Vorticity and particle transport in periodic flow leaving a channel

We investigate herein a periodically driven flow from a channel into an open domain. For this purpose, the equations of motion are solved with a pseudo spectral code based on a Chebyshev polynomial for the spatial coordinates and on a second-order finite difference method for time. During each driving period, the fluid that leaves the channel forms a coherent structure consisting of a pair of counter-rotating vortices, also known as a dipole. Dipole features, such as speed, intensity, and stability, depend on two dimensionless parameters: the Strouhal number and the Reynolds number. In some cases the dipole lifetime is greater than the driving period, so vortices may interact and even coalesce. The second part of the paper is devoted to calculating solid-particle trajectories immersed in this flow. For this purpose an equation deduced from first principles is solved considering drag, added mass, and history forces. We find that solid particles accumulate in certain regions and that a fraction of the particles leave the integration domain.