Recirculation flow and sloshing induced by submerged rectangular synthetic jets in a water tank

We investigated recirculating flow induced by submerged rectangular synthetic jets in a rectangular water tank. We employed particle image velocimetry to obtain velocity vectors and vorticity distributions in the tank. We also investigated sloshing of the air–water interface, evaluating its oscillation characteristics through flow visualization. The main results are summarized as follows: vortex pairs are generated by periodic expulsion and suction at a slot installed on a side wall of the rectangular water tank, thereby forming synthetic jets and recirculation regions inside the tank; the flow patterns depend on the slot eccentricity ratio, and when the distance from the slot to a boundary parallel to the jet axis is small, the jet is deflected toward the boundary regardless of whether it is a rigid or free boundary. In addition, based on the relationship between the stagnation-point location formed on the boundary of the system and the dimensionless stroke length (the inverse of the dimensionless oscillation frequency), we discussed the relationship between the time-averaged internal flow field and the dimensionless stroke length. Furthermore, when the input frequency of the synthetic jet approaches the natural frequency of the rectangular tank, sloshing occurs, and its oscillation frequency becomes locked in to the input frequency of the synthetic jet; the response curve indicates that the oscillation characteristics also depend on the slot eccentricity ratio and the system exhibits softening-spring characteristics when sloshing becomes pronounced.