Unsteady flow of a Newtonian fluid induced by eccentric-concentric rotation of a porous disk and the fluid at infinity

The unsteady flow of a Newtonian fluid produced by a sudden coincidence of the axes of a porous disk and the fluid at infinity has been investigated while they are initially rotating with the same angular velocity about non-coincident axes. The exact solutions of both the velocity field and the components of shear stress on the disk have been obtained with the use of the Laplace transform technique. During the transition from the initial time to the steady flow, the influence of both the suction and blowing has been scrutinized. It has been proved that the suction through the disk tends to thin the boundary layer near the disk while the blowing causes a thickening of the boundary layer. It has been shown that the horizontal components of the force for small times are absolutely greater in the case of suction. Furthermore, it has been pointed out that the flow reduces to a helical motion in the steady flow.