剪切来流中圆盘近尾迹的数值研究

采用直接数值模拟（DNS）方法对低雷诺数时剪切来流中圆盘近尾迹进行了数值研究，重点研究剪切率对尾迹结构的影响.选取的雷诺数是140，160和300，无量纲进口来流剪切率范围是0≤k<01.当Re=140和160时，尾迹均变为非稳态面对称结构，表明剪切来流中非稳态面对称模态出现的临界雷诺数减小.剪切来流中发夹涡头部在来流速度较高侧明显偏大，且当Re=160时对称面位置随剪切率的增加而逐渐趋于xoy面.当Re=300时，剪切来流中圆盘尾迹结构没有明显变化，仍呈弱紊乱状态.研究还发现，相较于均匀来流，在k值较低（k<01）的剪切来流中无量纲涡旋脱落频率基本不变.
Abstract：Numerical investigations on the near wake of a circular disk in a shear flow at low Reynolds numbers were performed using DNS, with focus on the effect of shear rate on the wake structures. The Reynolds numbers considered were 140, 160 and 300, and the non-dimensional shear rate k of inlet flow was varied from 0 to 01. At Re=140 and 160, the wake changes to the unsteady state with planar-symmetry, indicating that the critical Re of this mode decreases in the uniform shear flow. The head of the hairpin vortex loop is always much larger on the high-velocity side within the shear flow, and at Re=160 the planar symmetry gradually moves to the xoy plane with the increase of the shear rate k. At Re=300, no obvious changes of the wake structures are observed, and the wake is still in the weakly-chaotic state. It is also found that, for low values of k (k<01), the non-dimensional vortex shedding frequency of the shear flow is nearly the same as that of uniform flow.