Design of a Generic Rotor Noise Source for Helicopter Fuselage Scattering Tests

This paper deals with the activities conducted in the GARTEUR Action Group HC/AG-24 to address noise scattering of helicopter rotors in presence of the fuselage. The focus of the paper is on the design for a generic "tail rotor" noise source used in the fuselage scattering study. The main design criterion is that the generic rotor noise source should resemble the main characteristics of the tail rotor with clear harmonic components. A two bladed simplified tail rotor model is considered. The performance of the tail rotor model in terms of thrust and torque with respect to the advance ratio is calibrated in the POLIMI wind tunnel. Acoustic measurements of the tail rotor model were tested in the DLR Acoustic Wind tunnel Braunschweig AWB. The results of the rotor performance and the rotor acoustic characteristics are described. The spectral variations resulting from unsteadiness of the source are explored in both with and without wind. The noise characteristics such as the spectral content, sound levels at fixed distances, and the time varying nature of the sound field are discussed.