DNS OF SEPARATED FLOW AND HEAT TRANSFER AND AN EXPLORATION OF TURBULENCE MODELING

本文采用直接数值模拟方法对钝平板周围的分离流动和传热进行了研究。在Re = 11600和50000处，用动态Smagorinsky模型进行了大涡模拟（LES）。利用DNS分析了面装六面体的三维非定常流场和换热问题。所得主要结果总结如下。在二维流的情况下，对Re = 1000和Pr = 0.7进行DNS。分离的剪切层在形成涡旋的过程中卷起，并合并成一个大尺度的涡旋，几乎周期性地从再附着区向下游脱落。时间平均努塞尔数在再附着点上游一点处达到最大值。努塞尔数的最大值在大尺度涡旋下形成，瞬时促进了换热。在三维流的情况下，DNS结果与之前的实测数据吻合得很好。Re = 11600和50000时的LES结果较好地预测了上述分离流动和换热的详细机理。它们与实测数据也很吻合。DSM较好地预测了分离流的复杂流动和换热机理。采用DNS方法分析了面装六面体的分离流动和传热。结果阐明了六面体周围形成的马蹄形涡的重要作用。

The Direct Numerical Simulation (DNS) of a separated flow around a blunt flat plate and heat transfer has been conducted. Further, the Large Eddy Simulation (LES) With the Dynamic Smagorinsky Model (DSM) are made at Re = 11600 and 50000. A three-dimensional unsteady flow and heat transfer around a surface-mounted hexahedron was analyzed using the DNS.Main results obtained are summarized as follows.In the case of a two-dimensional flow, DNS was carried out for Re = 1000 and Pr 0.7. The separated shear layer rolls up as forming the vortices, and they coalesce into a large scale vortex, which is almost periodically shed from the reattachment region to the downstream.The time averaged Nusselt number reaches the maximum a little upstream of the reattachment point.The maximum of Nusselt number is formed under the large scale vortex, where the heat transfer is instantaneously promoted.In the case of a three-dimensional flow, the DNS results agree well with the previous measured data.LES results for Re = 11600 and 50000 predict well the detailed mechanisms of the separated flow and heat transfer described above. They also agree well with the measured data.The DSM predicts well the complicated flow and heat transfer mechanism of the separated flow.The separated flow and heat transfer around a surface mounted hexahedron were analyzed using the DNS method. The results clarified an important role of the horseshoe vortex formed around the hexahedron.