Simulation of Coaxial Rotor Interactional Aerodynamics using Coupled CFD-CSD

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Passe, Bradley
Baeder, James
Performance and range requirements for next-generation rotary-wing aircraft have sparked renewed interests in the coaxial rotor configuration, augmented with lift and/or thrust compounding. Often, thrust augmentation is provided in the form of a propeller or jet engine to counteract the airframe and rotor drag in high speed forward flight. A notional X2TD coaxial compound configuration has been chosen to perform numerical simulations in forward flight with CFD-CSD coupling. The delta loose coupling method is used to couple the CFD and CSD models. Using the CFD results to correct the reduced order aerodynamics in this loose coupling framework will drive toward a deeper understanding of rotor-rotor and rotor-fuselage interactions in the forward flight regime. Using unrestricted data of the X2TD flight test program the in-house CSD code (PRASADUM) was validated against both CAMRAD II and flight test data results. Helios, using both Overflow and NSU3D as near-body solvers was used as the CFD solver for the CFD-CSD coupling framework. The CFD-CSD coupling framework was used for several key flight conditions of the X2TD, namely 55, 100, and 150 knots. A comparison study at both 55 and 150 knots was conducted between an isolated coaxial rotor system case, and 3 other cases incorporating three different fuselage models to the CFD analysis: a simple fuselage body, a complex fuselage body containing horizontal and vertical stabilizers, and lastly the complex fuselage body with the added inclusion of the rotor mast.