Experimental investigation of a synthetic jet impinging on a fixed wall

The process of laminar vortex rings periodically impinging on a fixed wall is investigated experimentally using flow visualization and two-dimensional particle image velocimetry. The secondary vortex is found after the third impingement cycle, which is the first such observation at low Reynolds number of 126. In comparison, it does not form during the first three cycles, indicating that there exist obvious differences in the impingement process between the first few cycles and the rest. However, as the vortex ring continues to impinge on the wall, the differences eliminate gradually after about five cycles and similar impingement process among different cycles is found. The proper orthogonal decomposition fields and the statistical characteristics of the flow fields are also studied. In particular, both the streamwise velocity before the impingement and the radial velocity after the impingement exhibit self-similar behavior.