A second look at the role of the fast Fourier transform as an elliptic solver

A fast cosine transform (FCT) is coupled with a tridiagonal solver for the purpose of solving the Poisson equation on irregular and non-uniform rectangular staggered grids. This kind of solution is required for the pressure field during the simulation of the incompressible Navier-Stokes equations when using the projection method. A new technique using the FCT-tridiagonal solver is derived for the cases where the boundaries of the flow regime do not coincide with the boundaries of the computational domain and for non-uniform grids. The technique is based on an iterative procedure where a defect equation is solved in every iteration, followed by a relaxation procedure. The method is investigated analytically and numerically to show that the solution converges as a geometric series. The method is further investigated for the effects of the relative size of the rigid body, the grid stretching, size and aspect ratio. The new solver is incorporated with the direct numerical simulation (DNS) and large eddy simulation (LES) techniques to simulate the flows around a backward-facing step and a 3D rectangular obstacle, yielding results that qualitatively compare well with known results. Copyright (c) 2005 John Wiley & Sons, Ltd.