雷诺应力与涡黏性模型的分离流预测对比分析

Comparative analysis of Reynolds stress and eddy viscosity models in separation flow prediction

现代飞行器设计对流动分离的准确预测需求愈发迫切,但使用广泛的涡黏性模型预测结果却不尽如人意。雷诺应力模型凭借其扎实的理论基础有可能获得可信度更高的结果,但其性能优势仍需进一步评估与发掘。选取了SST模型、Stress-BSL(Baseline)模型分别作为涡黏性和雷诺应力模型的代表,对二维驼峰、二维跨声速凸块、跨声速三维ONERA M6机翼等算例进行了数值仿真。结果表明,相较于实验值,2种模型的预测结果均出现流动分离点提前,再附点滞后的现象,但Stress-BSL模型的预测误差更小,表现出了强逆压梯度下预测分离流动的优势。通过分析发现,2种模型对雷诺应力的低估导致了分离区较大。具体表现为SST模型引入的Bradshaw假设限制了湍动能的生成,使得模型计算的涡黏性系数偏小,强逆压梯度下低估边界层雷诺应力,导致流动分离提前。而分离区上缘处的雷诺应力预测偏小则被认为是流动再附滞后的主要原因。对于雷诺应力模型,误差主要来源于雷诺应力输运方程再分配项的模化不准。最后,针对上述原因,对SST模型关键封闭参数进行了重新标定,并进行了初步验证,结果表明修改后的模型预测表现好于原模型结果。

The demand for accurate prediction of flow separation in modern aircraft design is becoming increasingly urgent,yet the prediction results of the widely used eddy viscosity model are not satisfactory.With its solid theoretical foundation,the Reynolds stress model may obtain more reliable results;however,its performance advantages still need to be further evaluated and explored.In this paper,the shear stress transport model and stress baseline model are selected as the representatives of the eddy viscosity model and Reynolds stress model,respectively,and numeri⁃cal simulations are carried out for two-dimensional hump,two-dimensional transonic bump and three-dimensional tran⁃sonic ONERA M6 wing.Compared with the experimental values,the prediction results of the two models show that the flow separation point is ahead of time and the reattachment point lags behind,while the prediction error of the Stress BSL model is smaller,showing the advantage of separation flow prediction under strong reverse pressure gradi⁃ent.It is found that the two models underestimate the Reynolds stress,resulting in a large separation zone.Specifi⁃cally,the Bradshaw hypothesis introduced into the SST model limits the generation of turbulent kinetic energy,re⁃duces the eddy viscosity coefficient calculated by the model,underestimates the Reynolds stress in the boundary layer under strong adverse pressure gradient,and leads to early flow separation.The smaller Reynolds stress prediction value at the upper edge of the separation zone is considered to be the main cause for the lag of flow reattachment.For the Reynolds stress model,the error mainly originates from the inaccurate modeling of the redistribution term of the Reynolds stress transport equation.Finally,aiming at the above causes,we recalibrate and preliminarily verify the key closure parameters of the SST model.The results show that the modified model performs better than the original model.