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 2-D 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.