Rotor Airloads Prediction Using Loose Aerodynamic/Structural Coupling

TLDR

An iterative loose (weak) coupling of a high‑fidelity Navier–Stokes CFD code with a rotorcraft CSD code on a per‑revolution basis was applied to a UH‑60A Blackhawk at three challenging flight conditions and compared with flight‑test data. The loose coupling proved stable, convergent, and robust, yielding normal force and pitching moment predictions that agree in phase and magnitude with test data, accurately capturing airload curve shapes and outperforming traditional lifting‑line aerodynamics.

Abstract

A computational fluid dynamics (CFD) code and rotorcraft computational structural dynamics (CSD) code are coupled 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 code 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, three challenging level flight conditions are computed: 1) high speed, μ = 0.37, with advancing blade negative lift, 2) low speed, μ = 0.15, with blade‐vortex interaction, and 3) high thrust with dynamic stall, μ = 0.24. Results are compared with UH-60A Airloads Program flight test data. 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 phase and magnitude are in good agreement. The shapes of the airloads curves are well captured. Overall, the results are a noteworthy improvement over lifting line aerodynamics used in rotorcraft comprehensive codes.