共查询到19条相似文献,搜索用时 62 毫秒
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讨论了紊流数值模拟的发展历史、现状及趋势。比较了各类紊流模型的优缺点及适用范围 ,并对特殊效应 (曲率、近壁区 )的处理作了介绍和评述。为了提高模型的预报能力 ,多重尺度和非线性模型正逐步应用于工程计算。随着计算机的发展 ,大涡和直接数值模拟也取得了一些研究成果 相似文献
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采用经风洞实验验证的标准 k–ε数值模型,模拟了绿化空间布局及壁面加热条件对街道峡谷内流场和污染物扩散的影响。考虑了3种绿化组合方式与4种壁面加热条件,并采用无量纲浓度K与空气交换率RACH分别对街道峡谷内污染情况与通风性能进行评估。结果表明,不同的绿化空间布局和壁面加热条件会改变街道峡谷内流场和污染物浓度分布。选择绿化结合布局时,应尽量选择绿墙和绿篱的组合以减弱绿化阻塞作用对污染物扩散的不利影响。背风面加热和迎风面加热对街道峡谷的通风能力提升作用并不明显,而三壁加热能明显改善街道峡谷的通风性能。 相似文献
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为研究不同紊流模型对溢流坝泄洪数值模拟的适用性和准确度,采用标准κ-ε模型、RNGκ-ε模型及大涡模拟(LES)模型等3种经典紊流模型对某溢流坝泄流过程进行数值模拟;同时,将数值模拟出的溢流坝坝面的水流流态、流速及坝面压强等溢流坝泄流过程的重要水力指标结果与物理模型试验结果进行对比分析。结果表明,RNGκ-ε模型对溢流坝泄流的流态模拟效果最好,与物理模型试验结果最为一致;LES模型对坝面水流流速、坝面压强及空化数的模拟效果最好;采用标准κ-ε模型模拟出的各个指标精度最低。因此,针对溢流坝泄流过程数值模拟,应优先采用RNGκ-ε模型和LES模型。 相似文献
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数值模拟了单体自然通风建筑模型内的空气流动和污染物扩散,考察了紊流施密特数Sct对污染物模拟值的影响。结果表明,选取的3种紊流模型对时均流速和紊动能的模拟值和风洞试验值基本一致,标准k-ε模型与realizable k-ε模型模拟的流场较相似,其浓度场结果也基本相同,当Sct为0.8~1.0时,模拟值和试验值吻合得最好。由于RNG k-ε模型对地面污染源附近的时均流动模拟不准确,导致其浓度模拟值和试验值相差较大,因此,选取合理的Sct时,应基于准确的流动模拟,而不能仅考察浓度模拟值和试验值的吻合程度。 相似文献
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采用经修正的k-ω模型,即基线k-ω模型对线性波作用下边界层的流速、紊动能、涡粘系数分布及底床剪应力进行了数值模拟,验证了模型的合理性,进而采用该模型模拟了粗糙底床摩阻流速及具有不同相对粗糙度的粗糙底床紊流边界层特性,发现边界层内流速与自由流速的相位差随计算点至底床的距离和相对粗糙度的增大而减小。 相似文献
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Natural ventilation is one of the most efficient passive cooling techniques for buildings. Knowledge of the wind speed in street canyons is the necessary condition for the application of such a technique in dense urban configurations. Thus, prediction techniques to evaluate the microclimate and dispersion parameters in street canyons, has become a subject of intense scientific research in recent years. In most of cases, wind flow and pollutant dispersion characteristics have been studied numerically and experimentally with a view to provide an insight in urban dispersion. The microscale model MIMO was employed in order to perform a three-dimensional modelling of the wind field within three typical deep street canyons, located in the centre of Athens. Computational results were compared to field data collected during consecutive three-day experimental campaigns that took place in the summer period. Results from the computations have shown that the wind field in urban areas is quite complex, presenting areas of very low wind speeds and convergence of vortices. The model underestimated the measured wind speed intensities, which may be partly explained by the uncertainty of specific input parameters, the necessary simplifications for the application of such models and finally the geometrical complexity of the area modelled. Finally, computations were performed for a reference velocity of 2 m/s, which is considered to be a threshold value. The wind field developed departed from the one observed in the previous cases. 相似文献
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The paper presents the results of shading analysis which was carried out as part of a wider comparative analysis of two sites with different characteristics in terms of street geometry and urban density. The first experiment site was a traditional settlement in the island of Tinos, Greece, and the second was a relatively newly built part of the capital city of the island. Also a parametric shading analysis was carried out in order to examine a number of parameters that influence shading conditions in urban canyons.The paper aims in analyzing the effect of parameters such as urban layout, street geometry and orientation on solar access and shading conditions, which strongly affect urban canyon microclimate. The results of shading simulations are compared to the results of experimental measurements of air and surface temperatures and to parametric thermal analysis results. The conclusions can contribute in the formulation of urban design guidelines. 相似文献
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JUNLI CHENG-KANGWU 《热科学学报(英文版)》1993,2(4):275-281
Flame stabilization in attachment jet combustors is based on the existence of the high temperature recirculation zone, provided
by the Coanda effect of an attachment jet. The single attachment jet in a rectangular channel is a fundamental form of this
type of flow. In this paper, the detailed characteristics of turbulent flow of a single attachment jet were experimentally
studied by using a 2-D LDV. The flowfield consists of a forward flow and two reverse flows. The forward one is composed of
a curved and a straight section. The curved section resembles a bent turbulent free jet, and the straight part is basically
a section of turbulent wall jet. A turbulent counter-gradient transport region exists at the curved section. According to
the results, this kind of combustor should have a large sudden enlargement ratio and not too narrow in width.
Project supported by the National Natural Science Foundation of China. 相似文献
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V.I. Terekhov M.A. Pakhomov 《International Journal of Heat and Mass Transfer》2009,52(21-22):4711-4721
Droplets-laden turbulent flow downstream of a sudden pipe expansion has been investigated by using Euler/Euler two-fluid model for the gaseous and dispersed phases. Significant increase of heat transfer in separated flow at the adding of evaporating droplets has been demonstrated (more than 2 times compare with one-phase flow at the value of mass concentration of droplets ML1 0.05). Addition of dispersed phase to the turbulent gas flow results in insignificant increase of the reattachment length. Low-inertia droplets (d1 50 μm) are well entrained into the circulation flow and present over the whole pipe section. Large particles (d1 ≈ 100 μm) go through the shear layer not getting into the detached area. Comparison with experimental data on separated gas–droplets flows behind the plane backward-facing step has been carried out. 相似文献
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The motion of micro-particles with different mass flow rate in the planer turbulent jet flow has been simulated,using LES method to obtain the flow vorticity evolution and Lagrangian method to track micro-particles.The results showed that when the flow rate is small,the particles more likely to present in the vortex periphery,the distribution pattern is similar to the flow pattern.When the flow rate is high,some particles will escape from the motion region to the original static region,so that in the jet region,particles are relatively evenly distributed.When the flow field is full developed,the particles average concentration in the y direction affected by the mass flow rate relative slightly,the normalized mean particles concentrations at different flow rate were similar to Gaussian shape. 相似文献
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horoductionInverse casting is a technique for Producing nearnet-shape cast strips. T'he main idea of this technique isdeveloped from a successful inveshgation['], in which ithas been Proved that the inverse cashng teclmiquewould be applicable to produce the steel strip with aabackness of 0.5-3 nun, with a good material prOPertyand with a lower energy consumption in contrast withconventional conhnuous cashng process. The POssibilitytO p~ce composite strips is also one of the mostattrachve pro… 相似文献
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Numerical Calculation of 3—D TUrbulent Flow in Curvilinear Coordinate Systems with Nostaggered Grids 总被引:1,自引:0,他引:1
NumericalCalculationof3-DTurbulentFlowinCurvilinearCoordinateSystemswithNonstaggeredGridsZhangJingzhou;LiLiguo;WuGuochuan(Nam... 相似文献
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Hiroshi Kawanabe Kiyoshi Kawasaki Toshio Seno Chihiro Kondo Masahiro Shioji 《亚洲传热研究》2007,36(5):303-313
The flow and mixing process of unsteady jets are fundamentally analyzed by large eddy simulations. The effects of nozzle velocity and turbulence intensity on the turbulent eddy structure and mixing process between the nozzle fluid and ambient fluid were investigated. The results show that a toroidal‐shaped vortex, which emerges around the jet tip, primarily accelerates the entraining flow. Also, increasing the turbulence intensity in the nozzle encourages mixing in the jet without changing the jet‐contour. Furthermore, when the rise‐up time of the initial nozzle velocity is elongated, turbulent mixing is suppressed. © 2007 Wiley Periodicals, Inc. Heat Trans Asian Res, 36(5): 303–313, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20158 相似文献