钝体头部“逾越”型转捩的直接数值模拟

通过直接数值模拟,研究了钝体头部边界层"逾越"型转捩的问题.在计算上,利用高阶紧致差分格式和高分辨率的无反射边界条件,求解全N-S方程,并将局部有限幅值扰动直接引入到钝体头部的曲面边界层中.摈弃了目前国际上通常采用的周期边界条件,以及以平板代替曲面的做法.结果表明:流场转捩的发生与一种类似"发卡"状的拉伸结构出现有关,而国外的计算结果中并未发现这一结构.此外,流场的失稳过程和物理图像也存在较大差异.这说明国外目前的做法和结论是值得商榷的.同时,模拟的结果也说明,这种方法对研究大扰动转捩来说是一条行之有效的途径.

DNS of the Blunt Nose Bypass Transition

Bypass transition from laminar to turbulent flow in boundary layer of a blunt nose was studied by means of Direct Numerical Simulation(DNS).The full Navier-Stokes equations were numerically solved,using high-order compact finite difference schemes and high-resolution non-reflecting boundary conditions.The local finite amplitude disturbances were directly introduced into the boundary layer of a curved surface.The common calculating methods,i.e.using periodic boundary condition and curved surface replaced by flat plane,were discarded.The present result shows that transition in the flow field is correlated with the appearance of a kind of elongated structure,which is similar to a "hair-pin".This structure has not been found in other literatures.In addition,there are a lot of differences both in the instable process and in the structure pattern.The present results point out the direction of generalization of the observed transition mechanism to localized disturbances in wall bounded shear flow.