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旋流和无旋突扩流动的LES和RANS模拟 总被引:2,自引:0,他引:2
本文用smagorinsky-Lilly亚网格尺度湍流模型对旋流突扩流动(s=0.53)和无旋突扩流动(s=0)进行了大涡模拟(LES模拟),同时分别用压力应变项为IPCM和IPCM+Wall模型的雷诺应力方程模型进行了RANS模拟,和LES的统计结果对比。LES的统计结果与雷诺应力模型的模拟结果及实验对照表明,LES结果与实验结果的吻合比雷诺应力模型的好,说明所用的亚网格尺度湍流模型对旋流流动是适用的,LES结果是可信的。LES的瞬态结果揭示出在旋流作用下,流场中存在复杂的旋涡脱落现象。大涡结构极易破碎成小涡,而在无旋突扩流动的情况下,由于剪切的作用更强,大涡结构的尺寸和范围比旋流流动的要大。 相似文献
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针对大涡模拟涡粘性亚格子模式中使用网格尺度为特征尺度存在的不足,提出一种改进的亚格子特征尺度表达式,利用结合Sagaut混合尺度模式获得的改进模式与Smagorinsky模式、Germano模式和Sagaut模式等进行对比研究.时间发展混合层和中性大气边界层的大涡模拟结果表明,改进的有效亚格子特征尺度能合理反映亚格子脉动的时空分布特性,同时扩展了适用范围.在对耗散程度、流动演化过程、可解湍流强度和可解雷诺应力等方面的模拟,改进模式优于基准模式,表明亚格子脉动有效特征尺度在大涡模拟中具有一定的理论基础和广泛的应用价值. 相似文献
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加力燃烧室热态流场的大涡模拟 总被引:5,自引:0,他引:5
本文采用k方程亚网格尺度模型对带V形槽稳定器模型加力燃烧室紊流化学反应流进行大涡模拟的研究,采用亚网格EBU燃烧模型估算化学反应速率,用热通量辐射模型估算辐射通量。数值计算表明,在稳定器后面开始在短时间内出现涡的交替脱落和逐渐消失过程,然后形成稳定的回流区,数值计算结果与实验比较吻合,表明可用大涡模拟研究实际燃烧室瞬态燃烧流场。 相似文献
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应用分离涡模型计算斜圆柱孔气膜冷却 总被引:5,自引:0,他引:5
分离涡模型(DES,Detached eddy simulation)兼有雷诺时均湍流模型计算量较小和大涡模拟计算精度高的优点。本文利用DES对平板单斜圆柱孔的气膜冷却进行了数值模拟,并将结果同RANS湍流模型的计算结果以及实验数据相比较,表明DES能有效弥补RANS湍流模型在计算三维不均匀非定常湍流场的不足,更接近实际地反映了气膜冷却中的流动和换热的本质规律。 相似文献
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本文对空间发展的湍流气固两相平面混合层流动进行了大涡模拟研究,其中气相亚网格尺度(SGS)使用结构函数模型,气相控制方程组采用SIMPLE方法求解,固体颗粒运动用拉格朗日方法计算。计算结果正确重现了流体涡结构的卷起、合并和破碎过程,以及小尺寸颗粒在涡边缘(低涡度区)的局部富集现象。对直径分别为42μm、72μm和135μm分别进行了模拟,并将统计结果和实验测量结果(Hishida et al[1])比较,表明两者的平均速度吻合很好,但颗粒数密度和脉动速度存在较明显的差异,因此有必要对亚网格应力和颗粒之间的耦合作用以及拟序结构的三维性对颗粒运动的影响开展深入研究。 相似文献
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在传统大涡模拟方法的基础上引入显式滤波技术,有效地控制了最小解析尺度区域的各种数值误差.对有限差分格式的守恒特性进行了研究,发展了适用于三维平板通道大涡模拟的四阶精度守恒格式.分别利用二阶和四阶精度的传统与显式滤波大涡模拟程序模拟平板通道内的湍流流动,将计算结果与DNS数据进行了对比,得到了合理结果. 相似文献
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A necessary condition for the accurate prediction of turbulent flows using large-eddy simulation (LES) is the correct representation of energy transfer between the different scales of turbulence in the LES. For scalar turbulence, transfer of energy between turbulent length scales is described by a transport equation for the second moment of the scalar increment. For homogeneous isotropic turbulence, the underlying equation is the well-known Yaglom equation. In the present work, we study the turbulent mixing of a passive scalar with an imposed mean gradient by homogeneous isotropic turbulence. Both direct numerical simulations (DNS) and LES are performed for this configuration at various Schmidt numbers, ranging from 0.11 to 5.56. As the assumptions made in the derivation of the Yaglom equation are violated for the case considered here, a generalised Yaglom equation accounting for anisotropic effects, induced by the mean gradient, is derived in this work. This equation can be interpreted as a scale-by-scale energy-budget equation, as it relates at a certain scale r terms representing the production, turbulent transport, diffusive transport and dissipation of scalar energy. The equation is evaluated for the conducted DNS, followed by a discussion of physical effects present at different scales for various Schmidt numbers. For an analysis of the energy transfer in LES, a generalised Yaglom equation for the second moment of the filtered scalar increment is derived. In this equation, new terms appear due to the interaction between resolved and unresolved scales. In an a-priori test, this filtered energy-budget equation is evaluated by means of explicitly filtered DNS data. In addition, LES calculations of the same configuration are performed, and the energy budget as well as the different terms are thereby analysed in an a-posteriori test. It is shown that LES using an eddy viscosity model is able to fulfil the generalised filtered Yaglom equation for the present configuration. Further, the dependence of the terms appearing in the filtered energy-budget equation on varying Schmidt numbers is discussed. 相似文献
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采用二阶全展开ETG有限元方法作为大涡模拟空间离散格式,计算了Reynolds数为47625条件下的后台阶湍流流动,结果与相关实验资料符合良好,在此基础上分析了附加肋片高度和肋距对后台阶湍流流动的影响.计算结果表明,不同肋高和肋距对台阶下游流动具有较大的影响,相应条件下台阶下游的涡系及其时变过程都发生了很大的变化,计算给出了台阶回流段长度随肋高和随肋距变化的曲线,并指出,在台阶下游附加肋片可以作为后台阶湍流流动一种简单有效的被动控制方式. 相似文献
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N. Ansari G.M. Goldin M.R.H. Sheikhi P. Givi 《Journal of computational physics》2011,230(19):7132-7150
A new computational filtered density function (FDF) methodology is developed for large eddy simulation (LES) of turbulent reacting flows. This methodology is based on a Lagrangian Monte Carlo (MC) FDF solver constructed on a domain portrayed by an unstructured mesh. The base filtered transport equations on this mesh are solved by a finite-volume (FV) method. The consistency of the hybrid FV-MC solver and the realizability of the simulated results are demonstrated via LES of a temporally developing mixing layer. The overall performance of the model is appraised by comparison with direct numerical simulation (DNS) data. The algorithmic implementation in the commercial software ANSYS-FLUENT facilitates future FDF-LES of turbulent combustion in complex configurations. 相似文献
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采用理论分析和数值模拟相结合的方法,系统研究了尺度自适应模拟(scale-adaptive simulation,SAS)和大涡模拟(large-eddy simulation,LES)的关联性问题.在理论分析方面,对比分析了系综平均和滤波的定义、Spalart-Allmaras(SA)湍流模型和动态亚格子(subgrid-scale,SGS)模型关于湍流黏性系数的求解方式.理论分析结果表明,系综平均等价于盒式直接滤波,SAS和LES的控制方程在数学形式上具有一致性;SAS存在过多的湍流耗散,主要来自于SA输运方程中的扩散项.在数值模拟方面,选取来流Mach数0.55,Reynolds数2×105的圆柱可压缩绕流为分析算例.计算结果表明,SAS和LES预测的大尺度平均流场信息几乎一致,SAS预测的湍流脉动信息略低于LES.SAS在圆柱近尾迹区的湍流耗散过大,而在稍远的尾迹区几乎能够完全等效于LES. 相似文献
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The spatial evolution of a turbulent flow in the pilot stage of a jet pipe servo valve at the inlet pressure and deflection angle of the jet pipe is investigated using a large eddy simulation (LES). The pressure of the same flow field is measured by a high frequency dynamic pressure sensor in the experiments and is compared with the results of the LES, as well as their root-mean-square (RMS) and fast Fourier transform (FFT) results. The results of experiments and LES are in good agreement, indicating that LES is able to predict the flow dynamics. Velocity datasets based on LES are utilised to conduct the snapshot proper orthogonal decomposition (snapshot POD) technique. The snapshot POD analysis results of the first 4 modes show a full ability to directly visualise details of the coherent structures. The influences of the inlet pressure and deflection angle of the jet pipe are also discussed. Under different inlet pressures, the velocity eigenfunctions of the first mode are similar, while the locations and strengths of the vortices in high modes are different. The Lamb-Oseen vortices that affect the trajectory of jet streams are observed in the vicinity of the entrances of receiver channels only in the first mode, and several spindly vortices appear in the region of ?5?y/n??2 in the higher modes and act in opposite directions between adjacent vortices. The flow becomes more turbulent with increasing inlet pressure, and the turbulent structures of the high modes become ineffective from a deflection angle of 0.4° onward. 相似文献
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K. K.J. Ranga Dinesh K. W. Jenkins M. P. Kirkpatrick W. Malalasekera 《Combustion Theory and Modelling》2013,17(6):947-971
Large eddy simulations (LES) of turbulent non-premixed swirling flames based on the Sydney swirl burner experiments under different flame characteristics are used to uncover the underlying instability modes responsible for the centre jet precession and large scale recirculation zone. The selected flame series known as SMH flames have a fuel mixture of methane-hydrogen (50:50 by volume). The LES solves the governing equations on a structured Cartesian grid using a finite volume method, with turbulence and combustion modelling based on the localised dynamic Smagorinsky model and the steady laminar flamelet model respectively. The LES results are validated against experimental measurements and overall the LES yields good qualitative and quantitative agreement with the experimental observations. Analysis showed that the LES predicted two types of instability modes near fuel jet region and bluff body stabilised recirculation zone region. The mode I instability defined as cyclic precession of a centre jet is identified using the time periodicity of the centre jet in flames SMH1 and SMH2 and the mode II instability defined as cyclic expansion and collapse of the recirculation zone is identified using the time periodicity of the recirculation zone in flame SMH3. Finally frequency spectra obtained from the LES are found to be in good agreement with the experimentally observed precession frequencies. 相似文献
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An algebraic variational multiscale–multigrid method is proposed for large-eddy simulation of turbulent variable-density flow at low Mach number. Scale-separating operators generated by level-transfer operators from plain aggregation algebraic multigrid methods enable the application of modeling terms to selected scale groups (here, the smaller of the resolved scales) in a purely algebraic way. Thus, for scale separation, no additional discretization besides the basic one is required, in contrast to earlier approaches based on geometric multigrid methods. The proposed method is thoroughly validated via three numerical test cases of increasing complexity: a Rayleigh–Taylor instability, turbulent channel flow with a heated and a cooled wall, and turbulent flow past a backward-facing step with heating. Results obtained with the algebraic variational multiscale–multigrid method are compared to results obtained with residual-based variational multiscale methods as well as reference results from direct numerical simulation, experiments and LES published elsewhere. Particularly, mean and various second-order velocity and temperature results obtained for turbulent channel flow with a heated and a cooled wall indicate the higher prediction quality achievable when adding a small-scale subgrid-viscosity term within the algebraic multigrid framework instead of residual-based terms accounting for the subgrid-scale part of the non-linear convective term. 相似文献
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Sourabh V. Apte Krishnan Mahesh Parviz Moin 《Proceedings of the Combustion Institute》2009,32(2):2247-2256
Large-eddy simulation of an evaporating isopropyl alcohol spray in a coaxial combustor is performed. The Favre-averaged, variable density, low-Mach number Navier-Stokes equations are solved on unstructured grids with dynamic subgrid scale model to compute the turbulent gas-phase. The original incompressible flow algorithm for LES on unstructured grids by [Mahesh et al., J. Comp. Phys. 197 (2004) 215–240] is extended to include density variations and droplet evaporation. An efficient particle-tracking scheme on unstructured meshes is developed to compute the dispersed phase. Experimentally measured droplet size distribution and size-velocity correlation near the nozzle exit are used as the inlet conditions for the spray. The predictive capability of the LES approach on unstructured grids together with Lagrangian droplet dynamics models to capture the droplet dispersion characteristics, size distributions, and the spray evolution is examined in detail. The mean and turbulent quantities for the gas and particle phases are compared to experimental data to show good agreement. It is shown that for low evaporation rates considered in the present study, a well resolved large-eddy simulation together with simple subgrid models for droplet evaporation and motion provides good agreement of the mean and turbulent quantities for the gas and droplet phases compared to the experimental data. This work represents an important first step to assess the predictive capability of the unstructured grid LES approach applied to spray vaporization. The novelty of the results presented is that they establish a baseline fidelity in the ability to simulate complex flows on unstructured grids at conditions representative of gas-turbine combustors. 相似文献