Integration of Finite State Dynamic Wake Model for Rotor Interference with Comprehensive Rotorcraft Analysis

Aerodynamic interference is an important aspect of rotorcraft analysis, especially for current and future vertical lifting vehicles with multiple rotors or compound rotor/wing configurations. Extending the finite state dynamic wake to provide interference velocities at lifting surfaces above and below the rotor offers a computationally efficient, yet more accurate modeling approach than the cylindrical vortex sheet and horseshoe vortex methods currently used in comprehensive rotorcraft analysis, such as RCAS. As described in this paper, a finite state dynamic wake model with interference modeling capability that covers the entire flowfield has been integrated into RCAS. The new finite state dynamic wake model is verified by comparing prediction results with the exact solution of harmonic excitation problem and a verification test for the unsteady inflow response to a step collective pitch input. Numerical results from the finite state dynamic wake model in hover and forward flight conditions are validated against a set of test data for both self-induced velocity and off-rotor interference. The new finite state dynamic wake model predicts the fundamental flowfield characteristics and has a close correlation with measured data.