Simulation of Coaxial Rotor Interactional Aerodynamics using Coupled CFD-CSD

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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.