Passive scalar transport mediated by laminar vortex rings

Abstract

Numerical simulations were used to study the dynamics of a passive conservedscalar quantity entrained by a self-propelling viscous vortex ring. The trans-port and mixing process of the passive scalar variable were studied con-sidering two initial scalar distributions:(i)The scalar substance was introducedinto the ring during its formation, further focusing in the shedding into thewake of the ring;(ii)A disk-like scalar layer was placed in the ring’s pathwhere the entrainment of the scalar substance into the ring bubble was studiedas a function of the ring strength. In both cases, the scalar concentration insidethe vortex bubble exhibits a steady decay with time. In the second case, it wasshown that the entrained scalar mass grows with both the Reynolds number ofthe ring and the thickness of the scalar layer in the propagation direction. Thering can be viewed as a mechanism for scalar transportation along importantdistances.