中文摘要：

采用RANS/LES混合模式对汽车外部的平均流场进行计算分析。采用三方程的k-ε-v～2湍流模型作为RANS/LES混合模式中的RANS部分。针对k-ε-v～2湍流模型中的正应力（v 2）输送方程以及用于构造松弛函数f22的椭圆方程引起数值计算不稳定等问题,根据Boussinesq假设和量纲一分析对微分形式的v 2方程进行合理的简化,推导出代数形式的正应力v 2方程以及新的湍动粘度方程。最终获得新的准k-ε-v～2/LES混合模型,并将其应用于汽车外部流场计算仿真中。准2k-ε-v～2/LES模型的控制方程借用商业软件Fluent中的Realizable k-ε/LES模型中的k方程和方程,并采用Fluent UDF将代数形式的v 2方程以及新的湍动粘度方程写入计算程序中。计算结果与其他RANS/LES混合模型、完全大涡模拟以及风洞试验进行对比分析,结果表明,在同等的计算条件下该混合模型能更加准确且高效地模拟车身表面的气流分离以及尾部流场。

英文摘要：

The hybrid RANS/LES approach is employed to compute the exterior time-average flow field of a vehicle. The three-equation k-s- v2 turbulence model is employed as the RANS part in current research. To overcome the numerical oscillation induced by the normal stress （v2 ） transport equation and the elliptic equation which is used to constructed relaxation function J22 in the k-e-v2 model, the algebraic form of the normal stress （v2） equation and the new eddy-viscosity equation are derived, based on the Boussinesq approximation and non-dimensional analysis. Then, the new hybrid semi-k-e-v~/LES model which can be used to compute the vehicle exterior flow field is obtained. The control equations of the new model employed the same k and c equations as those in the realizable k- s/LES model in commercial software Fluent, with an algebraic equation for v2 and new eddy-viscosity programmed by Fluent-UDE The comparisons between the results obtained by semi-k-E-vz/LES model and other hybrid RANS/LES models, entire LES and wind tunnel experiment show that the new model is more accurate and efficient to simulate the flow separation around the body surface and the wake vortex.