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Blade vortex interaction (BVI) noise is a main source of helicopter noise especially during descending flight. Precise prediction of flow field around helicopters is required to establish the design technology of BVI noise reduction devices. Full CFD analysis including the rotor wake domain can predict flow field precisely, but it is computationally expensive. On the other hand, the prescribed wake model, which empirically predicts rotor trailing vortices, reduces computational cost greatly, but has less accuracy especially around the blade. Therefore, a hybrid method of CFD for the domain around the blade and the prescribed wake model is considered as a practical computational method in terms of the trade-off of computational accuracy and time. The base CFD code herein assumed is a structured grid Euler solver, hrFlow3Di, which has been intensively developed for helicopter applications at the Japan Aerospace Exploration Agency. In this study, computational accuracy of the hybrid method is improved by applying circulation distribution, induced velocity distribution, and blade tip vortex position obtained in CFD domain to the prescribed wake model. The normal force coefficient on blade and noise contour computed by the hybrid method show good agreement with the experiment.

Development of a Hybrid Method of CFD and Prescribed Wake Model for Helicopter BVI Noise Prediction