超声速边界层流动数值模拟的边界条件研究

在超声速边界层的计算中，出口处边界条件的好坏会影响计算结果。Poimot＆S．K．Lele曾建议一种NSCBC方法，被广泛采用。但它是建立在局部一维无粘关系假定上的，而靠近壁面处速度梯度大，粘性作用不能忽略，上述假定不一定成立。此外，NSCBC方法在亚声速区需要下游的某些已知条件，而这往往是无法预先知道的，从而不得不做一些假定。本文将分析这样做可能出现的问题，并对某一类问题，提出一种可以得到更好结果的方法。

A study of the boundary condition in the DNS of the supersonic boundary layer flow

In the direct numerical simulation of supersonic boundary layer flow, the outlet boundary condition will strongly effect the computational results. Poinsot & S.K.Lele had proposed the so-called Navier-Stokes characteristic boundary condition, NSCBC,which has been widely used. It is based on the local one-dimensional inviscid assumption. Yet the velocity gradient is large near the wall that the viscous effect may not be neglected. In addition, for subsonic part of the flow, effect from downstream may not be known in advance, thus NSCBC method may not be appropriately applied. In our paper, by analyzing the flow field, we did find that NSCBC method would lead to error near the outlet. Then we proposed a new method to deal with the boundary condition at the outlet, which yielded better results.