Coupled CFD/CSD Simulations of Helicopter Rotors with a Free Wake Model

Abstract

A Computational Fluid Dynamics/Computational Structural Dynamics (CFD/CSD) coupling technique is used to analyze the four-bladed UH-60A and Bell 427 main rotors, and the results are compared to flight test data. The unstructured Reynolds-Averaged Navier Stokes (RANS) solver UNCLE was coupled to DYMORE 2 by means of an automated script. A single blade was rendered in the CFD model for each case, and the wake of a four-bladed system was represented by a free wake model. The UH-60A loose coupling flight conditions considered were the forward flight high speed and moderate speed cases corresponding to flight counters c8534 and c8513, respectively. The Bell 427 flight case simulated was a high speed forward flight case. After convergence of the coupling procedure airload prediction was improved, and some flow features missed by the low fidelity aerodynamics of the CSD code were resolved by the high-fidelity flow solver. Aerodynamic loads associated with reverse flow and Blade-Vortex Interaction (BVI) showed the most improvement. Blade structural loads predicted by DYMORE 2 showed signs of moderate improvement as a result of the increased accuracy of the CFD-based airloads for one flight condition.