Parallel Simulation of Lifting Rotor Wakes in Forward Flight

A finite-volume implicit, unsteady, multiblock, multigrid, upwind solver, and structured multiblock grid generator for rotors are presented, and applied to lifting rotors in forward flight. These flows are particularly expensive to compute as the accurate capture of the detailed vortical wake requires fine meshes away from the blades and, hence, a parallel version of the code has been developed allowing the use of very fine meshes. Parallel performance of the code is presented, and grid dependence of the computed blade loads and wake analysed, by considering wake capturing, total blade load and sectional load variation around the azimuth. It is demonstrated that the vortical wake capture is severely influenced by grid density, and even with 32 million points grid convergence is not approached. It is also shown that if blade loads only are of interest the vorticity dissipation is not a severe problem, and coarser meshes can be used. However, if more detail is required, for example blade-vortex interaction or aero-acoustic analysis, it would appear very difficult to capture the wake to any reasonable accuracy.