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Influence of site selection on natural ventilation in Chinese traditional folk house

Journal of Southeast University(English Edition) 2010年第2期26卷 161-164页

作者：徐峰解明镜张泉张国强王科湖南大学建筑学院长沙410082 湖南大学土木工程学院长沙410082 中南大学土木建筑学院长沙410083

The relationship between the site selection of a hilly terrain and the natural ventilation of the Dangdamen building complex,which is a traditional folk house,is revealed by a computational fluid dynamics（CFD）*** wind press and speed distributions around the building in four cases with different weather conditions and topographies are *** simulation results show that a hill can reduce the absolute values of the wind pressure at the windward and leeward sides of the *** encouraging effect of the patio on the natural ventilation in a terrain with a hill is greater than that without a *** same situation occurs when comparing the patio effects between summer and *** wind speed around the building can be reduced by the hill as it is an obstacle and the degrees of the influence of the hill in summer and in winter are quite different because of different wind *** analysis results show that this kind of site selection,with the hill to the north,is a suitable way to settle the conflict of the natural ventilation requirements in summer and in winter under subtropical climate conditions,especially in houses with patios.

关键词： site selection traditional folk house natural ventilation computational fluid dynamics simulation

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Jet Impingement Heat Transfer from a Circular Cylinder Located Between Confining Walls

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JOURNAL OF THERMOPHYSICS AND HEAT TRANSFER 2010年第4期24卷 756-764页

作者： Imraan, Mustahib Sharma, Rajnish N. Univ Auckland Dept Mech Engn Auckland 1142 New Zealand

The heat-transfer characteristics of a circular cylinder (diameter d) located between confining walls (at a varying separation distance of H apart), exposed to a slot jet of air (of width w) from a contoured nozzle, and at a range of spacing z from the jet exit has been studied experimentally and computationally. The study focused on Reynolds numbers Re in the range of 1000-12,000. The results reveal that, while the slot jet impinging on a cylinder in confined space generally yields higher average heat-transfer rates, relative to the uniform crossflow case, these are, however, almost always found to yield lower heat-transfer rates in comparison with corresponding slot-jet impingement without confining walls. It was found that a dimensionless confinement spacing H/d = 10 exists that consistently exhibits a minimum in the cylinder heat-transfer rate over all of the nondimensional jet exit to the cylinder spacing z/w and ratio of the cylinder diameter to the slot width d/w that were investigated. It was established that the reduction in heat transfer for confinements H/d between 10 and 16 is due to the jet becoming unstable, thereby periodically flapping across the cylinder, switching between the confining walls, in tandem with vortex shedding from the cylinder. This reduces the effectiveness of impingement and, hence, reduces the heat-transfer rates. It is therefore concluded that jet impingement does not always enhance the heat-transfer rate, but it may, in fact, reduce it under conditions in which the impingement target is located in the midst of confining walls. It was observed that the average of all the Nusselt numbers in a confined space reduces by about 17% when compared with a nonconfined cylinder. In summary, therefore, the influence of confining walls around the cylinder has an unfavorable impact on the flow and, therefore, the heat-transfer rates with jet impingement.

关键词： Convective Heat Transfer Coefficient Freestream Velocity Vortex Shedding Contoured Nozzles computational fluid dynamics simulation Shear Layers Jet Flaps Approaching Flow Thermocouples Biot Number

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Optical Emission Spectroscopy During Plasmatron Testing of ZrB₂-SiC Ultrahigh-Temperature Ceramic Composites

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JOURNAL OF THERMOPHYSICS AND HEAT TRANSFER 2009年第2期23卷 279-285页

作者： Playez, Mickael Fletcher, Douglas G. Marschall, Jochen Fahrenholtz, William G. Hilmas, Greg E. Zhu, Sumin Von Karman Inst Fluid Dynam Aeronaut & Aerosp Dept B-1640 Rhode St Genese Belgium SRI Int Mol Phys Lab Menlo Pk CA 94025 USA Missouri Univ Sci & Technol Dept Mat Sci & Engn Rolla MO 65409 USA

Optical emission spectroscopy is used to investigate the oxidation of a hot-pressed ZrB2-SiC ultrahigh-temperature ceramic composite tested in the 1.2 MW Plasmatron facility at the von Karman Institute for fluid dynamics. Time-resolved spectra enable the in situ detection and temporal characterization of electronically excited B, BO, and BO2 specics concentrations directly adjacent to the oxidizing sample surface. The evolution of these boron species correlates well with the transient formation of a complex multilayer oxide scale containing a silica-rich glassy outer layer that limits oxide growth.

关键词： Optical Emission Spectroscopy Air Mass Flow Rates Emission Spectrum Gibbs Free Energy Vapour Pressure Freestream Scanning Electron Microscopy Charge Coupled Device computational fluid dynamics simulation Hypersonic Vehicles

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computational Modeling of a Segmented-Involute-Foil Regenerator for Stirling Engines

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JOURNAL OF THERMOPHYSICS AND HEAT TRANSFER 2009年第4期23卷 786-800页

作者： Ibrahim, Mounir B. Danila, Daniel Simon, Terrence W. Gedeon, David Tew, Roy Cleveland State Univ Dept Mech Engn Cleveland OH 44115 USA Univ Minnesota Dept Mech Engn Minneapolis MN 55455 USA Gedeon Associates Athens OH 45701 USA NASA John H Glenn Res Ctr Lewis Field Cleveland OH 44135 USA

A microfabricated, segmented-involute-foil regenerator was numerically investigated using the Fluent commercial software under both steady- and oscillatory-flow conditions and using two- and three-dimensional numerical simulations. Steady-state simulations were performed for Re = 50-2000. The oscillatory-flow conditions were performed for Re-max = 50 and Re-omega = 0.229, with the hot end at 310 K and the cold end at 293 K. For the steady-state three-dimensional simulation, both the local friction factor and the local mean Nusselt numbers started to depart from the two-dimensional simulation values upon entering the second layer. At the entrance of every layer, the forced reorientation of the flow results in small rises of both the friction factor and the mean Nusselt number, with subsequent decrease as the flow settles into the new layer. As for the oscillatory-flow simulations, the two-dimensional model was used to study the effects of changing 1) the oscillation amplitude and frequency, 2) the thermal contact resistance between layers, and 3) the solid material. The effects of these parameters on the total regenerator beat loss (convection and conduction) were documented and are expected to be a useful tool for further development of Stirling engine regenerators.

关键词： Heat Exchangers Stirling Engines Conduction Heat Transfer Friction Factor Thermal Conduction computational fluid dynamics simulation Flow Conditions Mass Flow Stirling Cycle fluid Flow

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Lessons Learned from Numerical simulations of the F-16XL Aircraft at Flight Conditions

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JOURNAL OF AIRCRAFT 2009年第2期46卷 423-441页

作者： Rizzi, Arthur Jirasek, Adam Lamar, John E. Crippa, Simone Badcock, Kenneth J. Boelens, Okko J. Royal Inst Technol Dept Aeronaut & Vehicle Engn S-10044 Stockholm Sweden Swedish Def Res Agcy Div Syst Technol S-16490 Stockholm Sweden NASA Langley Res Ctr Hampton VA 23681 USA Univ Liverpool Dept Engn Liverpool L69 3GH Merseyside England NLR Natl Aerosp Lab Dept Flight Phys & Loads Aerosp Vehicles Div NL-1059 CM Amsterdam Netherlands

Nine organizations participated in the Cranked-Arrow Wing Aerodynamics Project International study and have contributed steady and unsteady viscous simulations of a full-scale semispan model of the F-16XL aircraft. Three different categories of flight Reynolds/Mach number combinations are computed and compared with flight-test measurements for the purpose of code validation and improved understanding of the flight physics. Steady-state simulations are done with several turbulence models (of different complexity, with no topology information required) that overcome Boussinesq-assumption problems in vortical flows. Detached-eddy simulation and its successor, delayed detached-eddy simulation, are used to compute the time-accurate flow development. Common structured and unstructured grids as well as individually adapted unstructured grids were used. Although discrepancies are observed in the comparisons, overall reasonable agreement is demonstrated for surface pressure distribution, local skin friction, and boundary velocity profiles at subsonic speeds. The physical modeling, be it steady or unsteady flow, and the grid resolution both contribute to the discrepancies observed in the comparisons with flight data, but at this time, how much each part contributes to the whole cannot be determined. Overall, it can be said that the technology readiness of computational fluid dynamics simulation technology for the study of vehicle performance has matured since 2001, such that it can be used today with a reasonable level of confidence for complex configurations.

关键词： Transonic Flight computational fluid dynamics simulation Flight Testing Freestream Mach Number Supersonic Vortex Flow Skin Friction Coefficient Turbulence Models Unstructured Grid Flight Data Velocity Profiles

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Passive Control of the Flow Around the Stratospheric Observatory for Infrared Astronomy

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JOURNAL OF AIRCRAFT 2009年第4期46卷 1319-1325页

作者： Schmid, Sven Lutz, Thorsten Kraemer, Ewald Kuehn, Timo Univ Stuttgart German Stratospher Observ Infrared Astron Inst D-70569 Stuttgart Germany Univ Stuttgart Inst Aerodynam & Gas Dynam D-70569 Stuttgart Germany German Aerosp Ctr Inst Aerodynam & Flow Technol D-38108 Braunschweig Germany

The unsteady flowfield around the Stratospheric Observatory for Infrared Astronomy, a reflecting telescope carried inside an open port of a Boeing 747SP, has been simulated by means of detached eddy simulations and unsteady Reynolds-averaged Navier-Stokes simulations. Vortex generators have been placed upstream of the cavity to control the shear layer spanning the opening. The influence of baffles and displacement bodies placed inside the telescope port on the frequencies of acoustic resonant modes was investigated by acoustic simulations, based on the solution of the homogenous Helmholtz equation. The objective of this study is to improve the telescope's performance by mitigating the amplitudes and changing the characteristic frequencies of the pressure fluctuations inside the cavity. The present simulations show that the investigated measures have a high potential to increase the telescope's pointing stability.

关键词： Stratospheric Observatory for Infrared Astronomy Passive Control Boundary Layer Thickness Infrared Telescopes computational fluid dynamics simulation Vortex Generators Resonance Frequencies Reynolds Averaged Navier Stokes Transonic Wind Tunnel Acoustic Phenomena

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2D and 3D simulations of fluid dynamics in the Bubble Reactor for Liquid Fuel Synthesis: Comparisons Against Experiments

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ENERGY SOURCES PART A-RECOVERY UTILIZATION AND ENVIRONMENTAL EFFECTS 2009年第18期31卷 1598-1611页

作者： Qi, N. Zhang, K. Song, Q. Gao, X. Zhang, H. Lu, J. China Univ Petr State Key Lab Heavy Oil Proc Beijing 102249 Peoples R China Univ Adelaide Dept Chem Engn Adelaide SA 5005 Australia Taiyuan Univ Technol Shanxi Key Lab Coal Sci & Technol Taiyuan Peoples R China

Flow pattern, bubble size distribution, and gas holdup are investigated in the bubble columns. Simulated results by the standard k-epsilon turbulence model together with Grace drag model in the commercial computational fluid dynamics software platform (ANSYS CFX 10.0) show good agreement with experimental measurement within the 2D and 3D columns. Three flow regimes (homogeneous bubbly, transitional, and turbulent flows) are identified by the instantaneous velocity profiles of gas and liquid phases, and general flow patterns are summarized under different superficial gas velocities. The findings are useful for designing the slurry bubble columns for synthesizing liquid hydrocarbons and alcohols.

关键词： 2D and 3D bubble columns computational fluid dynamics simulation experimental measurement hydrodynamics

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Assessment of computational fluid dynamics for Supersonic Shock Containing Jets

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AIAA JOURNAL 2009年第11期47卷 2738-2746页

作者： Miller, Steven A. E. Veltin, Jeremy Morris, Philip J. McLaughlin, Dennis K. Penn State Univ Dept Aerosp Engn University Pk PA 16802 USA

This paper describes a combined experimental and computational investigation of supersonic jets operating off design. Axisymmetric steady-state computational fluid dynamics simulations were performed with a Reynolds-averaged Navier-Stokes solver using a two-equation turbulence model. These results were compared directly with experimental results for two different axisymmetric nozzles operating at over- and underexpanded conditions. Pitot and static pressure probes were used to measure the Mach number and local static pressure at various downstream locations. A comparison of both experimental and numerically predicted schlieren visualizations were performed for a qualitative assessment of the accuracy of the flowfield predictions. Quantitative comparisons of pitot and static pressures were made between the experiments and simulations. This provides an assessment of the quality of the numerical simulations as well as an indication of the errors associated with any interference between the pressure probes and the flow in the experiments.

关键词： computational fluid dynamics simulation Prandtl Meyer Expansion Fan Static Pressure Turbulent Boundary Layer Reynolds Averaged Navier Stokes Turbulence Models Oblique Shock Compressible Flow Pitot Probes Pressure Transducers

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Multidimensional Assessment of Modeling Error in Typical High-Speed Wind-Tunnel Heat-Transfer Data-Reduction Schemes

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JOURNAL OF THERMOPHYSICS AND HEAT TRANSFER 2009年第1期23卷 186-191页

作者： Kirk, Benjamin S. NASA Lyndon B Johnson Space Ctr Appl Aerosci & Computat Fluid Dynam Branch Houston TX 77058 USA

The modeling error induced by the combined factors of lateral high-speed wind-tunnel heal-flux distribution and multidimensional curvature for a specific geometry was investigated. A test series was conducted in the Arnold Engineering Development Center's Hypervelocity Wind Tunnel no. 9 (HVWT9) to measure laminar and turbulent conductive heat-transfer rates on a scaled model of NASA's Orion Crew Module. The surface temperature distribution is found to be visually similar to the applied heat-flux distribution. The depth to which the temperature profile has penetrated the model surface agrees qualitatively with dimensional analysis. A study of modeling-error shows that the minimum error occurs for the two acreage gauges, which is approximately ∓0.5%. The warmer substrate is found to be more resistive to heat flow than in the absence of the multidimensional conduction, thus requiring heat flux at the surface to affect the same response.

关键词： One Dimensional Heat Transfer Analysis Data Reduction Hypervelocity Wind Tunnels Transient Thermal Analysis Thermal Diffusivity Heat Shield computational fluid dynamics simulation Heat Flux Distribution Angle of Attack Thermocouples

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Dynamic simulations of Atmospheric-Entry Capsules

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JOURNAL OF SPACECRAFT AND ROCKETS 2009年第4期46卷 829-835页

作者： Murman, Scott M. NASA Ames Res Ctr Moffett Field CA 94035 USA

Viscous free-oscillation simulations with the OVERFLOW solver are used to predict the aerodynamic behavior of nonlifting capsule shapes in the supersonic-speed regime. Computations using hybrid Reynolds-averaged Navier-Stokes turbulence models are examined for two novel atmospheric-entry capsule configurations: an idealized inflatable decelerator concept and the Orion crew module. The simulation results are validated against nonlinear aerodynamic models determined from free-flight ballistic-range data analysis. For the Orion crew module, two separate methods of reducing identical range data, along with common models tested in separate range facilities, are included. The computations demonstrate the efficiency and accuracy of dynamic simulations for developing a nonlinear aerodynamic performance database. Analysis indicates that the typical nonlinear bluff-body behavior is characterized by a rate-dependent dynamic response, which is not currently accounted for in common aerodynamic models.

关键词： Aerodynamic Decelerator Aerodynamic Performance Reynolds Averaged Navier Stokes Turbulence Models Dynamic Response Supersonic Speed Data Analysis System Aerodynamic Characteristics computational fluid dynamics simulation Supersonic Flow

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