Interactional Aerodynamics of Single Main Rotor Helicopters in Steady Autorotation

Autorotation is an edge case flight regime where, instead of being powered by an engine, a rotorcraft is powered purely by the air moving up through the main rotor as the vehicle descends. In this paper, a full-vehicle UH-60A helicopter is simulated in steady autorotation using both the flight dynamics (FD) code HeliUM-A and the computational fluid dynamics/computational structural dynamics (CFD/CSD) solver CREATE-AV TM Helios. The CFD/CSD simulations model the full-vehicle geometry and are trimmed to an autorotative state that is representative of how the aircraft flies in practice. Despite significant differences in the predicted airloads, both FD and CFD/CSD predictions of the vehicle’s autorotational descent rate were in excellent agreement with available flight test data. CFD/CSD analysis further examined mutual interactions between the helicopter’s rotors and various airframe components. The airframe plays a critical role in determining the aircraft’s autorotational descent rate and its shed wake creates regions of loading loss in the rotor disk. On the other hand, the main rotor induces significant unsteadiness on the airframe loading and creates an effective downforce on the fuselage and stabilator.