平板边界层湍流的数值分析

对于不可压缩平板边界层的时间模式的直接数值模拟（DNS）而言，在转捩后继续计算，就可以得到湍流直接数值模拟结果．分析计算结果发现，当湍流充分发展后，其平均流剖面、各种量的脉动均方根值和雷诺应力等沿平板法向的分布都具有相似性．不过，从转捩完成至湍流充分发展之间有一过渡过程，其间上述相似性不成立．这一结果为简化但又较准确地计算工程技术问题中的湍流提供了一种可能性．此外，还分析了其他一些湍流特征，如形状因子和位移排移厚度随时间的演化规律．为了观察到相干结构，须将展向的计算域缩小一半，以增加分辨率，研究结果表明，湍流边界层近壁区存在相干结构，其主要表现是准流向涡或涡对．

Numerical Analysis of Turbulent Boundary Layer on a Flat Plate

As far as the temporal mode direction numerical simulation （DNS） has been considered in an incompressible boundary layer on a flat plate,the computation in laminar-turbulent transition might be continued to obtain the results of turbulent boundary-layer. Analytical results show that the normal-wise distribution of several statistical mean values of disturbances of a fully developed turbulence,such as the mean flow profile,the non-dimensional mean velocity defect,and the root mean square of the fluctuating velocity ,as well as the Reynolds stresses ,bear similarities in nature ,which might be used to simplify the computation of turbulent flows. It must be pointed out that,from the end of transition to the fully developed state of turbulence,there should be a transient period,during which the similarities do not hold. However,the results would helpfully provide a feasible way to make the turbulent computation simple and exact in some technical problems. Other characteristics of turbulence,such as the time history of shape factor and displacement thickness,were also analyzed. Based on the above results ,the computational domain in the stream-wise direction should be reduced to the half length in order to improve the resolving power to observe the coherent structures. Analytical results indicate the coherent structures,which were characterized by the quasi-stream-wise vortexes or vortex pairs ,exist in the wall region of a turbulent boundary layer.