Numerical Analysis of Active Flap for Noise Reduction Using Moving Overlapped Grid Method

A three-dimensional unsteady Euler code for the analysis of active flap control (AFC) has been developed in this study based on an advanced CFD code for the full configuration of helicopters. The effect of phase angle of AFC on blade-vortex interaction (BVI) noise is analyzed by combining the new CFD code with an acoustic code based on the Ffowcs Williams and Hawkings (FW-H) equation. As a result, a simple model is proposed to understand the effect of flap phase angle on BVI noise and 3D calculations by the present method confirm that the model properly works. The prediction of the effect of flap phase angle by the present method is remarkably improved by applying the understandings derived from the simple model. A quantitative noise reduction of 5.62dB is obtained at the flap phase angle of 60° and noise signal strongly propagates almost downward in a condition of one-bladed rotor.