A semi-analytical transient undisturbed velocity correction scheme for wall-bounded two-way coupled Euler-Lagrange simulations

TL;DR

This paper introduces a semi-analytical scheme to accurately compute the transient velocity disturbance caused by particles near walls in Euler-Lagrange simulations, improving the modeling of wall effects without fitted parameters.

Contribution

The authors develop a novel method combining analytical Green's functions with numerical convolution to efficiently estimate unsteady wall-bounded velocity disturbances in particle-laden flows.

Findings

Method exactly satisfies no-slip boundary condition.

Pre-computed correction maps enable efficient disturbance estimation.

Validated on settling and free-falling particles near walls.

Abstract

In the present paper, we model the velocity disturbance generated by a regularized forcing near a planar wall, which, along with the temporal nature of the forcing, provides an estimate of the unsteady velocity disturbance of the particle near a planar wall. We use the analytical solution for a singular in-time transient Stokeslet near a planar wall (Felderhof, 2009) and derive the corresponding time-persistent Stokeslets. The velocity disturbance due to a regularized forcing is then obtained numerically via a discrete convolution with the regularization kernel. The resulting Green's functions for parallel and perpendicular regularized forcing to the wall are stored as pre-computed temporal correction maps. By storing the time-dependent particle force on the fluid as fictitious particles, we estimate the unsteady velocity disturbance generated by the particle as a scalar product between the stored forces and the pre-computed Green's functions. Since the model depends on the analytical Green's function solution of the singular Stokeslet near a planar wall, the obtained velocity disturbance exactly satisfies the no-slip condition and does not require any fitted parameters to account for the rapid decay of the disturbance near the wall. The numerical evaluation of the convolution integral makes the present method suitable for arbitrary regularization kernels. Additionally, the generation of parallel and perpendicular correction maps enables to estimate the velocity disturbance due to particle motion in arbitrary directions relative to the local flow. The convergence of the method is studied on a fixed particle near a planar wall, and verification tests are performed on a settling particle parallel to a wall and a free-falling particle perpendicular to the wall.