The flow of suspensions through tubes IV: Oscillatory flow of rigid spheres

The theory of oscillatory flow of a homogeneous liquid in a straight circular tube developed by Lambossy and Womersley has been confirmed by direct measurements of the displacement profiles for a sinusoidal pressure gradient at various frequencies. Rigid spheres suspended in the liquid showed radial migration away from the walls and away from the tube axis when the particle Reynolds number was made sufficiently high. This is the analogue of the tubular pinch effect discovered by Segré and Silberberg for steady flow, and is also exhibited by concentrated suspensions. The modification of the flow behavior of suspensions by Miperposition of an oscillatory pressure is briefly discussed.