Coupled CFD/CSD Simulations of the UH-60A Main Rotor in High Thrust Forward Flight

Abstract

Two high thrust forward flight conditions for the UH-60A helicopter were simulated using a delta-airloads iterative CFD/CSD loose coupling procedure. The unstructured Reynolds-Averaged Navier Stokes (RANS) solver U 2 NCLE was coupled to DYMORE 2 through a Python script. CFD was applied to the analysis of one blade of the four-bladed rotor and a free wake model was used to represent effects of the remaining three blades in the system. Coupled results with CFD-based airloads were compared with those from aerodynamic model airloads and flight test data. CFD airloads captured important phenomena such as dynamic stall and reverse flow over the retreating blade, thereby improving the performance prediction while incurring a substantial computational cost as compared to an analysis using the CSD simplified aerodynamics model. A method of improving control system robustness was successfully used during the CFD/CSD coupling process to determine that the flight conditions were within the level flight envelope of the vehicle. Nomenclaturea ref = Reference speed of sound c ref = Reference chord length C n M 2 = Normal force coefficient, F n / 0.5 ρ a ref 2 c ref C m M 2 = Pitching moment coefficient, M x / 0.5 ρ a ref 2 c ref 2 F n = Blade sectional normal force M x = Blade sectional pitching moment Ψ = Azimuth position Ω = Rotor angular velocity μ = Advance ratio