DYNAMIC SIMULATION OF THE MOTION OF CAPSULES IN PIPELINES

In this paper we report results of two-dimensional simulations of the motion of elliptic capsules carried by a Poiseuille flow in a channel. The numerical method allows computation of the capsule motion and the fluid flow around the capsule, and accurate evaluation of the lift fo rce and torque. Results show that the motion of a capsule which is hea vier than the carrying fluid may be decomposed into three stages: init ial lift-off, transient oscillations and steady flying. The behaviour of the capsule during initial lift-off and steady flying is analysed b y studying the pressure and shear stress distributions on the capsule. The dominant mechanism for the lift force and torque is lubrication o r inertia or a combination of the two under different conditions. The lift-off velocity for the ellipse in two dimensions is compared with e xperimental values for cylindrical capsules in pipes. Finally. the mec hanisms of lift for capsules are applied to flying core flows, and it is argued that inertial forces are responsible for levitating heavy cr ude oil cores lubricated by water in a horizontal pipeline.