Analysis of hydrodynamic filtration performance in a cross-step filter for drip irrigation based on the CFD‒DEM coupling method

Abstract

To improve the retained capacity and filtration efficiency, the liquid‒solid two-phase flow inside the cross-step filter was simulated using the computational fluid dynamics (CFD) and discrete element method (DEM) coupled method. The cross-step filtration utilises the shear layer in the slot to scour the particles deposited on the overflow mesh to the corner edge of the upstream rib, improving the filtration efficiency and retained capacity of the screen filter. Crossflow filtration was the predominant filtration mechanism at the overflow mesh, while dead-end filtration was predominant at the posterior mesh. The proportion of retained particles on the overflow mesh ranged from 10.1% to 18.2%. Along the mainstream, the average filtration velocity in the slot gradually increases and then decreases except in the last slot, accompanied by a constant number of particles trapped on the posterior mesh. Additionally, in the direction of the mainstream flow, the average shear velocity in the slot and the rotational velocity of the vortex initially increase and then decrease except in the first slot, resulting in a subsequent decrease and then increase in the amount of particles in the corresponding slot, with the exception that the greatest amount of particles is found in the end slot. The filtration velocity in the individual slots gradually decreases from the posterior mesh to the anterior mesh, with backflow occurring in the anterior mesh, while the shear velocity in the individual slots rises and then falls, with the greatest shear velocity along the overflow mesh.