Validation of Aeromechanical Analysis using the Viscous Vortex Particle Method

An aeromechanical analysis using CFD based reduced order model for aerodynamic loads and the viscous vortrex particle method for rotor wake is developed to compute helicopter rotor airloads across a range of flight conditions. Flow separation due to dynamic stall is represented using the ONERA dynamic stall model and vortex particles shed from the leading edge of the rotor blade. The analysis is validated with flight test data of a UH-60A Blackhawk helicopter for three level flight conditions: 1) high speed flight at µ = 0.37, 2) low speed flight at µ = 0.15 with blade-vortex interaction effects, and 3) high thrust flight with dynamic stall at µ = 0.24. Results are compared with CFD and free wake based analysis from literature. Overall, the shapes of the normal force coefficient and moment coefficient for all flight conditions are well captured with the aeromechanical analysis. Several features in the normal force coefficient in the high speed flight condition are captured with the method that were previously not captured with the CFD or free wake based aeromechanical analyses. There are some discrepancies in the moment coefficient results compared to the flight test data, which are attributed to limiting assumptions of the blade airfoil unsteady aerodynamic response.