Investigation of Rotor Noise Shielding Effects by the Helicopter Fuselage in Forward Flight

Abstract

This paper presents a numerical study on the rotor noise shielding effects by the helicopter fuselage. The method used to assess acoustic shielding is based on a fast multipole boundary element method, which includes the Forward flight effect. A free-wake unsteady panel method, in combination with a Ffowcs Williams–Hawkings (FW-H) integral formulation, is used to compute the rotor noise sources for the blade vortex interaction flight condition. The prediction methodologies are described. Validation of boundary element method and the forward flight effect by means of Taylor’s transformation are conducted by using analytic solutions. The error estimation for the case without mean flow indicates that for sufficient grid resolution the maximum error occurring in the shadow region is less than 0.06 dB. The error estimation for the Taylor Transformation shows that the error can be up to 6% for M=0.2. In addition, a Kirchhoff source surface model used to treat the real rotor noise is described. Finally, the method is applied to a BO105 wind tunnel model to understand the noise shielding features of the main and tail Rotors.