Fourth order Multi-Time-Stepping Adams-Bashforth (MTSAB) scheme for NASA Glenn Research Center's Broadband Aeroacoustic Stator Simulation (BASS) code

By using a Multi-Time-Stepping Adams-Bashforth (MTSAB) scheme, different regions of the computational grid can march with different time steps based on their local stable time steps and on local minimum length and time scales. This can save computational time for problems with large range of length and time scales. In this work, a fourth order, automated MTSAB scheme was developed for NASA Glenn Research Center's Broadband Aeroacoustic Stator Simulation Code (BASS) code. BASS code solves the Navier-Stokes equations on structured multi-block grids. The automated MTSAB scheme, during the run assigns time steps to grid blocks, based on local stability and accuracy. The scheme automatically changes the time steps during the run as required. In this work, two automatic block cutting algorithms were also developed. The first block cutting algorithm cuts the existing grid blocks during the run, to minimize the number of points at the smallest time steps. The second block cutting algorithm cuts the grid blocks to maximize the parallel efficiency of the scheme. This scheme was tested on CAA workshop problems, highly nonlinear flows (Transonic flows) with grid motion, and viscous flow cases. Results from these cases and the speed gains from using the MTSAB scheme are presented.