Chaotic mixing of immiscible impurities in a two-dimensional flow

Abstract

Experiments compare the chaotic mixing of miscible and immiscible impurities in a two-dimensional flow composed of a chain of alternating vortices. Periodic time dependence is imposed on the system by sloshing the fluid slowly across the stationary vortices, mimicking the even oscillatory instability of Rayleigh–Bénard convection. The transport of a miscible impurity is diffusive with an enhanced diffusion coefficient D* that depends on the size of “lobes” which are, in turn, dependent on the oscillation amplitude. The lobes play an important role in the transport of immiscible impurities as well. In this case, the impurity is broken into a distribution of droplets, whose areas determine the nature of the transport. If the characteristic long-term droplet areas are appreciably smaller than the lobe areas, then there is long-range transport with D* equal to that for the miscible case with the same flow conditions. If the droplet areas remain larger than the lobe areas, then there is no long-range transport.