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

对钝化平板的分离流动和换热进行了直接数值模拟。进一步，在Re=11600和50000下，用动态Smagorinsky模式进行了大涡模拟。利用该程序对表面贴装六面体的三维非定常流动与换热进行了数值模拟，主要结果如下：在二维流动情况下，对Re=1000，Pr0.7进行了数值模拟。分离的剪切层在形成旋涡的过程中卷起并汇聚成大尺度的旋涡，几乎是周期性地从再附着区向下游脱落。时均努塞尔数在再附着点上游稍远的地方达到最大值。在大尺度旋涡的作用下形成了努塞尔数的极大值，在大尺度旋涡的作用下瞬时促进了换热。在三维流动的情况下，数值模拟结果与已有的测量数据吻合较好。雷诺数为11600和50000的LES结果较好地预测了上述分离流动和换热的详细机理。DSM模型较好地预测了分离流的复杂流动和换热机理。利用数值模拟方法对表面贴装六面体的分离流和换热进行了数值模拟。结果表明，在六面体周围形成的马蹄涡起着重要的作用。

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.