Rotor Airloads Prediction Using Loose Aerodynamic/structural Coupling

This work couples a computational fluid dynamics (CFD) code and rotorcraft computational structural dynamics (CSD) code to calculate helicopter rotor airloads across a range of flight conditions. An iterative loose (weak) coupling methodology is used to couple the CFD and CSD codes on a per revolution, periodic basis. The CFD uses a high fidelity, Navier-Stokes, overset grid methodology with first principles-based wake capturing. Modifications are made to the CFD code for the aeroelastic analysis. For a UH-60A Blackhawk helicopter, four challenging level flight conditions are computed: 1) low speed (μ = 0.15) with blade-vortex interaction, 2) high speed (μ = 0.37) with advancing blade negative lift, 3) high thrust with dynamic stall (μ = 0.24), and 4) hover. Results are compared with UH-60A Airloads Program flight test data. Most importantly, for all cases the loose coupling methodology is shown to be stable, convergent, and robust with full coupling of normal force, pitching moment, and chord force. In comparison with flight test data, normal force and pitching moment magnitudes are in good agreement. For the high speed and dynamic stall cases a phase lag in comparison with the data is seen, nonetheless, the shapes of the curves are very good. Overall, the results are a noteworthy improvement over lifting line aerodynamics used in rotorcraft comprehensive codes.