共查询到19条相似文献,搜索用时 62 毫秒
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采用数值模拟技术对室内发生火灾后的室内温度及烟气的流动做出模拟。对火焰的燃烧采用UDF编程以实现真实火灾发生时的场景。湍流模型采用LES模型,辐射采用P-1模型。通过温度云图,流场矢量图对火灾发生后,室内温度的变化以及烟气的流动情况做出详细的研究。 相似文献
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利用Fluent软件中的大涡模拟方法,对燃油锅炉1/10尺缩模型进行不同烟气再循环率的燃烧过程研究,分析0%,20%和30%烟气再循环率下温度场的分布特点以及污染物的排放特性.模拟结果表明:采用烟气再循环能有效降低锅炉的最高温度、平均温度以及污染物排放水平.其中,20%烟气工况降温最为明显,最高温度相较无烟气工况下降400 K,且随着烟气再循环率的增加,焰型缩短,着火点逐渐向炉膛前部移动,温度梯度减小.相较于0%烟气工况,20%和30%烟气工况的NOx排放浓度分别减少了 85.5%和72.7%;20%烟气工况下CO排放水平最低,出口排放浓度为110 mg/m3,而30%烟气工况下Soot排放水平最低,出口体积分数为2.14 ×10-5. 相似文献
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基于大涡模拟的发动机缸内湍流流动及拟序结构 总被引:2,自引:0,他引:2
应用大涡模拟方法对发动机缸内湍流流场进行了三维瞬态数值分析.主要从湍流脉动、湍动能和缸内拟序结构演变等方面考察了发动机缸内流场特性.计算结果表明:相比雷诺平均模型,大涡模拟方法可以更真实地反映发动机循环过程中缸内气体流动的细节和规律.利用大涡模拟结合Q准则判别法可以较好地识别缸内大尺度湍流拟序结构;拟序结构对于缸内大尺度动能的产生及湍流的维持具有关键的作用.RANS类模型则不具备充分捕获大尺度拟序结构的能力.湍流脉动与活塞平均运行速度接近于成正比. 相似文献
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大涡模拟最初用于大气与环境科学的研究,之后利用大涡模拟研究大气越来越广泛并取得多方面的成果.通过对端流的认识,了解研究湍流应具备的条件,由此引出大涡模拟方法在湍流研究中的优势,简单介绍大涡模拟理论.讨论亚格子模型.根据大涡模拟在水力、航天、传热及生态环境等方面已有的应用,说明其应用前景和亟待解决的问题。 相似文献
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通过修改发动机多维CFD计算程序KIVA-3V,建立了内燃机压缩过程冷态流场的大涡模拟(LES)计算模型。利用此模型对内燃机压缩过程中缸内流场的水平速度及湍流动能进行了详细分析,并与k-ε模型进行了比较。结果表明与采用k-ε模型计算时相比,采用LES计算时显示了更为复杂的湍流结构,而且LES所能捕捉到的涡团结构范围要大于k-ε模型。同时,采用LES计算时得到的湍流动能要远远低于k-ε模型。 相似文献
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通过修改发动机多维CFD计算程序KIVA-3V,建立了内燃机压缩过程冷态流场的大涡模拟(LES)计算模型.利用此模型对内燃机压缩过程中缸内流场的水平速度及湍流动能进行分析,同时,分析了网格密度对内燃机缸内流场大涡模拟的影响.结果表明,当采用k-ε模型计算时,网格的精细程度对流场结构影响不大;在相同的计算网格下,与采用k-ε模型计算相比,采用LES计算显示了更为复杂的湍流结构,而且LES所能捕捉到的涡团结构范围要大于k-ε模型,计算得到的湍流动能也要低于k-ε模型;同时,网格越精细,这种效应越明显. 相似文献
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The large eddy simulation (LES) is applied to an unconfined swirling flow of an air surrounding a bluff-body having a central jet of air, and the complicated flowfield that involves the recirculation and vortex breakdown is investigated. The Smagorinsky model is used as the sub-grid scale model. The results of the present numerical simulation are compared with the experimental data of the mean and stochastic root mean square (RMS) variations of two velocity components. Although the inflow conditions are specified in a simple manner, the obtained numerical results are in reasonable agreement with the experiments, except for a part of RMS variation values near downstream of the bluff body. The present numerical calculations can successfully reproduce the two characteristics of the flow, i.e., an upstream recirculation zone established just downstream of the burner plane and the additional recirculation zone established at the more downstream location. 相似文献
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MingzhouYU Lihua CHEN Hanhui JIN Jianren FAN College of Mechanical Energy Engineering Zhejiang University Hangzhou China 《热科学学报(英文版)》2005,14(2):150-155
The flow field of a rectangular exit, semi-confined and submerged turbulent jet impinging orthogonally on a flat plate with Reynolds number 8500 was studied by large eddy simulation (LES). A dynamic sub-grid stress model has been used for the small scales of turbulence. The evolvements such as the forming, developing, moving, pairing and merging of the coherent structures of vortex in the whole regions were obtained. The results revealed that the primary vortex structures were generated periodically, which was the key factor to make the secondary vortices generate in the wall jet region. In addition, the eddy intensity of the primary vortices and the secondary vortices induced by the primary vortices along with the time were also analyzed. 相似文献
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Zhide XI Bingde CHEN Pengzhou LI 《Frontiers of Energy and Power Engineering in China》2008,2(4):524-527
The pressure pulse filter and Smagorinsky subgrid stress model of the Large Eddy Simulation (LES) are introduced. The fluid field in the annular plenum between the pressure vessel and the core barrel of the1:5 model in the second phase of Qinshan Nuclear Power Plant is simulated, and the distribution of the total pressure in the space and time domains is obtained. The results show that the Power Spectrum Density (PSD) of LES from the calculation and the test are in the same quantity order. Thus, the pressure of LES can be a load to stimulate the barrel vibration. __________ Translated from Nuclear Power Engineering, 2007, 28(5): 14–17 [译自: 核动力工程] 相似文献
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Large eddy simulation (LES) was performed for a spatially developing round jet and its scalar transport at four steps of Reynolds number set between 1200 and 1,000,000. A simulated domain, which extends 30 times the nozzle diameter, includes initial, transitional, and established stage of jet. A modified version of convection outflow condition was proposed in order to diminish the effect of a downstream boundary. Tested were two kinds of subgrid scale (SOS) models: a Smagorinsky model (SM) and a dynamic Smagorinsky model (DSM). In the former model, parameters are kept at empirically deduced constants, while in the latter, they are calculated using different levels of space filtering. Data analysis based on the decay law of jet clearly presented the performance of SGS models. Simulated results by SM and DSM compared favorably with existing measurements of jet and its scalar transport. However, the quantitative accuracy of DSM was better than that of SM at a transitional stage of flow field. Computed parameters by DSM, coefficient for SGS stresses, CR and SGS eddy diffusivity ratio, ΓSGS, were not far from empirical constants of SM. Optimization of the model coefficient was suggested in DSM so that coefficient CR was nearly equal in the established stage of jet but it was reduced in low turbulence close to the jet nozzle. © 2004 Wiley Periodicals, Inc. Heat Trans Asian Res, 33(3): 175–188, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20001 相似文献
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Lei Wang 《International Journal of Heat and Mass Transfer》2005,48(10):1883-1897
Large eddy simulation of thermally stratified turbulent open channel flows with low- to high-Prandtl number is performed. The three-dimensional filtered Navier-Stokes and energy equations under the Boussinesq approximation are numerically solved using a fractional-step method. Dynamic subgrid-scale (SGS) models for the turbulent SGS stress and heat flux are employed to close the governing equations. The objective of this study is to reveal the effects of both the Prandtl number (Pr) and Richardson (Riτ) number on the characteristics of turbulent flow, heat transfer, and large-scale motions in weakly stratified turbulence. The stably stratified turbulent open channel flows are calculated for Pr from 0.1 up to 100, Riτ from 0 to 20, and the Reynolds number (Reτ) 180 based on the wall friction velocity and the channel height. To elucidate the turbulent flow and heat transfer behaviors, some typical quantities, including the mean velocity, temperature and their fluctuations, turbulent heat fluxes, and the structures of the velocity and temperature fluctuations, are analyzed. 相似文献
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The largest known experiment on hydrogen-air deflagration in the open atmosphere has been analysed by means of the large eddy simulation (LES). The combustion model is based on the progress variable equation to simulate a premixed flame front propagation and the gradient method to decouple the physical combustion rate from numerical peculiarities. The hydrodynamic instability has been partially resolved by LES and unresolved effects have been modelled by Yakhot's turbulent premixed combustion model. The main contributor to high flame propagation velocity is the additional turbulence generated by the flame front itself. It has been modelled based on the maximum flame wrinkling factor predicted by Karlovitz et al. theory and the transitional distance reported by Gostintsev with colleagues. Simulations are in a good agreement with experimental data on flame propagation dynamics, flame shape, and outgoing pressure wave peaks and structure. The model is built from the first principles and no adjustable parameters were applied to get agreement with the experiment. 相似文献
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A recently developed subgrid model for soot dynamics [H. El-Asrag, T. Lu, C.K. Law, S. Menon, Combust. Flame 150 (2007) 108-126] is used to study the soot formation in a non-premixed turbulent flame. The model allows coupling between reaction, diffusion and soot (including soot diffusion and thermophoretic forces) processes in the subgrid domain without requiring ad hoc filtering or model parameter adjustments. The combined model includes the entire process, from the initial phase, when the soot nucleus diameter is much smaller than the mean free path, to the final phase, after coagulation and aggregation, where it can be considered in the continuum regime. A relatively detailed but reduced kinetics for ethylene-air is used to simulate an experimentally studied non-premixed ethylene/air jet diffusion flame. Acetylene is used as a soot precursor species. The soot volume fraction order of magnitude, the location of its maxima, and the soot particle size distribution are all captured reasonably. Along the centerline, an initial region dominated by nucleation and surface growth is established followed by an oxidation region. The diffusion effect is found to be most important in the nucleation regime, while the thermophoretic forces become more influential downstream of the potential core in the oxidation zone. The particle size distribution shows a log-normal distribution in the nucleation region, and a more Gaussian like distribution further downstream. Limitations of the current approach and possible solution strategies are also discussed. 相似文献
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Joon Ahn Haecheon Choi Joon Sik Lee 《International Journal of Heat and Mass Transfer》2007,50(25-26):4937-4947
The internal cooling passage of a gas turbine blade equipped with ribs is modeled as a rotating ribbed channel. The flow and heat transfer in the ribbed channel have been investigated by conducting large eddy simulations with a dynamic subgrid-scale model. The Reynolds number considered is 30,000 and rotation numbers are 0, 0.1 and 0.3. The time-averaged results show good agreement with the experimental data. By comparing the present data with those of the smooth channel, it is observed that the vortices shed from the rib induce strong wall-normal motions, and they are augmented on the trailing-wall side by the rotation, resulting in a significant increase in the heat transfer due to rotation. It is also shown that the similarity between the streamwise velocity and temperature is significantly destroyed by both the rotation and the rib itself. 相似文献