Validation of Enhanced Rotorcraft Aeromechanics Simulations: Flow Field, Unsteady Loads and Vibrations

Robust and accurate predictions of rotorcraft aerodynamic and structural loads and vibrations are essential for designing advanced rotorcraft. The aerodynamic environment around the rotors is nonlinear and unsteady, the rotor and its wake interact strongly with fuselage and empennage to drive the structural vibrations. All of the components are elastic structures linked with one another by structural and aerodynamic interactions requiring a high fidelity coupled analysis. This paper presents simulations and validations for two examples: the aerodynamic interactions of a powered rotor - fuselage - empennage wind tunnel model using CFD (Computational Fluid Dynamics), and the structural loads and vibrations of a flight test aircraft using coupled CFD/CSD (Computational Structural Dynamics) - FEA (Finite Element Analysis). The NASTRAN FEA generated an elastic fuselage modal model which was coupled to the CFD/CSD tools in the CREATETM-AV HELIOS framework. The interactional aerodynamics simulation focused on lower advance ratio cases, which have a particularly strong rotor wake - empennage interaction and compared time averaged and periodic aerodynamic loads and flow velocity fields to experiment. Trends matched well, but quantitative differences remained, particularly at the lowest advance ratios. The full aircraft simulations were performed at increasing degrees of complexity and coupling. The agreement with measured rotor blade structural loads and horizontal stabilizer vibrations was best using the most complete model of the main rotor, tail rotor, fuselage and empennage.