Vortical cleaning of oil-impregnated porous surfaces

Vortex rings are found in many natural and industrial processes. The most fascinating thing about vortex rings are their self-propelling and sustaining feature that distinguishes it from fluid jets. Here, we work towards a novel idea of vortical cleaning where vortex rings of various strengths are utilized to clean oil-laden porous surfaces. Although there exist few literatures on the interaction of vortex rings with porous surfaces, to the best of authors' knowledge, no study has investigated the vortex interaction with an oil impregnated porous surface. We explore the physics behind the interaction process by changing the Reynolds number of the vortex ring till the turbulent regime using high-speed shadowgraphy images, Planar Laser-Induced Fluorescence (PLIF) and Particle Image Velocimetry (PIV) techniques. The interaction reveals interesting insights which have been discussed under three regimes: 1) Penetration, 2) Bag formation, and 3) Bag breakup. The interaction results in the formation of droplets via Rayleigh-Taylor and Rayleigh-Plateau type instabilities. Moreover, due to the rotational nature of the vortex ring, oil is taken out from both the sides of the porous surface. Although, vortex rings with higher strength are able to expunge more oil, the physics depends much on the shape of the porous surface. The present method can be applied to clean various porous surfaces, including industrial filters and surgical masks