基于湍流尺度的混合RANS/LES模型

比较BL(Baldwin-Lomax)湍流模型的内层模型与Smagorinsky亚格子模型,两者的主要差别在于湍流尺度的计算方法不同,而RANS(Reynolds Average Numerical Simulation)方程组与LES(Large Eddy Simulation)方程组在形式上又是相同的.基于这两点,发展了RANS/LES混合模型.该模型是在网格滤波尺度与到壁面的距离相等处将流场分区,在近壁区直接求解RANS方程组,在远离壁面区域,求解LES方程组.为了保证湍流粘性系数在内外层分界处的光滑过渡,内外层湍流粘性系数通过混合函数连接.混合方法减轻了对壁面附近网格分辨率的要求和时间步长的限制,因此比LES所需的计算成本少.用该混合模型模拟了绕双椭球的高超音复杂流场,结果表明采用混合模型可以准确地模拟可压缩湍流流场. 

Hybrid RANS/LES model based on turbulent scale

The main difference between the inner model of BL(Baldwin-Lomax) turbulent model and the Smagorinsky subgrid model lays in the different methods to calculate the turbulent scale.The governing equations of RANS(Reynolds average numerical simulation) and LES(large eddy simulation) are of same form.A hybrid RANS/LES model is developed here based on above observations.The governing equations of RANS are solved in inner region and the governing equations of LES are solved in outer region.A blending function is used to combine inner and outer turbulent viscous coefficients.The computational cost can be reduced compared with LES model.The hypersonic flow over double ellipsoidal spheres is simulated using the present model. Comparing with the experiment and the data of RANS model,the results show that the approach is validated.