串列双圆球的流场转捩研究

本文对虚拟边界法加以改善并推广到三维多连通区域的数值模拟上去,研究了不同雷诺数下串列双圆球的流场转捩现象.结果显示小间距比串列双圆球绕流场的第一分叉点位于雷诺数150～175,第二分叉点位于雷诺数225～250.大间距比绕流场的第一分叉点位于雷诺数170～200.转捩点的位置与单圆球绕流相比有不同程度的提前.给出了切面内流态沿流向的发展变化,捕捉到极限环现象,发现下游尾流场的涡结构分别脱落自下游圆球的上表面和下表面,两个来源处的涡脱频率为倍频的关系,随着雷诺数的增加存在频率竞争和占优频率交替的现象.

Study on transitions for flow past two spheres in tandem arrangement

The virtual boundary method was extended to 3D application and used to study the transitions for the flow field of two spheres in tandem arrangement at various Reynolds numbers. For the cases with small spacing ratio, the first transition Reynolds number is 150-175 and the second is 225-250. For the cases with large spacing ratio, the first transition Reynolds number is 170 - 200. The Reynolds numbers corresponding to the different transitions were found to be smaller than those in the single sphere case. The flow topologies on a few typical cross sections along the axis were presented and the limited circle was captured. The shedding frequency of the top side of the downstream sphere was found to be twice the frequency of the bottom side. Investigation of the flow spectra of various Reynolds numbers revealed the underlying competitive mechanism between two dominant frequencies.