Vortex merger in semi-dilute particle-laden flow*

We investigate the effect of inertial particles on the merger of a pair of co-rotating vortices in semi-dilute particle-laden flows. Unlike the merger process in particle-free flows where the separation between two vortex centers decreases monotonically, we show that the feedback force exerted by the suspended particles on the carrier fluid modulates the merger mechanism and may even inhibit it depending on the particle inertia. We perform a series of Eulerian-Lagrangian simulations at the circulation Reynolds number 500 and mass loading M=1. Particle diameter is varied such that the resulting Stokes number, which measures inertia, varies from 0.01 to 0.8. For particles with low inertia (St<0.05), the merger is delayed due to the suspension acting as an effective fluid with density (1+M) higher than that of the carrier fluid. For particles with moderate inertia (0.05