Direct Numerical Simulation of Turbulent Free Jet and Experimental Verification

本文对三维Navier-Stokes方程的对流项采用三阶迎风差分格式，直接模拟了狭缝喷管的自由射流。计算的流场范围从喷嘴出口到充分发展的湍流区。对对流项也设计了动能守恒格式。计算得到的平均速度分布和速度矢量图与实验数据进行了比较。网格宽度约为Kolmogorov微尺度的10倍;然而，自由射流中的平均速度分布与实验数据相当吻合。这是因为模拟很好地代表了在流场形成中起重要作用的大尺度涡流的运动。因此，三阶迎风差分格式中对小尺度的忽略并不会对大尺度涡的模拟产生很大影响。

The third-order upwind finite difference scheme is used for the convective terms in three-dimensional Navier-Stokes equations to simulate directly the free jet flow issuing from a slit nozzle. The calculated flow field ranges from the nozzle exit to the fully developed turbulent region. The kinetic energy conservation scheme is also devised for the convective terms. The calculated results of mean velocity distributions and velocity vector diagrams are compared with the experimental date. The mesh width is roughly ten times Kolmogorov microscale ; however, the mean velocity distributions in the free jet are in fairly good agreement with the experimental data. This is because the simulation well represents the motion of large-scale eddies which play an important role in a flow field formation. Hence the neglection of the small-scale in the third-order upwind finite difference scheme does not largely affect the simulation of large-scale eddies.