Evaluating Poisson solvers for fire simulations

The Fire Dynamics Simulator is a fire model commonly used by the fire protection community in design and evaluation of fire suppression systems in buildings and structures, as well as modeling outdoor fires. FDS computes thermally buoyant, chemically reacting flows by means of large eddy simulation of a low Mach approximation of the governing equations for fluid flow, heat and mass transport. Parallel computations are performed on hundreds of cores using the MPI standard. Recently, as part of a large scale fire simulation initiative, the developers started investigating the viability of use of GPU acceleration for computation intensive portions of the algorithm. In this presentation we focus on the pressure Poisson equation arising from the discrete time integration of the momentum equations. We compare GPU accelerated linear solvers being developed as part of the PETSc and associated libraries in an unstructured grid setting, to the classical fast trigonometric solvers used in combination with an immersed boundary method. Both single and multiple mesh, and multiple CPU and GPU test cases are compared in a representative fire scenario, providing some insights and suggestions.