High-Order Accurate CFD/CSD Simulation of the UH-60 Rotor in Forward Flight

Time-dependent Reynolds-averaged Navier-Stokes simulations for a highly flexible aeroelastic UH-60A rotor have been carried out for forward flight. The fluid structure interaction is accomplished by loosely coupling the OVERFLOW Computational Fluid Dynamics (CFD) code with the helicopter comprehensive code CAMRAD II. The latter includes Computational Structural Dynamics (CSD) with rotor trim capability. Computations are performed using spatial differences of 5 th -order for inviscid fluxes, 2 nd order accurate viscous fluxes, and 2 nd -order time accuracy. Dual time-stepping accuracy is examined and recommendations provided for an appropriate time step and number of subiterations. The predicted sectional normal forces and pitching moments are compared with flight-test data for high-speed and low-speed level-flight conditions. The low-speed case has significant Blade Vortex Interaction (BVI). The current simulations demonstrate a factor of two improvement in state-of-the-art airloads prediction accuracy for CFD/CSD simulations. This is attributed to the use of improved spatial accuracy. I. Introduction OMPUTATIONAL Fluid Dynamics (CFD) simulation of rotorcraft flow fields using the Reynolds-averaged Navier-Stokes (RANS) equations is a challenging multidisciplinary problem. This is primarily due to the need to model the aeroelastic interaction of the fluid dynamics with highly flexible rotor blades. A successful aerodynamic simulation of a rotor/fuselage system requires the modeling of unsteady three-dimensional flows that may include transonic shocks, dynamic stall with boundary layer separation, complex vortical wakes, blade/wake and wake/wake interactions, and body motions. Moreover, a stable and robust method to couple the CFD with a Computational Structural Dynamics (CSD) model is required. Consequently, the aerodynamic and aeroacoustic performance prediction for rotorcraft lags compared to its fixed-wing counterpart. The helicopter industry often uses comprehensive rotor codes as part of the design process. These comprehensive codes typically include a simplified linear aerodynamic model, a CSD method for flexible rotor blades, and a trim algorithm. However, this very efficient design tool lacks the high fidelity aerodynamics needed for nonlinear rotorcraft flows. It is common at NASA and in the rotorcraft industry to carry out a parameter sweep of rotorcraft simulations with a less computationally costly comprehensive code, such as CAMRAD II, 1 when linear