Lift and drag forces acting on a particle moving in the presence of slip and shear near a wall

摘要

The lift and drag forces acting on a small spherical particle moving with a finite slip in single-wall-bounded flows are investigated via direct numerical simulations. This study is an extension of our previous work that considered the lift and drag forces acting on a sphere moving near a wall in the presence shear, but in the absence of slip (Ekanayake et al., J. Fluid Mech., vol. 904, 2020, A6). The effect of slip velocity on the particle force is analysed as a function of separation distance for low slip and shear Reynolds numbers (10(-3) <= Re-slip <= 10(-1) and 10(-3) <= Re-gamma <= 10(-1)) in both quiescent and linear shear flows. A generalised lift model valid for arbitrary particle-wall separation distances and Re-gamma, Re-slip <= 10(-1) is developed based on the results of the simulations. The proposed model can now predict the lift forces in linear shear flows in the presence or absence of slip, and in quiescent flows when slip is present. Existing drag models are also compared with numerical results for both quiescent and linear shear flows to determine which models capture near-wall slip velocities most accurately for low particle Reynolds numbers. Finally, we compare the results of the proposed lift model to previous experimental results of negatively buoyant particles and to numerical results of neutrally buoyant (force-free) particles moving near a wall in quiescent and linear shear flows. The generalised lift model presented can be used to predict the behaviour of particle suspensions in biological and industrial flows where the particle Reynolds numbers based on slip and shear are O(10(-1)) and below.