BILU implicit multiblock Euler/Navier–Stokes simulation for rotor tip vortex and wake convection

Abstract

SUMMARYIn this paper, a block incomplete lower-upper (BILU) decomposition method is incorporated with a multiblock three-dimensional Euler/Navier-Stokes solver for simulation of hovering rotor tip vortices and rotor wake convection. Results of both Euler and Navier-Stokes simulations are obtained and compared with experimental observations. The comparisons include surface pressure distributions and tip vortex trajectories. The comparisons suggest that resolution of the boundary layer is important for the accurate evaluation of the blade surface loading, but is less so for the correct prediction of the vortex trajectory. Numerical tests show that, using Courant-Friedrichs-Lewy (CFL) number of 10 or 30 with the developed BILU implicit scheme can be 6-7 times faster than an explicit scheme. The importance of solution acceleration schemes that increase the permitted time-step is illustrated by comparing the evolving wake structures at different stages of the calculation. In contrast to fixed wing simulations, the extent of the wake structures is shown to require resolution of large physical time. This observation explains the poor performance that is obtained when employing convergence acceleration strategies originally intended for solution of equilibrium problems, such as the multigrid methods.