近壁区流向涡生成的数值模拟

Production of streamwise vortexes in a turbulent boundary layer

对于在湍流边界层近壁区,作为相干结构的主要特征的流向涡的产生及发展的全过程进行了研究.采用准二维的共振三波作为湍流边界层近壁区相干结构初值,用直接数值模拟方法模拟了准二维波发展到明显的三维扰动以及其中流向涡生成的整个过程,经分析发现,在该过程中,由于非线性作用,相干结构出现了明显的三维性,并产生了马蹄涡,与实验结果相一致,而且也研究了压力梯度对于流向涡生成以及发展的影响,在逆压梯度下,流向涡的生成得更早、更快,相干结构幅值增长较快,结构变得更加复杂.这些都说明了逆压梯度对相干结构具有激励作用.

The whole process of the production and the development of the streamwise vortexes are studied. By using the method of direct numerical simulation, the production of the streamwise vortexes and the process from quasi-2-dimensional coherent structures to 3-dimensional coherent structures in the wall region of a turbulent boundary layer are simulated. The initial values of the quasi-2-dimensional coherent structures in the wall region are obtained on the basis of the idea of resonant triad in the theory of hydrodynamic stability. The results show that due to the nonlinear interaction, the quasi 2-dimensional structures gradually grow to 3-dimensional structures; the streamwise vortexes and the hair-pin vortexes are produced in this process. And the results of the simulation agree well with the experimental results. The affects of the adverse gradient on the generation and the development of streamwise vortexes are also studied. With the adverse pressure gradient, the streamwise vortexes generates earlier, rise faster, the amplitude of the coherent structures grows faster, and the structures becomes more complicated, which means that adverse pressure gradient can actuate the coherent structure and the development of the streamwise vortexes.