Lateral forces on spheres in turbulent uniform shear flow

Abstract

The lateral force on a tethered rigid sphere submerged in a turbulent, uniform shear flow of water was measured. Periodic and non-periodic motions of the sphere were observed depending on flowrate, shear and sphere density. The direction of the observed lateral force was opposite to that predicted by inviscid theory and increased in magnitude as the sphere’s Reynolds numbers based on relative velocity, Re, and average shear, Re ∇, increased. The lateral force was found to correlate with the product Re Re ∇ . The data suggests that a sign reversal occurs at relatively small values of the product Re Re ∇ , where the lateral force is dominated by inviscid effects. The results are explained assuming that the lateral forces on rigid spheres are a consequence of two competing factors: namely, inviscid lift forces and the vortex shedding-induced lateral forces which are dominant for higher Reynolds numbers. An estimate of the kinetic energy in the wake was used to show that the vortex shedding-induced lateral forces correlate with the product Re Re ∇ and are in a direction opposite to the inviscid lift force. Combining the experimental data of this study with similar data a correlation for the lift coefficient of spheres in turbulent shear flows was developed. This correlation is applicable to turbulent multiphase flows having a spherical dispersed phase.