Prediction of high-resolution flowfields for rotorcraft aeroacoustics

The prediction of noise due to the impingement of the main-rotor wake of a helicopter on the tail rotor and other main-rotor blades requires the efficient computation of the wake-induced velocity field. This paper describes the development of a new treatment of the vortex wake of a helicopter that permits highly accurate resolution of the flowfield experienced by the tail rotor with modest computational effort relative to alternative models. The new approach incorporates an advanced full-span free wake model of the main rotor in a scheme that reconstructs high-resolution flow solutions from preliminary, computationally inexpensive simulations with coarse resolution. The heart of the reconstruction procedure is a novel method for using local velocity correction terms to capture the steep velocity gradients characteristic of the vortex-dominated incident flow. Sample calculations have been undertaken to examine the principal types of interactions between the tail rotor and the main-rotor wake and to examine the performance of the new method. The results confirm the success of this approach in capturing the high-resolution flows necessary for analysis of rotor-wake/rotor interactions with dramatically reduced computational cost. The steps required for the extension of this method to studies of more general classes of interactions are also discussed. © 1991 American Institute of Aeronautics and Astronautics, Inc., All rights reserved.