The impact of a vortex ring on a porous screen

Abstract

In this paper, we re-examine the issue raised by Morton(2000) regarding the impact of a vortex ring on a porous screen. We show, through a systematic experiment, that Morton's observation can only occur at very low Reynolds number or above a certain critical Reynolds number, which is dependent on the porosity of the screen. In particular, we found that a primary vortex ring of moderate Reynolds number impacting a porous screen can also undergo vortex rebound similar to that observed in vortex ring-solid wall interaction. At a higher Reynolds number, the self-induced flow of the primary vortex ring around the axis of symmetry passes through the screen as a jet-like flow, which later regenerates into a new vortex ring of the same sign but weaker circulation. At an even higher Reynolds number, the primary vortex ring has sufficient energy to pass through the screen via a possible mechanism of vortex stretching and reconnection, and continues as a modified ring in its lee. © 2009 The Japan Society of Fluid Mechanics and IOP Publishing Ltd.