Relevant bibliographies by topics / High Knudsen Number Flow

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  1. Journal articles
  2. Dissertations / Theses
  3. Books
  4. Book chapters
  5. Conference papers
  6. Reports

Academic literature on the topic 'High Knudsen Number Flow'

Author: Grafiati
Published: 4 June 2021
Last updated: 2 February 2022

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Journal articles on the topic "High Knudsen Number Flow"

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GU, XIAO-JUN, and DAVID R. EMERSON. "A high-order moment approach for capturing non-equilibrium phenomena in the transition regime." Journal of Fluid Mechanics 636 (September 25, 2009): 177–216. http://dx.doi.org/10.1017/s002211200900768x.

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The method of moments is employed to extend the validity of continuum-hydrodynamic models into the transition-flow regime. An evaluation of the regularized 13 moment equations for two confined flow problems, planar Couette and Poiseuille flows, indicates some important limitations. For planar Couette flow at a Knudsen number of 0.25, they fail to reproduce the Knudsen-layer velocity profile observed using a direct simulation Monte Carlo approach, and the higher-order moments are not captured particularly well. Moreover, for Poiseuille flow, this system of equations creates a large slip velocity leading to significant overprediction of the mass flow rate for Knudsen numbers above 0.4. To overcome some of these difficulties, the theory of regularized moment equations is extended to 26 moment equations. This new set of equations highlights the importance of both gradient and non-gradient transport mechanisms and is shown to overcome many of the limitations observed in the regularized 13 moment equations. In particular, for planar Couette flow, they can successfully capture the observed Knudsen-layer velocity profile well into the transition regime. Moreover, this new set of equations can correctly predict the Knudsen layer, the velocity profile and the mass flow rate of pressure-driven Poiseuille flow for Knudsen numbers up to 1.0 and captures the bimodal temperature profile in force-driven Poiseuille flow. Above this value, the 26 moment equations are not able to accurately capture the velocity profile in the centre of the channel. However, they are able to capture the basic trends and successfully predict a Knudsen minimum at the correct value of the Knudsen number.
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TAMAGUCHI, Hiroki, Yu MATSUDA, and Tomohide NIIMI. "W052001 Micro Gaseous Flow as a High Knudsen Number Flow." Proceedings of Mechanical Engineering Congress, Japan 2013 (2013): _W052001–1—_W052001–2. http://dx.doi.org/10.1299/jsmemecj.2013._w052001-1.

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Niimi, Tomohide, Hideo Mori, Hiroki Yamaguchi, and Yu Matsuda. "Experimental Analyses of High Knudsen Number Flows." International Journal of Emerging Multidisciplinary Fluid Sciences 1, no. 3 (September 2009): 213–27. http://dx.doi.org/10.1260/175683109789686691.

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Venugopal, Vishnu, and Sharath S. Girimaji. "Unified Gas Kinetic Scheme and Direct Simulation Monte Carlo Computations of High-Speed Lid-Driven Microcavity Flows." Communications in Computational Physics 17, no. 5 (May 2015): 1127–50. http://dx.doi.org/10.4208/cicp.2014.m391.

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AbstractAccurate simulations of high-speed rarefied flows present many physical and computational challenges. Toward this end, the present work extends the Unified Gas Kinetic Scheme (UGKS) to a wider range of Mach and Knudsen numbers by implementing WENO (Weighted Essentially Non-Oscillatory) interpolation. Then the UGKS is employed to simulate the canonical problem of lid-driven cavity flow at high speeds. Direct Simulation Monte Carlo (DSMC) computations are also performed when appropriate for comparison. The effect of aspect ratio, Knudsen number and Mach number on cavity flow physics is examined leading to important insight.
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Fukui, S., and R. Kaneko. "Experimental Investigation of Externally Pressurized Bearings Under High Knudsen Number Conditions." Journal of Tribology 110, no. 1 (January 1, 1988): 144–47. http://dx.doi.org/10.1115/1.3261554.

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The characteristics of the externally pressurized bearings under high Knudsen number conditions were investigated experimentally by the use of surface restriction bearings in a medium vacuum on the order of 0.1 kPa (10−3 atm.). The experimental results agreed well with the numerical results calculated from a generalized lubrication equation based on the Boltzmann equation. Therefore, it would appear that this generalized lubrication equation is valid even when flows are categorized into transition flow or free molecular flow.
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Fukui, S., and R. Kaneko. "Analysis of Ultra-Thin Gas Film Lubrication Based on Linearized Boltzmann Equation: First Report—Derivation of a Generalized Lubrication Equation Including Thermal Creep Flow." Journal of Tribology 110, no. 2 (April 1, 1988): 253–61. http://dx.doi.org/10.1115/1.3261594.

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A generalized Reynolds-type lubrication equation valid for arbitrary Knudsen numbers, defined as the ratio of the molecular mean free path to the film thickness, is derived from a linearized Boltzmann equation by semi-numerically calculating the flow rates of fundamental flows in the lubrication film: Poiseuille flow, Couette flow, and thermal creep flow. Numerical analysis of the equation for high Knudsen numbers reveals three principal results. First, Burgdorfer’s modified Reynolds equation featuring the first-order velocity slip boundary condition overestimates load carrying capacities, while the approximation equation including both the first- and second-order velocity slip boundary condition underestimates them. Second, since the flow rate of the Couette flow, which is independent of Knudsen numbers, becomes dominant as the bearing number increases, all the lubrication equation results tend toward the same asymptotic value for an infinite bearing number. Third, a new kind of load carrying capacity caused by thermal creep flow occurs if temperature gradients at the boundaries exist in the flow direction.
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Oh, C. K., E. S. Oran, and R. S. Sinkovits. "Computations of High-Speed, High Knudsen Number Microchannel Flows." Journal of Thermophysics and Heat Transfer 11, no. 4 (October 1997): 497–505. http://dx.doi.org/10.2514/2.6289.

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Lu, Qingzheng, Lynn A. Melton, C. K. Oh, E. S. Oran, and R. S. Sinkovits. "Computations of high-speed, high Knudsen number microchannel flows." Journal of Thermophysics and Heat Transfer 11 (January 1997): 497–505. http://dx.doi.org/10.2514/3.927.

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KUMARAN, V. "Granular flow of rough particles in the high-Knudsen-number limit." Journal of Fluid Mechanics 561 (August 2006): 43. http://dx.doi.org/10.1017/s0022112006000127.

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Malhotra, Chetan P., Roop L. Mahajan, and W. S. Sampath. "High Knudsen Number Physical Vapor Deposition: Predicting Deposition Rates and Uniformity." Journal of Heat Transfer 129, no. 11 (July 21, 2006): 1546–53. http://dx.doi.org/10.1115/1.2712855.

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The problem of predicting deposition rates and film thickness variation is relevant to many high-vacuum physical vapor deposition (PVD) processes. Analytical methods for modeling the molecular flow fail when the geometry is more complicated than simple tubular or planar sources. Monte Carlo methods, which have traditionally been used for modeling PVD processes in more complicated geometries, being probabilistic in nature, entail long computation times, and thus render geometry optimization for deposition uniformity a difficult task. Free molecular flow is governed by the same line-of-sight considerations as thermal radiation. Though the existence of an analogy between the two was recognized by Knudsen (1909, Ann. Phys., 4(28), pp. 75–130) during his early experiments, it has not been exploited toward mainstream analysis of deposition processes. With the availability of commercial finite element software having advanced geometry modelers and built-in cavity radiation solvers, the analysis of diffuse thermal radiation problems has become considerably simplified. Hence, it is proposed to use the geometry modeling and radiation analysis capabilities of commercial finite element software toward analyzing and optimizing high-vacuum deposition processes by applying the radiation-molecular flow analogy. In this paper, we lay down this analogy and use the commercial finite element software ABAQUS for predicting radiation flux profiles from planar as well as tube sources. These profiles are compared to corresponding deposition profiles presented in thin-film literature. In order to test the ability of the analogy in predicting absolute values of molecular flow rates, ABAQUS was also employed for calculating the radiative flux through a long tube. The predictions are compared to Knudsen’s analytical formula for free molecular flow through long tubes. Finally, in order to see the efficacy of using the analogy in modeling the film thickness variation in a complex source-substrate configuration, an experiment was conducted where chromium films were deposited on an asymmetric arrangement of glass slides in a high-vacuum PVD chamber. The thickness of the deposited films was measured and the source-substrate configuration was simulated in ABAQUS. The variation of radiation fluxes from the simulation was compared to variation of the measured film thicknesses across the slides. The close agreement between the predictions and experimental data establishes the feasibility of using commercial finite element software for analyzing high vacuum deposition processes.
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Dissertations / Theses on the topic "High Knudsen Number Flow"

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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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Books on the topic "High Knudsen Number Flow"

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Lepicovsky, J. Coherent large-scale structures in high Reynolds number supersonic jets. Marietta, Ga: Lockheed-Georgia Company, 1985.

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Mavriplis, Dimitri J. Unstructured and adaptive mesh generation for high Reynolds number viscous flows. Hampton, Va: Institute for Computer Applications in Science and Engineering, 1991.

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Sandborn, Virgil A. Evaluation of high reynolds number flow in a 180 degree turn-around duct. [Washington, DC: National Aeronautics and Space Administration, 1991.

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Stalker, R. J. Thermodynamics and wave processes in high Mach number propulsive ducts. Washington: AIAA, 1989.

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Bayliss, Alvin. Wave phenomena in a high Reynolds number compressible boundary layer. Hampton, Va: ICASE, 1985.

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Papageorgiou, D. T. The stability of two-dimensional wakes and shear-layers at high Mach numbers. Hampton, Va: National Aeronautics and Space Administration, Langley Research Center, 1990.

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Shigemi, Masashi. Finite element analysis of incompressible viscous flows around single and multi-element aerofoils in high Reynolds number region. Tokyo: National Aerospace Laboratory, 1988.

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Jacobs, P. A. Simulation of transient flow in a shock tunnel and a high Mach number nozzle. Hampton, Va: Institute for Computer Applications in Science and Engineering, 1991.

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Jacobs, Peter A. Simulation of transient flow in a shock tunnel and a high mach number nozzle. Hampton, Va: National Aeronautics and Space Administration, Langley Research Center, 1991.

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Ishida, Yoji. Numerical and experimental study of drag characteristics of two-dimensional HLFC airfoils in high subsonic, high Reynolds number flow. Chofu, Tokyo: National Aerospace Laboratory, 1994.

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Book chapters on the topic "High Knudsen Number Flow"

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Pozrikidis, C. "High-Reynolds-number flow." In Fluid Dynamics, 669–751. Boston, MA: Springer US, 2016. http://dx.doi.org/10.1007/978-1-4899-7991-9_10.

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Pozrikidis, Constantine. "High Reynolds Number Flow." In Fluid Dynamics, 562–630. Boston, MA: Springer US, 2009. http://dx.doi.org/10.1007/978-0-387-95871-2_10.

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Lauchle, Gerald C., Michael L. Billet, and Steven Deutsch. "High-Reynolds Number Liquid Flow Measurements." In Lecture Notes in Engineering, 95–157. Berlin, Heidelberg: Springer Berlin Heidelberg, 1989. http://dx.doi.org/10.1007/978-3-642-83831-6_3.

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Weinstein, Leonard M. "Flow Visualization." In High Reynolds Number Flows Using Liquid and Gaseous Helium, 87–103. New York, NY: Springer New York, 1991. http://dx.doi.org/10.1007/978-1-4612-3108-0_5.

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Segawa, T., M. Sano, A. Naert, and J. A. Glazier. "High Rayleigh Number Turbulence of a Low Prandtl Number Fluid." In Flow at Ultra-High Reynolds and Rayleigh Numbers, 247–57. New York, NY: Springer New York, 1998. http://dx.doi.org/10.1007/978-1-4612-2230-9_16.

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Kuwahara, Kunio. "Development of High-Reynolds-Number-Flow Computaion." In Lecture Notes in Engineering, 28–40. Berlin, Heidelberg: Springer Berlin Heidelberg, 1986. http://dx.doi.org/10.1007/978-3-642-82908-6_3.

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Hu, X. Y., and N. A. Adams. "Low Mach Number Effect in Simulation of High Mach Number Flow." In 29th International Symposium on Shock Waves 2, 933–37. Cham: Springer International Publishing, 2015. http://dx.doi.org/10.1007/978-3-319-16838-8_22.

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Bushnell, Dennis M. "High Reynolds Number Testing Requirements in (Civilian) Aeronautics." In Flow at Ultra-High Reynolds and Rayleigh Numbers, 323–28. New York, NY: Springer New York, 1998. http://dx.doi.org/10.1007/978-1-4612-2230-9_22.

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Moser, R. D., and P. Zandonade. "Development of High Reynolds Number Optimal Les Models." In IUTAM Symposium on Reynolds Number Scaling in Turbulent Flow, 169–74. Dordrecht: Springer Netherlands, 2004. http://dx.doi.org/10.1007/978-94-007-0997-3_29.

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McIntosh, G. E., and K. R. Leonard. "Helium Fluid Flow Facility Cryogenic System." In High Reynolds Number Flows Using Liquid and Gaseous Helium, 253–62. New York, NY: Springer New York, 1991. http://dx.doi.org/10.1007/978-1-4612-3108-0_18.

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Conference papers on the topic "High Knudsen Number Flow"

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Zou, Chun, and Chunpei Cai. "High Knudsen Number Planar Jet Impingement Flows." In 43rd AIAA Thermophysics Conference. Reston, Virigina: American Institute of Aeronautics and Astronautics, 2012. http://dx.doi.org/10.2514/6.2012-3313.

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Nguyen, Thuong, Choong Oh, Robert Sinkovits, Elaine Oran, John Anderson, Jr., Thuong Nguyen, Choong Oh, Robert Sinkovits, Elaine Oran, and John Anderson, Jr. "High-speed, high-Knudsen-number flows in a channel containing a wedge." In 35th Aerospace Sciences Meeting and Exhibit. Reston, Virigina: American Institute of Aeronautics and Astronautics, 1997. http://dx.doi.org/10.2514/6.1997-376.

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Malhotra, Chetan P., Roop L. Mahajan, and W. S. Sampath. "High Knudsen Number Physical Vapor Deporition: Predicting Deposition Rates and Uniformity." In ASME 2005 International Mechanical Engineering Congress and Exposition. ASMEDC, 2005. http://dx.doi.org/10.1115/imece2005-82329.

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Although the analogy between thermal radiation and collisionless molecular flow has been known since the experiments of Knudsen in the early 20th century, it has not been exploited for mainstream analysis of physical vapor deposition processes. With the availability of commercial finite element and computational fluid dynamics software having built-in cavity radiation solvers with features such as automatic surface definition, meshing and view factor calculation, the analysis of thermal radiation problems has become a straightforward procedure. A direct result of this is the ease with which high vacuum deposition processes can be analyzed via the radiation-molecular flow analogy. There are several advantages of using the analogy as opposed to analytical and Monte-Carlo methods which have been traditionally employed for analyzing PVD processes. These include the ease of handling complex geometries and reduced computing times due to the replacement of the probabilistic calculations in Monte Carlo simulations with a deterministic one. In this paper, we demonstrate the use of a commercial finite element software, ABAQUS, for predicting deposition profiles from planar as well as tube sources and compare them with those presented in thin-film literature. We also compare the prediction of flow rates through long tubes with those calculated analytically by Knudsen. The predictions are in good agreement with the analytical and experimental data thus establishing the validity of the method in analyzing real-life deposition and molecular flow problems. Finally, we employ ABAQUS for predicting the thickness variation in an actual thin-film deposition setup and compare the results with experimental measurements.
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Mori, Hideo. "Application of PSP to Surface Pressure Measurement in High Knudsen Number Flows." In RAREFIED GAS DYNAMICS: 24th International Symposium on Rarefied Gas Dynamics. AIP, 2005. http://dx.doi.org/10.1063/1.1941715.

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Christlieb, Andrew J. "Application of the Transition Probability Matrix Method to High Knudsen Number Flow Past a Micro-Plate." In RAREFIED GAS DYNAMICS: 23rd International Symposium. AIP, 2003. http://dx.doi.org/10.1063/1.1581620.

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Abu-Nada, Eiyad, and AbdelSalam Al-Sarkhi. "Numerical Study of Skin Friction Coefficient and Reattachment Length for a Slip Flow Encountered in a Partially Blocked Channel." In ASME 2004 2nd International Conference on Microchannels and Minichannels. ASMEDC, 2004. http://dx.doi.org/10.1115/icmm2004-2350.

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The current research investigates the effect of Reynolds number and Knudsen number on the coefficient of skin friction and reattachment length for a micro-scale fluid flow over a step mounted on a lower wall of a micro-channel. Five Reynolds numbers are studied Re = 1, 10, 25, 50, and 75 and the Knudsen number is varied from 1×10−3 to 0.1. Finite difference method with non-uniform grid is used to solve the incompressible Navier Stokes equations accompanied with velocity slip boundary condition. As Knudsen number (Kn) decreases the magnitude of modified local shear stress (1/2 Cf Re), on the upper wall of the channel, increases. In the circulation zone behind the step and for the case of high Reynolds number (Re = 50 and Re = 75) the modified local shear stress increases as Knudsen number increases. Results show that the modified total skin friction (1/2 CD Re) decreases as the Knudsen number increases. The modified total skin friction drops significantly with Knudsen number for Kn >= 1 × 10−2. However, (1/2 CD Re) is relatively independent of Knudsen number for Kn < 1 × 10−2. Finally, for 1 × 10−2 < Kn < 0.1, as Knudsen number increase the reattachment length increases.
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Farouk, Bakhtier, Katsuya Nagayama, and Choong K. Oh. "HEAT TRANSFER IN LOW PRESSURE (HIGH KNUDSEN NUMBER) DEVELOPING FLOWS THROUGH PARALLEL PLATES." In International Heat Transfer Conference 11. Connecticut: Begellhouse, 1998. http://dx.doi.org/10.1615/ihtc11.2540.

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Cheng, Chi-Yang, Yi Dai, Genong Li, Horst J. Richter, and Ming-Chia Lai. "Numerical Modeling of High-Speed Flows Over a Microsphere in the Slip and Early Transition Flow Regimes." In ASME 2013 Fluids Engineering Division Summer Meeting. American Society of Mechanical Engineers, 2013. http://dx.doi.org/10.1115/fedsm2013-16392.

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The focus of this paper is on using computational fluid dynamics to investigate the drag and convection heat transfer of high-speed flows over a microsphere. The flow under investigation is steady-state, subsonic, transonic or supersonic laminar flow over a sphere. Due to the small size of the particle (< 80 microns), the flow is in the slip and early transition regimes. Typical Reynolds number based on sphere’s diameter is between 10 and 6000, and the Knudsen number is between 0.001 and 0.75. For the slip flow as well as the early transition regimes, instead of using the Direct Simulation Monte Carlo methods (DSMC) or lattice Boltzmann methods, we use ANSYS FLUENT, a Navier-Stokes-Fourier solver with the first-order velocity-slip and temperature-jump boundary conditions. In order to capture the non-equilibrium effects in the Knudsen layer, a constitutive scaling model for gas viscosity and conductivity is also implemented in the CFD model. CFD simulations were performed at the free-stream Mach number from 0.6 to 3.0, with particle diameter from 1 to 80 microns and the Knudsen number from 1.4 × 10−3 to 0.14. The CFD results are in good agreement with experimental data. The deviations from the data are within 10%. The numerical model also provides additional insight to the concept of the thermal recovery temperature in high-speed convection. Due to the nature of the temperature-jump boundary condition, the thermal recovery temperature in the slip flow regime can be obtained numerically only by solving the conjugate heat transfer problem. A “thin-wall” model is introduced in this paper in order to determine the thermal recovery temperature (or recovery factor) for the given Mach and Reynolds numbers. Although a number of publications have been devoted to particle drag correlations as functions of particle Reynolds and Mach numbers, the dependence of drag on particle temperature has not been investigated. By using the rarefied gas flow model in this study, we have not only confirmed that the drag increases as particle temperature goes higher, but also found that rate of drag increase is higher for the transonic than for the supersonic flows.
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9

Cheikh, Mohamad I., Emma A. Schinstock, Grant P. Ferland, and James Chen. "A Molecular Dynamics-Based Model for Knudsen Number and Slip Velocity." In ASME 2017 Fluids Engineering Division Summer Meeting. American Society of Mechanical Engineers, 2017. http://dx.doi.org/10.1115/fedsm2017-69136.

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Much research has been devoted to incestigating the relationship between Knudsen number and slip velocity using different lattice Boltzmann methods. However, these models are complex to implement for simulations in continuum regime, and have shown to diverge when compared with Direct Simulation Monte Carlo (DSMC) simulations at high Knudsen numbers. In this study, a molecular dynamics (MD)-based Knudsen number is presented, and the relationship between Knudsen number and slip velocity is presented. The proposed slip model directly correlates the Knudsen number with the slip velocity. The model is implemented on a shear-driven MD simulation of a Couette flow, and curve fitting is used to get an exponential solution for the slip velocity. The solution obtained from the proposed model as well as the solutions from the literature are compared with a DSMC simulation. The results show that the proposed exponential solution agrees well with DSMC simulations in comparison with the models from the literature. The exponential solution can serve as boundary conditions for simulating flows at different Knudsen numbers in continuum regime.
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Wang, Peng, and Yonghao Zhang. "A high order off-lattice kinetic method for high speed flows with a moderate Knudsen number." In 31ST INTERNATIONAL SYMPOSIUM ON RAREFIED GAS DYNAMICS: RGD31. AIP Publishing, 2019. http://dx.doi.org/10.1063/1.5119633.

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Reports on the topic "High Knudsen Number Flow"

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Knight, Doyle D., and Hadassah Naiman. Towards High-Reynolds Number Quiet Flow in Hypersonic Tunnels. Fort Belvoir, VA: Defense Technical Information Center, February 2009. http://dx.doi.org/10.21236/ada498212.

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2

Tan, Choon S. Performance Limiting Flow Processes in High-State Loading High-Mach Number Compressors. Fort Belvoir, VA: Defense Technical Information Center, March 2008. http://dx.doi.org/10.21236/ada481548.

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3

Schneider, Steven P. Towards High-Reynolds-Number Quiet Flow in Hypersonic Wind Tunnels. Fort Belvoir, VA: Defense Technical Information Center, April 2009. http://dx.doi.org/10.21236/ada500049.

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4

Bettin, Giorgia. Evaluation of Computational Method of High Reynolds Number Slurry Flow for Caverns Backfilling. Office of Scientific and Technical Information (OSTI), May 2015. http://dx.doi.org/10.2172/1179537.

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5

Majda, Andrew J. Mathematical Analysis of Strong Fluid Mechanical Effects at High Mach Number in Reactive and Nonreactive Flow. Fort Belvoir, VA: Defense Technical Information Center, May 1992. http://dx.doi.org/10.21236/ada253617.

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6

Brown, R. A. Thermal-capillary model with axisymmetric fluid flow for analysis of Czochralski crystal growth of high Prandtl number materials: Final report. Office of Scientific and Technical Information (OSTI), September 1987. http://dx.doi.org/10.2172/6237678.

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Ayoul-Guilmard, Q., S. Ganesh, M. Nuñez, R. Tosi, F. Nobile, R. Rossi, and C. Soriano. D5.4 Report on MLMC for time dependent problems. Scipedia, 2021. http://dx.doi.org/10.23967/exaqute.2021.2.005.

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In this report, we study the use of Multi-Level Monte Carlo (MLMC) methods for time dependent problems. It was found that the usability of MLMC methods depends strongly on whether or not the underlying time dependent problem is chaotic in nature. Numerical experiments are conducted on both simple problems, as well as fluid flow problems of practical interest to the ExaQUte project, to demonstrate this. For the non-chaotic cases, the hypotheses that enable the use of MLMC methods were found to be satisfied. For the chaotic cases, especially the case of high Reynolds’ number fluid flow, the hypotheses were not satisfied. However, it was found that correlations between the different levels were high enough to merit the use of multi-fidelity or control-variate approaches. It was also noted that MLMC methods could work for chaotic problems if the time window of analysis were chosen to be small enough. Future studies are proposed to examine this possibility.
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Johnson, Mark, John Wachen, and Steven McGee. Entrepreneurship, Federalism, and Chicago: Setting the Computer Science Agenda at the Local and National Levels. The Learning Partnership, April 2020. http://dx.doi.org/10.51420/conf.2020.1.

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From 2012-13 to 2018-19, the number of Chicago Public Schools (CPS) high school students taking an introductory computer science course rose from three thousand per year to twelve thousand per year. Our analysis examines the policy entrepreneurship that helped drive the rapid expansion of computer science education in CPS, within the broader context of the development of computer science at the national level. We describe how actions at the national level (e.g., federal policy action and advocacy work by national organizations) created opportunities in Chicago and, likewise, how actions at the local level (e.g., district policy action and advocacy by local educators and stakeholders) influenced agenda setting at the national level. Data from interviews with prominent computer science advocates are used to document and explain the multidirectional (vertical and horizontal) flow of advocacy efforts and how these efforts influenced policy decisions in the area of computer science. These interviews with subsystem actors––which include district leaders, National Science Foundation program officers, academic researchers, and leaders from advocacy organizations––provide an insider’s perspective on the unfolding of events and highlight how advocates from various organizations worked to achieve their policy objectives.
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Financial Stability Report - Second Semester of 2020. Banco de la República de Colombia, March 2021. http://dx.doi.org/10.32468/rept-estab-fin.sem2.eng-2020.

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The Colombian financial system has not suffered major structural disruptions during these months of deep economic contraction and has continued to carry out its basic functions as usual, thus facilitating the economy's response to extreme conditions. This is the result of the soundness of financial institutions at the beginning of the crisis, which was reflected in high liquidity and capital adequacy indicators as well as in the timely response of various authorities. Banco de la República lowered its policy interest rates 250 points to 1.75%, the lowest level since the creation of the new independent bank in 1991, and provided ample temporary and permanent liquidity in both pesos and foreign currency. The Office of the Financial Superintendent of Colombia, in turn, adopted prudential measures to facilitate changes in the conditions for loans in effect and temporary rules for rating and loan-loss provisions. Finally, the national government expanded the transfers as well as the guaranteed credit programs for the economy. The supply of real credit (i.e. discounting inflation) in the economy is 4% higher today than it was 12 months ago with especially marked growth in the housing (5.6%) and commercial (4.7%) loan portfolios (2.3% in consumer and -0.1% in microloans), but there have been significant changes over time. During the first few months of the quarantine, firms increased their demands for liquidity sharply while consumers reduced theirs. Since then, the growth of credit to firms has tended to slow down, while consumer and housing credit has grown. The financial system has responded satisfactorily to the changes in the respective demands of each group or sector and loans may grow at high rates in 2021 if GDP grows at rates close to 4.6% as the technical staff at the Bank expects; but the forecasts are highly uncertain. After the strict quarantine implemented by authorities in Colombia, the turmoil seen in March and early April, which was evident in the sudden reddening of macroeconomic variables on the risk heatmap in Graph A,[1] and the drop in crude oil and coal prices (note the high volatility registered in market risk for the region on Graph A) the local financial markets stabilized relatively quickly. Banco de la República’s credible and sustained policy response played a decisive role in this stabilization in terms of liquidity provision through a sharp expansion of repo operations (and changes in amounts, terms, counterparties, and eligible instruments), the purchases of public and private debt, and the reduction in bank reserve requirements. In this respect, there is now abundant aggregate liquidity and significant improvements in the liquidity position of investment funds. In this context, the main vulnerability factor for financial stability in the short term is still the high degree of uncertainty surrounding loan quality. First, the future trajectory of the number of people infected and deceased by the virus and the possible need for additional health measures is uncertain. For that reason, there is also uncertainty about the path for economic recovery in the short and medium term. Second, the degree to which the current shock will be reflected in loan quality once the risk materializes in banks’ financial statements is uncertain. For the time being, the credit risk heatmap (Graph B) indicates that non-performing and risky loans have not shown major deterioration, but past experience indicates that periods of sharp economic slowdown eventually tend to coincide with rises in non-performing loans: the calculations included in this report suggest that the impact of the recession on credit quality could be significant in the short term. This is particularly worrying since the profitability of credit establishments has been declining in recent months, and this could affect their ability to provide credit to the real sector of the economy. In order to adopt a forward-looking approach to this vulnerability, this Report presents several stress tests that evaluate the resilience of the liquidity and capital adequacy of credit institutions and investment funds in the event of a hypothetical scenario that seeks to simulate an extreme version of current macroeconomic conditions. The results suggest that even though there could be strong impacts on the credit institutions’ volume of credit and profitability under such scenarios, aggregate indicators of total and core capital adequacy will probably remain at levels that are above the regulatory limits over the horizon of a year. At the same time, the exercises highlight the high capacity of the system's liquidity to face adverse scenarios. In compliance with its constitutional objectives and in coordination with the financial system's security network, Banco de la República will continue to closely monitor the outlook for financial stability at this juncture and will make the decisions that are necessary to ensure the proper functioning of the economy, facilitate the flow of sufficient credit and liquidity resources, and further the smooth operation of the payment systems. Juan José Echavarría Governor
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