Simulation of a rotor in forward flight using topology-based refinement of multi-block structured meshes

The simulation of blade-vortex interaction (BVI) for helicopter rotors remains a challenge for Computational Fluid Dynamics (CFD). In the current paper a high-order, block-structured, finite volume flow solver is applied to the well-known HART-II baseline case. A new grid generation algorithm is presented which allows the automatic generation of locally refined meshes in user-specified regions, based on a regular block-structured mesh. The algorithm is used to generate a mesh with a given uniform resolution in the rotor disk area. The convection of the tip vortices is expected to improve on such a mesh. Flow results on both the unrefined and refined mesh confirm this expectation. Symbols and abbreviations BVI Blade-Vortex Interaction CFD Computational Fluid Dynamics NLR National Aerospace Laboratory R rotor radius CNM 2 normal force coefficient CNM = N 1 2 ρ∞a 2 ∞A N normal force [N] ρ∞ atmospheric air density [ kg/m] a∞ atmospheric speed of sound [m/s] A reference area [m] θ0 collective pitch [◦] θ1c longitudinal cyclic pitch [◦] θ1s lateral cyclic pitch [◦] ψ azimuth angle [◦] Q Q-criterion: Ω − S [s−2] S magnitude of strain rate tensor [s−1] U∞ forward rotor speed [m/s] Ω magnitude of vorticity [s−1]