Localized parallel algorithm for bubble coalescence in free surface lattice-Boltzmann method

Abstract

The lattice Boltzmann method is a popular method from computational fluid dynamics. An extension of this method handling liquid flows with free surfaces can be used to simulate bubbly flows. It is based on a volume-of-fluids approach and an explicit tracking of the interface, including a reconstruction of the curvature to model surface tension. When this algorithm is parallelized, complicated data exchange is required, in particular when bubbles extend across several subdomains and when topological changes occur through coalescence of bubbles. In a previous implementation this was handled by using all-to-all MPI communication in each time step, restricting the scalability of the simulations to a moderate parallelism on a small number of processors. In this paper, a new parallel bubble merge algorithm will be introduced that communicates updates of the bubble status only locally in a restricted neighborhood. This results in better scalability and is suitable for massive parallelism. The algorithm has been implemented in the lattice Boltzmann software framework waLBerla, resulting in parallel efficiency of 90% on up to 4080 cores. © 2009 Springer.