Coupling of fluctuating vorticity and voidage fluxes in free shear flows

The key role played by large scale eddies in turbulent free shear dispersion of particles and bubbles is now well documented, and our earlier demonstrations (Sene et al. 1994; Yang 1996) have shown that local dispersed phase (voidage) transport is highly correlated with transient vorticity. We now seek to quantify the couplings between the fluxes of fluctuating vorticity and bubbles or particles, utilising the simulations described in Yang (1996) and following the methods of Sene et al. (1994), that is by sampling the Lagrangian trajectories at different positions within an Eulerian frame. Our results show that the correlation between the fluctuation fluxes is higher in the core region of the mixing layer for bubbles, but lower for particles, as compared with the correlation along the edges of the mixing layer for particles. This finding is both consistent with and quantifies previous results (Sene et al. 1994; Martin & Meiburg 1994) on trapping confinement of bubbles and centrifuged expulsion of particles, the latter hovering around the edges of the large scale vortices in the mixing layer.