Airbus Racer - CFD Rotor Simulation Challenges At High Speed

Abstract

This paper presents a computational analysis of the Airbus Helicopters RACER main rotor at high speeds from 240kt up to 261kt, with a focus on predicting pitch link loads and inter-blade damper displacement. Numerical results are validated against flight test data. At these flight conditions, the stability of coupled CFD simulations is highly sensitive to the selected trim strategy, posing significant convergence challenges. Two trim strategies are investigated. The first is designed with high fidelity to the flight test procedure, wherein high speed was achieved through a shallow descent with a constant collective pitch, using airframe pitch as a trim variable. While accurately replicating the test condition, this approach induced limit-cycle oscillations in the simulation, which are attributed to phase variations of the computed shock on the advancing blade. A second, more conventional trim strategy employing only collective and cyclic controls demonstrated superior numerical stability, enabling simulation convergence. Although this method produced minor discrepancies in predicted control angles relative to the flight data, the resulting pitch link loads and damper displacements show good agreement with the measurements in flight up to 261kt.