The inertial lift on an oscillating sphere in a linear shear flow

In a shear flow, a small sphere may experience a lift force due to fluid in ertia. Most previous workers assumed that the particle was stationary so th at they could treat the fluid motion as steady. In spite of this, the resul ts of previous analyses have generally been applied to problems in which pa rticles move in an unsteady fashion. This paper presents the results of sin gular perturbation calculations of the lift on a sphere in a linear shear f low. The velocity of the sphere oscillates sinusoidally in time. Although t he problem is idealized, the results provide some physical understanding of the effects of unsteadiness and the frequency regime in which one may assu me quasisteady conditions. (C) 1999 Elsevier Science Ltd. All rights reserv ed.