Aspects of unsteady incompressible flow simulations

Since unsteady incompressible flow simulations involving complex geometry require long computing times, it is crucial to select computationally efficient solvers. For this purpose, two numerical procedures, one based on artificial compressibility and the other pressure projection method, are investigated for obtaining time-accurate solutions of the incompressible Navier-Stokes equations. The performance of the two methods is compared by obtaining unsteady solutions for the evolution of twin vortices behind a flat plate. Calculated results are compared with experimental and other numerical results. For an unsteady flow, which requires small physical time step, the pressure projection method was found to be computationally efficient since it does not require a subiteration procedure. It was also observed that the artificial compressibility method requires a fast convergence scheme at each physical time step in order to satisfy the incompressibility condition. This was obtained by employing a GMRES-ILU(0) solver in the artificial compressibility solver. Published by Elsevier Science Ltd.