A non-reflective boundary condition for LBM based on the assumption of non-equilibrium symmetry

TL;DR

This paper introduces a novel non-reflective boundary condition for the Lattice Boltzmann Method that effectively absorbs acoustic waves and vortices, reducing reflections to nearly zero.

Contribution

The paper proposes the Non-equilibrium Symmetry Boundary Condition (NSBC), a new boundary condition for LBM based on non-equilibrium distribution symmetry, enhancing wave absorption.

Findings

Nearly zero reflection of acoustic waves

Effective absorption of vortices

Demonstrated through two distinct tests

Abstract

In this study a new type of non-reflective boundary condition (NRBC) for the Lattice Boltzmann Method (LBM) is proposed; the Non-equilibrium Symmetry Boundary Condition (NSBC). The idea behind this boundary condition is to utilize the characteristics of the non-equilibrium distribution function to assign values to the incoming populations. A simple gradient based extrapolation technique and a far-field criterion are used to predict the macroscopic fluid variables. To demonstrate the non-reflective behaviour of the NSBC, two different tests have been carried out, examining the capability of the boundary to absorb acoustic waves respectively vortices. The results for both tests show that the amount of reflection generated by the NSBC is nearly zero.