THE TURNING COUPLES ON AN ELLIPTIC PARTICLE SETTLING IN A VERTICAL CHANNEL

We do a direct two-dimensional finite-element simulation of the Navier -Stokes equations and compute the forces which turn an ellipse settlin g in a vertical channel of viscous fluid in a regime in which the elli pse oscillates under the action of vortex shedding. Turning this way a nd that is induced by large and unequal values of negative pressure at the rear separation points which are here identified with the two poi nts on the back face where the shear stress vanishes. The main restori ng mechanism which turns the broadside of the ellipse perpendicular to the fall is the high pressure at the 'stagnation point' on the front face, as in potential flow, which is here identified with the one poin t on the front face where the shear stress vanishes.