Quantifying the finite wall effects in a vortex ring wall interaction*

Vortex rings are a common flow feature found in various applications such as solar flares, the exhaust of an impulsively firing thruster, and in a human expiratory event such as coughing, sneezing, or speech. Such expiratory events, in addition to their vortical nature, are laden with aerosols that can spread infectious airborne diseases. Therefore, it is critical to understand vortex dynamics when evaluating the implementation of see-through barriers used to reduce the risk of exposure through direct contact. This study investigates the effectiveness of such strategies by studying the impingement of a vortex ring on a finite-size flat plate. Previous studies with 2D vortex dipoles indicate that finiteness can have a noticeable effect on the interaction. To understand this behavior in 3D, we study the impingement of vortex rings of varying circulation-based vortex Reynolds numbers on plates of various diameters. Flow visualization and particle image velocimetry are employed to quantify vortex ring trajectory, circulation, and secondary vorticity produced during the interaction. The effect of this finiteness is found to affect the roll up of secondary vorticity and the trajectory of the vortex rebound and could therefore influence the efficacy of barriers as a countermeasure.