Prediction of UH-60A Dynamic Stall Loads in High Altitude Level Flight Using CFD/CSD Coupling

This paper predicts rotor loads under dynamic stall. The goal is to gain fundamental understanding of the stall mechanisms involved, and their accurate prediction. The approach is to decouple the physics of structural dynamics and aerodynamics in a high altitude level flight. Measured airloads from UH-60A Flight 9017 are used to validate the structural model. Once validated, the predicted blade deformations are used to calculate airloads. The focus is on Reynolds Averaged Navier-Stokes (RANS) CFD. The CFD model is first validated for an oscillating UH-60A airfoil (SC1095). The rotor airloads are then predicted using a Baldwin-Lomax turbulence model. Both single bladed CFD, and multi-bladed CFD with direct wake capture are studied. Finally, a CFD/CSD loose coupling is performed using the single bladed CFD to obtain airloads, blade loads and pitch link loads from first principles. The study shows that the first stall cycle is caused by high trim angles in the retreating blade. The second stall cycle is caused by the elastic twist deformation. CFD wake capture appears to improve airloads in the advancing side, but does not alter stall predictions in the retreating side. Stall near the tip (96.5% R) is not well predicted. The lower harmonics of structural loads (up to 4/rev) are predicted accurately. Discrepancies are noted in higher harmonics of torsion. This discrepancy stems from structural modeling, and is not resolved using the measured airloads.