Lattice Boltzmann Simulation of Acoustic Fields, with Special Attention to Non-reflecting Boundary Conditions

Abstract

Non-reflecting boundary conditions (NRBCs) are of great importance in computational fluid dynamics. Ideal NRBCs will fully absorb every incoming wave, thereby eliminating reflections from the boundaries which would otherwise interfere with the simulation inside the domain.In this thesis, three different types of existing NRBCs, perfectly matching layers (PMLs), characteristic boundary conditions (CBCs) and sponge layers, for the lattice Boltzmann method are summarized and compared against each other and an ideal case. In addition, tweaking of performance related parameters in each NRBC is performed to achieve the best performance. Simulations are done with two types of acoustic field excitations, a Gaussian pulse and a sinusoidally varying single point source.In both cases the lattice Boltzmann method with PMLs performed slightly better than CBCs, and gave the least reflections, while the lattice Boltzmann method with sponge layers gave the most reflections.