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松田, 佑., Yu MATSUDA, 英男 森, Hideo MORI, 智秀 新美, Tomohide NIIMI, 裕之 上西, Hiroyuki UENISHI, 円. 平光, and Madoka HIRAKO. "高クヌッセン数流れでの圧力計測に適した感圧分子膜の開発." 日本機械学会, 2006. http://hdl.handle.net/2237/9015.
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Mori, Hideo, Tomohide Niimi, Madoka Hirako, and Hiroyuki Uenishi. "Pressure Sensitive Paint Suitable to High Knudsen Number Regime." IOP, 2006. http://hdl.handle.net/2237/6960.
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Hattori, Masanari. "Generalized slip-flow theory and its related Knudsen-layer analysis." 京都大学 (Kyoto University), 2016. http://hdl.handle.net/2433/215508.
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The content of Chapter 1 is an author produced version of a paper published in Physics of Fluids. The final publication is available at AIP via http://dx.doi.org/10.1063/1.3691262. The content of Chapters 2 and 4 is an author produced version of papers published in Journal of Statistical Physics. The final publications are available at Springer via http://dx.doi.org/10.1007/s10955-012-0512-z and http://dx.doi.org/10.1007/s10955-015-1364-0, respectively.Kyoto University (京都大学)
0048
新制・課程博士
博士(工学)
甲第19682号
工博第4137号
新制||工||1638(附属図書館)
32718
京都大学大学院工学研究科機械理工学専攻
(主査)教授 青木 一生, 教授 髙田 滋, 教授 稲室 隆二
学位規則第4条第1項該当
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Guneratne, Julie Clare. "High Reynolds number flow in a collapsible channel." Thesis, University of Cambridge, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.340767.
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Kirby, Simon. "High Reynolds number flow : past configurations of multiple blades." Thesis, University of East Anglia, 2010. https://ueaeprints.uea.ac.uk/19105/.
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Davenport, W. J. "Separation bubbles at high Reynolds number : measurement and computation." Thesis, University of Cambridge, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.232788.
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Cleaver, David. "Low Reynolds number flow control through small-amplitude high-frequency motion." Thesis, University of Bath, 2011. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.547620.
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There is currently growing interest in the field of Micro Air Vehicles (MAVs). A MAV is characterized by its low Reynolds numbers flight regime which makes lift and thrust creation a significant challenge. One possible solution inspired by nature is flapping flight, but instead of the large-amplitude low-frequency motion suited to the muscular actuators of nature, small-amplitude high-frequency motion may be more suitable for electrical actuators. In this thesis the effect of small-amplitude high-frequency motion is experimentally investigated focusing on three aspects: general performance improvement, deflected jets, and the effect of geometryResults presented herein demonstrate that using small-amplitude high-frequency plunging motion on a NACA 0012 airfoil at a post-stall angle of attack of 15° can lead to significant thrust production accompanying a 305% increase in lift coefficient. At low Strouhal numbers vortices form at the leading-edge during the downward motion and then convect into the wake. This ‘mode 1’ flow field is associated with high lift but low thrust. The maximum lift enhancement was due to resonance with the natural shedding frequency, its harmonics and subharmonics. At higher Strouhal numbers the vortex remains over the leading-edge area for a larger portion of the cycle and therefore loses its coherency through impingement with the upward moving airfoil. This ‘mode 2’ flowfield is associated with low lift and high thrust. At angles of attack below 12.5° very large force bifurcations are observed. These are associated with the formation of upwards or downwards deflected jets with the direction determined by initial conditions. The upwards deflected jet is associated with the counter-clockwise Trailing Edge Vortex (TEV) loitering over the airfoil and thereby pairing with the clockwise TEV to form a dipole that convects upwards. It therefore draws fluid from the upper surface enhancing the upper surface vortex leading to high lift. The downwards deflected jet is associated with the inverse. Deflected jets were not observed at larger angles of attack as the asymmetry in the strength of the TEVs was too great; nor at smaller amplitudes as the TEV strength was insufficient. To understand the effect of geometry comparable experiments were performed for a flat plate geometry. At zero degrees angle of attack deflected jets would form, as for the NACA 0012 airfoil, however their direction would switch sinusoidally with a period on the order of 100 cycles. The lift coefficient therefore also switched. At 15° angle of attack for Strouhal numbers up to unity the performance of the flat plate was comparable to the NACA 0012 airfoil. Above unity, the upper surface and lower surface leading-edge vortices form a dipole which convects away from the upper surface resulting in increased time-averaged separation and reduced lift.
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Keiderling, Felix. "Direct noise computation of high Reynolds number subsonic jet flow using LES /." Zürich : ETH, 2008. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=17955.
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Awasthi, Manuj. "High Reynolds Number Turbulent Boundary Layer Flow over Small Forward Facing Steps." Thesis, Virginia Tech, 2012. http://hdl.handle.net/10919/33820.
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Measurements were made on three forward steps with step height to boundary layer ratio of approximately 3.8%, 15% and 60% and Reynolds number based on step height ranging from 6640 to 213,000. The measurements included mean wall pressure, single and 2 point wall pressure fluctuations, single and 2 point velocity fluctuations and, oil flow visualization. Pressure fluctuation measurements were made 5 boundary layer thicknesses upstream of step to 22 boundary layer thickness (or 600 step heights for smallest step size) downstream of the step. The results show that the steps remarkably enhance the wall pressure fluctuations that scale on the step height in the vicinity of the step and far downstream of the step. The decay of wall pressure fluctuations post reattachment is a slow process and elevated levels can be seen as far as 150 step heights downstream for the mid step size. The enhanced pressure fluctuations come from the unsteady reattachment region on top face of the step which was found to be a strong function of flow geometry and flow parameters such as Reynolds number. The 2 point pressure and velocity space-time correlations show a quasi-periodic structure which begins to develop close to the reattachment and grows in intensity and scale further downstream of reattachment and is responsible for the elevated pressure fluctuations downstream of the step. However, the velocity correlations lack in scale reflecting the fact that large scales reflected in pressure are masked by smaller scales that exist within them.Master of Science
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Lim, Choon Peng. "Experimental investigation of vortex shedding in high Reynolds number flow over compressor blades in cascade." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2003. http://library.nps.navy.mil/uhtbin/hyperion-image/03Mar%5FLim.pdf.
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Thesis (M.S. in Aeronautical Engineering)--Naval Postgraduate School, March 2003.Thesis advisor(s): Garth V. Hobson, Raymond P. Shreeve. Includes bibliographical references (p. 81-82). Also available online.
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Power, Gregory D. "A novel approach for analyzing supersonic high reynolds number flows with separation." Diss., Georgia Institute of Technology, 1990. http://hdl.handle.net/1853/13403.
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Frucht, Yaacov I. "High Reynolds number incompressible flow simulation about parachute canopies and similar bluff bodies." Thesis, University of Leicester, 1987. http://hdl.handle.net/2381/9152.
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A model for the flow around bluff bodies has been developed. It is applied to an investigation of parachute canopy aerodynamic characteristics. Since the model assumes an axisymmetric incompressible high Reynolds number flow, it is only applicable to the calculation of aerodynamic characteristics at zero angle of attack. The flow is assumed to separate from the canopy at its surface discontinuity, i.e. the canopy hemline. The vorticity created in the boundary layer over the canopy upper surface is carried downstream, forming a free shear layer. In the flow field vorticity is confined to the this shear layer, outside it the flow is irrotational. Consequently, in this part of the fluid field a velocity potential can be defined. The wake flow created by bluff canopies is found to consist of a cluster of vortex rings which are shed periodically to the wake. Consequently, the axial aerodynamic force developed on the canopy will exhibit periodic behaviour. The resulting Strouhal number, has been determined to be about 0.13, based on the canopy projected area diameter. For all axisymmetric bluff canopies considered the calculated mean axial force coefficient, based on the canopy projected diameter, was found to be between 1.20 and 1.45. These values, together with the calculated pressure distribution and the wake flow periodicity, are in good agreement with known experiments. For parachute canopies performing an oscillatory axial motion the calculated results compare well with experimental data. However, it is shown that Morison's formula for this axial force is, generally, inadequate. Limited calculations of axial forces developed on the inflating parachute canopies agree with the sparse experimental data available. In the model the real flow field is simulated, basically, by a potential model. The canopy surface is replaced by a vortex ring panel lattice. Each panel contains a circular bound vortex ring which is located at one quarter panel length. For each panel the flow boundary conditions on the canopy surface are fulfilled along a control circle at three quarters of the panel length. A standing eddy which is generated by the high back-flow developed near the canopy hemline, on the canopy under surface is simulated by a standing vortex ring. The simulation of a two-dimensional discrete vortex separated wake is extended to the axisymmetric case by representing the separated wake with axisymmetric discrete vortex rings. The free shear layer emanating from the canopy hemline is represented by discrete free vortex rings which leave the canopy surface tangentially. At each time step in the calculation process a newly-created vortex ring is shed to the wake. In the vortex modelling of the separated wake a number of new elements have been introduced: -improvement of the near wake simulation by accounting for the standing eddy on the canopy under surface; -a simple method of calculating the newly created vortex ring strength & location; -reduction of the free parameters from two, the time step and the number of panels representing the canopy surface to one, i.e. the number of panels. Further model validation & implementation have been suggested. Methods of model development for asymmetric canopy representation have been discussed.
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Johansson, Martin Viktor. "Gas transport in porous media : an investigation of the hydrodynamic to free molecular flow regime." Thesis, Aix-Marseille, 2019. http://www.theses.fr/2019AIXM0278.
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La thèse porte sur le transport de gaz raréfié dans des milieux poreux causé par des gradients de pression ou de température. Un gaz en milieu poreux se raréfie lorsque l'échelle est petite, comme pour les milieux micro et nanoporeux, ou lorsque la pression est faible (conditions de vide). Les méthodes de mesure des gradients respectifs sont élaborées et les résultats sont analysés. Dans le cas d'un écoulement de gaz à gradient de pression, la perméabilité est une propriété intrinsèque et une mesure de la manière avec laquelle le gaz circule dans le milieu poreux. Le comportement du flux de gaz diffère considérablement selon le degré de raréfaction. Pour caractériser le niveau de raréfaction de l'écoulement de gaz à l'intérieur d'un milieu poreux, une propriété intrinsèque supplémentaire est proposée, la dimension caractéristique de l'écoulement. Cette propriété a également une interprétation physique, et sa mesure pour un échantillon poreux peut être utilisée pour caractériser l'échantillon comme une méthode d'analyse non destructive. Lorsque le milieu poreux est soumis à un gradient de température dans des conditions raréfiées, l'effet de transpiration thermique provoque des flux gazeux du côté froid vers le côté chaud. Les propriétés transitoires et stationnaires de la transpiration thermique en milieu poreux sont analysées. Les méthodologies développées sont appliquées pour analyser les membranes céramiques microporeuses et les milieux poreux en acier inoxydable fritté. Le dernier type de milieu poreux est particulièrement adapté à l'étalonnage des jauges à vide poussé. La méthode d'étalonnage présentée est facile à utiliser, fiable et préciseThe thesis investigates the transport of rarefied gas in porous media caused by either pressure or temperature gradients. A gas in porous media becomes rarefied when either the scale is small, as for micro and nanoporous media, or when the pressure is low (vacuum conditions). The measurement methodologies for the respective gradients are developed, and the results are analyzed. For a pressure gradient driven gas flow, the permeability is an intrinsic property and measure of how easily gas flows through the porous media. The gas flow behavior differs significantly depending on the degree of rarefaction. To characterize the rarefaction level of the gas flow inside a porous medium an additional intrinsic property is proposed, the characteristic flow dimension. This property also has a physical interpretation, and its measure for a porous sample can be used to characterize the sample as a non-destructive analysis method. When the porous media is subject to a temperature gradient under rarefied conditions, the thermal transpiration effect, causes gas flows from the cold side toward the hot end. Both the transient and stationary properties of the thermal transpiration in porous media are analyzed. The developed methodologies are applied to analyze the microporous ceramic membranes and sintered stainless steel porous media. The last type of porous media is particularly suitable for high-vacuum gauge calibration. The presented calibration method is easy to use, reliable and accurate
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König, Franziska [Verfasser], and Christoph [Akademischer Betreuer] Egbers. "Investigation of high Reynolds number pipe flow - CoLaPipe experiments / Franziska König ; Betreuer: Christoph Egbers." Cottbus : BTU Cottbus - Senftenberg, 2015. http://d-nb.info/1114283894/34.
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Sund, Stig. "The Effect of Blockage on High Reynolds Number Flow over a semi-circular Obstacle." Thesis, Norwegian University of Science and Technology, Department of Energy and Process Engineering, 2010. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-10815.
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In order to map the effects of blockage and aspect ratio, pressure distributions were measured around four different floor-mounted semi-circular cylinders in nominally two-dimensional flow. Diameters ranged from 0.05m to 0.30m for 0.3·10^5<3.5·10^5. No significant blockage effects were found for B=0.05. It was shown that by using the bulk flow velocity as the reference velocity, blockage and aspect ratio effects could be partially counteracted. The use of the bulk flow velocity was identified to be especially efficient in correcting the base pressure coefficient, but led to a larger variation of the minimum pressure coefficient with Re, for a given blockage ratio. Results also indicate that blockage is the governing factor of the base pressure coefficient for L/D>10, while the aspect ratio has the largest influence below this threshold. Separation bubbles occur in a manner similar to that of circular cylinders. The results do, however, indicate that the progression from laminar separation to purely turbulent separation may be accelerated by increased blockage. Further, the speed up over the cylinder was found to be approximately constant for a given blockage, and proportional to the square root of the blockage.
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Samouda, Feriel. "Développement de la technique de vélocimétrie par marquage moléculaire pour l'étude expérimentale des micro-écoulements gazeux." Thesis, Toulouse, INSA, 2012. http://www.theses.fr/2012ISAT0034/document.
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Ce travail de thèse porte sur le développement de la technique de Vélocimétrie par Marquage Moléculaire (Molecular Tagging Velocimetry - MTV) pour l’étude expérimentale des micro-écoulements gazeux internes. Les micro-écoulements gazeux sont des écoulements raréfiés, caractérisés par un nombre de Knudsen non négligeable. L’analyse de la littérature montre un besoin crucial de données expérimentales de grandeurs locales relatives aux micro-écoulements gazeux. Ces données permettraient une discussion pertinente de la précision et des limites d’applicabilité des différents modèles théoriques proposés dans la littérature pour l’étude du régime de glissement, régime raréfié le plus souvent rencontré en microfluidique gazeuse. Dans cette optique, un banc d’essais expérimental a été développé pour la mesure de champs de vitesses par MTV. La technique consiste à suivre des molécules traceuses d’acétone introduites dans le gaz en écoulement et qui deviennent phosphorescentes lorsqu’elles sont excitées par une source lumineuse UV. Les différents compromis pris en compte pour le développement de ce banc (choix du traceur et du matériau, conception du canal instrumenté,…), ainsi que les techniques d’acquisition et de traitement de signal sont détaillés dans le manuscrit. L’analyse expérimentale commence par une étude du signal de phosphorescence de l’acétone. Ensuite, la technique de vélocimétrie par marquage moléculaire est validée par la mesure de champs de vitesses dans des écoulements laminaires confinés en régime non raréfié. Les résultats obtenus sont comparés à des profils de vitesse théoriques d’un écoulement de Poiseuille à pression atmosphérique. Enfin, les premiers résultats obtenus à basse pression sont présentés et commentés. La détection du signal à un niveau de pression de 1kPa est encourageante et offre de nombreuses perspectives pour l’exploration d’écoulements en régime raréfiéThis thesis focuses on the development of Molecular Tagging Velocimetry (MTV) technique for the experimental analysis of internal microflows of gases. Gaseous microflows are rarefied flows characterized by a non-negligible Knudsen number. A literature review highlights a crucial need of experimental data on velocity fields within gaseous microflows. These data are required for a relevant discussion on the validity and limits of applicability of the different boundary conditions proposed in the slip flow, which is a regime often encountered in gaseous microsystems. An experimental setup has been designed for analyzing by MTV the velocity distribution in microchannels. The technique consists in detecting the displacement of acetone molecules, introduced as tracers in a gas flow; these molecules exhibit phosphorescence once excited by a UV light source. The various compromises taken into account for the setup design (choice of tracer, laser, channel material and design, camera and intensifier…), as well as the acquisition and processing techniques are detailed in the manuscript. The experimental analysis starts with a study of the acetone phosphorescence signal. Then, the MTV technique is validated by velocity field measurements in internal laminar flows through a rectangular minichannel in non-rarefied regime. The obtained results are successfully compared to the theoretical velocity profile of a Poiseuille flow. Finally, preliminary results obtained at lower pressures are presented and commented. The signal detection at a pressure level as low as 1 kPa is encouraging and draws various perspectives for the exploration of rarefied regimes
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Miller, Mark A. "Experimental Characterization of Roughness and Flow Injection Effects in a High Reynolds Number Turbulent Channel." UKnowledge, 2013. http://uknowledge.uky.edu/me_etds/26.
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A turbulent channel flow was used to study the scaling of the combined effects of roughness and flow injection on the mean flow and turbulence statistics of turbulent plane Poiseuille flow. It was found that the additional momentum injected through the rough surface acted primarily to enhance the roughness effects and, with respect to the mean flow, blowing produced similar mean flow effects as increasing the roughness height. This was not found to hold for the turbulence statistics, as a departure from Townsend’s hypothesis was seen. Instead, the resulting outer-scaled streamwise Reynolds stress for cases with roughness and blowing deviated significantly from the roughness only condition well throughout the inner and outer layers. Investigation into this phenomena indicated that suppression of the large-scale motions due to blowing may have been contributing to this deviation.
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Smith, Benjamin Robert. "Mean flow measurements of heated supersonic slot injection into a high Reynolds number supersonic stream." Thesis, Virginia Polytechnic Institute and State University, 1989. http://hdl.handle.net/10919/74537.
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Mean flow measurements and short-duration Schlieren and Shadowgraph photographs of heated and unheated supersonic slot injection of air into a supersonic air stream are presented for the purpose of observing the mixing which occurs in the resulting shear layer. The heated injected jet (Mj, Ptj = 10.7 psia, and Ttj = 760°R) passes through a slot of height 0.475 inches (1.2 cm) tangent to a free stream with M∞ = 3.0, P∞= 95 psia and Tt∞ = 540°R. The resulting density ratio is Pj / P∞ = 0.3. The free stream Re/ft = 6.1 x 10⁷ (Re/cm = 2 x 10⁶). The thickness of the plate which separates the primary and secondary flows is 0.021 inches (0.052 cm). Pitot pressure, cone static pressure and stagnation temperature profiles are obtained at four axial stations downstream of the slot (x/H = 0.25, 4, 10, 20). An additional set of measurements is obtained at Station 4 for the case of a weak shock (P₂/P₁ = 1.8) interacting with the shear layer just upstream of Station 4. From the pressure and temperature measurements, Mach number, velocity, density, mass flux and static pressure profiles are generated. An unheated injection study is also performed at the same flow conditions for comparison to the heated case. The heated and unheated cases are very similar except in the slot where the temperature difference creates changes inp, U, and pU. This study is thus concerned with the effects of changes in Pj / P∞ and Uj / U∞, especially (Uj - U∞), which are created by heating the injected flow. The heated slot flow did not create a marked difference in the location of the merging of the free stream boundary layer with the slot flow when compared to the unheated slot flow. Indeed, the appearance of the two flows on Schlieren photographs is similar even though the injected mass flow in the heated case is about 15% less than that in the unheated case. The pressure adjustments in the slot lip region are different for the two different cases. The flowfields are documented for both the heated and unheated cases with the added measurements and photographs for the shock impingement case.Master of Science
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Ebrinc, Ali Aslan. "High Speed Viscous Plane Couette-poiseuille Flow Stability." Phd thesis, METU, 2004. http://etd.lib.metu.edu.tr/upload/3/12604769/index.pdf.
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The linear stability of high speed-viscous plane Couette and Couette-Poiseuille flows are investigated numerically. The conservation equations along with Sutherland�
s viscosity law are studied using a second-order finite difference scheme. The basic velocity and temperature distributions are perturbed by a small-amplitude normalmode disturbance. The small-amplitude disturbance equations are solved numerically using a global method using QZ algorithm to find all the eigenvalues at finite Reynolds numbers, and the incompressible limit of these equations is investigated for Couette-Poiseuille flow. It is found that the instabilities occur, although the corresponding growth rates are often small. Two families of wave modes, Mode I (odd modes) and Mode II (even modes), were found to be unstable at finite Reynolds numbers, where Mode II is the dominant instability among the unstable modes for plane Couette flow. The most unstable mode for plane Couette &
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Poiseuille flow is Mode 0, which is not a member of the even modes. Both even and odd modes are acoustic modes created by acoustic reflections between a will and a relative sonic line. The necessary condition for the existence of such acoustic wave modes is that there is a region of locally supersonic mean flow relative to the phase speed of the instability wave. The effects of viscosity and compressibility are also investigated and shown to have a stabilizing role in all cases studied. Couette-Poiseuille flow stability is investigated in case of a choked channel flow, where the maximum velocity in the channel corresponds to sonic velocity. Neutral stability contours were obtained for this flow as a function if the wave number,Reynolds number and the upper wall Mach number. The critical Reynolds number is found as 5718.338 for an upper wall Mach number of 0.0001, corresponding to the fully Poiseuille case.
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Wang, Aihua. "Effects of free surface heat transfer and shape on thermocapillary flow of high Prandtl number fluids." online version, 2005. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=case1094225212.
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Wang, Xiaojun. "Well-posedness results for a class of complex flow problems in the high Weissenberg number limit." Diss., Virginia Tech, 2012. http://hdl.handle.net/10919/27669.
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For simple fluids, or Newtonian fluids, the study of the Navier-Stokes equations in the high Reynolds number limit brings about two fundamental research subjects, the Euler equations and the Prandtl's system. The consideration of infinite Reynolds number reduces the Navier-Stokes equations to the Euler equations, both of which are dealing with the entire flow region. Prandtl's system consists of the governing equations of the boundary layer, a thin layer formed at the wall boundary where viscosity cannot be neglected.
In this dissertation, we investigate the upper convected Maxwell(UCM) model for complex fluids, or non-Newtonian fluids, in the high Weissenberg number limit. This is analogous to the Newtonian fluids in the high Reynolds number limit. We present two well-posedness results.
The first result is on an initial-boundary value problem for incompressible hypoelastic materials which arise as a high Weissenberg number limit of viscoelastic fluids. We first assume the stress tensor is rank-one and develop energy estimates to show the problem is locally well-posed. Then we show the more general case can be handled in the same spirit. This problem is closely related to the incompressible ideal magneto-hydrodynamics (MHD) system.
The second result addresses the formulation of a time-dependent elastic boundary layer through scaling analysis. We show the well-posedness of this boundary layer by transforming to Lagrangian coordinates. In contrast to the possible ill-posedness of Prandtl's system in Newtonian fluids, we prove that in non-Newtonian fluids the stress boundary layer problem is well-posed.Ph. D.
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WANG, AIHUA. "EFFECTS OF FREE SURFACE HEAT TRANSFER AND SHAPE ON THERMOCAPILLARY FLOW OF HIGH PANDTL NUMBER FLUIDS." Case Western Reserve University School of Graduate Studies / OhioLINK, 2005. http://rave.ohiolink.edu/etdc/view?acc_num=case1094682055.
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Souccar, Adham W. "Heat Transfer and Mass Transfer with Heat Generation in Drops at High Peclet Number." University of Toledo / OhioLINK, 2007. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1177603981.
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Labadin, Jane. "Theory and computation of high Reynolds number fluid flow over and around two and three dimensional obstacles." Thesis, Imperial College London, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.397653.
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Nguyen, Cuong Quoc. "Interaction between secondary flow & film cooling jets of a realistic annular airfoil cascade (high mach number)." Doctoral diss., University of Central Florida, 2010. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/4601.
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Film cooling is investigated on a flat plate both numerically and experimentally. Conical shaped film hole are investigated extensively and contribute to the current literature data, which is extremely rare in the open public domain. Both configuration of the cylindrical film holes, with and without a trench, are investigated in detail. Design of experiment technique was performed to find an optimum combination of both geometrical and fluid parameters to achieve the best film cooling performance. From this part of the study, it shows that film cooling performance can be enhanced up to 250% with the trenched film cooling versus non-trenched case provided the same amount of coolant. Since most of the relevant open literature is about film cooling on flat plate endwall cascade with linear extrusion airfoil, the purpose of the second part of this study is to examine the interaction of the secondary flow inside a 3D cascade and the injected film cooling jets. This is employed on the first stage of the aircraft gas turbine engine to protect the curvilinear (annular) endwall platform. The current study investigates the interaction between injected film jets and the secondary flow both experimentally and numerically at high Mach number (M=0.7). Validation shows good agreement between obtained data with the open literature. In general, it can be concluded that with an appropriate film coolant to mainstream blowing ratio, one can not only achieve the best film cooling effectiveness (FCE or eta]) on the downstream endwall but also maintain almost the same aerodynamic loss as in the un-cooled baseline case. Film performance acts nonlinearly with respect to blowing ratios as with film cooling on flat plate, in the other hand, with a right blowing ratio, film cooling performance is not affect much by secondary flow. In turn, film cooling jets do not increase pressure loss at the downstream wake area of the blades.ID: 029050151; System requirements: World Wide Web browser and PDF reader.; Mode of access: World Wide Web.; Thesis (Ph.D.)--University of Central Florida, 2010.; Includes bibliographical references (p. 146-149).
Ph.D.
Doctorate
Department of Mechanical, Materials and Aerospace Engineering
Engineering and Computer Science
Thermo-Fluid Sciences
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Ai, Wei. "Glissement moléculaire dans les matériaux lignocellulosiques : mesures de perméabilité apparente et identification de paramètres morphologiques." Thesis, Université Paris-Saclay (ComUE), 2016. http://www.theses.fr/2016SACLC074/document.
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La perméabilité est l'un de paramètres importants pour tous les procédés faisant intervenir des transferts couplés de chaleur et de masse. Sa valeur est directement liée à la morphologie du réseau de pores, clairement double échelle dans le cas du bois. Il existe plusieurs outils d’investigation 3-D par exemple la micro-tomographie voire nano-tomographie pour décrire la morphologie des pores. Néanmoins, ces investigations 3-D échouent pour les plus petits pores dans le bois, qui peuvent avoir une taille largement inférieure au micromètre. Ce travail de thèse utilise l'effet du libre parcours moyen du gaz sur la perméabilité apparente pour identifier la taille des pores utilisés par le cheminement du fluide.Une approche équilibrée entre expérimentation et modélisation est proposée. Dans la première partie du travail, nous avons développé un dispositif original destiné à mesurer la perméabilité apparente sur une large plage de niveau de pression moyenne. Ce dispositif ne comporte pas de débitmètre : le flux massique est simplement obtenu par la relaxation de la différence de pression entre deux réservoirs de volume connu.Ce dispositif a permis de mesurer la perméabilité apparente en fonction de la pression moyenne pour différents matériaux. Les valeurs obtenues de perméabilité intrinsèque sont en bon accord avec les publications précédentes.L'effet de la pression moyenne sur la perméabilité apparente a été analysé pour identifier des paramètres structuraux des milieux poreux. Partant d'un agencement série/parallèle de pores, les paramètres structuraux sont identifiés par méthode inverse en tirant profit du changement de régime d’écoulement avec le nombre de Knudsen (du régime de Darcy vers le régime de glissement moléculaire lorsque le nombre de Knudsen passe de zéro à l’infini).Cette approche a été validée avec des membranes à pore monodisperse grâce à une observation en microscopie électronique à balayage. Les paramètres ont ensuite été identifiés sur des échantillons de bois, selon différentes directions et sur des matériaux à base de bois. Ils confirment certaines données de la littérature, et apportent un éclairage nouveau, notamment sur les chemins de migration transverse chez le hêtrePermeability is one of the important parameters for all processes involving coupled heat and mass transfer. Its value is directly related to the morphology of the pore network, clearly a dual scale organisation in the case of wood. Nowadays, several 3D investigative tools exist, such as micro-tomography or nano-tomography. However, these 3-D investigations fail for the smallest pores active in fluid flow in wood, due to their submicron size. The present work takes advantage of the effect of the mean free path on the apparent gaseous permeability to identify the pore size of the pore network.A balanced approach between experimentation and modelling is proposed. In the first part of the work we have developed an original device for measuring the apparent permeability over a wide range of average pressure. This device was conceived to work without flowmeter: the mass flow is obtained by the relaxation of the pressure difference between two tanks. This device was used to measure the apparent permeability as a function of the average pressure for different materials.The intrinsic permeability values obtained are in good agreement with literature data.The effect of the average pressure on the apparent permeability was analysed to identify structural parameters of the porous media. Starting from a serial / parallel arrangement, the structural parameters are identified by inverse method taking advantage of the dependence of the flow regime with Knudsen's number (from Darcy's regime to pure molecular slip regime when Knudsen's number shifts from zero to infinity).This approach was validated with a monodisperse membrane, whose pore size was determined using a scanning electron microscopy. Structural parameters were then identified on wood samples, measured along different directions and on wood-based materials. They confirm literature data and bring new outcomes, namely regarding the fluid pathway in beech in radial and tangential directions
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Fritzelas, Anastasios E. "A water tunnel investigation of the influence of Reynolds number on the high-incidence flow over double-delta wings." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1996. http://handle.dtic.mil/100.2/ADA310282.
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Athanasiadis, Aristotelis. "Three-dimensional hybrid grid generation with application to high Reynolds number viscous flows." Doctoral thesis, Universite Libre de Bruxelles, 2004. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/211130.
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In this thesis, an approach is presented for the generation of grids suitable for the simulation of high Reynolds number viscous flows in complex three-dimensional geometries. The automatic and reliable generation of such grids is today on the biggest bottlenecks in the industrial CFD simulation environment.In the proposed approach, unstructured tetrahedral grids are employed for the regions far from the viscous boundaries of the domain, while semi-structured layers of high aspect ratio prismatic and hexahedral elements are used to provide the necessary grid resolution inside the boundary layers and normal to the viscous walls. The definition of the domain model is based on the STEP ISO standard and the topological information contained in the model is used for applying the hierarchical grid generation parameters defined by the user. An efficient, high-quality and robust algorithm is presented for the generation of the unstructured simplicial (triangular of tetrahedral) part of the grid. The algorithm is based on the Delaunay triangulation and the internal grid points are created following a centroid or frontal approach. For the surface grid generation, a hybrid approach is also proposed similar to the volume.
Semi-structured grids are generated on the surface grid (both on the edges and faces of the domain) to improve the grid resolution around convex and concave ridges and corners, by aligning the grid elements in the directions of high solution gradients along the surface. A method is also developed for automatically setting the grid generation parameters related to the surface grid generation based on the curvature of the surface in order to obtain an accurate and smooth surface grid. Finally, a semi-structured prismatic/hexahedral grid generation algorithm is presented for the generation of the part of grid close to the viscous walls of the domain. The algorithm is further extended with improvements meant to increase the grid quality around concave and convex ridges of the domain, where the semi-structured grids are known to be inadequate.
The combined methodology is demonstrated on a variety of complex examples mainly from the automotive and aeronautical industry.
Doctorat en sciences appliquées
info:eu-repo/semantics/nonPublished
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Bennington, Jeremy Lawrence. "Effects of Various Shaped Roughness Elements in Two-Dimensional High Reynolds Number Turbulent Boundary Layers." Thesis, Virginia Tech, 2004. http://hdl.handle.net/10919/34907.
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Modeling the effects of surface roughness is an area of concern in many practical engineering applications. Many current roughness models to this point have involved the use of empirical 'constants' and equivalent sand grain roughness. These underdeveloped concepts have little direct relationship to realistic roughness and cannot predict accurately and consistently the flow characteristics for different roughness shapes. In order to aid in the development of turbulence models, the present research is centered around the experimental investigation of seven various shaped single roughness elements and their effects on turbulence quantities in a two-dimensional turbulent boundary layer.
The elements under scrutiny are as follows: cone, cone with spatial variations equal to the smallest sublayer structure length scale, cone with spatial variations equal to 2.5 times the smallest sublayer structure length scale, Gaussian-shaped element, hemisphere, cube aligned perpendicular to the flow (cube at 90°), and a cube rotated 45° relative to the flow. The roughness element heights, k+, non-dimensionalized by the friction velocity (U_tau) of the approaching turbulent boundary layer, are 145, 145, 145, 145, 80, 98, and 98 respectively. Analysis of a three-dimensional fetch of the same Gaussian-shaped elements described previously was also undertaken. In order to analyze the complex flow fields, detailed measurements were obtained using a fine-measurement-volume (50 micron diameter) three-velocity component laser-Doppler velocimetry (LDV) system.
The data reveals the formation of a horseshoe vortex in front of the element, which induces the downwash of higher momentum fluid toward the wall. This 'sweep' motion not only creates high Reynolds stresses (v^2, w^2, -uv) downstream of the element, but also leads to higher skin-friction drag. Triple products were also found to be very significant near the height of the element. These parameters are important in regards to the contribution of the production and diffusion of the turbulent kinetic energy in the flow. The 'peakiness' of the roughness element was found to have a direct correlation to the production of circulation, whereas the spatial smoothing does not have an immense effect on this parameter. The peaked elements were found to have a similar trend in the decay of circulation in the streamwise direction. These elements tend to show a decay proportional to (x/d)^-1.12, whereas the cube elements and the hemisphere do not have a common trend.
A model equation is proposed for a drag correlation common to all roughness elements. This equation takes into account the viscous drag and pressure drag terms in the calculation of the actual drag due to the roughness elements presence in the boundary layer. The size, shape, frontal and wetted surface areas of the roughness elements are related to one another via this model equation. Flow drawings related to each element are presented which gives rise to a deeper understanding of the physics of the flow associated with each roughness element.
Master of Science
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Kubrak, Boris. "Direct numerical simulation of gas transfer at the air-water interface in a buoyant-convective flow environment." Thesis, Brunel University, 2014. http://bura.brunel.ac.uk/handle/2438/10196.
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The gas transfer process across the air-water interface in a buoyant-convective environment has been investigated by Direct Numerical Simulation (DNS) to gain improved understanding of the mechanisms that control the process. The process is controlled by a combination of molecular diffusion and turbulent transport by natural convection. The convection when a water surface is cooled is combination of the Rayleigh-B´enard convection and the Rayleigh-Taylor instability. It is therefore necessary to accurately resolve the flow field as well as the molecular diffusion and the turbulent transport which contribute to the total flux. One of the challenges from a numerical point of view is to handle the very different levels of diffusion when solving the convection-diffusion equation. The temperature diffusion in water is relatively high whereas the molecular diffusion for most environmentally important gases is very low. This low molecular diffusion leads to steep gradients in the gas concentration, especially near the interface. Resolving the steep gradients is the limiting factor for an accurate resolution of the gas concentration field. Therefore a detailed study has been carried out to find the limits of an accurate resolution of the transport for a low diffusivity scalar. This problem of diffusive scalar transport was studied in numerous 1D, 2D and 3D numerical simulations. A fifth-order weighted non-oscillatory scheme (WENO) was deployed to solve the convection of the scalars, in this case gas concentration and temperature. The WENO-scheme was modified and tested in 1D scalar transport to work on non-uniform meshes. To solve the 2D and 3D velocity field the incompressible Navier-Stokes equations were solved on a staggered mesh. The convective terms were solved using a fourth-order accurate kinetic energy conserving discretization while the diffusive terms were solved using a fourth-order central method. The diffusive terms were discretized using a fourth-order central finite difference method for the second derivative. For the time-integration of the velocity field a second-order Adams-Bashworth method was employed. The Boussinesq approximation was employed to model the buoyancy due to temperature differences in the water. A linear relationship between temperature and density was assumed. A mesh sensitivity study found that the velocity field is fully resolved on a relatively coarse mesh as the level of turbulence is relatively low. However a finer mesh for the gas concentration field is required to fully capture the steep gradients that occur because of its low diffusivity. A combined dual meshing approach was used where the velocity field was solved on a coarser mesh and the scalar field (gas concentration and temperature) was solved on an overlaying finer submesh. The velocities were interpolated by a second-order method onto the finer sub-mesh. A mesh sensitivity study identified a minimum mesh size required for an accurate solution of the scalar field for a range of Schmidt numbers from Sc = 20 to Sc = 500. Initially the Rayleigh-B´enard convection leads to very fine plumes of cold liquid of high gas concentration that penetrate the deeper regions. High concentration areas remain in fine tubes that are fed from the surface. The temperature however diffuses much stronger and faster over time and the results show that temperature alone is not a good identifier for detailed high concentration areas when the gas transfer is investigated experimentally. For large timescales the temperature field becomes much more homogeneous whereas the concentration field stays more heterogeneous. However, the temperature can be used to estimate the overall transfer velocity KL. If the temperature behaves like a passive scalar a relation between Schmidt or Prandtl number and KL is evident. A qualitative comparison of the numerical results from this work to existing experiments was also carried out. Laser Induced Fluorescence (LIF) images of the oxygen concentration field and Schlieren photography has been compared to the results from the 3D simulations, which were found to be in good agreement. A detailed quantitative analysis of the process was carried out. A study of the horizontally averaged convective and diffusive mass flux enabled the calculation of transfer velocity KL at the interface. With KL known the renewal rate r for the so called surface renewal model could be determined. It was found that the renewal rates are higher than in experiments in a grid stirred tank. The horizontally averaged mean and fluctuating concentration profiles were analysed and from that the boundary layer thickness could be accurately monitored over time. A lot of this new DNS data obtained in this research might be inaccessible in experiments and reveal previously unknown details of the gas transfer at the air water interface.
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Xu, Ying. "TWO-DIMENSIONAL SIMULATION OF SOLIDIFICATION IN FLOW FIELD USING PHASE-FIELD MODEL|MULTISCALE METHOD IMPLEMENTATION." Lexington, Ky. : [University of Kentucky Libraries], 2006. http://lib.uky.edu/ETD/ukymeen2006d00524/YingXu_Dissertation_2006.pdf.
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Thesis (Ph. D.)--University of Kentucky, 2006.Title from document title page (viewed on January 25, 2007). Document formatted into pages; contains: xiii, 162 p. : ill. (some col.). Includes abstract and vita. Includes bibliographical references (p. 151-157).
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Russ, Thomas William. "A surface flow visualization study of boundary layer behavior on the blades of a solid-wall compressor cascade at high angles of attack." Thesis, Virginia Polytechnic Institute and State University, 1987. http://hdl.handle.net/10919/53161.
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The oil-film surface flow visualization technique was applied to circular arc compressor blades in a solid wall, high aspect ratio cascade for the purpose of describing the transition from corner stall to full blade stall, and the blade surface flow under fully stalled conditions. Photos of the visualizations for three stagger angles are presented and analyzed. A map quantitatively describing the observed boundary layer development at midspan is presented.
The most interesting discovery of the work showed the suction surface flow to be essentially two-dimensional, in the geometric sense, preceding and following the transition to a fully separated flow at the leading edge. Corner stall was the observed three-dimensional mechanism prior to full stall. For fully-stalled conditions, the three-dimensional mechanism took the form of recirculating flow regions at the blade ends. Complete separation at the leading edge occurred at lower angles of attack for the higher stagger angles. Special blade oil-flow tests were conducted to evaluate Reynolds number and tip clearance effects on boundary layer development.
The experimental work was done as part of a larger research program aimed at measuring and predicting the stalled performance of a compressor cascade.Master of Science
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Busquet, Denis. "Study of a high Reynolds number flow around a two dimensional airfoil at stall : an approach coupling a RANS framework and bifurcation theory." Thesis, Institut polytechnique de Paris, 2020. http://www.theses.fr/2020IPPAX027.
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Le phénomène de décrochage est souvent décrit comme une chute soudaine de portance lorsque l'angle d'incidence augmente. Ce phénomène est préjudiciable aux avions et aux hélicoptères et limite leur enveloppe de vol. Plusieurs études numériques et expérimentales, particulièrement centrées sur le décrochage statique (i.e. pour des ailes fixes), ont révélé des phénomènes apparaissant proche de l'angle de décrochage : des oscillations basses fréquences et une hystérésis des coefficients aérodynamiques. Le premier phénomène se traduit par une oscillation de la portance entre une valeur maximale et une valeur minimale obtenues quand l'écoulement est respectivement attaché ou détaché. Le nombre de Strouhal associé (St ~ 0.02) est habituellement un ordre de grandeur plus faible que le nombre de Strouhal (St ~ 0.2) du lâcher tourbillonnaire qui apparaît pour de plus grandes incidences. Le second phénomène est caractérisé par l'existence de solutions moyennées en temps autour de l'angle de décrochage qui diffèrent selon que l'angle d'attaque est augmenté ou diminué.L'objectif de cette thèse est d'avoir une meilleure compréhension de l'origine du décrochage et de ces deux phénomènes grâce à des simulations numériques d'écoulements turbulents modélisés par une approche RANS (Reynolds-Averaged Navier-Stokes). Une combinaison de diverses approches numériques et théoriques (simulations instationnaires, continuation de solutions stationnaires, stabilité linéaire et analyse de bifurcation) est développée et appliquée dans le cas du décrochage d'un profil 2D de pale d'hélicoptère, le OA209, à bas nombre de Mach (M~0.2) et haut nombre de Reynolds (Re~1.8x10^6).Des solutions stationnaires sont calculées pour différents angles d'attaques en considérant le modèle de turbulence de Spalart-Allmaras et en utilisant des méthodes de continuation (continuation naïve et méthode du pseudo-arclength). Les résultats mettent en évidence une branche supérieure (à haute portance), une branche inférieure (à basse portance) et, entre les deux, une branche du milieu. Pour un même angle d'attaque, des solutions coexistent proche de l’angle de décrochage sur chacune des branches, ce qui est caractéristique d’un phénomène d'hystérésis. Des analyses de stabilité linéaire réalisées autour de ces états d'équilibres révèlent l'existence d'un mode instable basse fréquence associé au décrochage. L'évolution des valeurs propres associées à ce mode le long des branches stationnaires nous permet d'établir une première version du diagramme de bifurcation. Afin de le compléter, des calculs RANS instationnaires sont réalisés et des cycles limites basse fréquence sont identifiés sur une plage réduite d'angles d'attaque proches du décrochage. Ces solutions périodiques sont caractérisées par des valeurs de portance maximales et minimales plus grandes et plus petites que celles des solutions stationnaires à haute et basse portance associées, respectivement. Pour clarifier la formation et la disparition de ce cycle limite basse fréquence et permettre une meilleure compréhension du scénario de bifurcation, un modèle à une équation reproduisant les caractéristiques linéaires du phénomène est proposé. Ce modèle non-linéaire du décrochage statique est calibré sur les états stationnaires et leur comportement linéaire obtenus par calculs RANS. Une étude du comportement non-linéaire de ce modèle révèle un scenario possible qui pourrait conduire à l'apparition et à la disparition du cycle limite basse fréquence. Finalement, le cas d'un NACA0012 à nombre de Reynolds Re~1.0x10^6 est considéré pour valider la robustesse du scenario identifiéAirfoil stall is commonly described as a sudden drop of lift when increasing the angle of attack. This phenomenon is detrimental to aircrafts and helicopters, since it strongly limits their flight envelope. Past experimental and numerical investigations, specifically dedicated to static stall (i.e. for rigid wings), have clearly identified two phenomena which appear close to the stall angle: low-frequency oscillations and hysteresis of the lift coefficient. The first one is an oscillation of the lift between maximal and minimal values obtained when the instantaneous flow is attached and fully separated, respectively. The corresponding Strouhal number (St ~ 0.02) is usually an order of magnitude lower than the Strouhal number (St ~ 0.2) of the vortex-shedding that may appear for larger angles of attack. The second phenomenon is characterized by the existence of different time-averaged solutions around the stall angle depending on whether the angle of attack is increased or decreased.The objective of this thesis is to better understand the origin of stall and of these two phenomena using numerical simulations of turbulent flows modelled in the RANS (Reynolds-Averaged Navier-Stokes) framework. A combination of various numerical and theoretical approaches (unsteady simulations, continuation of steady solutions, linear stability and bifurcation analyses) have been developed and applied to the stall of a 2D helicopter blade airfoil OA209 at low Mach number (M~0.2) and high Reynolds number (Re~1.8x10^6).Steady RANS computations are performed using Spalart-Allmaras model to obtain steady states for several angles of attack taking advantage of continuation methods (naive continuation and pseudo-arclength method). The results highlight one upper branch (of high lift), one lower branch (of low lift) and, in between, a middle branch. Close to stall, for a same angle of attack, solutions coexist on each branch, characterizing a hysteresis phenomenon. Linear stability analyses performed around these equilibrium states reveal the existence of a low-frequency unstable mode associated to stall. The evolution of the corresponding eigenvalues along the branches of steady solutions allows us to establish a first sketch of the bifurcation scenario. Unsteady RANS computations are carried out to complete it. Low-frequency limit-cycle solutions have been identified in a narrow range of angles of attack close stall. These periodic solutions are characterized by maximal and minimal instantaneous values of the lift that are larger and lower than the associated high-lift and low-lift steady solutions, respectively. To clarify the formation and disappearance of this low-frequency limit cycle, and thus improve our knowledge about the bifurcation scenario, a one-equation model reproducing the linear characteristics of the phenomenon is proposed. This nonlinear static-stall model is calibrated on the steady states and their linear behavior obtained with RANS computations. A study of the nonlinear behavior of this model then reveals a possible scenario leading to the appearance and collapsing of the low frequency limit cycle. Finally, the case of a NACA0012 at Re~1.0x10^6 is considered to check the robustness of the scenario identified
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Popoola, Olubunmi Tolulope. "Numerical, Analytical, and Experimental Studies of Reciprocating Mechanism Driven Heat Loops for High Heat Flux Cooling." FIU Digital Commons, 2017. https://digitalcommons.fiu.edu/etd/3505.
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The Reciprocating Mechanism Driven Heat Loop (RMDHL) is a novel heat transfer device that utilizes reciprocating flow, either single-phase or two-phase flow, to enhance the thermal management in high tech inventions. The device attains a high heat transfer rate through a reciprocating flow of the working fluid inside the heat transfer device. Although the concept of the device has been tested and validated experimentally, analytical or numerical studies have not been undertaken to understand its working mechanism and provide guidance for the device design. The objectives of this study are to understand the underlying physical mechanisms of heat transfer in internal reciprocating flow, formulate corresponding heat transfer correlations, conduct an experimental study for the heat transfer coefficient, and numerically model the single-phase and two-phase operations of the RMDHL to predict its performance under different working conditions. The two-phase flow boiling model was developed from the Rensselaer Polytechnic Institute (RPI) model, and a virtual loop written in C programming language was used to eliminate the need for fluid structure interaction (FSI) modelling. The accuracy of several turbulence formulations, including the Standard, RNG, and Realizable k-ɛ Models, Standard and SST k-ω Models, Transition k - - ω Model, and Transition SST Model, have been tested in conjunction with a CFD solver to select the most suitable turbulence modelling techniques. The numerical results obtained from the single-phase and two-phase models are compared with relevant experimental data with good agreement. Three-dimensional numerical results indicate that the RMDHL can meaningfully reduce the peak temperature of an electronic device and result in significantly more uniform temperature across the device. In addition to the numerical study, experimental studies in conjunction with analytical studies are undertaken. Experimental data and related heat transfer coefficient as well as practically useful semi-empirical correlations have been produced, all of which provide archival information for the design of heat transfer devices involving a reciprocating flow. In particular, this research will lead to the development of more powerful RMDHLs, achieve a heat flux goal of 600 W/cm2, and significantly advance the thermal management at various levels. Considering the other advantages of coolant leakage free and the absence of cavitation problems, the RMDHL could also be employed for aerospace and battery cooling applications.
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Crispatzu, Giuliano [Verfasser], Michael [Gutachter] Nothnagel, Bernd [Gutachter] Wollnik, Joachim [Gutachter] Krug, and Holger [Gutachter] Thiele. "Integrative approaches to high-throughput data in lymphoid leukemias (on transcriptomes, the whole-genome mutational landscape, flow cytometry and gene copy-number alterations) / Giuliano Crispatzu ; Gutachter: Michael Nothnagel, Bernd Wollnik, Joachim Krug, Holger Thiele." Köln : Universitäts- und Stadtbibliothek Köln, 2017. http://d-nb.info/1141904438/34.
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Ferdos, Farzad. "Internal Erosion Phenomena in Embankment Dams : Throughflow and internal erosion mechanisms." Doctoral thesis, KTH, Byggvetenskap, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-193627.
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In this study, two major internal erosion initiation processes, suffusion and concentrated leak mechanisms, which lead to both defect formation in a dam’s body and its foundation and high throughflow in dams subjected to internal erosion were studied. This understanding has the potential to facilitate numerical modelling and expedite dam safety assessment studies. The throughflow properties of coarse rockfill material were studied by; analysing filed pump test data, performing extensive laboratory experiments with a large-scale apparatus and numerically simulating the three-dimensional flow through coarse rock materials, replicating the material used in the laboratory experiments. Results from the tests demonstrate that the parameters of the nonlinear momentum equation of the flow depend on the Reynolds number for pore Reynolds numbers lower than 60000. Numerical studies were also carried out to conduct numerical experiments. By applying a Lagrangian particle tracking method, a model for estimating the lengths of the flow channels in the porous media was developed. The shear forces exerted on the coarse particles in the porous media were found to be significantly dependent on the inertial forces of the flow. Suffusion and concentrated leak mechanisms were also studied by means of laboratory experiments to develop a theoretical framework for continuum-based numerical modelling. An erosion apparatus was designed and constructed with the capability of applying hydraulic and mechanical loading. Results were then used to develop constitutive laws of the soil erosion as a function of the applied hydromechanical load for both suffusion and concentrated leak mechanisms. Both the initiation and mass removal rate of were found to be dependent on the soil in-situ stresses. A three-dimensional electrical-resistivity-based tomography method was also adopted for the internal erosion apparatus and was found to be successful in visualising the porosity evolution due to suffusion.QC 20161006
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Padioleau, Thomas. "Development of "all-régime" AMR simulation methods for fluid dynamics, application in astrophysics and two-phase flows." Thesis, université Paris-Saclay, 2020. http://www.theses.fr/2020UPASP086.
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Bien que performantes pour la capture des chocs, la plupart des méthodes de simulation standards ne sont pas adaptées à des régimes de Mach variés. Des méthodes numériques innovantes, utilisant des schémas de type Volumes Finis, robustes et précises uniformément selon le nombre de Mach (dites "tout régime") ont été récemment élaborées au CEA. Ces méthodes permettent de résoudre les équations de la mécanique des fluides compressibles pour capturer des chocs, mais aussi pour simuler des écoulements à très faible vitesse. Fort de ces résultats prometteurs, nous proposons dans cette thèse de mettre à l’épreuve ces nouvelles méthodes dans deux domaines applicatifs différents: les écoulements diphasiques à petit échelle et les écoulements compressibles en astrophysique. Pour ces deux domaines la simulation multi-régime est un point difficile. En effet, ces deux contextes d’applications ont pour cœur une modélisation d’écoulement compressible mais mettent en jeu des phénomènes de convection et de compressibilité à des régimes de Mach très variés. L’approche "tout régime" permettra de capturer des phénomènes très compressibles tout en gardant la précision sur les écoulements basse vitesseAlthough classic simulation methods for compressible flow are efficient for shock capturing, they are not adapted to variable Mach regimes. Innovative methods using Finite Volume numerical schemes, robust and uniformly accurate with respect to the Mach number (so-called "all-regime"), were recently developed at CEA. These methods allow to solve the equations of compressible flows for both shocks capturing and flows involving very low material speed. Using the ground of these promising results, we propose within this thesis to challenge these new methods in two different application areas: small scale two-phase flows and compressible flows in astrophysics. For both contexts the multi-regime simulation is a key issue: they both rely on a compressible flow modeling but involve convection and compressibility in highly-variable Mach regimes. The "all-regime" approach is a good candidate for capturing highly compressible phenomena while preserving the accuracy in the low speed flows
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Capelo, Holly. "Dynamics of Suspended Dust Grains: Experimental Investigations and Implications for Protoplanetary Discs." Doctoral thesis, 2017. http://hdl.handle.net/11858/00-1735-0000-002E-E402-0.
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"A MEMS Knudsen pump for high gas flow applications." UNIVERSITY OF LOUISVILLE, 2008. http://pqdtopen.proquest.com/#viewpdf?dispub=1455160.
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Copic, Davor. "A MEMS Knudsen pump for high gas flow applications." 2008. http://etd.louisville.edu/data/UofL0414t2008.pdf.
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Thesis (M.Eng.)--University of Louisville, 2008.Title and description from thesis home page (viewed May 14, 2008). Department of Mechanical Engineering. "April 2008." Includes bibliographical references (p. 55-56).
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Nadge, Pankaj M. "High Reynolds Number Flow Over A Backward-Facing Step." Thesis, 2012. http://etd.iisc.ernet.in/handle/2005/2542.
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Flow separation and reattachment happens in many fluid mechanical situations occurring in engineering applications as well as in nature. The flow over a backward-facing step represents a geometrically simple flow situation exhibiting both flow separation and reattachment. Broadly speaking there are only two important parameters in the problem, the Reynolds number(Re) based on the step height(h),and a geometrical parameter, referred to as the Expansion ratio(ER), defined as the downstream channel height to the upstream channel height. In spite of the relative simplicity of this geometry, the flow downstream is quite complex. The main focus of the present work is to elucidate the unsteady three-dimensional coherent structures present in this flow at large Re, Re>36,000,based on the step height(h). For this, we use velocity field measurements from Particle Image Velocimetry (PIV)in conjunction with hotwire anemometry measurements.
The time-averaged structure of this flow is first studied in detail, including the effect of Reynolds number(Re) and Expansion Ratio(ER), on it. These studies show that at sufficiently large Re (Re>20,000), the reattachment length becomes independent of Re. The detailed internal structure of the separation bubble is also found to be independent of Re, but for Revalues that are relatively larger(Re>36,000). At large Re, the main effect of ER ,is found to be on the reattachment length, which increases with ER and saturates for ER values greater than about 1.8. The detailed internal structure of the separation bubble has been mapped at high Re and is found to be nearly the same for all ER, when the streamwise length is normalized by the reattachment length.
In order to elucidate the unsteady coherent vortical structures, PIV measurements are done in two orthogonal planes downstream of the backward-facing step. These measurements are done for ER= 1.50 at large Re(Re=36,000) and in a large aspect ratio facility(AR= span length/step height= 24); the latter being important to avoid any effects due to span-wise confinement. In the spanwise plane parallel to the lower wall(x-z plane),instantaneous velocity fields show counter rotating vortex pairs, which is a signature of the three-dimensional vortical structures in this plane. Using conditional averaging, this counter-rotating vortex pair signature is captured right from upstream of the step, to well after reattachment. Spatial correlations are used to get the length scale of these coherent vortical structures, which varies substantially from the attached boundary layer before separation to the region after reattachment. The variation of these structures in the cross-stream (vertical) direction at reattachment and beyond gives an idea about their three dimensional shape. The circulation of these counter-rotating pairs is measured from the conditionally aver-aged fields, and is found to increase with streamwise distance reaching normalized circulation values (Γ/Uoh) of about 0.5 around reattachment.
Velocity spectra downstream of the step show peaks corresponding to both the shear layer frequency(Stsl)and a relatively lower frequency that corresponds to large-scale shedding from the separation bubble (Stb); the latter in particular being quasi-periodic. Small amplitude sinusoidal forcing at the shedding frequency(Stb) is applied close to the step, by blowing and suction, to make the quasi-periodic shedding more regular. Measurements show that this has a very small effect on both the mean separation bubble and on the counter-rotating structures in the x-z plane. This mild forcing however enables phase locked PIV measurements to be made which shows the bubble shedding phenomenon in the cross-stream plane(side view or x-y plane).
The phase-averaged velocity fields show significant variations from phase to phase. Although there is some hint of structures being shed, from these phase-averaged fields, it is not very clear. One of the primary reasons is the fact that the flow is effectively spanwise averaged, as the three-dimensional structures are not locked in the spanwise direction. To get a three dimensional view of the sheddin gphenomenon, it is necessary to lock the spanwise location with respect to the three-dimensional vortical structures before averaging across the different phases. We use the condition, u’<- urms, to locate the central plane between the counter-rotating structures, which in effect are the “legs” of the three-dimensional structure. With this condition, we effectively get a slice of the shedding cycle cutting through the “head” of the three-dimensional structure. Apart from this cut, we also get a cut between adjacent structures from the weak sweep events, with the condition u’<- urms. Using these conditions, on the phase-locked velocity fields, we effectively lock the structures in time, as well as in the spanwise direction. With this ,a clearer picture of the shedding process emerges. The flow is highly three-dimensional near reattachment and the shedding of the separation bubble is modulated in the spanwise direction owing to the three-dimensional hairpin like vortical structures in the flow. The separation bubble is seen bulged out and lifted high at locations where the head of the hairpin vortex passes, owing to the strong ejection of fluid caused by the vortical structure. On the other hand, outside the hairpin vortices, weak sweep events push the flow towards the wall and make it shallow and less prominent, with the shedding being very weak in this plane. From these observations, a three-dimensional picture of the flow is proposed.
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Ma, Huiping. "Microscopic analysis of high Forchheimer number flow in porous media." 1994. http://hdl.handle.net/1993/18178.
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Dekoschak, Alison Leah. "Active and passive flow control of a high Reynolds number axisymmetric jet." 2004. http://etd.nd.edu/ETD-db/theses/available/etd-12162004-114804/.
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Thesis (M.S.)--University of Notre Dame, 2004.Thesis directed by Flint O. Thomas for the Department of Aerospace and Mechanical Engineering. "November 2004." Includes bibliographical references (leaves [62-63]).
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LAI, Hsin Chung, and 賴信忠. "Analysis of Convective Flow in an Isothermal Tube for High Rayleigh Number." Thesis, 1993. http://ndltd.ncl.edu.tw/handle/38422617092704594471.
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Peng, HsiuChin, and 彭修慶. "Flow field at high incoming velocity and Reynolds number measurements using Particle Imaging Velocimetry." Thesis, 2003. http://ndltd.ncl.edu.tw/handle/16111905132216223270.
Full textAbstract:
碩士國立臺灣大學
工程科學與海洋工程學系
91
This study aims to establish a P.I.V.（Particle Image Velocimetry）system by measuring the juncture vortex come up near the intersection of a circular cylinder and a flat plate in a recurring hydraulic tank. Two identifying particle methods ,（1）Using cross-correlation principle method and（2）an artificial neural network method are used to verify the practicality of this P.I.V. system. The result shows that the P.I.V. system can get a good quantitative analysis. The result also shows that the neutral network method had a better outcome to the measurement of juncture vortices than the using cross-correlation principle methods at lower incoming velocities, but the cross-correlation principle method identifies more particles than the neutral network method at higher incoming velocity conditions.
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Fuzier, Sylvie Van Sciver Steven W. "Heat transfer and pressure drop in forced flow helium II at high Reynolds numbers." Diss., 2004. http://etd.lib.fsu.edu/theses/available/etd-11222004-173235.
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Thesis (Ph. D.)--Florida State University, 2004.Advisor: Dr. Steven W. Van Sciver, Florida State University, College of Engineering, Dept. of Mechanical Engineering. Title and description from dissertation home page (viewed May 25, 2005). Includes bibliographical references.
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戴可茵. "A Numerical Study on Different Shape Column under 3D Flow Field with High Reynolds Number." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/39712499462668708114.
Full textAbstract:
碩士國立臺灣海洋大學
機械與機電工程學系
100
The purpose of this thesis is that hope to establish the assessment procedure for flow fields of cylinder from the result, and to provide an auxiliary instument to industry and standard of engineering. specifications of a viable reference tool for the study of the main purpose of and motivation. In this study, to explore the intensity of the flow through the different shape of the cylinder by FLOW-3D, and to compare them of the total drag coefficient. In this study, to simulate and compare the results the single cylinder, the round-shaped end of cylinder, the tip-shaped end of cylinder, side-by-side cylinder and parallel cylinders.The scope of wake for each cylinders are all increase as speed increases. The wake region for round-shaped and the tip-shaped end of cylinder is more large than a single cylinder. The total drag coefficient of single cylinder is higher than side-by-side cylinder in the shallows. The total drag coefficient of single cylinder is more closer as the depth increases with side-by-side cylinder. The total drag coefficients of parallel cylindrical are higher than single cylinder and side-by-side cylindrical.The drage force make the effects of flow are greater than lateral force with side-by-side and parallel cylinders. The lateral force coefficient of tip-shaped cylinder is greater than the single cylinder and the round-shaped end of cylinder. The lateral force coefficients of the former of sid-by-side cylinder are negative. On the other hand, the lateral force coefficients of the later of side-by- side cylinder are positive. Overall, each cylinder of the lateral force coefficient are less than the total drag coefficient. Therefore, the drage force make the effects of flow field are greater than lateral force.
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Goswami, Partha Sarathi. "Particle Dynamics In A Turbulent Particle-Gas Suspension At High Stokes Number." Thesis, 2009. http://hdl.handle.net/2005/963.
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Particle laden turbulent flows find applications in many industrial processes such as energy conversion, air pollution control etc. In these types of flows, there are strong coupling between the turbulent fluctuations in the fluid velocity fields, and the fluctuating velocities of the particles. In order to analyze the stresses and the heat and mass transfer properties in turbulent suspensions, it is necessary to have a good understanding of not just the mean flow of the gas and particles, but also of the fluctuations in the two phases. The coupling is a two-way coupling; the fluid turbulence contributes to the velocity fluctuations in the particles, and conversely, the particle velocity fluctuations generate fluctuations in the fluid. Two-phase flow models capture these interactions only in an indirect way, usually through a ‘particle pressure’ term for the particle phase.
In the present work the effect of fluid velocity fluctuations on the dynamics of the particles in a turbulent gas-solid suspension is analyzed in the low Reynolds number and high Stokes number limit, where the particle relaxation time is long compared to the correlation time for the fluid velocity fluctuations. The direct numerical simulation (DNS) is used for solving the Navier-Stokes equations for the fluid, the particles are modeled as hard spheres which undergo elastic collisions. A one-way coupling algorithm is used where the force exerted by the fluid on the particles is incorporated, but not the reverse force exerted by the particles on the fluid. This is because the main focus of our study is to examine the effect of the fluid turbulence on the particle fluctuations, and we are interested in examining whether a Langevin model with random forcing can accurately capture the effect of fluid turbulence on the particle phase.
First, the turbulent flow in a plane Couette is analyzed. Though this is a model flow which is not encountered often in applications, it is easier to analyze because the turbulent velocity fluctuations are maximum at the center of the channel, in contrast to the Poiseuille flow, where the velocity fluctuations are maximum at a location between the center and the wall. Also, in a Couette flow, the wall-normal and the spanwise root mean square velocities are nearly a constant in the central region in the channel, and the percentage variation in the stream-wise velocity fluctuations is also less than that in a pressure driven Poiseuille flow. Therefore, it is possible to treat the central region as a region with homogeneous, but anisotropic, fluid velocity fluctuations and with a linear mean velocity variation. The particle mean and root mean square fluctuating velocities, as well as the probability distribution function for the fluid velocity fluctuations and the distribution of acceleration of the particles in the central region of the Couette, which comprises about 20% of the entire channel have been studied. It is found that the distribution of particle velocities is very different from a Gaussian, especially in the span-wise and wall-normal directions. However, the distribution of the acceleration fluctuation on the particles is found to be close to a Gaussian, though the distribution is highly anisotropic and there is a correlation between the fluctuations in the flow and gradient directions. The non-Gaussian nature of the fluid velocity fluctuations is found to be due to inter-particle collisions induced by the large particle velocity fluctuations in the flow direction.
Another interesting result is a comparison of the distribution of the acceleration on a particle due to the fluid velocity fluctuation at the particle position, and the distribution of the ratio of fluid velocity fluctuation to the viscous relaxation time in the fluid. The comparison shows that these two distributions are almost identical, indicating that the fluid velocity fluctuations are not correlated over time scales comparable to the relaxation time of a particle. This result is important because it indicates that in order to model the fluctuating force on the particle, it is sufficient to obtain the variance of the force distribution from the variance of the fluid velocity distribution function.
Finally, the correlation time for the acceleration correlations is calculated along the trajectory of a particle. The correlation time is found to be of the same magnitude as the correlation time for the fluid velocity in an Eulerian reference frame, and much smaller than the viscous relaxation time and the time between collisions of the particles. All of these results indicate that the effect of the turbulent fluid velocity fluctuations can be accurately represented by an anisotropic Gaussian white noise.
The above results are used to formulate a ‘fluctuating force’ model for the particle phase alone, where the force exerted by the fluid turbulent velocity fluctuations is modeled as random Gaussian white noise, which is incorporated into the equation of motion for the particles. The variance of the distribution function for the fluctuating force distribution is obtained from the variance of the local turbulent fluid velocity fluctuations, assuming linear Stokes drag law. The force distribution is anisotropic, and it has a non-zero correlation between the flow and gradient directions. It is found that the results of the fluctuating force simulations are in quantitative agreement with the results of the complete DNS, both for the particle concentration and variances of the particle velocity fluctuations, at relatively low volume fractions where the viscous relaxation time is small compared to the time between collisions, as well as at higher volume fractions where the time between collisions is small compared to the viscous relaxation time. The simulations are also able to predict the velocity distributions in the center of the Couette, even in cases where the velocity distribution is very different from a Gaussian distribution.
The fluctuating force model is applied to the turbulent flow of a gas-particle suspension in a vertical channel in the limit of high Stokes number. In contrast to the Couette flow analyzed the fluid velocity variances in the different directions in the channel are highly non-homogeneous, and they exhibit a significant variation across the channel. First, we analyze the fluctuating particle velocity and acceleration distributions at different locations across the channel using direct numerical simulation. The distributions are found to be non-Gaussian near the center of the channel, and they exhibit significant skewness. The time correlations of the fluid velocity fluctuations and the acceleration fluctuations on the particles are evaluated and compared. Unlike the case of Couette flow it is found that the time correlation functions for the fluid in the fixed Eulerian frame are not in agreement with the time correlation of the acceleration on the particles. However, the time correlations of the particle acceleration are in good agreement with the velocity time correlations in the fluid in a ‘moving Eulerian’ reference frame, moving with the mean velocity of the fluid. The fluctuating force simulations are used to model the particle phase, where the force on the particles due to the fluid velocity fluctuations are substituted by random white noise in the equations for the particle motion. The random noise is assumed to be Gaussian and anisotropic. The variances of the fluctuating force are calculated form the fluid velocity fluctuations in a moving Eulerian reference frame using DNS. The results from the fluctuating force simulations are then compared with the results obtained from DNS. Quantitative agreement between the two simulations are obtained provided the particle viscous relaxation time is at least five times larger than the fluid integral time.
The interactions between the solid particles and the fluid turbulence have been investigated experimentally in a vertical fully developed channel flow of air and solid particles. Experiments are conducted at low volume fraction for which viscous relaxation time of the particle is expected to be lower than the particle particle collision time, as well as at moderately high volume fraction where the particle particle collision time is expected to be lower than the particle relaxation time. Velocity statistics of both the particle and gas phases are obtained using high spatial resolution Particle Image Velocimetry (PIV) system. It is observed that at low solid volume fraction, the particle root mean square velocities and the velocity distribution are in good agreement with those predicted by the fluctuating force simulation, provided the polydispersity in the particle size distribution is incorporated in the fluctuating force simulations. In this case, the modification of turbulence in the center of the channel due to the particles is small. At much higher volume fraction, the mean gas flow is significantly affected by the presence of particles, and the mean flow is no longer symmetric about the center line of the channel. Simultaneously, there is also a significant change in the volume fraction across the channel, and the volume fraction is also not symmetric about the center line. This seems to indicate that there is a spontaneous instability of the symmetric volume fraction and velocity profiles, giving rise to a region of high fluid velocity and high particle volume fraction coexisting with a region of low gas velocity and low particle volume fraction. There is some recirculation of the gas within the channel, and the gas phase turbulence intensity is significantly enhanced when the velocity and volume fraction profiles become asymmetric. As we have considered only one way coupling in the computation of the particle laden flow it is expected that the particle statistics obtained for this condition can not be predicted by our fluctuating force model due to modification of the gas phase statistics.
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HUAN-TANG, YAO, and 姚煥堂. "High Reynolds Number Flow Field and Temperature Field Analysis with the Finite Volume Method in the Rectangular Duct." Thesis, 2001. http://ndltd.ncl.edu.tw/handle/59810928845054393126.
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碩士國立臺灣科技大學
機械工程系
89
Abstract The purpose of this study is to use the finite volume method of the numerical method to investigate high Reynolds number flow in the developing situation of fluid in a rectangular duct with baffles.The flow is laminar and with isothermal boundary. The influences of various factors, such as the ratio of obstacle’s height and rectangle’s height (F/H) on the velocity and temperature distributions are studied.
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"High resolution numerical study of a liquid bridge Marangoni flow with applied axial magnetic field for low Prandtl number fluids." Thesis, 2010. http://hdl.handle.net/1911/62073.
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The Full Zone model of the thermocapillary (Marangoni) flow in a liquid bridge with an axial magnetic field, measured by the Hartmann number Ha, is studied using a Chebyshev spectral method for low Prandtl number fluids. By introducing a 2nd order vorticity transport formulation, high resolution Gauss-Lobatto grids can be used to investigate the strong stabilization effects from intermediate magnetic fields, which were impossible with previous formulations. The instability mechanism of the axisymmetric base flow is studied up to Ha=500 for Pr=0.001 and up to Ha=300 for Pr=0.02 using linear stability analyses. Over these parameter spaces, the base flow first transitions to three-dimensional stationary disturbances with different axial symmetries. Solutions from the 2nd order vorticity transport formulation show good agreement with previous studies on weak magnetic fields. This work provides better understanding of the magnetohydrodynamic flow in intermediate field strengths, as well as guidance for optically heated float-zone crystal growth processes.