圆柱尾迹影响平板边界层转捩的实验研究

利用氢气泡和染色液流动显示的方法,在水槽中研究了圆柱尾迹对平板边界层转捩的影响。重点讨论圆柱与平板的流向距离和法向距离以及圆柱直径等几何参数对边界层转捩的不同作用,发现平板边界层转捩开始点的位置由尾迹与边界层作用的初始位置决定,这一位置由圆柱与平板的相对几何位置来确定。转捩区长度与边界层内部流体性质、扰动强度等有关,同时也受到圆柱、平板相对几何位置的影响。对转捩区近壁二次涡的产生和演化进行分析,发现尾迹对平板边界层的扰动是通过在近壁面诱导二次涡并影响二次涡的后续运动来体现,二次涡及其演化是边界层转捩位置大为提前的重要原因。

Experiment investigation on the boundary layer transition influenced by the cylinder wake

The process of a strong wake-induced laminar/turbulent transition on a flat-plate boundary layer was investigated by using hydrogen bubble and dye-stream visualization technique in the water tunnel.The wake was generated by a 2D cylinder above the plate.With disturbance of the cylinder,the transition of flat-plate boundary layer was put forward greatly.The investigation was focused on the influence of geometric parameters of the cylinder's position and diameter.The onset and end point of transition was mainly decided by the diameter and the normal position of the cylinder,streamwise position played a less role,comparing with the above two factors.The second-vortex near the wall,induced by the vortex street of the cylinder,was also recorded and investigated.Strong bursts were captured after the breakdown of the secondary vortex.So we regarded that the disturbance brought into the boundary layer could be mainly traced back to the evolvement of the secondary vortex and its interaction with the main one.