Lift on Janus and stick spheres in laminar channel flow: a computational study

The instantaneous motion of a spherical particle in a channel flow is governed by the forces experienced by the particle. The magnitude and direction of the forces depend on the particle to channel size ratio, particle position, nature of the sphere surface (sticky/slippery), fluid properties and relative velocity between the fluid and the particle. In this work, we report the lift, the force component directed normal to the streamwise direction, on two classes of spheres, sticky and Janus, in a channel of square cross-section. The Janus spheres considered have both sticky and slippery hemispheres with the boundary between the two hemispheres parallel to the channel midplane. The effect of particle to channel size ratio, dimensionless particle position and particle Reynolds number on the lift are studied. The Janus sphere placed at the channel centerline is observed to experience the lift directed from the sticky to the slippery hemisphere. A correlation is proposed to predict the lift on the Janus sphere placed at the centerline of the channel. A sticky sphere positioned close to the channel wall experiences a significant lift directed away from it. For the Janus sphere placed at an off-center position two possibilities arise—slippery hemisphere facing the channel centerline (case A) or sticky hemisphere facing the channel centerline (case B). For case A, the lift is always directed away from the wall. For case B, the direction of lift depends on the particle position as well as particle Reynolds number. The moment coefficients for the sticky and Janus sphere are also presented.