Dynamic mesh re-partitioning considering iterative convergence rate for multiphase flows in OpenFOAM.

For parallel multiphase flows, the core procedure is solving linear systems using preconditioned iterative methods, and the iterative convergence rate is crucial to the overall efficiency. How the mesh is partitioned influences the iterative convergence rate. However, the numerical characteristics of the linear systems vary significantly along with the time steps because of the dramatic change of the flow fields. Traditional static mesh partition cannot guarantee a good convergence feature throughout the simulation. A dynamic mesh re-partitioning scheme MDMRPar (Multiphase Dynamic Mesh Re-Partitioning) is proposed and implemented in OpenFOAM (Open Field Operation And Manipulation). MDMRPar employs a new surface field to record the linear system information in every time step. For simple multiphase problems with topo-invariant mesh, MDMRPar periodically adopts the numerical information from the previous time step and calculates a weighted graph from the mesh topology in a straightforward way. For multiphase flows using adaptive mesh refinement method, a coarse graph with vertex weights is built based on the mesh topology and refinement history. The numerical information on the surface field is integrated into the coarse graph as edge weights. In both cases, weighted graphs are re-partitioned by ParMetis, a general multi-level parallel graph re-partitioning package. Experimental results on three multiphase flows show that MDMRPar significantly outperforms the traditional partitioning/re-partitioning schemes both in the iterative convergence rate and the total simulation time.