Helicopter Noise Reduction By Actively Controlled Flaps

Abstract

A detailed computational study was conducted to evaluate actively-controlled trailing-edge flaps as a noise reduction device. The helicopter noise problem is first introduced, noting that active control of blade-vortex interaction (BVI) noise is a relatively new field for computational research. Two structural models are considered for the present study; the first is a modal approach suitable for four-bladed hingeless rotors. The second is a finite element approach that is used to consider a five-bladed bearingless rotor. First, open-loop control is implemented with actively-controlled flaps (ACFs) and with conventional root-actuated individual blade control. The effectiveness of both techniques at noise reduction, vibration reduction, and rotor power reduction are considered in BVI descent flight. Subsequently, the BVI noise directivity in the near-field and far-field are examined for baseline and dual ACF noise control cases. Finally, reduction of noise and vibration is successfully demonstrated with a single plain flap configuration on a five-bladed bearingless rotor resembling that of the MD-900.