Simulation of Dynamic Stall on an Elastic Rotor in High-Speed Turn Flight

A highly loaded, high-speed turn flight of Airbus Helicopters' Bluecopter demonstrator helicopter is simulated using a loose computational fluid dynamics/structural dynamics (CFD/CSD) coupling of the flow solver FLOWer and the rotorcraft comprehensive code CAMRAD II. The rotor aerodynamics is computed using a high-fidelity delayed detached-eddy simulation (DDES). A three-degree-of-freedom trim of an isolated rotor is performed, yielding main- rotor control angles that agree well with the flight-test measurements. The flow field in this flight condition is found to be highly unsteady and complex, featuring massively separated flow, blade-vortex-interaction, multiple dynamic-stall events and shock-induced separation. The trim target rotor thrust, turbulence model and considered helicopter components like the fuselage are varied. Then, the computed pitch-link loads are compared to flight-test measurements. It shows that all CFD/CSD cases underpredict the amplitudes of the flight test and yield phase shifts. However, overall trends agree reasonably. Also, the SST DDES turbulence model performs better than Spalart-Allmaras (SA) DDES and the consideration of the rotor hub and fuselage improves the agreement with flight-test data.