The effect of grid topology and density on inviscid hovering rotor solutions

Grid dependence is examined for Euler simulations of multibladed rotors in hover. The numerical simulation of rotor flows poses a unique problem for f low solvers. The solution is extremely sensitive to the accuracy of capture of the vortical wake over several turns; this means that a much finer grid density is required away from the blade than for a fixed-wing case, result ing in excessive run-times. An attempt is made to determine the number of g rid points required to obtain practical results, by performing grid converg ence tests for O-H and O-C grid topologies and determining the optimum rati o of grid densities in each parametric direction, for two- and four-bladed test cases. An upwind Euler solver is used on O-H and O-C structured grids, generated by transfinite interpolation along with a periodic transformatio n. It is shown that O-H grids produce more accurate solutions than O-C grid s with the same number of points, and that 3 x 10(5) grid points produce in viscid solutions of sufficient accuracy for initial design. It is also show n that solutions can be improved by choosing optimum ratios of grid density in each parametric direction.