Proceedings of the Advanced Seminar on one-dimensional, open-channel Flow and transport modeling

    USGS Publications Warehouse

    Schaffranek, R. W., (compiler)

    1989-01-01

    If several limiting assumptions are valid, flow in a waterbody can be represented by one-dimensional equations of unsteady open-channel flow. The equations can be expressed in a number of forms of varying complexity, depending upon the choice of dependent variables used in their formulation and on possible additional limiting assumptions which allow various terms to be excluded. The assumptions are related to the physical characteristics of water and water flow, characteristics of the flow channel, and the effects of boundary friction and turbulence. With the assumptions, unsteady open-channel flow can be described by two dependent variables, either flow discharge and water surface elevation or flow velocity and cross-sectional area. These variables are expressed as a function of distance and time at a given cross section. The equations are derived from the principles of conservation of mass and momentum. Additional variables may be included to account for wind effects , the Coriolis effect, overbank storage, and other influences. Equations are formulated for unsteady gradually varied flow, steady gradually varied flow, steady uniform flow (the Manning equation), and other variations. More rudimentary continuity-based equations, such as the kinematic wave equation and storage-routing equations, are inherently more empirical and considerable caution must be exercised in their use. Models employing the full dynamic equations for simulating unsteady open-channel flow should be used whenever possible. (See also W90-10652) (Tappert-PTT)

  8. Flow over a Ram-Air Parachute Canopy

    NASA Astrophysics Data System (ADS)

    Eslambolchi, Ali; Johari, Hamid

    2012-11-01

    The flow field over a full-scale, ram-air personnel parachute canopy was investigated numerically using a finite-volume flow solver coupled with the Spalart-Allmaras turbulence model. Ram-air parachute canopies resemble wings with arc-anhedral, surface protuberances, and an open leading edge for inflation. The rectangular planform canopy had an aspect ratio of 2.2 and was assumed to be rigid and impermeable. The chord-based Reynolds number was 3.2 million. Results indicate that the oncoming flow barely penetrates the canopy opening, and creates a large separation bubble below the lower lip of canopy. A thick boundary layer exists over the entire lower surface of the canopy. The flow over the upper surface of the canopy remains attached for an extended fraction of the chord. Lift increases linearly with angle of attack up to about 12 degrees. To assess the capability of lifting-line theory in predicting the forces on the canopy, the lift and drag data from a two-dimensional simulation of the canopy profile were extended using finite-wing expressions and compared with the forces from the present simulations. The finite-wing predicted lift and drag trends compare poorly against the full-span simulation, and the maximum lift-to-drag ratio is over-predicted by 36%. Sponsored by the US Army NRDEC.

  9. Thermistor based, low velocity isothermal, air flow sensor

    NASA Astrophysics Data System (ADS)

    Cabrita, Admésio A. C. M.; Mendes, Ricardo; Quintela, Divo A.

    2016-03-01

    The semiconductor thermistor technology is applied as a flow sensor to measure low isothermal air velocities (<2 ms-1). The sensor is subjected to heating and cooling cycles controlled by a multifunctional timer. In the heating stage, the alternating current of a main AC power supply source guarantees a uniform thermistor temperature distribution. The conditioning circuit assures an adequate increase of the sensors temperature and avoids the thermal disturbance of the flow. The power supply interruption reduces the consumption from the source and extends the sensors life time. In the cooling stage, the resistance variation of the flow sensor is recorded by the measuring chain. The resistive sensor parameters proposed vary significantly and feature a high sensitivity to the flow velocity. With the aid of a computer, the data transfer, storage and analysis provides a great advantage over the traditional local anemometer readings. The data acquisition chain has a good repeatability and low standard uncertainties. The proposed method measures isothermal air mean velocities from 0.1 ms-1 to 2 ms-1 with a standard uncertainty error less than 4%.

  10. The dominant role of surface conduction in electro-osmotic flows through periodically varying narrow channels

    NASA Astrophysics Data System (ADS)

    Ludar, Lotan; Yariv, Ehud

    2015-11-01

    As surface conduction has no effect on electro-osmosis in uniform channel flows, where the tangential Debye-layer currents are longitudinally uniform, it may appear as it would only result in a small modifying correction in lubrication analyses of slowly varying channels. This misconception is refuted here by analyzing flows through periodic channels of slowly varying but otherwise arbitrary geometry. Assuming that the channel width is still large compared with the Debye thickness we employ the simplest thin-double-layer model which incorporates surface conduction. We find that surface conduction affects the leading-order flow and the consequent net volumetric flux, introducing a nonlinear dependence upon the zeta potential. Remarkably, as the channel becomes more and more narrow, the scaled flux approaches a limit which is independent of the Dukhin number yet different from that calculated for zero Dukhin number.

  11. Effects of Recent Debris Flows on Channel Conditions in Small Watersheds in the Central Klamath Mountains, NW California

    NASA Astrophysics Data System (ADS)

    de La Fuente, J.; Elder, D.; Bell, A.; Staisch, L.

    2008-12-01

    Debris flow histories were developed for ten small watersheds, tributary to the Klamath and Scott Rivers, averaging about 3,800 acres in size. This was accomplished by examining air photos dating from 1944 to 1997 and conducting field inventories. The primary objective of the work was to investigate the influence which debris flows of varying age have on macroinvertebrate populations and their habitat. Major flood and debris flow events in this area occurred in 1955, 1964, 1974, and 1997. The largest of the four was in 1964. At the Klamath River gauging station in Seiad Valley, estimated recurrence intervals were 23.7 years in 1955, 71.0 years in 1964, 35.5 years in 1974 and 17.8 years in 1997. Field investigations were conducted in 2006 & 2007, where longitudinal profiles and transverse cross sections were obtained on all channels. Dating trees by coring constrained the ages of individual debris flow terrace surfaces. These terraces were then correlated with findings from the air photo analysis. Disturbance histories varied considerably across the watersheds. Some were relatively undisturbed, lying primarily in wilderness, while others had complex histories of wildfire, road construction, mining and logging. Some of the drainages experienced multiple events that affected the entire valley floor (up to 100-feet wide), while others had no evidence of recent debris flows. Debris flows were entirely natural in some drainages, but closely linked to roads, harvest, and fire in others.

  12. 3D Simulation of Velocity Profile of Turbulent Flow in Open Channel with Complex Geometry

    NASA Astrophysics Data System (ADS)

    Kamel, Benoumessad; Ilhem, Kriba; Ali, Fourar; Abdelbaki, Djebaili

    Simulation of open channel flow or river flow presents unique challenge to numerical simulators, which is widely used in the applications of computational fluid dynamics. The prediction is extremely difficult because the flow in open channel is usually transient and turbulent, the geometry is irregular and curved, and the free-surface elevation is varying with time. The results from a 3D non-linear k- ɛ turbulence model are presented to investigate the flow structure, the velocity distribution and mass transport process in a meandering compound open channel and a straight open channel. The 3D numerical model for calculating flow is set up in cylinder coordinates in order to calculate the complex boundary channel. The finite volume method is used to disperse the governing equations and the SIMPLE algorithm is applied to acquire the coupling of velocity and pressure. The non-linear k- ɛ turbulent model has good useful value because of taking into account the anisotropy and not increasing the computational time. The main contributions of this study are developing a numerical method that can be applied to predict the flow in river bends with various bend curvatures and different width-depth ratios. This study demonstrates that the 3D non-linear k- ɛ turbulence model can be used for analyzing flow structures, the velocity distribution and pollutant transport in the complex boundary open channel, this model is applicable for real river and wetland problem.

  13. Effects of Alluvial and Debris Flow Fans on Channel Morphology in Idaho, Washington, and Oregon

    NASA Astrophysics Data System (ADS)

    Bigelow, P. E.; Benda, L.; Miller, D.; Andras, K.

    2003-12-01

    Formation of debris flow and alluvial fans at tributary confluences from episodic erosion associated with large storms and fires ("extreme events") are often viewed negatively over short time spans (years). However, when viewed over long periods of time (decades to centuries), fans that form at tributary junctions are often sources of morphological diversity in streams and rivers. To evaluate effects of tributary fans on the morphology of mainstem channels, we surveyed a total of 44 km of streams in the Sawtooth Mountains of Idaho (27 km), Olympic Mountains of Washington (10 km), and Central Coast Range of Oregon (7 km). Rejuvenated alluvial fans resulting from post-fire gully erosion in the Sawtooth Mountains created gradient nick points in 4th to 6th order mainstem channels (30 to 350 km2 drainage area) that increased sediment storage upstream resulting in decreased channel gradients, widened flood plains, side channel construction, and the beginning of terrace formation. Downstream effects included increased channel gradients, often creating rapids. In 3rd and 4th order mainstem channels (< 10 km2 drainage area) in the Olympic Mountains, there was statistically significant association between low-order confluences containing debris flow deposits and gravel abundance, wide channels, and numbers of logs and large pools. Moreover, heterogeneity of mainstem channel morphology increased in proximity to low-order confluences prone to debris flows in the Olympic study sites. In 3rd and 4th order channels in the Oregon Coast Range, density of large wood and boulders in mainstem channels (< 30 km2 drainage area) increased with proximity to all debris flow fans at low-order confluences regardless of fan age, while channel gradients and sediment depth in mainstem channels increased with proximity to recent (< 60 yrs old) debris fans. Consequently, alluvial and debris flow fans can be significant agents of heterogeneity in riverine habitats, similar to other sources of

  14. Fluid undercutting in the successive channel flow of two gases.

    NASA Technical Reports Server (NTRS)

    Guy, R. W.; Jenkins, R. V.

    1973-01-01

    A fluid piston technique wherein one gas displaces another gas from a horizontal channel was investigated experimentally in a laboratory simulation of the operating concept of a Mach number 9, true-energy wind tunnel. Tests were conducted over a Froude number range from 0.0015 to 0.543 at driver-to-driven gas density ratios from 0.637 to 11.0 to find the effect of fluid undercutting (or overcutting) on test duration. Other variables studied, either experimentally or analytically, include channel cross-sectional shape, channel inlet design, channel length-to-diameter ratio, Reynolds number, pretest pressurization, and channel inclination angle. Results from shadowgraph movies and pressure measurements provide a correlation of actual-to-ideal test durations for a wide range of Froude numbers and gas density ratios and indicate that the application of the fluid piston technique to the wind-tunnel concept is feasible. However, severe fluid undercutting (or overcutting) in horizontal channels occurs at lower Froude numbers and at density ratios significantly different from unity.

  15. Multiscale modeling of mechanosensing channels on vesicles and cell membranes in 3D constricted flows and shear flows

    NASA Astrophysics Data System (ADS)

    Peng, Zhangli; Pak, On Shun; Young, Yuan-Nan; Liu, Allen; Stone, Howard

    2015-11-01

    We investigate the gating of mechanosensing channels (Mscls) on vesicles and cell membranes under different flow conditions using a multiscale approach. At the cell level (microns), the membrane tension is calculated using a 3D two-component whole-cell membrane model based on dissipative particle dynamics (DPD), including the cortex cytoskeleton and its interactions with the lipid bilayer. At the Mscl level (nanometers), we predict the relation between channel gating and the membrane tension obtained from a cell-level model using a semi-analytical model based on the bilayer hydrophobic mismatch energy. We systematically study the gating of Mscls of vesicles and cell membranes in constricted channel flows and shear flows, and explore the dependence of the gating on flow rate, cell shape and size. The results provide guidance for future experiments in inducing Mscl opening for various purposes such as drug delivery.

  16. Control works in debris-flow channels: influence on morphology and sediment transfer

    NASA Astrophysics Data System (ADS)

    Marchi, L.

    2012-04-01

    Extensive torrent control works, such as grade-control dams, debris basins, deflecting walls, etc. have been implemented in the European Alps since the last decades of 19th century. These structural measures, aimed at stabilizing channels and to control sediment transport, are also widespread in Japan and are increasingly present in other mountain regions. As debris flows are one of the most destructive processes in steep mountain channels, hydraulic works are often intended to attenuate debris-flow hazard. Multi-temporal aerial photos and historic records permit evaluating the long term effects of torrent control works on the morphological settings of the channels and the delivery of sediment. The experience arising from over one century of torrent control works in debris-flow channels of the Alps permits also to improve the management of steep headwater catchments. A basic issue in the management of debris-flow channels is the recognition of success versus failure of engineering control works. Successful debris-flow control works provide benchmarks for further implementations, whereas the failure in reducing debris-flow hazard may lead to refinements in planning and design of control works or to the choice of preferring non-structural measures for coping with debris flows. Data from historical archives on debris-flow occurrence and on the performance of control works are the basic sources of information for these analyses. Moreover, when dealing with hydraulic structures for debris-flow control, it should be reminded that the artificial morphology resulting from the construction of check dams provides only a temporary stability to the channel and adjacent banks. This stresses the importance of evaluating the state of conservation and the effectiveness of control works and implies the need for their careful and continuous maintenance. Inventories of hydraulic structures, coupled with detailed data on catchment and channel topography, sediment sources and supply

  17. A NON-OSCILLATORY SCHEME FOR OPEN CHANNEL FLOWS. (R825200)

    EPA Science Inventory

    In modeling shocks in open channel flows, the traditional finite difference schemes become inefficient and warrant special numerical treatment for smooth computations. This paper provides a general introduction to the non-oscillatory high-resolution methodology, coupled with the ...

  18. SIMPLIFIED MODELING OF AIR FLOW DYNAMICS IN SSD RADON MITIGATION SYSTEMS FOR RESIDENCES WITH GRAVEL BEDS

    EPA Science Inventory

    In an attempt to better understand the dynamics of subslab air flow, the report suggests that subslab air flow induced by a central suction point be treated as radial air flow through a porous bed contained between two impermeable disks. (NOTE: Many subslab depressurization syste...

  19. 30 CFR 75.152 - Tests of air flow; qualified person.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 30 Mineral Resources 1 2010-07-01 2010-07-01 false Tests of air flow; qualified person. 75.152....152 Tests of air flow; qualified person. A person is a qualified person within the meaning of the provisions of Subpart D—Ventilation of this part requiring that tests of air flow be made by a...

  20. Modeling the effects of emergent vegetation on open channel flow using a lattice model

    Technology Transfer Automated Retrieval System (TEKTRAN)

    A two-dimensional lattice model is developed to describe the influence of vegetation on the turbulent flow structure in an open channel. The model includes the influence of vegetation density on the frictional effect of the channel bed and walls. For the walls, a slip boundary condition is considere...

  1. Burnout and distribution of liquid between the flow core and wall films in narrow slot channels

    NASA Astrophysics Data System (ADS)

    Boltenko, E. A.; Shpakovskii, A. A.

    2010-03-01

    Previous works on studying distribution of liquid between the flow core and wall films in narrow slot channels are briefly reviewed. Interrelation between mass transfer processes and burnout is shown. A procedure for calculating burnout on convex and concave heat-transfer surfaces in narrow slot channels is presented.

  2. Sediment budgets and channel scouring of two alpine debris-flow torrents (SE France)

    NASA Astrophysics Data System (ADS)

    Theule, J. I.; Liébault, F.; Loye, A.; Jaboyedoff, M.; Laigle, D.

    2011-12-01

    Steep mountain catchments typically experience sediment pulses from hillslopes which are stored in headwater channels and flushed out by debris-flows. Event-based sediment budget monitoring in two active debris-flow torrents in the French Alps (Manival and Réal) during a two-year period gave insights about catchment-scale sediment routing during rainfall forcings of moderate intensity. This study allowed for further investigation on channel scour relationships with gradient. The monitoring was based on intensive topographic resurveys of low- and high-order channels using different techniques (cross-section surveys with total station and high-resolution channel surveys with terrestrial and airborne laser scanning). For the Manival Torrent, sediment outputs from the main channel were obtained by a sediment trap. Two debris-flows were observed in the Manival and three in the Réal, as well as several bedload transport flow events. Sediment budget reconstitution of the five debris-flows revealed that most of the debris-flow volumes were supplied by channel scouring (always more than 92%). Bedload transport during autumn contributed to the sediment recharge of high-order channels by the deposition of large gravel wedges. This process is recognized as being fundamental for debris-flow occurrence during the subsequent spring and summer. A time shift of scour-and-fill sequences was observed between low- and high-order channels, revealing the discontinuous sediment transfer in the catchment during common flow events. A conceptual model of sediment routing for different event magnitude was proposed. Significant channel scouring by debris-flows took place in alluvial reaches. Throughout the torrent channel, the upstream channel gradient (from a local reach) is identified to play a role in debris-flow scour. Maximum scours normally occur between slopes ranging from 0.18 to 0.20 (depending on sediment availability at the time of occurrence). It is found that above this

  3. Analysis of heat and mass transfer between air and falling film desiccant for different flow configurations in the presence of ultrafine particles

    NASA Astrophysics Data System (ADS)

    Ali, Ahmad A.

    This work focuses on the enhancement of heat and mass transfer between air and falling desiccant film for different flow channel configurations. Cu-Ultrafine particles are added to the desiccant film to investigate the enhancement in heat and mass transfer between air and desiccant film for dehumidification and cooling processes of the air and regeneration of desiccant film. A detailed comparative study between parallel and counter flow channels is performed using a parametric study to investigate the enhancements in dehumidification, cooling, and regeneration processes in terms of the pertinent parameters. The results reveal that the parallel flow arrangement provides better dehumidification and cooling for the air than the counter flow channel for a wide range of parameters. Next, the inclined parallel and counter flow configurations are investigated using an Alternating Direction Implicit (ADI) and successive over-relaxation methods to discretize the vorticity and stream-function equations, respectively. A parametric study is employed to investigate the inclination angle effects in enhancing the heat and mass transfer in terms of the controlling parameters. It is shown that inclination angle plays a significant role in enhancing the dehumidification, cooling, and regeneration processes. Finally, the enhancements in heat and mass transfer in cross flow channel between air and desiccant film is examined based on a parametric study to investigate the dehumidification and cooling processes of the air in terms of the pertinent controlling parameters. These parameters are air and desiccant Reynolds numbers, dimensions of the channel, volume fraction of Cu-ultrafine particles, and thermal dispersion effects. It is found that an increase in the Cu-volume fraction increases dehumidification and cooling capabilities and produce more stable Cu-desiccant film.

  4. THREE-DIMENSIONAL TURBULENT STRUCTURE IN AN OPEN CHANNEL WITH SIDE-OVERTOPPING FLOW

    NASA Astrophysics Data System (ADS)

    Ohmoto, Terunori; Tanaka, Takayuki; Yamashita, Naoki

    Vegetation communities are often observed to grow in stripe pattern or patches within many stream channels. In such a situation, hydraulic engineers should examine an appropriate vegetation management system paying attention to flood control and vegetation ecosystem. In this paper, the flow resistance and momentum transport in open channel flow with discontinuous vegetation in longitudinal direction were examined experimentally. Velocity fluctuations were measured using a particle-image-velocimetry (PIV). Results showed that the flow resistance significantly depended on the longitudinal length of cavity between vegetation zones and the reason could be explained by the difference of momentum transport through the interaction among main flow, discontinuous vegetation and cavity.

  5. Temperature and Pressure Measurements and Visualization of He II Cavitation Flow through Venturi Channel

    SciTech Connect

    Ishii, T.; Murakami, M.; Harada, K.

    2004-06-23

    He II cavitation flow through a Venturi channel was experimentally investigated through temperature and pressure measurements and optical visualization. So far some distinctive features of cavitation between He II and He I flows were clarified. Then, detailed measurements were added for further investigation, such as the measurements of the temperature drop distribution throughout the flow channel and the void fraction. Further considerations were given on the cavitation inception with emphasis on the superheating of liquid helium, and the effect of the flow separation on cavitation.

  6. An analysis of pressure driven cross-flow through a long slot connecting two parallel channels

    SciTech Connect

    Shadday, M.A. Jr.

    1992-12-31

    Cross-flow between two parallel channels that were connected by a long narrow slot has been measured. The data was presented primarily in terms of transverse resistance coefficients. This data has been analyzed with momentum balances applied to both the axial and transverse components of the slot flow. The importance of wall friction to the slot flow and the necessity of calculating the axial component of the slot flow is demonstrated.

  7. 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.

  8. Self-Similarity in One-Dimensional Unsteady Open Channel Flow through Irregular Channel Cross-Sections

    NASA Astrophysics Data System (ADS)

    Ercan, A.; Kavvas, M. L.; Haltas, I.

    2014-12-01

    Geophysical processes could be self-similar under certain similarity transformations at certain time and space dimensions. In this study, the conditions under which the Saint Venant equations system for unsteady open channel flow through irregular channel cross-sections becomes self-similar under various time and space scales are investigated by utilizing one-parameter Lie group of point scaling transformations. Self-similarity conditions due to the initial and boundary conditions are also investigated thoroughly in addition to the conditions due to the governing equations. The proposed scaling relations may provide additional spatial, temporal, and economical flexibility in setting up physical hydraulic models.

  9. The capillary channel flow experiments on the International Space Station: experiment set-up and first results

    NASA Astrophysics Data System (ADS)

    Canfield, P. J.; Bronowicki, P. M.; Chen, Y.; Kiewidt, L.; Grah, A.; Klatte, J.; Jenson, R.; Blackmore, W.; Weislogel, M. M.; Dreyer, M. E.

    2013-05-01

    This paper describes the experiments on flow rate limitation in open capillary channel flow that were performed on board the International Space Station in 2011. Free surfaces (gas-liquid interfaces) of open capillary channels balance the pressure difference between the flow of the liquid in the channel and the ambient gas by changing their curvature in accordance with the Young-Laplace equation. A critical flow rate of the liquid in the channel is exceeded when the curvature of the free surface is no longer able to balance the pressure difference and, consequently, the free surface collapses and gas is ingested into the liquid. This phenomenon was observed using the set-up described herein and critical flow rates are presented for steady flow over a range of channel lengths in three different cross-sectional geometries (parallel plates, groove, and wedge). All channel shapes displayed decreasing critical flow rates for increasing channel lengths. Bubble ingestion frequencies and bubble volumes are presented for gas ingestion at supercritical flow rates in the groove channel and in the wedge channel. At flow rates above the critical flow rate, bubble ingestion frequency appears to depend on the flow rate in a linear fashion, while bubble volume remains more or less constant. The performed experiments yield vast data sets on flow rate limitation in capillary channel flow in microgravity and can be utilised to validate numerical and analytical methods.

  10. Flow-induced oscillations of tandem tethered cylinders in a channel flow

    NASA Astrophysics Data System (ADS)

    Nave, Gary; Michael, Tyler; Vlachos, Pavlos; Stremler, Mark

    2014-11-01

    In single degree-of-freedom (DOF) flow-induced oscillation studies of tandem rigid cylinders, the system most often consists of a front fixed cylinder and a trailing cylinder that is constrained to move perpendicular to the flow. We have conducted experiments in a water channel to investigate the behavior of a single DOF system of cylinders in which the trailing cylinder is constrained to move in a circular arc about the leading cylinder. We will discuss the dynamic response of the trailing cylinder for Reynolds numbers ranging from 10,000 to 20,000 and for inter-cylinder spacings from 3D to 5D, where D is the diameter of the cylinders. The experiments show a multi-frequency response that cannot be classified as a simple harmonic oscillator, as is assumed in typical tandem cylinder models. We compare our results with existing work on transversely constrained cylinders to determine the effect of tethering the cylinders. Work made possible by funding from the Virginia Commonwealth Research Commercialization Fund.

  11. A model for simulation of flow in singular and interconnected channels

    USGS Publications Warehouse

    Schaffranek, Raymond W.; Baltzer, R.A.; Goldberg, D.E.

    1981-01-01

    A one-dimensional numerical model is presented for simulating the unsteady flow in singular riverine or estuarine reaches and in networks of reaches composed of interconnected channels. The model is both general and flexible in that it can be used to simulate a wide range of flow conditions for various channel configurations. The channel geometry of the network to be modeled should be sufficiently simple so as to lend itself to characterization in one spatial dimension. The flow must be substantially homogenous in density, and hydrostatic pressure must prevail everywhere in the network channels. The slope of each channel bottom ought to be mild and reasonably constant over its length so that the flow remains subcritical. The model accommodates tributary inflows and diversions and includes the effects of wind shear on the water surface as a forcing function in the flow equations. Water-surface elevations and flow discharges are computed at channel junctions, as well as at specified intermediate locations within the network channels. The one-dimensional branch-network flow model uses a four-point, implicit, finite-difference approximation of the unsteady-flow equations. The flow equations are linearized over a time step, and branch transformations are formulated that describe the relationship between the unknowns at the end points of the channels. The resultant matrix of branch-transformation equations and required boundary-condition equations is solved by Gaussian elimination using maximum pivot strategy. Five example applications of the flow model are illustrated. The applications cover such diverse conditions as a singular upland river reach in which unsteady flow results from hydropower regulations, coastal rivers composed of sequentially connected reaches subject to unsteady tide-driven flow, and a multiply connected network of channels whose flow is principally governed by wind tides and seiches in adjoining lakes. The report includes a listing of the FORTRAN

  12. Characterising flow-vegetation interactions in open channel flows across a range of plant forms

    NASA Astrophysics Data System (ADS)

    Marjoribanks, T.; Hardy, R. J.; Lane, S. N.; Parsons, D. R.

    2013-12-01

    The dynamic interactions between flow and vegetation within open channels have important implications for channel management. Vegetation canopies can alter the mean and turbulent flow properties, via drag, which in turn can affect conveyance and sediment transport. Therefore, a good understanding of these interactions is key to effective river management. Consequently, much research has been conducted into canopy layer theory. This has predominantly focused on terrestrial (semi-rigid) canopies of a particular morphology, such that a good understanding of canopy layer turbulence structure within these canopies has been developed. This conceptual model of the canopy shear layer hypothesizes that roller vortices form at the canopy top, due to the inflection in the velocity profile. These vortices then develop further into hairpin vortices with associated turbulent quadrant events. However, there has been little investigation of turbulence structure above complex, highly flexible, aquatic macrophyte canopies of the kind often found in lowland rivers. Therefore, there is a need to characterize turbulent flow dynamics in such cases. Here we report on a series of high resolution numerical experiments over a wide range of plant forms. These experiments are undertaken using two biomechanical vegetation models, developed to represent different plant morphologies. The models are implemented within a Large Eddy Simulation framework, enabling investigation of time-dependent vortex generation and evolution at high temporal and spatial resolution. In order to investigate the role of characteristics such as canopy density and flexural rigidity in determining turbulent structure, experiments were conducted across a wide parameter set. The results from the semi-rigid canopies support previous work, showing the development of a canopy shear layer. However, as canopy density increases, the system switches and more closely resembles a boundary layer. For the highly flexible canopies

  13. Flow channeling in strongly heterogeneous porous media: A numerical study

    SciTech Connect

    Moreno, L.; Tsang, C.F.

    1994-05-01

    The variation of hydraulic conductivity in a porous medium causes the fluids flowing through it to have nonuniform velocities. Variation in fluid velocity is one of the main contributors to solute dispersion, causing a part of the contaminants dissolved in the fluid to be transported with greater than average velocities. In practical problems concerning transport of radioactive or toxic wastes, the velocity of contaminant flow may be of vital importance. This paper examines a three dimensional case, considering also the similarities and differences between parallel flow and convergent/divergent flow. Fluid flow in a porous medium is shown to perfer the most conductive paths. For a medium with strongly variable permeability this effect can be very pronounced. This paper discusses the impact of this flow distribution upon solute transport. 28 refs., 11 figs., 2 tabs.

  14. Effects of the curvature of a lava channel on flow dynamics and crust formation

    NASA Astrophysics Data System (ADS)

    Valerio, Antonella; Tallarico, Andrea; Dragoni, Michele

    2011-11-01

    Bends in lava channels are often observed in volcanic fields. The curvature of a channel affects flow dynamics and surface morphology and may be a trigger for the formation of lava tube. We propose a model to describe the effects of curvature on velocity, shear stress and the formation of crust at the flow surface. Lava is described as a Newtonian, homogeneous, isotropic and incompressible fluid. The steady-state solution of the Navier-Stokes equation is found for a unidirectional flow, in cylindrical coordinates. The flow levees are described as arcs of concentric circumferences, with their centres in the origin of the coordinate system. Under the assumption that the gravity force has no radial component, in the bend the fluid moves parallel to the levees. The velocity is assumed to depend on the radial coordinate only. As an effect of curvature, velocity and shear stress are asymmetric with respect to the centre of the channel. The maximum of surface velocity is shifted toward the internal levee, and the shear stress has larger values close to the internal levee. This effect is greater for wider channels. Heat radiation and convection into the atmosphere are considered as the main cooling mechanisms and the temperature distribution along the channel is calculated. Crust formation at the flow surface is considered under the assumption that solid lava is a plastic body. The amount of crust coverage is mainly controlled by the channel width: narrow channels have a greater coverage than wide channels for a given radius of curvature. The effect of a bend is to favour the crust growth toward the internal levee, while the crust coverage toward the external levee decreases. The presence of a bend in a lava channel may favour the formation of a lava tube. The analytical solution will serve as a benchmark for numerical models. Understanding the mechanism of formation of lava tubes is crucial to the simulation of actual lava flows and to evaluation of the associated hazard.

  15. MHD flows in the channels of plasma accelerators with a longitudinal magnetic field

    SciTech Connect

    Brushlinskii, K. V.; Zhdanova, N. S.

    2008-12-15

    Plasma flows caused by the interaction of the discharge current with the azimuthal magnetic self-field in coaxial channels (nozzles) of plasma accelerators are strongly affected by the longitudinal field produced by external conductors. A two-dimensional MHD model of flows in channels in the presence of a longitudinal magnetic field is proposed. Depending on the ratio between the characteristic values of the longitudinal and azimuthal field components, one of three types of flow is established in the channel: super-Alfven, sub-Alfven, or combined. The properties of different types of flows are analyzed. The acceleration process in sub-Alfven flows differs qualitatively from that in regimes without a longitudinal field in transitions between the kinetic, thermal, and magnetic energy components.

  16. MHD flows in the channels of plasma accelerators with a longitudinal magnetic field

    NASA Astrophysics Data System (ADS)

    Brushlinskii, K. V.; Zhdanova, N. S.

    2008-12-01

    Plasma flows caused by the interaction of the discharge current with the azimuthal magnetic self-field in coaxial channels (nozzles) of plasma accelerators are strongly affected by the longitudinal field produced by external conductors. A two-dimensional MHD model of flows in channels in the presence of a longitudinal magnetic field is proposed. Depending on the ratio between the characteristic values of the longitudinal and azimuthal field components, one of three types of flow is established in the channel: super-Alfvén, sub-Alfvén, or combined. The properties of different types of flows are analyzed. The acceleration process in sub-Alfvén flows differs qualitatively from that in regimes without a longitudinal field in transitions between the kinetic, thermal, and magnetic energy components.

  17. Interfacial wave behavior in oil-water channel flows: Prospects for a general understanding

    SciTech Connect

    McCready, M.J.; Uphold, D.D.; Gifford, K.A.

    1997-12-31

    Oil-water pressure driven channel flow is examined as a model for general two-layer flows where interfacial disturbances are important. The goal is to develop sufficient understanding of this system so that the utility and limitations of linear and nonlinear theories can be known a priori. Experiments show that sometimes linear stability is useful at predicting the steady or dominant evolving waves. However in other situations there is no agreement between the linearly fastest growing wave and the spectral peak. An interesting preliminary result is that the bifurcation to interfacial waves is supercritical for all conditions that were studied for an oil-water channel flow, gas-liquid channel flow and two-liquid Couette flow. However, three different mechanisms are dominant for each of these three situations.

  18. Numerical study of heat transfer enhancement in a channel flow using an oscillating vortex generator

    NASA Astrophysics Data System (ADS)

    Yang, S.-J.

    2002-04-01

    A numerical simulation is performed to study the unsteady flow and heat transfer in a channel with an oscillating bar, which is called an oscillating vortex generator. The behavior of the oscillating bar and flow is coupled, and the variation of the flow and thermal fields is classified as a moving boundary problem. An arbitrary Lagrangian-Eulerian kinematic description method is adopted to describe the flow and thermal fields, and a Galerkin finite element formulation with moving meshes is applied to solve the governing equations. The effects of Reynolds number, maximum oscillating speed, oscillating amplitude, and oscillating frequency of the bar on the flow and heat transfer are examined in details. The results show that the unsteady flow of transverse vortices is actively and largely formed behind the bar as the bar oscillates in the channel. The transverse vortices transport the low-temperature and high-speed core flow toward the heated regions of the channel. Also, the high-temperature wall flow is carried away from the heated regions of the channel to mix with the low-temperature core flow by transverse vortices. Based upon the fixed heat transfer area, the efficiency index is greater than 1.0 for almost all cases.

  19. Arsenic removal from flowing irrigation water in bangladesh: impacts of channel properties.

    PubMed

    Lineberger, Ethan M; Badruzzaman, A Borhan M; Ali, M Ashraf; Polizzotto, Matthew L

    2013-11-01

    Across Bangladesh, dry-season irrigation with arsenic-contaminated well water is loading arsenic onto rice paddies, leading to increased arsenic concentrations in plants, diminished crop yields, and increased human health risks. As irrigation water flows through conveyance channels between wells and rice fields, arsenic concentrations change over space and time, indicating that channels may provide a location for removing arsenic from solution. However, few studies have systematically evaluated the processes controlling arsenic concentrations in irrigation channels, limiting the ability to manipulate these systems and enhance arsenic removal from solution. The central goal of this study was to quantify how channel design affected removal of dissolved arsenic from flowing irrigation water. Field experiments were conducted in Bangladesh using a chemically constant source of arsenic-contaminated irrigation water and an array of constructed channels with varying geometries. The resulting hydraulic conditions affected the quantity of arsenic removed from solution within the channels by promoting known hydrogeochemical processes. Channels three times the width of control channels removed ∼3 times the mass of arsenic over 32 min of flowing conditions, whereas negligible arsenic removal was observed in tarp-lined channels, which prevented soil-water contact. Arsenic removal from solution was ∼7 times higher in a winding, 200-m-long channel than in the straight, 45-m-long control channels. Arsenic concentrations were governed by oxidative iron-arsenic coprecipitation within the water column, sorption to soils, and phosphate competition. Collectively, these results suggest that better design and management of irrigation channels may play a part in arsenic mitigation strategies for rice fields in Southern Asia. PMID:25602413

  20. Unidirectionally migrating deep-water channels: Architectural styles and flow processes

    NASA Astrophysics Data System (ADS)

    Gong, C.; Steel, R. J.; Wang, Y.; Xu, Q.

    2014-12-01

    3D seismic data are used to investigate flow processes and sedimentation in deep-water slope channels of an alternate type characterized by short and straight channel courses, a lack of levees, and absence of any coeval fans. The study allows a picture of unusual flow processes in submarine channels. The studied channels can be divided into two discrete segments: (1) Upper segments are characterized by low aspect ratio(W/T), little lateral offset (Lm), and low migration/aggradation ratios (Lm/Va). These upper segment channels build vertically-stacked channel-complex sets (CCSs), each of which is characterized by a facies transition from fine-grained sands in the lower part overlain by debris flow deposits and then shale drapes. Energetic sediment density flows triggered by fluid escape and/or strong wave action were well able to bypass sediment and to mask relatively weak bottom currents, yielding deep-water channels characterized by little lateral offset and dominantly aggradational stacking patterns. (2) Lower segments are characterized by higher W/T, wide lateral offset (Lm), and high Lm/Va. They consist of laterally-migrated CCSs, each of which consists of fine-grained reworked sands in the lower part overlain by debris flow deposits and, finally, shale drapes. Bottom currents restricted within the channels would have induced a tilt of the interface between turbidity currents and the overriding bottom currents (Wedderburn number > 1). This would have deflected turbidity currents downward and back toward the gentle channel bank, thus causing channel migration (the steep bank) by ~2° to 15°, and yielding a helical flow circulation composed of a high-velocity zone along the steep bank and a low-velocity zone along the gentle bank. This bottom current-induced helical flow circulation promoted deposition on the gentle bank, but it favored erosion on the steep banke, yielding deep-water channels exhibiting wide lateral offset and dominantly laterally

  1. The hydraulic geometry of narrow and deep channels; evidence for flow optimisation and controlled peatland growth

    NASA Astrophysics Data System (ADS)

    Nanson, Rachel A.; Nanson, Gerald C.; Huang, He Qing

    2010-04-01

    At-a-station and bankfull hydraulic geometry analyses of peatland channels at Barrington Tops, New South Wales, Australia, reveal adjustments in self-forming channels in the absence of sediment load. Using Rhodes ternary diagram, comparisons are made with hydraulic geometry data from self-forming channels carrying bedload in alluvial settings elsewhere. Despite constraints on channel depths caused at some locations by the restricted thickness of peat, most stations have cohesive, near-vertical, well-vegetated banks, and width/depth (w/d) ratios of ∼ 2 that are optimal for sediment-free flow. Because banks are strong, resist erosion and can stand nearly vertical, and depth is sometimes constrained, adjustments to discharge are accommodated largely by changes in velocity. These findings are consistent with the model of maximum flow efficiency and the overarching least action principle in open channels. The bankfull depth of freely adjusting laterally active channels in clastic alluvium is well known to be related to the thickness of floodplain alluvium and a similar condition appears to apply to these swamps that grow in situ and are formed almost entirely of organic matter. The thickness of peat in these swamps rarely exceeds that required to form a bankfull channel of optimum w/d ratio for the transport of sediment-free water. Swamp vegetation is highly dependent on proximity to the water table. To maintain a swamp-channel and associated floodplain system, the channels must flow with sufficient water much of the time; they not only offer an efficient morphology for flow but do so in a way that enables bankfull conditions to occur many times a year. They also prevent the swamp from growing above a level linked to the depth of the channel. Once the channel attains the most efficient cross section, further growth of the swamp vertically is restricted by enhanced flow velocities and limited flow depths. This means that the volume of peat in such swamps is determined

  2. Optical observation of ultrafine droplets and air flows from newly designed supersonic air assist spray nozzles

    NASA Astrophysics Data System (ADS)

    Miyashiro, Seiji S.; Mori, H.; Takechi, H.

    2001-04-01

    One of the authors developed a new spray drying nozzle (special quadruplet fluid spray nozzle) for drug manufacturing and it has succeeded in manufacturing fine particles of 2 micrometer diameter of 1/15 ratios to those currently in use. The flow visualization results show that the two air jets become under-expanded on both edge sides of the nozzle, generate shock and expansion waves alternately on each side and reach the edge tip, where they collide, unite, and spout out while shock and expansion waves are again formed in the mixed jet. When the edge surfaces are supplied with water, the water is extended into thin film by the air jet and intensely disturbed. At the nozzle tip it is torn into droplets, which are further atomized afterwards in shock waves. At the spray tip, the friction with ambient air shears the droplets furthermore, and they decrease further in size.

  3. Environmental Flows Can Reduce the Encroachment of Terrestrial Vegetation into River Channels: A Systematic Literature Review

    NASA Astrophysics Data System (ADS)

    Miller, Kimberly A.; Webb, J. Angus; de Little, Siobhan C.; Stewardson, Michael J.

    2013-11-01

    Encroachment of riparian vegetation into regulated river channels exerts control over fluvial processes, channel morphology, and aquatic ecology. Reducing encroachment of terrestrial vegetation is an oft-cited objective of environmental flow recommendations, but there has been no systematic assessment of the evidence for and against the widely-accepted cause-and-effect mechanisms involved. We systematically reviewed the literature to test whether environmental flows can reduce the encroachment of terrestrial vegetation into river channels. We quantified the level of support for five explicit cause-effect hypotheses drawn from a conceptual model of the effects of flow on vegetation. We found that greater inundation, variously expressed as changes in the area, depth, duration, frequency, seasonality, and volume of surface water, generally reduces riparian vegetation abundance in channels, but most studies did not investigate the specific mechanisms causing these changes. Those that did show that increased inundation results in increased mortality, but also increased germination. The evidence was insufficient to determine whether increased inundation decreases reproduction. Our results contribute to hydro-ecological understanding by using the published literature to test for general cause-effect relationships between flow regime and terrestrial vegetation encroachment. Reviews of this nature provide robust support for flow management, and are more defensible than expert judgement-based approaches. Overall, we predict that restoration of more natural flow regimes will reduce encroachment of terrestrial vegetation into regulated river channels, partly through increased mortality. Conversely, infrequent deliveries of environmental flows may actually increase germination and subsequent encroachment.

  4. Non-equilibrium Flows of Reacting Air Components in Nozzles

    NASA Astrophysics Data System (ADS)

    Bazilevich, S. S.; Sinitsyn, K. A.; Nagnibeda, E. A.

    2008-12-01

    The paper presents the results of the investigation of non-equilibrium flows of reacting air mixtures in nozzles. State-to-state approach based on the solution of the equations for vibrational level populations of molecules and atomic concentrations coupled to the gas dynamics equations is used. For the 5-component air mixture (N2, O2, NO, N, O) non-equilibrium distributions and gasdynamical parameters are calculated for different conditions in a nozzle throat. The influence of various kinetic processes on distributions and gas dynamics parameters is studied. The paper presents the comparison of the results with ones obtained for binary mixtures of molecules and atoms and various models of elementary processes.

  5. Heat and mass transfer for turbulent flow of chemically reacting gas in eccentric annular channels

    SciTech Connect

    Besedina, T.V.; Tverkovkin, B.E.; Udot, A.V.; Yakushev, A.P.

    1988-02-01

    Because of the possibility of using dissociating gases as coolants and working bodies of nuclear power plants, it is necessary to develop computational algorithms for calculating heat and mass transfer processes under conditions of nonequilibrium flow of chemically reacting gases not only in axisymmetric channels, but also in channels with a complex transverse cross section (including also in eccentric annular channels). An algorithm is proposed for calculating the velocity, temperature, and concentration fields under conditions of cooling of a cylindrical heat-releasing rod, placed off-center in a circular casing pipe, by a longitudinal flow of chemically reacting gas (N/sub 2/O/sub 4/).

  6. Computation of Turbulent Recirculating Flow in Channels, and for Impingement Cooling

    NASA Technical Reports Server (NTRS)

    Chang, Byong Hoon

    1992-01-01

    Fully elliptic forms of the transport equations have been solved numerically for two flow configurations. The first is turbulent flow in a channel with transverse rectangular ribs, and the second is impingement cooling of a plane surface. Both flows are relevant to proposed designs for active cooling of hypersonic vehicles using supercritical hydrogen as the coolant. Flow downstream of an abrupt pipe expansion and of a backward-facing step were also solved with various near-wall turbulence models as benchmark problems. A simple form of periodicity boundary condition was used for the channel flow with transverse rectangular ribs. The effects of various parameters on heat transfer in channel flow with transverse ribs and in impingement cooling were investigated using the Yap modified Jones and Launder low Reynolds number k-epsilon turbulence model. For the channel flow, predictions were in adequate agreement with experiment for constant property flow, with the results for friction superior to those for heat transfer. For impingement cooling, the agreement with experiment was generally good, but the results suggest that improved modelling of the dissipation rate of turbulence kinetic energy is required in order to obtain improved heat transfer prediction, especially near the stagnation point. The k-epsilon turbulence model was used to predict the mean flow and heat transfer for constant and variable property flows. The effect of variable properties for channel flow was investigated using the same turbulence model, but comparison with experiment yielded no clear conclusions. Also, the wall function method was modified for use in the variable properties flow with a non-adiabatic surface, and an empirical model is suggested to correctly account for the behavior of the viscous sublayer with heating.

  7. Seepage from channeled flows as influenced by PAM and sediment

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Seepage from water streams into unlined channels determines the proportion of water distributed to adjacent soil for plant use or soil or groundwater recharge, or conveyed to downstream reaches. We conducted a laboratory study to determine how sediment type (none, clay, silt), sediment concentratio...

  8. Sediment and polyacrylamide effects on seepage losses from channeled flows

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Seepage from water streams into unlined channels determines the proportion of water distributed to adjacent soil for plant use or soil or groundwater recharge, or conveyed to downstream reaches. We conducted a laboratory study to determine how inflow amendment and related factors, sediment type (no...

  9. Chryse Basin channels: low-gradients and ponded flows.

    USGS Publications Warehouse

    Lucchitta, B.K.; Ferguson, H.M.

    1983-01-01

    Gradients on the floors of the Martian outflow channels that are derived from radar-elevation profiles across Lunae Planum and Chryse Basin have much lower values than those obtained from the U.S. Geological Survey's topographic map. Whereas the gradients of Maja and Ares Valles are similar to those of the catastrophic flood channels in the Scablands of Washington State, the gradients of Simud and Tiu Valles are essentially level, and the movement of fluids to the N poses problems. It is proposed that ponding may have formed lakes in depressions associated with the Valles Marineris grabens, ancient craters in the chaotic terrain area, and possibly even the regional low where most chaotic terrains occur. It is envisaged that lakes eventually overflowed, forming the present channels. When dams broke, floods were released catastrophically, with a final gigantic flood from the Valles Marineris system of troughs, which would have had sufficient head to move fluids across nearly level gradients through the Simud and Tiu channels. -P.Br.

  10. Flow boiling with enhancement devices for cold plate coolant channel design

    NASA Technical Reports Server (NTRS)

    Boyd, Ronald D., Sr.

    1989-01-01

    A research program to study the effect of enhancement devices on flow boiling heat transfer in coolant channels, which are heated either from the top side or uniformly, is discussed. Freon 11 is the working fluid involved. The specific objectives are: (1) examine the variations in both the mean and local (axial and circumferential) heat transfer coefficients for a circular coolant channel with either smooth walls or with both a twisted tape and spiral finned walls, (2) examine the effect channel diameter (and the length-to-diameter aspect ratio) variations for the smooth wall channel, and (3) develop an improved data reduction analysis.

  11. Two-phase flow instability and dryout in parallel channels in natural circulation

    SciTech Connect

    Duffey, R.B.; Rohatgi, U.S.; Hughes, E.D.

    1993-06-01

    The unique feature of parallel channel flows is that the pressure drop or driving head for the flow is maintained constant across any given channel by the flow in all the others, or by having a large downcomer or bypass in a natural circulation loop. This boundary condition is common in all heat exchangers, reactor cores and boilers, it is well known that the two-phase flow in parallel channels can exhibit both so-called static and dynamic instability. This leads to the question of the separability of the flow and pressure drop boundary conditions in the study of stability and dryout. For the areas of practical interest, the flow can be considered as incompressible. The dynamic instability is characterized by density (kinematic) or continuity waves, and the static instability by inertial (pressure drop) or manometric escalations. The static has been considered to be the zero-frequency or lowest mode of the dynamic case. We briefly review the status of the existing literature on both parallel channel static and dynamic instability, and the latest developments in theory and experiment. The difference between the two derivations lies in the retention of the time-dependent terms in the conservation equations. The effects and impact of design options are also discussed. Since dryout in parallel systems follows instability, it has been traditional to determine the dryout power for a parallel channel by testing a single channel with a given (inlet) flow boundary condition without particular regard for the pressure drop. Thus all modern dryout correlations are based on constant or fixed flow tests, a so-called hard inlet, and subchannel and multiple bundle effects are corrected for separately. We review the thinking that lead to this approach, and suggest that for all multiple channel and natural circulation systems close attention should be paid to the actual (untested) pressure drop conditions. A conceptual formulation is suggested as a basis for discussion.

  12. Flow boiling with enhancement devices for cold plate coolant channel design

    NASA Technical Reports Server (NTRS)

    Boyd, Ronald D., Sr.; Smith, Alvin

    1990-01-01

    The use of flow boiling for thermal energy transport is intended to provide an alternative for accommodating higher heat fluxes in commercial space systems. The objectives are to: (1) examine the variations in both the mean and local (axial and circumferential) heat transfer coefficients for a circular coolant channel with either smooth walls, spiral fins, or both spiral fins and a twisted tape; (2) examine the effects of channel diameter and subcooling; and (3) develop an improved reduction analysis and/or suggest possible heat transfer correlation of the present data. Freon-11 is the working fluid. Two-dimensional (circumferential and axial) wall temperature distributions were measured for coolant channels with the above noted internal geometries. The flow regimes which are being studied are: (1) single phase; (2) subcooled flow boiling; and (3) stratified flow boiling. The inside diameter of all test sections is near 1.0 cm. Cicumferentially averaged heat transfer coefficients at several axial locations were obtained for selected coolant channels for a mass velocity of 210 kg/sq m s, an exit pressure of 0.19 MPa (absolute), and an inlet subcooling of 20.8 C. Overall (averaged over the entire channel) heat transfer coefficients were compared for the above channel geometries. This comparison showed that the channel with large pitch spiral fins had higher heat transfer coefficients at all power levels.

  13. Mean annual runoff and peak flow estimates based on channel geometry of streams in southeastern Montana

    USGS Publications Warehouse

    Omang, R.J.; Parrett, Charles; Hull, J.A.

    1983-01-01

    Equations using channel-geometry measurements were developed for estimating mean runoff and peak flows of ungaged streams in southeastern Montana. Two separate sets of esitmating equations were developed for determining mean annual runoff: one for perennial streams and one for ephemeral and intermittent streams. Data from 29 gaged sites on perennial streams and 21 gaged sites on ephemeral and intermittent streams were used in these analyses. Data from 78 gaged sites were used in the peak-flow analyses. Southeastern Montana was divided into three regions and separate multiple-regression equations for each region were developed that relate channel dimensions to peak discharge having recurrence intervals of 2, 5, 10, 25, 50, and 100 years. Channel-geometery relations were developed using measurements of the active-channel width and bankfull width. Active-channel width and bankfull width were the most significant channel features for estimating mean annual runoff for al types of streams. Use of this method requires that onsite measurements be made of channel width. The standard error of estimate for predicting mean annual runoff ranged from about 38 to 79 percent. The standard error of estimate relating active-channel width or bankfull width to peak flow ranged from about 37 to 115 percent. (USGS)

  14. Geologic Controls on Channel Morphology and Low-Flow Habitat; Rattlesnake Creek, Santa Barbara, California

    NASA Astrophysics Data System (ADS)

    Bean, G.; Keller, E.

    2006-12-01

    Channel morphology and baseflow are limiting factors in sustaining low-flow habitat for the spawning and rearing of endangered southern steelhead trout in southern California. To aid the recovery of steelhead trout, it is imperative to determine how pools are formed and maintained in steep mountain streams, and what hydrogeologic factors control baseflow. Rattlesnake Creek, a steep (6 to 31%) boulder-bedrock channel in Santa Barbara, California, was investigated to determine if geologic and hydrogeologic properties, specifically rock strength and fracture density, control channel morphology and low-flow habitat. Analysis of rock strength, fracture density, and channel morphology using a single-factor analysis of variance, Kolmorgorov-Smirnov test and t-test suggest that rock strength and fracture density of the underlying lithology (bed and banks) does not significantly affect the channel morphology at the 0.05 level of significance. However, this study does show that boulder large roughness elements (LREs) armor the channel, controlling channel gradient and the location, abundance and type of pools. Step pools are the dominant pool type, found in reaches up to 18% where cascades might be expected, and steps are composed of resistant sandstone boulder LREs. Although fracture density does not influence the morphology of the channel, baseflow for low-flow habitat is predominantly supplied through fractures in the coldwater sandstone.

  15. Time-resolved Fast Neutron Radiography of Air-water Two-phase Flows

    NASA Astrophysics Data System (ADS)

    Zboray, Robert; Dangendorf, Volker; Mor, Ilan; Tittelmeier, Kai; Bromberger, Benjamin; Prasser, Horst-Michael

    Neutron imaging, in general, is a useful technique for visualizing low-Z materials (such as water or plastics) obscured by high-Z materials. However, when significant amounts of both materials are present and full-bodied samples have to be examined, cold and thermal neutrons rapidly reach their applicability limit as the samples become opaque. In such cases one can benefit from the high penetrating power of fast neutrons. In this work we demonstrate the feasibility of time-resolved, fast neutron radiography of generic air-water two-phase flows in a 1.5 cm thick flow channel with Aluminum walls and rectangular cross section. The experiments have been carried out at the high-intensity, white-beam facility of the Physikalisch-Technische Bundesanstalt, Germany. Exposure times down to 3.33 ms have been achieved at reasonable image quality and acceptable motion artifacts. Different two-phase flow regimes such as bubbly slug and churn flows have been examined. Two-phase flow parameters like the volumetric gas fraction, bubble size and bubble velocities have been measured.

  16. Formation of plasma channels in air under filamentation of focused ultrashort laser pulses

    NASA Astrophysics Data System (ADS)

    Ionin, A. A.; Seleznev, L. V.; Sunchugasheva, E. S.

    2015-03-01

    The formation of plasma channels in air under filamentation of focused ultrashort laser pulses was experimentally and theoretically studied together with theoreticians of the Moscow State University and the Institute of Atmospheric Optics. The influence of various characteristics of ultrashort laser pulses on these plasma channels is discussed. Plasma channels formed under filamentation of focused laser beams with a wavefront distorted by spherical aberration (introduced by adaptive optics) and by astigmatism, with cross-section spatially formed by various diaphragms and with different UV and IR wavelengths, were experimentally and numerically studied. The influence of plasma channels created by a filament of a focused UV or IR femtosecond laser pulse (λ = 248 nm or 740 nm) on characteristics of other plasma channels formed by a femtosecond pulse at the same wavelength following the first one with varied nanosecond time delay was also experimentally studied. An application of plasma channels formed due to the filamentation of focused UV ultrashort laser pulses including a train of such pulses and a combination of ultrashort and long (~100 ns) laser pulses for triggering and guiding long (~1 m) electric discharges is discussed.

  17. Flow regimes in a single dimple on the channel surface

    NASA Astrophysics Data System (ADS)

    Kovalenko, G. V.; Terekhov, V. I.; Khalatov, A. A.

    2010-12-01

    The boundaries of the domains of existence of flow regimes past single dimples made as spherical segments on a flat plate are determined with the use of available experimental results. Regimes of a diffuser-confuser flow, a horseshoe vortex, and a tornado-like vortex in the dimple are considered. Neither a horseshoe vortex nor a tornado-like vortex is observed in dimples with the relative depth smaller than 0.1. Transformations from the diffuser-confuser flow regime to the horseshoe vortex regime and from the horseshoe vortex flow to the tornado-like vortex flow are found to depend not only on the Reynolds number, but also on the relative depth of the spherical segment. Dependences for determining the boundaries of the regime existence domains are proposed, and parameters at which the experimental results can be generalized are given.

  18. Oscillating flow and separation of species in rectangular channels

    NASA Astrophysics Data System (ADS)

    Hacioglu, A.; Narayanan, R.

    2016-07-01

    The mass transfer and separation of species in a tube using oscillatory flows are strongly affected by the fluid flow profiles in the tube. It has been well established that oscillatory motion in a one-dimensional flow configuration leads to a single tuning dimensionless frequency, where optimum separation may be effected. In this work, the effect on species separation by two-dimensional laminar flow arising in a rectangular cross section is studied and a surprising result is that a second tuning frequency may occur at lower dimensionless oscillation frequencies. The physics reveals that this new optimum disappears when the aspect ratio is either very large or close to unity. These observations are related to the flow profiles at different aspect ratios.

  19. Deformation of an Elastic beam due to Viscous Flow in an Embedded Channel Network

    NASA Astrophysics Data System (ADS)

    Matia, Yoav; Gat, Amir

    2015-11-01

    Elastic deformation due to embedded fluidic networks is currently studied in the context of soft-actuators and soft-robotic applications. In this work, we analyze the time dependent interaction between elastic deformation of a slender beam and viscous flow within a long serpentine channel, embedded in the elastic structure. The channel is positioned asymmetrically with regard to the midplane of the elastic beam, and thus pressure within the channel creates a local moment deforming the beam. We focus on creeping flows and small deformations of the elastic beam and obtain, in leading order, a convection-diffusion equation governing the pressure-field within the serpentine channel. The beam time-dependent deformation is then obtained as a function of the pressure-field and the geometry of the embedded network. This relation enables the design of complex time-dependent deformation patterns of beams with embedded channel networks. Our theoretical results were illustrated and verified by numerical computations.

  20. Experimental Investigation and Flow Process Computer Simulation of the Single Mini Channel Condenser for Vapor Compression Refrigeration System

    NASA Astrophysics Data System (ADS)

    Pabilona, L. L.; Villanueva, E. P.

    2015-09-01

    This study is a computer simulation of the temperature profiles and experimental investigation of three 100 mm x 50 mm x 18 mm single mini channel condensers with hydraulic diameters of 3 mm, 2 mm, and 1mm. The mini channels which were made of copper were designed, fabricated and tested. Each unit was connected in a vapor compression cycle with R-134a as the refrigerant. The average refrigerant mass flow rates were varied from 1.296 - 69.471 g/s, and the average inlet and outlet condenser pressure variations were 102.5 - 121.8 kPa and 101.74 -121.23 kPa, respectively. Each condenser was placed inside a mini wind tunnel system where forced draft air was introduced to initiate convective heat transfer. Each condenser was tested and data were gathered every five minute interval for one hour using a Lab View Software. Computer simulations on the flow process were conducted using Solid Works software. The experimental results presented the inlet and outlet condenser pressures, and pressure drops. The experimental heat transfer coefficients were calculated at different mass fluxes during condensation. The values ranged from 3900 to 5200 W/m2-°K for the 3 mm, 2600 to 9000 W/m2-°K for the 2 mm, and 13 to 98 W/m2-°K for the 1 mm. The heat transfer coefficients calculated from experiments were then compared with the computed values using the correlations developed by Dittus-Boelter and Lee-Son. The results showed increasing deviation as the diameter decreased. The discrepancies could be attributed to the appropriateness of the Dittus-Boelter and Lee-Son correlations in small diameter channels, complexities in the flow process which involved two phase flow heat transfer in very small tubes, and the difficulties in attaining very accurate measurements in small channels.

  1. Flow Analysis over Batten Reinforced Wings for Micro Air Vehicles

    NASA Astrophysics Data System (ADS)

    Townsend, Kurtis; Hicks, Travis; Hubner, James P.

    2008-11-01

    Flexible membrane wings modify the flow separation of low Reynolds number micro air vehicles (MAVs). A specific type of fixed-wing geometry is a batten-reinforced configuration in which the membrane is attached to a rigid frame with chordwise battens, allowing the vibration of the membrane at the trailing-edge. In this study, smoke-wire visualization and hot-wire anemometry, both near the trailing-edge and further downstream in the wake, are used to quantify the frequency and energy of these fluctuations for various cell geometries and flow angles-of-attack. Improvement in the wake momentum deficit will be analyzed to determine preferred membrane cell geometries for MAV flight conditions.

  2. Surface-slip equations for multicomponent, nonequilibrium air flow

    NASA Technical Reports Server (NTRS)

    Gupta, Roop N.; Scott, Carl D.; Moss, James N.; Goglia, Gene

    1985-01-01

    Equations are presented for the surface slip (or jump) values of species concentration, pressure, velocity, and temperature in the low-Reynolds-number, high-altitude flight regime of a space vehicle. These are obtained from closed-form solutions of the mass, momentum, and energy flux equations using the Chapman-Enskog velocity distribution function. This function represents a solution of the Boltzmann equation in the Navier-Stokes approximation. The analysis, obtained for nonequilibrium multicomponent air flow, includes the finite-rate surface catalytic recombination and changes in the internal energy during reflection from the surface. Expressions for the various slip quantities have been obtained in a form which can readily be employed in flow-field computations. A consistent set of equations is provided for multicomponent, binary, and single species mixtures. Expression is also provided for the finite-rate species-concentration boundary condition for a multicomponent mixture in absence of slip.

  3. Flow boiling with enhancement devices for cold plate coolant channel design

    NASA Technical Reports Server (NTRS)

    Boyd, Ronald D.

    1991-01-01

    Future space exploration and commercialization will require more efficient heat rejection systems. For the required heat transfer rates, such systems must use advanced heat transfer techniques. Forced two phase flow boiling heat transfer with enhancements falls in this category. However, moderate to high quality two phase systems tend to require higher pressure losses. This report is divided into two major parts: (1) Multidimensional wall temperature measurement and heat transfer enhancement for top heated horizontal channels with flow boiling; and (2) Improved analytical heat transfer data reduction for a single side heated coolant channel. Part 1 summarizes over forty experiments which involve both single phase convection and flow boiling in a horizontal channel heated externally from the top side. Part 2 contains parametric dimensionless curves with parameters such as the coolant channel radius ratio, the Biot number, and the circumferential coordinate.

  4. Darcy Flow in a Wavy Channel Filled with a Porous Medium

    SciTech Connect

    Gray, Donald D; Ogretim, Egemen; Bromhal, Grant S

    2013-05-17

    Flow in channels bounded by wavy or corrugated walls is of interest in both technological and geological contexts. This paper presents an analytical solution for the steady Darcy flow of an incompressible fluid through a homogeneous, isotropic porous medium filling a channel bounded by symmetric wavy walls. This packed channel may represent an idealized packed fracture, a situation which is of interest as a potential pathway for the leakage of carbon dioxide from a geological sequestration site. The channel walls change from parallel planes, to small amplitude sine waves, to large amplitude nonsinusoidal waves as certain parameters are increased. The direction of gravity is arbitrary. A plot of piezometric head against distance in the direction of mean flow changes from a straight line for parallel planes to a series of steeply sloping sections in the reaches of small aperture alternating with nearly constant sections in the large aperture bulges. Expressions are given for the stream function, specific discharge, piezometric head, and pressure.

  5. Laboratory Evaluation of Air Flow Measurement Methods for Residential HVAC Returns

    SciTech Connect

    Walker, Iain; Stratton, Chris

    2015-07-01

    This project improved the accuracy of air flow measurements used in commissioning California heating and air conditioning systems in Title 24 (Building and Appliance Efficiency Standards), thereby improving system performance and efficiency of California residences. The research team at Lawrence Berkeley National Laboratory addressed the issue that typical tools used by contractors in the field to test air flows may not be accurate enough to measure return flows used in Title 24 applications. The team developed guidance on performance of current diagnostics as well as a draft test method for use in future evaluations. The series of tests performed measured air flow using a range of techniques and devices. The measured air flows were compared to reference air flow measurements using inline air flow meters built into the test apparatus. The experimental results showed that some devices had reasonable results (typical errors of 5 percent or less) but others had much bigger errors (up to 25 percent).

  6. Upper air teleconnections to Ob River flows and tree rings

    NASA Astrophysics Data System (ADS)

    Meko, David; Panyushkina, Irina; Agafonov, Leonid

    2015-04-01

    The Ob River, one of the world's greatest rivers, with a catchment basin about the size of Western Europe, contributes 12% or more of the annual freshwater inflow to the Arctic Ocean. The input of heat and fresh water is important to the global climate system through effects on sea ice, salinity, and the thermohaline circulation of the ocean. As part of a tree-ring project to obtain multi-century long information on variability of Ob River flows, a network of 18 sites of Pinus, Larix, Populus and Salix has been collected along the Ob in the summers of 2013 and 2014. Analysis of collections processed so far indicates a significant relationship of tree-growth to river discharge. Moderation of the floodplain air temperature regime by flooding appears to be an important driver of the tree-ring response. In unraveling the relationship of tree-growth to river flows, it is important to identify atmospheric circulation features directly linked to observed time series variations of flow and tree growth. In this study we examine statistical links between primary teleconnection modes of Northern Hemisphere upper-air (500 mb) circulation, Ob River flow, and tree-ring chronologies. Annual discharge at the mouth of the Ob River is found to be significantly positively related to the phase of the East Atlantic (EA) pattern, the second prominent mode of low-frequency variability over the North Atlantic. The EA pattern, consisting of a north-south dipole of pressure-anomaly centers spanning the North Atlantic from east to west, is associated with a low-pressure anomaly centered over the Ob River Basin, and with a pattern of positive precipitation anomaly of the same region. The positive correlation of discharge and EA is consistent with these know patterns, and is contrasted with generally negative (though smaller) correlations between EA and tree-ring chronologies. The signs of correlations are consistent with a conceptual model of river influence on tree growth through air

  7. Soil cleanup by in-situ aeration. XXII. Effect of air channeling

    SciTech Connect

    Wilson, D.J.; Rodriguez-Maroto, J.M.; Gomez-Lahoz, C.

    1995-07-01

    A distributed diffusion model for soil vapor extraction (SVE) is developed in which air advection occurs through conducting channels or tubes of high air permeability; volatile organic compound (VOC) is removed by diffusion from the surrounding porous medium to these channels, where it is removed by advection. The results obtained with this model are similar to those obtained with other distributed diffusion SVE models in that initial rapid VOC removal is followed by a rather rapid decrease in effluent soil gas VOC concentration and extended tailing of the cleanup. It is noted that soil gas VOC concentration rebound after SVE well shutdown provides useful information about the extent of cleanup only if the soil gas is recovered from the domain which was actually contaminated.

  8. Day-night coupling by a localized flow channel visualized by polar cap patch propagation

    NASA Astrophysics Data System (ADS)

    Nishimura, T.; Lyons, L. R.; Zou, Y.; Wang, B.; Oksavik, K.; Moen, J. I.; Clausen, L.; Donovan, E.; Angelopoulos, V.; Shiokawa, K.; Ruohoniemi, J. M.; Nishitani, N.; McWilliams, K. A.; Lester, M.

    2014-12-01

    Although plasma convection in the polar cap is often thought of large-scale two-cell convection, recent radar observations have shown that dynamic meso-scale fast flows of the order of 100 km size are embedded within the large-scale convection. Those flow channels are colocated with polar cap airglow patches in many cases, and thus optical measurements can be used to track the origin of such flows, evolution in the polar cap, and their influence on nightside auroral activity. We present unique coordinated observations of the dayside auroral oval, polar cap, and nightside auroral oval by three All-Sky Imagers (ASIs), two SuperDARN radars, and DMSP. This dataset revealed that a dayside Poleward-Moving Auroral Form (PMAF) evolved into a polar cap airglow patch that propagated across the polar cap, and then nightside poleward boundary intensifications (PBIs). Radar observations detected fast anti-sunward flows associated with the PMAF, and the DMSP satellite, whose conjunction occurred within a few minutes after the PMAF initiation, measured enhanced Low-Latitude Boundary Layer (LLBL) precipitation and enhanced plasma density with a strong anti-sunward flow burst. The polar cap patch was spatially and temporally coincident with a localized anti-sunward flow channel. The propagation across the polar cap and the subsequent PBIs suggest that the flow channel originated from dayside reconnection and then reached the nightside open-closed boundary, triggering localized nightside reconnection and flow bursts within the plasma sheet. In addition, we have also statistically investigated the property of dayside and nightside polar cap flow channels using imagers, radars and low-altitude satellites. The flow channels are typically found to have a ~300 km width, propagate a few hundred km/s faster than background flows, and to occur during a By-dominant IMF with a weak southward component.

  9. Ozone concentrations in air flowing into New York State

    NASA Astrophysics Data System (ADS)

    Aleksic, Nenad; Kent, John; Walcek, Chris

    2016-09-01

    Ozone (O3) concentrations measured at Pinnacle State Park (PSPNY), very close to the southern border of New York State, are used to estimate concentrations in air flowing into New York. On 20% of the ozone season (April-September) afternoons from 2004 to 2015, mid-afternoon 500-m back trajectories calculated from PSPNY cross New York border from the south and spend less than three hours in New York State, in this area of negligible local pollution emissions. One-hour (2p.m.-3p.m.) O3 concentrations during these inflowing conditions were 46 ± 13 ppb, and ranged from a minimum of 15 ppb to a maximum of 84 ppb. On average during 2004-2015, each year experienced 11.8 days with inflowing 1-hr O3 concentrations exceeding 50 ppb, 4.3 days with O3 > 60 ppb, and 1.5 days had O3 > 70 ppb. During the same period, 8-hr average concentrations (10a.m. to 6p.m.) exceeded 50 ppb on 10.0 days per season, while 3.9 days exceeded 60 ppb, and 70 ppb was exceeded 1.2 days per season. Two afternoons of minimal in-state emission influences with high ozone concentrations were analyzed in more detail. Synoptic and back trajectory analysis, including comparison with upwind ozone concentrations, indicated that the two periods were characterized as photo-chemically aged air containing high inflowing O3 concentrations most likely heavily influenced by pollution emissions from states upwind of New York including Pennsylvania, Tennessee, West Virginia, and Ohio. These results suggest that New York state-level attempts to comply with National Ambient Air Quality Standards by regulating in-state O3 precursor NOx and organic emissions would be very difficult, since air frequently enters New York State very close to or in excess of Federal Air Quality Standards.

  10. 3D Numerical Simulation of Turbulent Buoyant Flow and Heat Transport in a Curved Open Channel

    Technology Transfer Automated Retrieval System (TEKTRAN)

    A three-dimensional buoyancy-extended version of kappa-epsilon turbulence model was developed for simulating the turbulent flow and heat transport in a curved open channel. The density- induced buoyant force was included in the model, and the influence of temperature stratification on flow field was...

  11. Computation of turbulent channel flow using Large-Eddy Interaction Model

    NASA Technical Reports Server (NTRS)

    Hong, S. K.; Payne, F. R.

    1987-01-01

    The objective of the paper is to investigate the nature and values of closure parameters appearing in the proposed Large-Eddy Interaction Model for prediction of turbulent flow field. Effects of two closure parameters on predicted Reynolds stresses and other turbulence structural quantities are examined for channel flows at two Reynolds numbers.

  12. Direct numerical simulation of sharkskin denticles in turbulent channel flow

    NASA Astrophysics Data System (ADS)

    Boomsma, A.; Sotiropoulos, F.

    2016-03-01

    The hydrodynamic function of sharkskin has been under investigation for the past 30 years. Current literature conflicts on whether sharkskin is able to reduce skin friction similar to riblets. To contribute insights toward reconciling these conflicting views, direct numerical simulations are carried out to obtain detailed flow fields around realistic denticles. A sharp interface immersed boundary method is employed to simulate two arrangements of actual sharkskin denticles (from Isurus oxyrinchus) in a turbulent boundary layer at Reτ ≈ 180. For comparison, turbulent flow over drag-reducing scalloped riblets is also simulated with similar flow conditions and with the same numerical method. Although the denticles resemble riblets, both sharkskin arrangements increase total drag by 44%-50%, while the riblets reduce drag by 5%. Analysis of the simulated flow fields shows that the turbulent flow around denticles is highly three-dimensional and separated, with 25% of the total drag being form drag. The complex three-dimensional shape of the denticles gives rise to a mean flow dominated by strong secondary flows in sharp contrast with the mean flow generated by riblets, which is largely two-dimensional. The so resulting three-dimensionality of sharkskin flows leads to an increase in the magnitude of the turbulent statistics near the denticles, which further contributes to increasing the total drag. The simulations also show that, at least for the simulated arrangements, sharkskin, in sharp contrast with drag-reducing riblets, is unable to isolate high shear stress near denticle ridges causing a significant portion of the denticle surface to be exposed to high mean shear.

  13. Estimates of the Range in Flow Velocities Associated with the Circum-Chryse Outflow Channels

    NASA Astrophysics Data System (ADS)

    Craddock, R. A.; Tanaka, K. L.

    1996-03-01

    To know what we're getting out of the Mars Pathfinder "grab bag" landing site it is imperative that the detailed geology and hydraulic history of the circum-Chryse outflow channel complex be understood ahead of time. Crude estimates of the maximum channel flow velocities can be made simply by knowing the depth and slopes of the outflow channels themselves. Although these characteristics have been derived in part by stereophotogrammetry, they are subject to a considerable amount of error. Fortunately some Earth-based radar data exist which are both reasonably accurate and provide the spatial coverage necessary for determining the slopes of some of the channels. Using these data, the bed shear stress of a flow, or the retarding stress at the base of a flow, Tb, can be estimated from the depth-slope formula ~b = pghS where p is the density of the fluid, g is gravitational acceleration, h is the flow (or channel) depth, and S is the slope of the channel. This is equal to the bottom stress created by a flow, tau, where tau = pCf-u2 and Cf is a dimensionless drag coefficient and u is the mean flow velocity. Thus, the mean flow velocity for a channel can be calculated from -u = (ghS/Cf) 1/2. The dimensionless drag coefficient can be adjustment for gravity by the expression Cf = g(n21hll3) where n is the Manning roughness coefficient (units of s/ml/2), which has been derived empirically from terrestrial observations. Application of an appropriate Manning roughness coefficient, n, to Martian outflow channels is uncertain, so a range of reasonable values (0.015 to 0.035) is used. Estimates of the mean flow velocities were calculated from this method, however, at best these represent maximum values. Large-scale geologic mapping indicates that most channels were subjected to multiple episodes of flooding, which suggests that the channels may not have been completely full of water at any one time (i.e., bankfull discharge). This method is also not directly applicable to Simud

  14. Turbulent jet flow in a channel with a circulation region

    NASA Astrophysics Data System (ADS)

    Glebov, G. A.; Petrov, V. N.

    1985-01-01

    An approximation method is proposed for calculating flows resulting from the interaction between a turbulent jet and a slipstream inside a duct, including the case where a back stream is formed near the wall. In accordance with the approach proposed here, the velocity profile in the mixing region is determined using the well known method of the polynomial approximation of the Reynolds shear stress profile in the duct cross-sections. The flow parameters are then determined using integral equations of flow rate and momentum. The results obtained using the approximation method are found to be in good agreement with experiment data.

  15. Residence time of water film and slug flow features in fuel cell gas channels and their effect on instantaneous area coverage ratio

    NASA Astrophysics Data System (ADS)

    Lorenzini-Gutierrez, Daniel; Kandlikar, Satish G.; Hernandez-Guerrero, Abel; Elizalde-Blancas, Francisco

    2015-04-01

    Water in the gas channels of a Proton Exchange Membrane Fuel Cell is modeled as slugs and film, and removal mechanisms for these flow patterns are numerically investigated. The removal of excess liquid water is simulated using computational fluid dynamics (CFD) through the volume of fluid (VOF) model. The computational domain consists of a gas flow channel appropriate for commercial stacks for automotive applications. The effects of superficial air velocity, channel surface wettability, and channel cross-section geometry are investigated through quantitative comparison of two-phase pressure drop, area coverage ratio (ACR) over the gas diffusion layer (GDL) and liquid removal time. Top wall film flow was identified as a desirable feature since it did not cover the GDL and facilitated transport of oxygen to the reaction sites while removing the water. A range of hydrophilic channel walls in combination with a hydrophobic GDL is proposed to promote this behavior while reducing the fluctuations in two-phase pressure drop for different contact angles. Additional enhancements to liquid water removal were associated with the channel cross-section geometry. An alternative trapezoidal shape is suggested for improved top wall film flow while improving the manufacturability of the bipolar plates for mass production.

  16. Improved Determination of Surface and Atmospheric Temperatures Using Only Shortwave AIRS Channels

    NASA Technical Reports Server (NTRS)

    Susskind,Joel

    2009-01-01

    AIRS was launched on EOS Aqua on May 4, 2002, together with AMSU-A and HSB, to form a next generation polar orbiting infrared and microwave atmospheric sounding system. AIRS is a grating spectrometer with a number of linear arrays of detectors with each detector sensitive to outgoing radiation in a characteristic frequency v(sub i) with a spectral band pass delta v(sub i) of roughly v(sub i) /1200. AIRS contains 2378 spectral channels covering portions of the spectral region 650 cm(exp -1) (15.38 gm) - 2665 cm(exp -1)' (3.752 micrometers). These spectral regions contain significant absorption features from two CO2 absorption bands, the 15 micrometer (longwave) CO2 band, and the 4.3 micrometer (shortwave) CO, absorption band. There are also two atmospheric window regions, the 12 micrometerm - 8 micrometer (longwave) window, and the 4.17 micrometer - 3.75 micrometer (shortwave) window. Historically, determination of surface and atmospheric temperatures from satellite observations was performed using primarily observations in the longwave window and CO2 absorption regions. One reason for this was concerns about the effects, during the day, of reflected sunlight and non-Local Thermodynamic Equilibrium (non-LTE) on the observed radiances in the shortwave portion of the spectrum. According to cloud clearing theory, more accurate soundings of both surface skin and atmospheric temperatures can be obtained under partial cloud cover conditions if one uses the longwave channels to determine cloud cleared radiances R(sub i) for all channels, and uses R(sub i) only from shortwave channels in the determination of surface and atmospheric temperatures. This procedure is now being used by the AIRS Science Team in preparation for the AIRS Version 6 Retrieval Algorithm. This paper describes how the effects on the radiances of solar radiation reflected by clouds and the Earth's surface, and also of non-LTE, are accounted for in the analysis of the data. Results are presented for both

  17. Nonmodal instability of a stratified plane-channel suspension flow with fine particles.

    PubMed

    Boronin, Sergei A; Osiptsov, Alexander N

    2016-03-01

    We consider the nonmodal instability and transient growth of small disturbances in a plane-channel suspension flow with a nonuniform concentration profile of fine noncolloidal particles accumulated in two localized layers, symmetric about the channel axis. A single-velocity model of an effective Newtonian fluid with a finite particle volume fraction is employed. It is established that fine particles distributed nonuniformly in the main flow significantly modify the growth rate of the first mode in a wide range of governing parameters. The most pronounced destabilizing effect is produced by the particles localized in the vicinity of the walls. A parametric study of the so-called optimal disturbances showed that they are streaks elongated in the flow direction, similar to the optimal disturbances in the flow devoid of particles. The transverse wave number of the optimal disturbances depends strongly on the location of the particle layers. Even when the particle mass concentration (averaged over the channel cross section) is small (of the order of a percent) and the particles are localized in the middle between the walls and the channel axis, the energy of the optimal disturbances is by several orders of magnitude larger than in dusty-gas and pure-fluid flows. When the particle layers are located in the vicinity of the walls or the channel axis, the nonmodal instability mechanism is less pronounced, as compared to the flow devoid of particles. PMID:27078447

  18. Flow characteristics on the blade channel vortex in the Francis turbine

    NASA Astrophysics Data System (ADS)

    Guo, P. C.; Wang, Z. N.; Luo, X. Q.; Wang, Y. L.; Zuo, J. L.

    2016-05-01

    Depending on the long-term hydraulic development of Francis turbine, the blade channel vortex phenomenon was investigated systematically from hydraulic design, experimental and numerical computation in this paper. The blade channel vortex difference between the high water head and low water head turbine was also analyzed. Meanwhile, the relationship between the blade channel vortex and the operating stability of hydraulic turbine was also investigated. The results show that the phenomenon of blade channel vortex is an intrinsic property for Francis turbine under small flow rate condition, the turning-point of the blade channel vortex inception curve appears at low unit speed region, and the variation trend of the blade channel vortex inception curve is closely related to the blade inlet edge profile. In addition to, the vortex of the high water head turbine can generally be excluded from the stable operation region, while which is more different for the one of the low water head turbine.

  19. Pressure drop of two-phase dry-plug flow in round mini-channels: Effect of moving contact line

    SciTech Connect

    Lee, Chi Young; Lee, Sang Yong

    2010-01-15

    In the present experimental study, the pressure drop of the two-phase dry-plug flow (dry wall condition at the gas portions) in round mini-channels was investigated. The air-water mixtures were flowed through the round mini-channels made of polyurethane and Teflon, respectively, with their inner diameters ranging from 1.62 to 2.16 mm. In the dry-plug flow regime, the pressure drop measured became larger either by increasing the liquid superficial velocity or by decreasing the gas superficial velocity due to the increase of the number of the moving contact lines in the test section. In such a case, the role of the moving contact lines turned out to be significant. Therefore, a pressure drop model of dry-plug flow was proposed through modification of the dynamic contact angle analysis taking account of the energy dissipation by the moving contact lines, which represents the experimental data within the mean deviation of 4%. (author)

  20. Flow-dependent channel formation in clots by an erythrocyte-bound fibrinolytic agent

    PubMed Central

    Gersh, Kathryn C.; Zaitsev, Sergei; Cines, Douglas B.; Muzykantov, Vladimir

    2011-01-01

    Studies in animal models have shown that plasminogen activators bound to erythrocytes (RBC-PA) have an extended lifetime in the circulation and are safer than free PAs. RBC-PAs incorporate into nascent thrombi, which are focally lysed from within, an attractive thromboprophylactic option. In static systems, RBC-PAs cleave surrounding fibrin fibers, forming pores larger than the cells themselves, and move around the pore edges, enlarging them until eventual clot dissolution. We hypothesized that under flow in blood vessels, RBC-PAs form functional patent channels before clot dissolution. Here we used perfusion chambers to study clot lysis by RBC-PAs under static versus arterial and venous flow conditions. We found that flow decelerates bulk clot lysis but quickly generates patent channels filled with passing RBCs, via pore enlargement and merging in the direction of flow. Formation of such channels by RBC-PAs may help rescue ischemic tissue before bulk dissolution of potentially occlusive clots. PMID:21389322

  1. Onset of unsteady flow in wavy walled channels at low Reynolds number

    NASA Astrophysics Data System (ADS)

    Shah, Tapan; Mills, Zachary; Alexeev, Alexander

    2014-11-01

    Using computational modeling, we examine the development of an unsteady laminar flow of a Newtonian fluid in a channel with sinusoidal walls, driven by a constant pressure gradient. The lattice Boltzmann method was used as our computational model. Our simulations revealed two types of unsteady flows occurring in sinusoidal channels. When the amplitude of the wavy walls is relatively small, vortices forming in the channel furrows are shed downstream. For larger wall wave amplitudes, vortices remain inside the furrows and exhibit periodic oscillations and topological changes. Our simulations establish the optimum wall amplitude and period leading to an unsteady flow at the minimum pressure gradient. The results are important for designing laminar heat/mass exchangers utilizing unsteady flows for enhancing transport processes. This work is supported by General Motors Corporation.

  2. Extended plasma channels created by UV laser in air and their application to control electric discharges

    SciTech Connect

    Zvorykin, V. D. Ionin, A. A.; Levchenko, A. O.; Seleznev, L. V.; Sinitsyn, D. V.; Smetanin, I. V.; Ustinovskii, N. N.; Shutov, A. V.

    2015-02-15

    Results are presented from a series of experimental and theoretical studies on creating weakly ionized extended plasma channels in atmospheric air by 248-nm UV laser radiation and their application to control long high-voltage discharges. The main mechanisms of air ionization by UV laser pulses with durations from 100 fs to 25 ns and intensities in the ranges of 3×10{sup 11}–1.5×10{sup 13} and 3×10{sup 6}–3×10{sup 11} W/cm{sup 2}, respectively, which are below the threshold for optical gas breakdown, as well as the main relaxation processes in plasma with a density of 10{sup 9}–10{sup 17} cm{sup −3}, are considered. It is shown that plasma channels in air can be efficiently created by amplitude-modulated UV pulses consisting of a train of subpicosecond pulses producing primary photoelectrons and a long UV pulse suppressing electron attachment and sustaining the density of free electrons in plasma. Different modes of the generation and amplification of trains of subterawatt subpicosecond pulses and amplitude-modulated UV pulses with an energy of several tens of joules were implemented on the GARPUN-MTW hybrid Ti:sapphire-KrF laser facility. The filamentation of such UV laser beams during their propagation in air over distances of up to 100 m and the parameters of the corresponding plasma channels were studied experimentally and theoretically. Laser initiation of high-voltage electric discharges and control of their trajectories by means of amplitude-modulated UV pulses, as well as the spatiotemporal structure of breakdowns in air gaps with length of up to 80 cm, were studied.

  3. Flow visualization study in high aspect ratio cooling channels for rocket engines

    NASA Technical Reports Server (NTRS)

    Meyer, Michael L.; Giuliani, James E.

    1993-01-01

    The structural integrity of high pressure liquid propellant rocket engine thrust chambers is typically maintained through regenerative cooling. The coolant flows through passages formed either by constructing the chamber liner from tubes or by milling channels in a solid liner. Recently, Carlile and Quentmeyer showed life extending advantages (by lowering hot gas wall temperatures) of milling channels with larger height to width aspect ratios (AR is greater than 4) than the traditional, approximately square cross section, passages. Further, the total coolant pressure drop in the thrust chamber could also be reduced, resulting in lower turbomachinery power requirements. High aspect ratio cooling channels could offer many benefits to designers developing new high performance engines, such as the European Vulcain engine (which uses an aspect ratio up to 9). With platelet manufacturing technology, channel aspect ratios up to 15 could be formed offering potentially greater benefits. Some issues still exist with the high aspect ratio coolant channels. In a coolant passage of circular or square cross section, strong secondary vortices develop as the fluid passes through the curved throat region. These vortices mix the fluid and bring lower temperature coolant to the hot wall. Typically, the circulation enhances the heat transfer at the hot gas wall by about 40 percent over a straight channel. The effect that increasing channel aspect ratio has on the curvature heat transfer enhancement has not been sufficiently studied. If the increase in aspect ratio degrades the secondary flow, the fluid mixing will be reduced. Analysis has shown that reduced coolant mixing will result in significantly higher wall temperatures, due to thermal stratification in the coolant, thus decreasing the benefits of the high aspect ratio geometry. A better understanding of the fundamental flow phenomena in high aspect ratio channels with curvature is needed to fully evaluate the benefits of this

  4. Thermal analysis and two-directional air flow thermal management for lithium-ion battery pack

    NASA Astrophysics Data System (ADS)

    Yu, Kuahai; Yang, Xi; Cheng, Yongzhou; Li, Changhao

    2014-12-01

    Thermal management is a routine but crucial strategy to ensure thermal stability and long-term durability of the lithium-ion batteries. An air-flow-integrated thermal management system is designed in the present study to dissipate heat generation and uniformize the distribution of temperature in the lithium-ion batteries. The system contains of two types of air ducts with independent intake channels and fans. One is to cool the batteries through the regular channel, and the other minimizes the heat accumulations in the middle pack of batteries through jet cooling. A three-dimensional anisotropic heat transfer model is developed to describe the thermal behavior of the lithium-ion batteries with the integration of heat generation theory, and validated through both simulations and experiments. Moreover, the simulations and experiments show that the maximum temperature can be decreased to 33.1 °C through the new thermal management system in comparison with 42.3 °C through the traditional ones, and temperature uniformity of the lithium-ion battery packs is enhanced, significantly.

  5. Air-flow separation over unsteady breaking wind waves

    NASA Astrophysics Data System (ADS)

    Saxena, Gaurav

    2005-11-01

    In air-sea interaction processes, when considering wind stress over small-scale breaking waves, there are few direct quantitative experimental investigations into the role of air-flow separation on the interfacial momentum flux. Reul et. al, (1999), found multiple coherent patches of vorticity downwind of the crest that were strongly influenced by the geometric characteristics of the breaker. However, their breakers were generated by dispersive focusing techniques and, therefore, independent of the wind stress. We present experimental results obtained with particle image velocimetry (PIV) where moderate to strong winds directly generate unsteady small-scale breaking waves, a scenario commonly found in the open ocean. Particular attention has been devoted to capturing the spatio-temporal evolution of the air-water interface. Specifically, texture segmentation algorithms typically used for face recognition (Grey Level Co-occurrence Matrix (GLCM) and the Cross-Diagonal Texture Matrix (CDTM)) have been combined to yield robust and accurate estimates of the instantaneous breaker geometry.

  6. Numerical simulation of air flow in a model of lungs with mouth cavity

    NASA Astrophysics Data System (ADS)

    Elcner, Jakub; Lizal, Frantisek; Jedelsky, Jan; Jicha, Miroslav

    2012-04-01

    The air flow in a realistic geometry of human lung is simulated with computational flow dynamics approach as stationary inspiration. Geometry used for the simulation includes oral cavity, larynx, trachea and bronchial tree up to the seventh generation of branching. Unsteady RANS approach was used for the air flow simulation. Velocities corresponding to 15, 30 and 60 litres/min of flow rate were set as boundary conditions at the inlet to the model. These flow rates are frequently used as a representation of typical human activities. Character of air flow in the model for these different flow rates is discussed with respect to future investigation of particle deposition.

  7. Transient receptor potential (TRP) channels, vascular tone and autoregulation of cerebral blood flow.

    PubMed

    Brayden, Joseph E; Earley, Scott; Nelson, Mark T; Reading, Stacey

    2008-09-01

    Members of the transient receptor potential (TRP) channel superfamily are present in vascular smooth muscle cells and play important roles in the regulation of vascular contractility. The TRPC3 and TRPC6 channels are activated by stimulation of several excitatory receptors in vascular smooth muscle cells. Activation of these channels leads to myocyte depolarization, which stimulates Ca2+ entry via voltage-dependent Ca2+ channels (VDCC), leading to vasoconstriction. The TRPV4 channels in arterial myocytes are activated by epoxyeicosatrienoic acids, and activation of the channels enhances Ca2+ spark and transient Ca2+-sensitive K+ channel activity, thereby hyperpolarizing and relaxing vascular smooth muscle cells. The TRPC6 and TRPM4 channels are activated by mechanical stimulation of cerebral artery myocytes. Subsequent depolarization and activation of VDCC Ca2+ entry is directly linked to the development of myogenic tone in vitro and to autoregulation of cerebral blood flow in vivo. These findings imply a fundamental importance of TRP channels in the regulation of vascular smooth muscle tone and suggest that TRP channels could be important targets for drug therapy under conditions in which vascular contractility is disturbed (e.g. hypertension, stroke, vasospasm). PMID:18215190

  8. Graphical User Interface Development for Representing Air Flow Patterns

    NASA Technical Reports Server (NTRS)

    Chaudhary, Nilika

    2004-01-01

    In the Turbine Branch, scientists carry out experimental and computational work to advance the efficiency and diminish the noise production of jet engine turbines. One way to do this is by decreasing the heat that the turbine blades receive. Most of the experimental work is carried out by taking a single turbine blade and analyzing the air flow patterns around it, because this data indicates the sections of the turbine blade that are getting too hot. Since the cost of doing turbine blade air flow experiments is very high, researchers try to do computational work that fits the experimental data. The goal of computational fluid dynamics is for scientists to find a numerical way to predict the complex flow patterns around different turbine blades without physically having to perform tests or costly experiments. When visualizing flow patterns, scientists need a way to represent the flow conditions around a turbine blade. A researcher will assign specific zones that surround the turbine blade. In a two-dimensional view, the zones are usually quadrilaterals. The next step is to assign boundary conditions which define how the flow enters or exits one side of a zone. way of setting up computational zones and grids, visualizing flow patterns, and storing all the flow conditions in a file on the computer for future computation. Such a program is necessary because the only method for creating flow pattern graphs is by hand, which is tedious and time-consuming. By using a computer program to create the zones and grids, the graph would be faster to make and easier to edit. Basically, the user would run a program that is an editable graph. The user could click and drag with the mouse to form various zones and grids, then edit the locations of these grids, add flow and boundary conditions, and finally save the graph for future use and analysis. My goal this summer is to create a graphical user interface (GUI) that incorporates all of these elements. I am writing the program in

  9. A Self-Replication Model for Long Channelized Lava Flows on the Mars Plains

    NASA Technical Reports Server (NTRS)

    Baloga, S. M.; Glaze, L. S.

    2008-01-01

    A model is presented for channelized lava flows emplaced by a self-replicating, levee-building process over long distances on the plains of Mars. Such flows may exhibit morphologic evidence of stagnation, overspills, and upstream breakouts. However, these processes do not inhibit the formation and persistence of a prominent central channel that can often be traced for more than 100 km. The two central assumptions of the self-replication model are (1) the flow advances at the average upstream velocity of the molten core and (2) the fraction of the lava that travels faster than the average upstream velocity forms stationary margins in the advancing distal zone to preserve the self-replication process. For an exemplary 300 km long flow north of Pavonis Mons, the model indicates that 8 m of crust must have formed during emplacement, as determined from the channel and levee dimensions. When combined with independent thermal dynamic estimates for the crustal growth rate, relatively narrow constraints are obtained for the flow rate (2250 m3 s 1), emplacement duration (600 d), and the lava viscosity of the molten interior (106 Pa s). Minor, transient overspills and breakouts increase the emplacement time by only a factor of 2. The primary difference between the prodigious channelized Martian flows and their smaller terrestrial counterparts is that high volumetric flow rates must have persisted for many hundreds of days on Mars, in contrast to a few hours or days on Earth.

  10. The LES of the channel flow in a non aligned system of coordinates

    NASA Astrophysics Data System (ADS)

    Germano, Massimo; Abbà, Antonella

    2010-11-01

    The plane channel flow continues to be a very important test case for the verification and the validation of LES. In the channel flow test there is a privileged direction, usually one reference axis is oriented along the stream and the size of the computational box is increased in the streamwise direction in order to capture correctly the dominant turbulent structures and to produce a fully developed flow. All that is peculiar of this particular test, and in this paper we will investigate the sensitivity of the channel test to the particular alignment of the coordinate system with the mean flow. In a non aligned system of coordinates there is no privileged direction, there are two components of the forcing term, the mean pressure gradient, and the homogeneities of the Reynolds stresses are destroyed. In our paper we simulate the channel flow in a rotated system of coordinates, and we compare the results with the stream aligned data. We think that this test could evidence the flexibility of different LES codes and LES subgrid models to simulate the turbulent flow and to capture the correct statistical values in non aligned conditions. The first preliminary results are slightly contradictory: the resolved Reynolds stresses seem degraded while the mean flow is better predicted. The dynamic anisotropic subgrid model of Abbà, Cercignani and Valdettaro seems well fitted to represent correctly the large scales in non aligned conditions.

  11. Visualization of Secondary Flow Development in High Aspect Ratio Channels with Curvature

    NASA Technical Reports Server (NTRS)

    Meyer, Michael L.; Giuliani, James E.

    1994-01-01

    The results of an experimental project to visually examine the secondary flow structure that develops in curved, high aspect-ratio rectangular channels are presented. The results provide insight into the fluid dynamics within high aspect ratio channels. A water flow test rig constructed out of plexiglass, with an adjustable aspect ratio, was used for these experiments. Results were obtained for a channel geometry with a hydraulic diameter of 10.6 mm (0.417 in.), an aspect ratio of 5.0, and a hydraulic radius to curvature radius ratio of 0.0417. Flow conditions were varied to achieve Reynolds numbers up to 5,100. A new particle imaging velocimetry technique was developed which could resolve velocity information from particles entering and leaving the field of view. Time averaged secondary flow velocity vectors, obtained using this velocimetry technique, are presented for 30 degrees, 60 degrees, and 90 degrees into a 180 degrees bend and at a Reynolds number of 5,100. The secondary flow results suggest the coexistence of both the classical curvature induced vortex pair flow structure and the eddies seen in straight turbulent channel flow.

  12. Self-adjustment of stream bed roughness and flow velocity in a steep mountain channel

    NASA Astrophysics Data System (ADS)

    Schneider, Johannes M.; Rickenmann, Dieter; Turowski, Jens M.; Kirchner, James W.

    2015-10-01

    Understanding how channel bed morphology affects flow conditions (and vice versa) is important for a wide range of fluvial processes and practical applications. We investigated interactions between bed roughness and flow velocity in a steep, glacier-fed mountain stream (Riedbach, Ct. Valais, Switzerland) with almost flume-like boundary conditions. Bed gradient increases along the 1 km study reach by roughly 1 order of magnitude (S = 3-41%), with a corresponding increase in streambed roughness, while flow discharge and width remain approximately constant due to the glacial runoff regime. Streambed roughness was characterized by semivariograms and standard deviations of point clouds derived from terrestrial laser scanning. Reach-averaged flow velocity was derived from dye tracer breakthrough curves measured by 10 fluorometers installed along the channel. Commonly used flow resistance approaches (Darcy-Weisbach equation and dimensionless hydraulic geometry) were used to relate the measured bulk velocity to bed characteristics. As a roughness measure, D84 yielded comparable results to more laborious measures derived from point clouds. Flow resistance behavior across this large range of steep slopes agreed with patterns established in previous studies for both lower-gradient and steep reaches, regardless of which roughness measures were used. We linked empirical critical shear stress approaches to the variable power equation for flow resistance to investigate the change of bed roughness with channel slope. The predicted increase in D84 with increasing channel slope was in good agreement with field observations.

  13. Effects of roughness on density-weighted particle statistics in turbulent channel flows

    NASA Astrophysics Data System (ADS)

    Milici, Barbara

    2015-12-01

    The distribution of inertial particles in turbulent flows is strongly influenced by the characteristics of the coherent turbulent structures which develop in the carrier flow field. In wall-bounded flows, these turbulent structures, which control the turbulent regeneration cycles, are strongly affected by the roughness of the wall, nevertheless its effects on the particle transport in two-phase turbulent flows has been still poorly investigated. The issue is discussed here by addressing DNS combined with LPT to obtain statistics of velocity and preferential accumulation of a dilute dispersion of heavy particles in a turbulent channel flow, bounded by irregular two-dimensional rough surfaces, in the one-way coupling regime.

  14. Effects of roughness on density-weighted particle statistics in turbulent channel flows

    SciTech Connect

    Milici, Barbara

    2015-12-31

    The distribution of inertial particles in turbulent flows is strongly influenced by the characteristics of the coherent turbulent structures which develop in the carrier flow field. In wall-bounded flows, these turbulent structures, which control the turbulent regeneration cycles, are strongly affected by the roughness of the wall, nevertheless its effects on the particle transport in two-phase turbulent flows has been still poorly investigated. The issue is discussed here by addressing DNS combined with LPT to obtain statistics of velocity and preferential accumulation of a dilute dispersion of heavy particles in a turbulent channel flow, bounded by irregular two-dimensional rough surfaces, in the one-way coupling regime.

  15. A Rotary Flow Channel for Shear Stress Sensor Calibration

    NASA Technical Reports Server (NTRS)

    Zuckerwar, Allan J.; Scott, Michael A.

    2004-01-01

    A proposed shear sensor calibrator consists of a rotating wheel with the sensor mounted tangential to the rim and positioned in close proximity to the rim. The shear stress generated by the flow at the sensor position is simply tau(sub omega) = (mu)r(omega)/h, where mu is the viscosity of the ambient gas, r the wheel radius, omega the angular velocity of the wheel, and h the width of the gap between the wheel rim and the sensor. With numerical values of mu = 31 (mu)Pa s (neon at room temperature), r = 0.5 m, omega = 754 /s (7200 rpm), and h = 50.8 m, a shear stress of tau(sub omega) = 231 Pa can be generated. An analysis based on one-dimensional flow, with the flow velocity having only an angular component as a function of the axial and radial coordinates, yields corrections to the above simple formula for the curvature of the wheel, flatness of the sensor, and finite width of the wheel. It is assumed that the sensor mount contains a trough (sidewalls) to render a velocity release boundary condition at the edges of the rim. The Taylor number under maximum flow conditions is found to be 62.3, sufficiently low to obviate flow instability. The fact that the parameters entering into the evaluation of the shear stress can be measured to high accuracy with well-defined uncertainties makes the proposed calibrator suitable for a physical standard for shear stress calibration.

  16. Considerations of Air Flow in Combustion Chambers of High-Speed Compression-Ignition Engines

    NASA Technical Reports Server (NTRS)

    Spanogle, J A; Moore, C S

    1932-01-01

    The air flow in combustion chambers is divided into three fundamental classes - induced, forced, and residual. A generalized resume is given of the present status of air flow investigations and of the work done at this and other laboratories to determine the direction and velocity of air movement in auxiliary and integral combustion chambers. The effects of air flow on engine performance are mentioned to show that although air flow improves the combustion efficiency, considerable induction, friction, and thermal losses must be guarded against.

  17. Generation of extended plasma channels in air using femtosecond Bessel beams.

    PubMed

    Polynkin, Pavel; Kolesik, Miroslav; Roberts, Adam; Faccio, Daniele; Di Trapani, Paolo; Moloney, Jerome

    2008-09-29

    Extending the longitudinal range of plasma channels created by ultrashort laser pulses in atmosphere is important in practical applications of laser-induced plasma such as remote spectroscopy and lightning control. Weakly focused femtosecond Gaussian beams that are commonly used for generating plasma channels offer only a limited control of filamentation. Increasing the pulse energy in this case typically results in creation of multiple filaments and does not appreciably extend the longitudinal range of filamentation. Bessel beams with their extended linear foci intuitively appear to be better suited for generation of long plasma channels. We report experimental results on creating extended filaments in air using femtosecond Bessel beams. By probing the linear plasma density along the filament, we show that apertured Bessel beams produce stable single plasma channels that span the entire extent of the linear focus of the beam. We further show that by temporally chirping the pulse, the plasma channel can be longitudinally shifted beyond the linear-focus zone, an important effect that may potentially offer additional means of controlling filament formation. PMID:18825212

  18. Hydrodynamic Coupling in Microbially Mediated Fracture Mineralization: Formation of Self-Organized Groundwater Flow Channels

    NASA Astrophysics Data System (ADS)

    Lunn, R. J.; El Mountassir, G.; MacLachlan, E.; Moir, H.

    2013-12-01

    Evidence of fossilized microorganisms embedded within mineral veins and mineral-filled fractures has been observed in a wide range of geological environments. Microorganisms can act as sites for mineral nucleation and also contribute to mineral precipitation by inducing local geochemical changes. In this study, we explore fundamental controls on microbially induced mineralization in rock fractures. Specifically, we systematically investigate the influence of hydrodynamics (velocity, flow rate, aperture) on microbially mediated calcite precipitation. We use a case study of microbially induced calcite precipitation as a model biomineralization system to investigate potential feedback mechanisms between the temporally varying patterns of mineral precipitation within a fracture and the resulting variations in the local velocity field. Fractures are represented as a series of precision-etched parallel channels between a pair of sealed Perspex plates. Multiple channels are designed to maintain a constant flow rate, whilst independently adjusting channel aperture and width to explore the effects of aperture and fluid velocity on biomineral precipitation. Our experimental results demonstrate that a feedback mechanism exists between the gradual reduction in fracture aperture due to precipitation, and its effect on the local fluid velocity. This feedback results in mineral fill distributions that focus flow into a small number of self-organizing channels that remain open, ultimately controlling the final aperture profile that governs flow within the fracture. This feedback mechanism exists because precipitation on the fracture walls (as opposed to in solution) requires the bacteria to be transported to the fracture surface. Bacteria settle out of a quiescent solution at a velocity that is dependent on individual floc size and density. This settling velocity competes with the bed shear velocity, inhibiting deposition via entrainment. As precipitation progresses, the flow

  19. Dry Flowing Abrasive Decontamination Technique for Pipe Systems with Swirling Air Flow

    SciTech Connect

    Kameo, Yutaka; Nakashima, Mikio; Hirabayashi, Takakuni

    2003-10-15

    A dry abrasive decontamination method was developed for removing radioactive corrosion products from surfaces of coolant pipe systems in decommissioning of a nuclear power plant. Erosion behavior of inside surfaces of stainless and carbon steel pipes by a swirling air flow containing alumina or cast-iron grit abrasive was studied. Erosion depths of the test pipes were approximately proportional to an abrasive concentration in air and an exponent of flow rate of airstream. The experimental results indicated that the present method could keep satisfactory erosion ability of abrasives even for a large-size pipe. The present method was successfully applied to {sup 60}Co-contaminated specimens sampled from a pipe of the water cleanup system of the Japan Power Demonstration Reactor.

  20. Simulation of air gap vibration on aerostatic bearing under flow/structure coupled conditions

    NASA Astrophysics Data System (ADS)

    Wang, Qian; Wu, Jianjin; Li, Dongsheng

    2008-10-01

    The vibration of aerostatic bearing air gap is one of the main factors, which restricts the precision of nano-processing and nano-measurement. Finite volume method was employed to obtain the air gap steady flow of different air gap thicknesses for the demonstration of vibrations under flow/structure coupled conditions. The unsteady flow of air gap was analyzed numerically by using the air gap flow & boundary movement control equations to get the pressure distribution on the slide surface and the amplitude of air gap for further study on the self-excited vibration of aerostatic bearings. Numerical analyses show that the highest aerostatic bearing amplitude is relative to the difference between load capacity and gravity at the initial moment as air gap rises, and the final air gap thickness has nothing to do with the initial air gap thickness. The results presented a new analytic demonstration for the research on the reduction of aerostatic bearing vibration.

  1. Empirical Formulation of Flow Characteristics in Trapezoidal Channels

    NASA Astrophysics Data System (ADS)

    Gandhi, S.; Singh, R. P.

    2016-05-01

    Empirical relations for hydraulic jump characteristics, viz. sequent depth ratio (Y2/Y1), efficiency of jump (E2/E1) and relative length of jump (Lj/Y1) in trapezoidal channel with/without appurtenances are developed by introducing dimensionless Reynolds number, and neglecting the frictional effect for approach Froude number (varied between 2 and 10 under different conditions). Developed empirical models were also validated and compared with acquired experimental data as well as with literature data. Close fitness of the empirical models with appurtenances under varying dimensions, positions of baffle blocks provides accurate prediction of same for higher value of Froude number.

  2. Air-structure coupling features analysis of mining contra-rotating axial flow fan cascade

    NASA Astrophysics Data System (ADS)

    Chen, Q. G.; Sun, W.; Li, F.; Zhang, Y. J.

    2013-12-01

    The interaction between contra-rotating axial flow fan blade and working gas has been studied by means of establishing air-structure coupling control equation and combining Computational Fluid Dynamics (CFD) and Computational solid mechanics (CSM). Based on the single flow channel model, the Finite Volume Method was used to make the field discrete. Additionally, the SIMPLE algorithm, the Standard k-ε model and the Arbitrary Lagrangian-Eulerian dynamic grids technology were utilized to get the airflow motion by solving the discrete governing equations. At the same time, the Finite Element Method was used to make the field discrete to solve dynamic response characteristics of blade. Based on weak coupling method, data exchange from the fluid solver and the solid solver was processed on the coupling interface. Then interpolation was used to obtain the coupling characteristics. The results showed that the blade's maximum amplitude was on the tip of the last-stage blade and aerodynamic force signal could reflect the blade working conditions to some extent. By analyzing the flow regime in contra-rotating axial flow fan, it could be found that the vortex core region was mainly in the blade surface, the hub and the blade clearance. In those regions, the turbulence intensity was very high. The last-stage blade's operating life is shorter than that of the pre-stage blade due to the fatigue fracture occurs much more easily on the last-stage blade which bears more stress.

  3. Laser ignition of hypersonic air-hydrogen flow

    NASA Astrophysics Data System (ADS)

    Brieschenk, S.; Kleine, H.; O'Byrne, S.

    2013-09-01

    An experimental investigation of the behaviour of laser-induced ignition in a hypersonic air-hydrogen flow is presented. A compression-ramp model with port-hole injection, fuelled with hydrogen gas, is used in the study. The experiments were conducted in the T-ADFA shock tunnel using a flow condition with a specific total enthalpy of 2.5 MJ/kg and a freestream velocity of 2 km/s. This study is the first comprehensive laser spark study in a hypersonic flow and demonstrates that laser-induced ignition at the fuel-injection site can be effective in terms of hydroxyl production. A semi-empirical method to estimate the conditions in the laser-heated gas kernel is presented in the paper. This method uses blast-wave theory together with an expansion-wave model to estimate the laser-heated gas conditions. The spatially averaged conditions found with this approach are matched to enthalpy curves generated using a standard chemical equilibrium code (NASA CEA). This allows us to account for differences that are introduced due to the idealised description of the blast wave, the isentropic expansion wave as well as thermochemical effects.

  4. MHD mixed convection flow through a diverging channel with heated circular obstacle

    NASA Astrophysics Data System (ADS)

    Alam, Md. S.; Shaha, J.; Khan, M. A. H.; Nasrin, R.

    2016-07-01

    A numerical study of steady MHD mixed convection heat transfer and fluid flow through a diverging channel with heated circular obstacle is carried out in this paper. The circular obstacle placed at the centre of the channel is hot with temperature Th. The top and bottom walls are non-adiabatic. The basic nonlinear governing partial differential equations are transformed into dimensionless ordinary differential equations using similarity transformations. These equations have been solved numerically for different values of the governing parameters, namely Reynolds number (Re), Hartmann number (Ha), Richardson number (Ri) and Prandtl number (Pr) using finite element method. The streamlines, isotherms, average Nusselt number and average temperature of the fluid for various relevant dimensionless parameters are displayed graphically. The study revealed that the flow and thermal fields in the diverging channel depend significantly on the heated body. In addition, it is observed that the magnetic field acts to increase the rate of heat transfer within the channel.

  5. Flow reversal and heat transfer of fully developed mixed convection in vertical channels

    NASA Astrophysics Data System (ADS)

    Cheng, Chin-Hsiang; Kou, Hong-Sen; Huang, Wen-Hsiung

    1990-07-01

    The present analysis is concerned with flow reversal phenomena and heat transfer characteristics of the fully developed laminar combined free and forced convection in the heated vertical channels. Three fundamental combinations of thermal boundary conditions on the respective wall surface (namely isoflux-isoflux, isoflux-isothermal, and isothermal-isothermal) are considered separately so as to investigate extensively their distinct influence on the flow pattern. Results of the velocity distribution and temperature distribution as well as the Nusselt number in terms of bulk mean temperature are carried out. Based on the analytical solutions obtained, flow reversal adjacent to the relatively colder wall is found to exist within the channel as Re/Gr is below a threshold value related to the thermal boundary conditions. Parameter zones for the occurrence of reversed flow are presented. Comparisons and verification are made using the existing numerical solutions at locations far downstream of developing flow.

  6. 40 CFR 1065.240 - Dilution air and diluted exhaust flow meters.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... meter, a thermal-mass meter, an averaging Pitot tube, or a hot-wire anemometer. (c) Flow conditioning... 40 Protection of Environment 33 2011-07-01 2011-07-01 false Dilution air and diluted exhaust flow...) AIR POLLUTION CONTROLS ENGINE-TESTING PROCEDURES Measurement Instruments Flow-Related...

  7. 40 CFR 1065.240 - Dilution air and diluted exhaust flow meters.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... meter, a thermal-mass meter, an averaging Pitot tube, or a hot-wire anemometer. (c) Flow conditioning... 40 Protection of Environment 32 2010-07-01 2010-07-01 false Dilution air and diluted exhaust flow...) AIR POLLUTION CONTROLS ENGINE-TESTING PROCEDURES Measurement Instruments Flow-Related...

  8. 40 CFR 1065.240 - Dilution air and diluted exhaust flow meters.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... meter, a thermal-mass meter, an averaging Pitot tube, or a hot-wire anemometer. (c) Flow conditioning... 40 Protection of Environment 34 2012-07-01 2012-07-01 false Dilution air and diluted exhaust flow...) AIR POLLUTION CONTROLS ENGINE-TESTING PROCEDURES Measurement Instruments Flow-Related...

  9. 40 CFR 1065.240 - Dilution air and diluted exhaust flow meters.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... meter, a thermal-mass meter, an averaging Pitot tube, or a hot-wire anemometer. (c) Flow conditioning... 40 Protection of Environment 34 2013-07-01 2013-07-01 false Dilution air and diluted exhaust flow...) AIR POLLUTION CONTROLS ENGINE-TESTING PROCEDURES Measurement Instruments Flow-Related...

  10. 40 CFR 1065.240 - Dilution air and diluted exhaust flow meters.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... meter, a thermal-mass meter, an averaging Pitot tube, or a hot-wire anemometer. (c) Flow conditioning... 40 Protection of Environment 33 2014-07-01 2014-07-01 false Dilution air and diluted exhaust flow...) AIR POLLUTION CONTROLS ENGINE-TESTING PROCEDURES Measurement Instruments Flow-Related...

  11. Log-Law scaling of a convective boundary layer in an unstably stratified turbulent channel flow

    NASA Astrophysics Data System (ADS)

    Scagliarini, Andrea; Einarsson, Halldor; Gylfason, Armann; Toschi, Federico

    2014-11-01

    Turbulent convection is ubiquitous in a variety of natural and industrial flows. In particular, convective motions may play a role in sheared flows. In this work, we are concerned with the interplay of buoyancy and shear in the dynamical boundary layer structure. The lattice Boltzmann Method (LBM) is applied to study numerically an unstably-stratified, fully developed, turbulent channel flow, driven by a longitudinal pressure gradient and with an imposed transverse wall temperature difference along the direction of gravity. Spanning the friction Reynolds (Retau <= 205) and Rayleigh numbers (Ra <= 1 . 3 ×107) we could systematically study the influence of the convection on the boundary layer structure and mean profiles of flow quantities in the channel. Our focus is on providing physical understanding of the deviations observed from the logarithmic law of the wall due to the buoyant motions as well as providing a model of this behavior, and link with fundamental quantities of heat transfer in the convective channel flow. Our findings show that the introduction of an unstably stratified thermal field results in an effective drag increase in the channel flow, quantified in the logarithmic region by a modified log-law, with model parameters dependent on Ra , Retau .

  12. The Extent of Channelized Basal Water Flow Under the Greenland Ice Sheet

    NASA Astrophysics Data System (ADS)

    Downs, J.; Johnson, J. V.; Harper, J. T.

    2015-12-01

    Glacial ice flows due to a combination of deformation and basal sliding, with sliding accounting for most of the fastest ice flow. Basal sliding is controlled by the transport of water at the glacier's bed, which can be accomplished through both high pressure, low discharge, distributed flow, or low pressure, high discharge, channelized flow. Higher pressures are generally associated with more complete decoupling of a glacier from its bed and faster flow. As the intensity of summer melt in Greenland has increased, our poor understanding of the drainage network's discharge capacity and its coupling to sliding has generated fundamental questions, such as: will larger fluxes of liquid water promote or inhibit basal sliding? To investigate this question we have implemented a model of distributed and channelized flow developed by Werder et. al 2013. The sensitivity of the modeled channel network to basal and surface geometry, melt rate, boundary conditions, and other parameters is examined in a sequence of experiments using synthetic geometries. Expanding on these experiments, we run the model with realistic surface and bedrock data from Issunguata Sermia in Western Central Greenland. These experiments benefit from a wealth of in-situ data, including observations of basal water pressure. Our results suggest that the development of large channels is limited to the margins of the ice sheet, and that higher pressures continue to prevail in the interior.

  13. Channelization of viscoplastic flow in a rough Hele-Shaw cell

    NASA Astrophysics Data System (ADS)

    Hewitt, Duncan; Balmforth, Neil

    2015-11-01

    The flow of viscoplastic fluid down slender conduits or through porous media has application in a range of industrial and geophysical settings, from the plumbing of mud volcanoes to the transport of proppant slurries in hydraulic fracturing. The yield stress can cause the fluid locally to clog up, which can significantly affect the flow patterns. Flow of a viscoplastic fluid in a Hele-Shaw cell that has randomly ``roughened'' walls is investigated, both numerically and using analogue laboratory experiments. Fluid injected into the centre of the rough cell, which is initially full of the same fluid, show pronounced channelization: above a critical pressure drop (below which there is no flow and all the fluid is unyielded and stagnant), one or more thin conduits of yielded, flowing fluid develop. At larger pressure drops, more channels of yielded fluid develop. The quantity and width of the channels, and the value of the critical pressure drop, depend on the amplitude of the roughness of the walls of the cell. If this roughness is known, the locations of the first channels to flow and the corresponding pressure drop can be predicted by an optimization algorithm.

  14. On the impact of entrapped air in infiltration under ponding conditions: Part a: Preferential air flow path effects on infiltration

    NASA Astrophysics Data System (ADS)

    Weisbord, N.; Mizrahi, G.; Furman, A.

    2015-12-01

    Entrapped air effects on infiltration under ponding conditions could be important for massive infiltration of managed aquifer recharge or soil aquifer treatment. Earlier studies found that under ponding conditions air could reduce infiltration by 70-90%. Most studies have dealt with entrapped air effects when soil surface topography is flat. The objective of this study is to investigate the effects of: (1) irregular surface topography on preferential air flow path development; (2) preferential air flow path on infiltration; and (3) hydraulic head on infiltration when air is trapped. Column experiments were used to investigate these particular effects. A 140 cm deep and 30 cm wide column packed with silica sand was used under two boundary conditions: in the first, air can only escape vertically upward through the soil surface; in the second, air is free to escape. The surface was flooded with 13 liters of water, with ponding depth decreasing with time. Two soil surface conditions were tested: flat surface and irregular. It was found that in irregular surfaces, stable air flow through preferential paths was developed in the high altitude zones. Flat surface topography caused unstable air flow through random paths. Comparison between irregular and flat surface topography showed that the entrapped air pressure was lower and the infiltration rate was about 40% higher in the irregular surface topography than in the flat surface topography. No difference of infiltration rate between flat and irregular surface topography was observed when air was free to escape along the infiltration path. It was also found that at the first stage of infiltration, higher hydraulic heads caused higher entrapped air pressures and lower infiltration rates. In contrast, higher hydraulic head results in higher infiltration rate, when air was free to escape. Our results suggest that during ponding conditions: (1) preferential air flow paths develop at high surface zones of irregular topography

  15. Quantifying downstream impacts of impoundment on flow regime and channel planform, lower Trinity River, Texas

    NASA Astrophysics Data System (ADS)

    Wellmeyer, Jessica L.; Slattery, Michael C.; Phillips, Jonathan D.

    2005-07-01

    As human population worldwide has grown, so has interest in harnessing and manipulating the flow of water for the benefit of humans. The Trinity River of eastern Texas is one such watershed greatly impacted by engineering and urbanization. Draining the Dallas-Fort Worth metroplex, just under 30 reservoirs are in operation in the basin, regulating flow while containing public supplies, supporting recreation, and providing flood control. Lake Livingston is the lowest, as well as largest, reservoir in the basin, a mere 95 km above the Trinity's outlet near Galveston Bay. This study seeks to describe and quantify channel activity and flow regime, identifying effects of the 1968 closure of Livingston dam. Using historic daily and peak discharge data from USGS gauging stations, flow duration curves are constructed, identifying pre- and post-dam flow conditions. A digital historic photo archive was also constructed using six sets of aerial photographs spanning from 1938 to 1995, and three measures of channel activity applied using a GIS. Results show no changes in high flow conditions following impoundment, while low flows are elevated. However, the entire post-dam period is characterized by significantly higher rainfall, which may be obscuring the full impact of flow regulation. Channel activity rates do not indicate a more stabilized planform following dam closure; rather they suggest that the Trinity River is adjusting itself to the stress of Livingston dam in a slow, gradual process that may not be apparent in a modern time scale.

  16. Vascular TRP Channels: Performing Under Pressure and Going with the Flow

    PubMed Central

    Hill-Eubanks, David C.; Gonzales, Albert L.; Sonkusare, Swapnil K.

    2014-01-01

    Endothelial cells and smooth muscle cells of resistance arteries mediate opposing responses to mechanical forces acting on the vasculature, promoting dilation in response to flow and constriction in response to pressure, respectively. In this review, we explore the role of TRP channels, particularly endothelial TRPV4 and smooth muscle TRPC6 and TRPM4 channels, in vascular mechanosensing circuits, placing their putative mechanosensitivity in context with other proposed upstream and downstream signaling pathways. PMID:25180264

  17. Analytical solution to the equations for parallel-flow four-channel heat exchangers

    SciTech Connect

    Malinowski, L.

    2000-04-01

    Assuming that the thermophysical parameters of the fluids are independent on temperature, the stationary temperature field in a parallel-flow multi-channel heat exchanger can be described by a set of linear differential equations of the first order with constant coefficients. A compact analytical solution to this set is presented for the case of four-channel exchangers and simple eigenvalues of the coefficient matrix of the set.

  18. Air-Flow Navigated Crystal Growth for TIPS Pentacene-Based Organic Thin-Film Transistors

    SciTech Connect

    He, Zhengran; Chen, Jihua; Sun, Zhenzhong; Szulczewski, Greg; Li, Dawen

    2012-01-01

    6,13-bis(triisopropylsilylethynyl)pentacene (TIPS pentacene) is a promising active channel material of organic thin-film transistors (OTFTs) due to its solubility, stability, and high mobility. However, the growth of TIPS pentacene crystals is intrinsically anisotropic and thus leads to significant variation in the performance of OTFTs. In this paper, air flow is utilized to effectively reduce the TIPS pentacene crystal anisotropy and enhance performance consistency in OTFTs, and the resulted films are examined with optical microscopy, grazing-incidence X-ray diffraction, and thin-film transistor measurements. Under air-flow navigation (AFN), TIPS pentacene drop-cast from toluene solution has been observed to form thin films with improved crystal orientation and increased areal coverage on substrates, which subsequently lead to a four-fold increase of average hole mobility and one order of magnitude enhancement in performance consistency defined by the ratio of average mobility to the standard deviation of the field-effect mobilities.

  19. Technical Note: Variability of flow discharge in lateral inflow-dominated stream channels

    NASA Astrophysics Data System (ADS)

    Chang, C.-M.; Yeh, H.-D.

    2015-02-01

    The influence of the temporal changes in lateral inflow rate on the discharge variability in stream channels is explored through the analysis of diffusion wave equation (the linearized St. Venant equations). To account for variability and uncertainty, the lateral inflow rate is regarded as a temporal random function. Based on the spectral representation theory, analytical expressions for the covariance function and evolutionary power spectral density of the random discharge perturbation process are derived to quantify variability in stream flow discharge induced by the temporal changes in lateral inflow rate. Upon evaluating the closed-form expressions, it is found that the variability in stream flow discharge increases with distance from the upstream boundary of the channel and time as well. The temporal correlation scale of inflow rate fluctuations plays a positive role in enhancing the variability of the flow discharge in channels. The treatment of the discharge variance gives us a quantitative estimate of uncertainty from the use of the deterministic model.

  20. Fully nonlinear Goertler vortices in constricted channel flows and their effect on the onset of separation

    NASA Technical Reports Server (NTRS)

    Denier, James P.; Hall, Philip

    1992-01-01

    The development of fully nonlinear Goertler vortices in high Reynolds number flow in a symmetrically constricted channel is investigated. Attention is restricted to the case of 'strongly' constricted channels considered by Smith and Daniels (1981) for which the scaled constriction height is asymptotically large. Such flows are known to develop a Goldstein singularity and subsequently become separated at some downstream station past the point of maximum channel constriction. It is shown that these flows can support fully nonlinear Goertler vortices, of the form elucidated by Hall and Lakin (1988), for constrictions which have an appreciable region of local concave curvature upstream of the position at which separation occurs. The effect on the onset of separation due to the nonlinear Goertler modes is discussed. A brief discussion of other possible nonlinear states which may also have a dramatic effect in delaying (or promoting) separation is given.

  1. An exact solution for Stokes flow in an infinite channel with permeable walls

    NASA Astrophysics Data System (ADS)

    Herschlag, Gregory; Liu, Jian-Guo; Layton, Anita

    2014-11-01

    We derive an exact solution for Stokes flow in an infinite channel with permeable walls. We assume that at the channel walls, the normal component of the fluid velocity is described by Darcy's law and the tangential component of the fluid velocity is described by the no slip condition. The pressure exterior to the channel is assumed to be constant. We verify that in the limit of small permeability, Poiseuille flow is recovered to leading order, and demonstrate that our exact result agrees with previous approximate results in this limit. By comparing our solution to existing assumptions on inlet profiles in the literature, we find that although the error is small, Poiseuille and Berman flow do not provide correct inlet conditions. DK089066, DMS1263995, DMS0943760, DMS1107444.

  2. Relief, nocturnal cold-air flow and air quality in Kigali, Rwanda

    NASA Astrophysics Data System (ADS)

    Henninger, Sascha

    2013-04-01

    , this result is not reassuringly, because all measured residential districts in Kigali exceeded the recommendations of the WHO, too. This suggests that the inhabitants of Kigali are exposed to enormous levels of PM10 during most of their time outdoors. So PM10 levels are increasing in areas with high rates of traffic due to the exhaust of the vehicles and the stirring up of dust from the ground, but also in fact of burning wood for cooking etc. within the residential districts. Hazardous measuring trips could be detected for nighttime measurements. Because of high temperatures, high solar radiation and a non-typical missing cloud cover the urban surface could heat up extremely, which produced a cold-air flow from the ridges and the slopes down to the "Marais" at night. This cold-air flow takes away the suspended particulate matters, which tends to accumulate within the "Marais" on the bottom of the hills, the places where most residential neighborhoods could be found and agricultural fields were used. The distinctive relief caused an accumulation within small valleys. Unfortunately, these are the favourite places of living and agriculture and this tends to high indoor-air pollution.

  3. Unsteady transonic flow control around an airfoil in a channel

    NASA Astrophysics Data System (ADS)

    Hamid, Md. Abdul; Hasan, A. B. M. Toufique; Ali, Mohammad; Mitsutake, Yuichi; Setoguchi, Toshiaki; Yu, Shen

    2016-04-01

    Transonic internal flow around an airfoil is associated with self-excited unsteady shock wave oscillation. This unsteady phenomenon generates buffet, high speed impulsive noise, non-synchronous vibration, high cycle fatigue failure and so on. Present study investigates the effectiveness of perforated cavity to control this unsteady flow field. The cavity has been incorporated on the airfoil surface. The degree of perforation of the cavity is kept constant as 30%. However, the number of openings (perforation) at the cavity upper wall has been varied. Results showed that this passive control reduces the strength of shock wave compared to that of baseline airfoil. As a result, the intensity of shock wave/boundary layer interaction and the root mean square (RMS) of pressure oscillation around the airfoil have been reduced with the control method.

  4. The Evolution of Finite Amplitude Wavetrains in Plane Channel Flow

    NASA Technical Reports Server (NTRS)

    Hewitt, R. E.; Hall, P.

    1996-01-01

    We consider a viscous incompressible fluid flow driven between two parallel plates by a constant pressure gradient. The flow is at a finite Reynolds number, with an 0(l) disturbance in the form of a traveling wave. A phase equation approach is used to discuss the evolution of slowly varying fully nonlinear two dimensional wavetrains. We consider uniform wavetrains in detail, showing that the development of a wavenumber perturbation is governed by Burgers equation in most cases. The wavenumber perturbation theory, constructed using the phase equation approach for a uniform wavetrain, is shown to be distinct from an amplitude perturbation expansion about the periodic flow. In fact we show that the amplitude equation contains only linear terms and is simply the heat equation. We review, briefly, the well known dynamics of Burgers equation, which imply that both shock structures and finite time singularities of the wavenumber perturbation can occur with respect to the slow scales. Numerical computations have been performed to identify areas of the (wavenumber, Reynolds number, energy) neutral surface for which each of these possibilities can occur. We note that the evolution equations will breakdown under certain circumstances, in particular for a weakly nonlinear secondary flow. Finally we extend the theory to three dimensions and discuss the limit of a weak spanwise dependence for uniform wavetrains, showing that two functions are required to describe the evolution. These unknowns are a phase and a pressure function which satisfy a pair of linearly coupled partial differential equations. The results obtained from applying the same analysis to the fully three dimensional problem are included as an appendix.

  5. New sensor for measurement of low air flow velocity. Phase I final report

    SciTech Connect

    Hashemian, H.M.; Hashemian, M.; Riggsbee, E.T.

    1995-08-01

    The project described here is the Phase I feasibility study of a two-phase program to integrate existing technologies to provide a system for determining air flow velocity and direction in radiation work areas. Basically, a low air flow sensor referred to as a thermocouple flow sensor has been developed. The sensor uses a thermocouple as its sensing element. The response time of the thermocouple is measured using an existing in-situ method called the Loop Current Step Response (LCSR) test. The response time results are then converted to a flow signal using a response time-versus-flow correlation. The Phase I effort has shown that a strong correlation exists between the response time of small diameter thermocouples and the ambient flow rate. As such, it has been demonstrated that thermocouple flow sensors can be used successfully to measure low air flow rates that can not be measured with conventional flow sensors. While the thermocouple flow sensor developed in this project was very successful in determining air flow velocity, determining air flow direction was beyond the scope of the Phase I project. Nevertheless, work was performed during Phase I to determine how the new flow sensor can be used to determine the direction, as well as the velocity, of ambient air movements. Basically, it is necessary to use either multiple flow sensors or move a single sensor in the monitoring area and make flow measurements at various locations sweeping the area from top to bottom and from left to right. The results can then be used with empirical or physical models, or in terms of directional vectors to estimate air flow patterns. The measurements can be made continuously or periodically to update the flow patterns as they change when people and objects are moved in the monitoring area. The potential for using multiple thermocouple flow sensors for determining air flow patterns will be examined in Phase II.

  6. Laser prepulse induced plasma channel formation in air and relativistic self focusing of an intense short pulse

    SciTech Connect

    Kumar, Ashok; Dahiya, Deepak; Sharma, A. K.

    2011-02-15

    An analytical formalism is developed and particle-in-cell simulations are carried out to study plasma channel formation in air by a two pulse technique and subsequent relativistic self focusing of the third intense laser through it. The first prepulse causes tunnel ionization of air. The second pulse heats the plasma electrons and establishes a prolonged channel. The third pulse focuses under the combined effect of density nonuniformity of the channel and relativistic mass nonlinearity. A channel with 20% density variation over the spot size of the third pulse is seen to strongly influence relativistic self focusing at normalized laser amplitude {approx}0.4-1. In deeper plasma channels, self focusing is less sensitive to laser amplitude variation. These results are reproduced in particle-in-cell simulations. The present treatment is valid for millimeter range plasma channels.

  7. Microscale flow visualization of nucleate boiling in small channels: Mechanisms influencing heat transfer

    SciTech Connect

    Kasza, K.E.; Didascalou, T.; Wambsganss, M.W.

    1997-07-01

    This paper describes the use of a new test apparatus employing flow visualization via ultra-high-speed video and microscope optics to study microscale nucleate boiling in a small, rectangular, heated channel. The results presented are for water. Because of confinement effects produced by the channel cross section being of the same nominal size as the individual vapor bubbles nucleating at discrete wall sites, flow regimes and heat transfer mechanisms that occur in small channels are shown to be considerably different than those in large channels. Flow visualization data are presented depicting discrete bubble/bubble and bubble/wall interactions for moderate and high heat flux. Quantitative data are also presented on nucleate bubble growth behavior for a single nucleation site in the form of growth rates, bubble sizes, and frequency of generation in the presence and absence of a thin wall liquid layer. Mechanistic boiling behavior and trends are observed which support the use of this type of research as a powerful means to gain fundamental insights into why, under some conditions, nucleate boiling heat transfer coefficients are considerably larger in small channels than in large channels.

  8. Computational modeling of flow and combustion in a couette channel simulating microgravity

    NASA Astrophysics Data System (ADS)

    Hamdan, Ghaleb

    Theoretically a Couette flow in a narrow channel can be utilized to simulate microgravity conditions experienced by a surface flame due to the linear velocity profile. Hence, the Couette channel is a potential apparatus for the study of flame spread in an environment that recreated microgravity flow conditions. Simulated microgravity conditions were achieved by limiting the vertical extent over and under the flame to suppress buoyancy. This numerical study was done for a 2-D channel using Fire Dynamics Simulator (FDS). This thesis is divided into two sections; the first is the study of Couette flow with a non-reacting cold flow in a finite length channel, a subject with surprisingly little past research, despite the ubiquity of "infinite" Couette channels in text books. The channel was placed in a room to allow for a better representation of a realistic channel and allow the flow and pressure field to develop without forcing them at the inlet and outlet. The plate's velocities, channel's gap and the channel's length were varied and the results of the u-velocity profile, w-velocity profile and pressure were investigated. The entrance length relationship with Reynolds number for a finite Couette Channel was determined for the first time - as far as the author knows - in order to ensure the flame occurs in a fully developed flow. In contrast to an infinite channel, the u-velocity was found to be nonlinear due to an adverse pressure differential created along the channel attributed to the pull force along the entrance of the channel created by the top plate a well as the pressure differential created by the flow exiting the channel. The linearity constant was derived for the one moving plate case. The domain consisted of a rectangular region with the top plate moving and the bottom plate fixed except for a few cases in which the bottom plate also moved and were compared with only one moving plate. The second section describes the combustion of a thin cellulose sample

  9. Surface-slip equations for multicomponent nonequilibrium air flow

    NASA Technical Reports Server (NTRS)

    Gupta, R. N.; Scott, C. D.; Moss, J. N.

    1985-01-01

    Equations are presented for the surface-slip (or jump) values of species concentration, pressure, velocity, and temperature in the low-Reynolds number, high-altitude flight regime of a space vehicle. The equations are obtained from closed form solutions of the mass, momentum, and energy flux equations using the Chapman-Enskog velocity distribution function. This function represents a solution of the Boltzmann equation in the Navier-Stokes approximation. The analysis, obtained for nonequilibrium multicomponent air flow, includes the finite-rate surface catalytic recombination and changes in the internal energy during reflection from the surface. Expressions for the various slip quantities were obtained in a form which can be employed in flowfield computations. A consistent set of equations is provided for multicomponent, binary, and single species mixtures. Expression is also provided for the finite-rate, species-concentration boundary condition for a multicomponent mixture in absence of slip.

  10. Theory for nanoparticle retention time in the helical channel of quadrupole magnetic field-flow fractionation

    NASA Astrophysics Data System (ADS)

    Williams, P. Stephen; Carpino, Francesca; Zborowski, Maciej

    2009-05-01

    Quadrupole magnetic field-flow fractionation (QMgFFF) is a separation and characterization technique for magnetic nanoparticles such as those used for cell labeling and for targeted drug therapy. A helical separation channel is used to efficiently exploit the quadrupole magnetic field. The fluid and sample components therefore have angular and longitudinal components to their motion in the thin annular space occupied by the helical channel. The retention ratio is defined as the ratio of the times for non-retained and a retained material to pass through the channel. Equations are derived for the respective angular and longitudinal components to retention ratio.

  11. Field observations of pressure fluctuations in debris flows and debris floods at the Illgraben torrent channel with implications for channel-bed erosion

    NASA Astrophysics Data System (ADS)

    McArdell, Brian

    2014-05-01

    The Illgraben catchment in southwestern Switzerland experiences frequent debris flows and debris floods, providing an ideal location to study the properties of debris flows. A large (2m long, 4m wide) force plate in the channel bed is outfitted with normal and shear force sensors as well as a geophone and an accelerometer. A vertical flow-parallel concrete wall immediately upstream of the large force plate is instrumented with 18 geophones and 6 force plates, each mounted on a 0.3m by 0.3m square steel plate. The flow height near the wall and over the force plate are measured using laser sensors. Three video cameras have been installed to record the passage of debris flows. While the measurement system was designed for observing debris flows, large debris floods also trigger the observation station, providing an opportunity to compare their flow properties. Debris flows tend to have steep flow fronts, with flow depths increasing from 0 to several meters over about 10 seconds; the flow front generally appears to be granular with little turbulent water visible on the surface. Debris floods tend to have undular fronts which visibly resemble flash floods, increasing from flow depths on the order of a few cm to several meters typically over several 100's of seconds. Both types of flow produce strong fluctuations in normal force on the channel bed, however the magnitude of fluctuations at the base of debris flows tend to be substantially larger than in debris floods. In debris flows the pressure fluctuations are largest at the bed and decrease in amplitude with height above the channel bed, which is consistent with the idea that the pressure fluctuations in the flow are generated at the contact between the debris flow and channel bed. Pressure fluctuations in debris floods (when the measuring system at the wall is triggered) are much smaller. Mean shear stresses on the channel bed are similar in both types of flow, however the pressure fluctuations at the base of debris

  12. Elasto-inertial particle focusing under the viscoelastic flow of DNA solution in a square channel.

    PubMed

    Kim, Bookun; Kim, Ju Min

    2016-03-01

    Particle focusing is an essential step in a wide range of applications such as cell counting and sorting. Recently, viscoelastic particle focusing, which exploits the spatially non-uniform viscoelastic properties of a polymer solution under Poiseuille flow, has attracted much attention because the particles are focused along the channel centerline without any external force. Lateral particle migration in polymer solutions in square channels has been studied due to its practical importance in lab-on-a-chip applications. However, there are still many questions about how the rheological properties of the medium alter the equilibrium particle positions and about the flow rate ranges for particle focusing. In this study, we investigated lateral particle migration in a viscoelastic flow of DNA solution in a square microchannel. The elastic property is relevant due to the long relaxation time of a DNA molecule, even when the DNA concentration is extremely low. Further, the shear viscosity of the solution is essentially constant irrespective of shear rate. Our current results demonstrate that the particles migrate toward the channel centerline and the four corners of a square channel in the dilute DNA solution when the inertia is negligible (elasticity-dominant flow). As the flow rate increases, the multiple equilibrium particle positions are reduced to a single file along the channel centerline, due to the elasto-inertial particle focusing mechanism. The current results support that elasto-inertial particle focusing mechanism is a universal phenomenon in a viscoelastic fluid with constant shear viscosity (Boger fluid). Also, the effective flow rate ranges for three-dimensional particle focusing in the DNA solution were significantly higher and wider than those for the previous synthetic polymer solution case, which facilitates high throughput analysis of particulate systems. In addition, we demonstrated that the DNA solution can be applied to focus a wide range of

  13. Build up An Operational Flood Simulation from Existing 1D Channel Flow Works

    NASA Astrophysics Data System (ADS)

    Chang, Che-Hao; Hsu, Chih-Tsung; Wu, Shiang-Jen; Lien, Ho-Cheng; Shen, Jhih-Cyuan; Chung, Ming-Ko

    2016-04-01

    Several 2D flood simulations will be developed for urban area in recent years in Taiwan. Original ideas focus on the static flood maps produced by the 2D flood simulation with respect to design events, which could be useful no matter for planning or disaster awareness. However, an extra bonus is expected to see if we can reuse the 2D flood simulation framework for operational use or not. Such a project goal inspire us to setup a standard operation procedure before any progress from existing 1D channel flow works. 3 key issues are taken into account in the SOP: 1. High Resolution Terrain: A 1m resolution digital terrain model (DTM) is considered as a reference. The Channels and structures should be setup in 1D channel flow works if we can identify under such high resolution. One should examine the existing 1D channel flow works consistent with the DTM or not. 2. Meteo Stations Referenced: Real time precipitation would be send to referenced location in RR models during an operational forecast. Existing 1D channels flow works are usually specifically for design events which are not necessarily equipped with such references. 3. Time Consuming: A full scale 2D flood simulation needs a lot of computation resources. A solution should be derived within practical time limits. Under the above consideration, some impacts and procedures will be analyzed and developed to setup the SOP for further model modification.

  14. Direct simulation of turbulent swept flow over a wire in a channel.

    SciTech Connect

    Ranjan, R.; Pantano, C.; Fischer, P.; Mathematics and Computer Science; Univ. of Illinois

    2010-05-25

    Turbulent swept flow over a cylindrical wire placed on a wall of a channel is investigated using direct numerical simulations. This geometry is a model of the flow through the wire-wrapped fuel pins, the heat exchanger, typical of many nuclear reactor designs. Mean flow along and across the wire axis is imposed, leading to the formation of separated flow regions. The Reynolds number based on the bulk velocity along the wire axis direction and the channel half height is 5400 and four cases are simulated with different flowrates across the wire. This configuration is topologically similar to backward-facing steps or slots with swept flow, except that the dominant flow is along the obstacle axis in the present study and the crossflow is smaller than the axial flow, i.e. the sweep angle is large. Mean velocities, turbulence statistics, wall shear stress and instantaneous flow structures are investigated. Particular attention is devoted to the statistics of the shear stress on the walls of the channel and the wire in the recirculation zone. The flow around the mean reattachment region, at the termination of the recirculating bubble, does not exhibit the typical decay of the mean shear stress observed in classical backward-facing step flows owing to the presence of a strong axial flow. The evolution of the mean wall shear stress angle after reattachment indicates that the flow recovers towards equilibrium at a rather slow rate, which decreases with sweep angle. Finally, the database is analysed to estimate resolution requirements, in particular around the recirculation zones, for large-eddy simulations. This has implications in more complete geometrical models of a wire-wrapped assembly, involving hundreds of fuel pins, where only turbulence modelling can be afforded computationally.

  15. Evaluation of the 3-D channeling flow in a fractured type of oil/gas reservoir

    NASA Astrophysics Data System (ADS)

    Ishibashi, T.; Watanabe, N.; Tsuchiya, N.; Tamagawa, T.

    2013-12-01

    An understanding of the flow and transport characteristics through rock fracture networks is of critical importance in many engineering and scientific applications. These include effective recovery of targeted fluid such as oil/gas, geothermal, or potable waters, and isolation of hazardous materials. Here, the formation of preferential flow path (i.e. channeling flow) is one of the most significant characteristics in considering fluid flow through rock fracture networks; however, the impact of channeling flow remains poorly understood. In order to deepen our understanding of channeling flow, the authors have developed a novel discrete fracture network (DFN) model simulator, GeoFlow. Different from the conventional DFN model simulators, we can characterize each fracture not by a single aperture value but by a heterogeneous aperture distribution in GeoFlow [Ishibashi et al., 2012]. As a result, the formation of 3-D preferential flow paths within fracture network can be considered by using this simulator. Therefore, we would challenge to construct the precise fracture networks whose fractures have heterogeneous aperture distributions in field scale, and to analyze fluid flows through the fracture networks by GeoFlow. In the present study, the Yufutsu oil/gas field in Hokkaido, Japan is selected as the subject area for study. This field is known as the fractured type of reservoir, and reliable DFN models can be constructed for this field based on the 3-D seismic data, well logging, in-situ stress measurement, and acoustic emission data [Tamagawa et al., 2012]. Based on these DFN models, new DFN models for 1,080 (East-West) × 1,080 (North-South) × 1,080 (Depth) m^3, where fractures are represented by squares of 44-346 m on a side, are re-constructed. In these new models, scale-dependent aperture distributions are considered for all fractures constructing the fracture networks. Note that the multi-scale modeling of fracture flow has been developed by the authors

  16. Hydrodynamics and heat transfer in a laminar flow of viscoelastic fluid in a flat slot channel

    NASA Astrophysics Data System (ADS)

    Ananyev, D. V.; Halitova, G. R.; Vachagina, E. K.

    2015-01-01

    Results of the numerical study of hydrodynamics and heat transfer in a laminar flow of viscoelastic fluid in a flat slot channel are presented in the present paper. The model of nonlinear viscoelastic fluid of Phan-Thien—Tanner is used to describe the viscoelastic properties of fluid. The solution to the stated problem by software package "COMSOL Multiphysics" is considered. The method of solution is verified, and results are compared with data of the other authors. It is determined that in the flow of viscoelastic fluid in a flat slot channel, the maximal contribution of heating due to dissipation is approximately 7-8 %.

  17. The Influence of Electrode and Channel Configurations on Flow Battery Performance

    SciTech Connect

    Darling, RM; Perry, ML

    2014-05-21

    Flow batteries with flow-through porous electrodes are compared to cells with porous electrodes adjacent to either parallel or interdigitated channels. Resistances and pressure drops are measured for different configurations to augment the electrochemical data. Cell tests are done with an electrolyte containing VO2+ and VO2+ in sulfuric acid that is circulated through both anode and cathode from a single reservoir. Performance is found to depend sensitively on the combination of electrode and flow field. Theoretical explanations for this dependence are provided. Scale-up of flow through and interdigitated designs to large active areas is also discussed. (C) 2014 The Electrochemical Society. All rights reserved.

  18. Heterogeneous physical and chemical processes in a rarefied-gas flow in channels

    NASA Astrophysics Data System (ADS)

    Rebrov, A. K.; Yudin, I. B.

    2016-05-01

    A flow with physical and chemical reactions on hot surfaces is investigated. On the basis of physical experiments, determining the hydrogen-dissociation degree in rarefied gas and calculation of the flow by the method of direct simulation Monte Carlo (DSMC), it is possible to specify certain unknown constants of interaction of molecules and atoms with a tungsten surface. By the example of the hydrogen flow in a hightemperature tungsten cylindrical channel, the role of dissociation, sorption, and recombination processes is shown in a wide range of flow regimes from free-molecular to continuum.

  19. Rotating annulus laboratory experiments with application to baroclinic channel flows with narrows

    NASA Astrophysics Data System (ADS)

    Harlander, Uwe; Wenzel, Julia; Egbers, Christoph

    2010-05-01

    The differentially heated rotating annulus is a classical experiment of geophysical fluid dynamics that shows many similarities with large-scale atmospheric flows. Still, many features of the annulus flow are not well understood and modern non-intrusive measurement techniques can help to clarify them. Moreover, blocked or partly blocked annulus flows are less well studied although such flows show resemblance with oceanic channel flows. We present experimental results from a heated rotating annulus with a barrier that constricts the flow along the inner wall and at the bottom [1]. For the experiments a flow regime has been chosen that is characterized by an Eady wave with azimuthal wave number three. Without the barrier, the wave propagates prograde with no significant structural change. In contrast, when the barrier is mounted, wave crests break approaching it but redevelop downstream of the barrier. We are interested in the transient wave behavior and in particular in the dominant frequencies that occur in the narrow and downstrean or upstream of it. Moreover, we study the impact of a slowly varying radial temperature gradient on the wave's phase speed and the period it takes for the reestablishment of the baroclinic wave downstream of the barrier. It is suggested that the experiments are useful in understanding some features of the flow through the Mozambique Channel. It has been shown that the flow characteristic within the Channel is quite different from the one downstream of it [2]. [1] J. Wenzel (2009): Barokline Wellen in einem rotierenden asymmetrischen Tank, Studienarbeit BTU Cottbus, Univ. Leipzig, 55pp. [2] U. Harlander, H. Ridderinkhof, M.W. Schouten, and W.P.M. De Ruijter (2009): Long term observations of transport, eddies, and Rossby waves in the Mozambique Channel, J. Geophys. Res., 114, C02003, doi:10.1029/2008JC004846.

  20. Influence of fluctuating supply on the emplacement dynamics of channelized lava flows

    NASA Astrophysics Data System (ADS)

    Tarquini, Simone; de'Michieli Vitturi, Mattia

    2014-03-01

    The evolution of lava flows emplaced on Mount Etna (Italy) in September 2004 is examined in detail through the analysis of morphometric measurements of flow units. The growth of the main channelized flow is consistent with a layering of lava blankets, which maintains the initial geometry of the channel (although levees are widened and raised), and is here explicitly related to the repeated overflow of lava pulses. A simple analytical model is introduced describing the evolution of the flow level in a channelized flow unit fed by a fluctuating supply. The model, named FLOWPULSE, shows that a fluctuation in the velocity of lava extrusion at the vent triggers the formation of pulses, which become increasingly high the farther they are from the vent, and are invariably destined to overflow within a given distance. The FLOWPULSE simulations are in accordance with the observed morphology, characterized by a very flat initial profile followed by a massive increase in flow unit cross-section area between 600 and 700 m downflow. The modeled emplacement dynamics provides also an explanation for the observed substantial "loss" of the original flowing mass with increasing distance from the vent.