有壁均匀切交流中马蹄涡发展的数值模拟

从Ｎａｖｉｅｒ—Ｓｔｏｋｅｓ方程出发．应用渐近衔接方法研究了马蹄涡在均匀切变流中的发展。在外层，用涡方法模拟了上抛和下扫两种马蹄涡的发展过程，初步地探讨了有壁切交流中马蹄涡的相干性。例如发现两种渴都向基本流的第一主变形率方向偏转，不断受到拉伸而增强等等。在内层，通过直接求解Ｓｔｏｋｅｓ方程而得到流场的发展过程，发现在外层扰动作用下，内层有新的涡产生并且随其厚度增加而缓缓升起。数值计算的结果与已有的流场显示结果相一致，从而说明涡动力学方法在研究切变层的拟序结构中是有效的。

Numerical Simulation of the Development of a Horseshoe Vortex in Uniform Wall Shear Flow

This paper investigates the development of a horseshoe vortex in the uniform wall shear flow by means of the asymptotic marching method based on the Navier-Stokes equation. The evolution of the ejection and sweep events in the outer layer of a disturbed shear flow are simulated by vortex dynamics, and a strong coherent motion of the vortex has been discovered. For instance, both vortices, representing the ejection and sweep events respectively, are rotating towards the first principal direction of the strain rate tensor, and strengthened by stretching ete. The development of the flow field in the inner layer is directly calculated by numerical integration of analytical solutions. Under the action of the disturbances from outer layer new vortices are generated, they slowly lift up while the thickness of the Stokes layer is gradually increasing. The numerical results are in good agreement with previous flow visualization pictures, thus it indicates that vortex dynamics is an applicable method for investigating the coherent structure in wall shear flow.