Many-particle interactions in Couette flows

A Lattice Boltzmann simulation is employed to investigate the inertial effect of particles on migrations and rotation of neutrally buoyant dumbbells in a shear flow. We demonstrate that the single dumbbell rotates around the minor axis and with its major axis perpendicular to the vorticity direction of the shear flow. This 'tumbling' rotation behaviour is similar to that of the single ellipsoid and cylinder at lower Reynolds numbers due to inertia. The shearing plane is an attractor for the dumbbell particle. A rotation transition is not observed for the dumbbell in the tested Reynolds number range, although the rotation transition occurs for other non-spberical particle. It is the gap, between the two spheres in a dumbbell, that reduces the circulating flow around the centre of the dumbbell and greatly releases the turbulence due to streamline separation. We also investigate the effects of many-particle interactions on orientation and rotation and find that most dumbbells predominately rotate with their long bodies perpendicular to the vorticity vector. As the Reynolds number increases, the probability of the dumbbells rotating with their major axis perpendicular to the flow vorticity is gradually reduced due to many-particle interactions.