Application of Fast Projection Methods to the Fire Dynamics Simulator

We present a fast, second-order projection scheme for variable-density low Mach number flows and demonstrate its integration into the Fire Dynamics Simulator (FDS). The proposed method is based on the so-called fast-projection methods that were recently developed for low-Mach reacting flows (Presented at the 2024 APS DFD conference). These methods achieve speedup by eliminating the pressure Poisson solves at the intermediate stage (predictor) of the FDS time marching algorithm and replacing those with suitable approximations built from previously computed corrector-stage pressures. This approach reduces the number of pressure solves per timestep without compromising the temporal order-of-accuracy. We verify the scheme using standard FDS benchmarks, demonstrating global second-order convergence in time and very good agreement with the conventional solver. This work highlights the significant computational savings achievable in large-scale simulations and provides a path toward efficient high-order low-Mach solvers such as FDS. Ongoing efforts explore the application of these methods to reacting flows with detailed chemistry as well as parallel performance at scale.