INTERACTING 2-DIMENSIONAL VORTEX STRUCTURES - POINT VORTICES, CONTOURKINEMATICS AND STIRRING PROPERTIES

This paper addresses the stirring properties of interacting two-dimens ional vortex structures. It is well known from previous studies that e ssential features of dipole-dipole and dipole-monopole interactions, l ike partner exchange, are captured by simple point-vortex models of th ese structures. In order to investigate the mixing induced by such int eractions, the method of contour kinematics is adopted here, which all ows us to trace fluid particles that are initially confined within som e closed contour. For example, by tracing the deformations of the sepa ratrix enclosing the 'atmosphere' of a point-vortex dipole during the interaction with another single point vortex or vortex pair, the conto ur kinematics method provides information about the processes of entra inment and detrainment that take place during the interaction. Compari son of the modelling results with both full numerical simulations and laboratory experiments on dye-visualised vortex interactions in a stra tified fluid reveals a surprisingly good qualitative agreement.