Numerical study on the drag and flow characteristics of porous particles at intermediate Reynolds numbers

Abstract

Flow entrained with permeable particles is frequently encountered in natural and engineering applications. However, the lack of knowledge about the drag on the porous spheres and the corresponding complex flow structures has been a hindrance for better understanding of these flow systems In this work, we perform a comprehensive numerical simulation of flow past a porous particle with a wide range of Reynolds number (5 ≤ Re ≤ 200) and porosity (0.1 ≤ ɛ ≤ 0.95). Furthermore, considering that few studies has reported the flows with moving porous spheres, the simulation of both a single and two porous spheres settling in an enclosure is conducted for further evaluating the effect of moving porous media on the fluid–solid flows. The lattice Boltzmann method (LBM) is applied to the fluid flow, and particularly, the immersed moving boundary (IMB) scheme describes the interaction between the fluid and porous solid body. The accuracy of that the hybrid IMB-LBM for modeling porous sphere flows, to our knowledge, is first explored and established by the present study. The results suggest that both Re and ɛ have a significant influence on the drag and recirculation flow of porous particles. At Re ≤ 75, the porous particle experiences a lower resistance than that of the impermeable counterpart. When Re exceeds 75, the drag ratio is higher than unity for ɛ ≤ 0.85. With increasing porosity, the recirculation wake penetrates the particle, then detaches from the particle, and eventually disappears in the particle rear. Based on the simulated results, a new drag correlation for porous spheres is developed. As for the moving porous spheres, they fall slower than the solid counterparts, and their drafting, kissing and tumbling (DKT) process can also be slowed down.