Assessment of preconditioning methods for multidimensional aerodynamics

We consider the steady state equations for a compressible fluid. For low speed flow the system is stiff since the ratio of the convective speed to the speed of sound is very small. To overcome this difficulty we alter the time dependency of the equations while retaining the same steady state operator. In order to achieve high numerical resolution we also alter the artificial dissipation (or Roe matrix) of the numerical scheme. The definition of preconditioners and artificial dissipation terms can be formulated conveniently by using other sets of dependent variables rather than the conservation variables. The effects of different preconditioners, artificial dissipation and grid density on accuracy and convergence to the steady state of the numerical solutions are presented in detail. The numerical results obtained for inviscid and viscous two- and three-dimensional flows over external aerodynamic bodies indicate that efficient multigrid computations of flows with very low Mach numbers are now possible.