Implicit multi-block Euler/Navier-Stokes simulations for hovering helicopter rotor
A three dimensional implicit multiblock Navier-Stokes solver for hovering rotor vortical flow simulations has been developed. The governing equations used are cast in an attached blade rotating frame. Two formulations of the governing equations using the relative or absolute velocity as variables respectively are employed and investigated. The Osher's approximate Riemann solver is used for the convective fluxes evaluation. A modified MUSCL scheme is employed for improving the accuracy of the discretisation for the in viscid fluxes. A Block Incomplete Lower and Upper Decomposition (BILU) is adopted for solving the linear system resulted from the use of an implicit scheme. Special treatment for the terms, including extra flux terms and source terms, arising from the non-inertial reference system are implemented. A multiblock technique is used to obtain the exibility for quality grid generation. The suitability of different grid topologies for vortex wake capturing is demonstrated. Numerical tests show that significant improvement in computational efficiency is achieved by utilising the BILU implicit scheme in both fixed wing and hovering rotor calculations. Numerical simulations also demonstrate Navier-Stokes solutions give more accurate results than that from Euler solutions, especially in transonic tip speed cases. Computed results including surface pressure distributions and tip vortex trajectories are compared with the experimental data, which shows that the developed solver and the numerical scheme can simulate hovering rotor flows with good accuracy.