Validation of incompressible flow computation of forces and moments on axisymmetric bodies at incidence

摘要

A numerical approach based on multiblock, multigrid, local refinement and preconditioning methods has been developed to solve the incompressible Reynolds-averaged Navier-Stokes (RANS) equations. Three-dimensional flow computations for four axisymmetric bodies at angles of attack of 0, 4, 8 12, and 16 degrees are presented. The definitions of a converged solution and grid-independent solution are given appropriate for engineering problems. Two measures of computational and experimental errors are also given for systematic assessment of errors. Computations on four grids: 24x8x12, 48x24x32, 96x32x48 and 144x48x72 were performed to study the behavior of convergence and grid sensitivity. It is conluded that the solution with the 144x48x72 grid is both converged and grid independent. The convergence rate is fast and is on the order of 1.5x10-5 cpu second per grid point per multigrid cycle based on a computation on a grid with 0.5 million grid cells on a single Cray C90 processor. The accuracy in the prediction of the forces and moments at various incidence angles is as good as the experimental accuracy. To achieve this level of accuracy, it is essential to modify the standard Baldwin-Limax turbulence model for the effects of the thickn boundary layer near the stern and the cross-flow separation near the leeward side as the angle of attack increases. Both modifications are described. The present work has made a significant advance towards the accurate prediction of the forces and moments acting on four axisymmetric bodies at varous angles of attack. This advance is an essential step towards the accurate prediction of the forces and moments on realistic maneuvering vehicles for practical design purposes.