Forces on a rotating particle in a shear flow of a highly rarefied gas

The determination of the forces on a particle is required for the simulation of the particle’s motion, which in turn is necessary for the simulation of particle contamination in a hard disk drive. In this paper, the forces on a rotating sphere in a shear flow of a highly rarefied gas are investigated analytically. The Chapman–Enskog distribution function is used to describe the molecules in the shear flow and a Maxwell-type boundary condition is assumed on the surface of the sphere. Expressions are obtained for the drag force as well as lift forces for the special case where the gradient of the shear flow is along the same direction as the axis of the particle’s rotation. The effects of particle rotation and shear flow are shown to be decoupled. These lift forces also turn out to be in the opposite directions from their corresponding forces when the fluid is modeled as a continuum.