Aeroacoustic investigation of a helicopter tail rotor.

The present study focuses on the aeroacoustic aspects of a full-scale helicopter tail rotor. To this end, the newly conceived, Electronically Distributed Anti Torque (EDAT), tail rotor is investigated both experimentally and numerically. Acoustic directivity in the far-field was measured in the anechoic wind tunnel at Université de Sherbrooke. These acoustic measurements confirm the presence of tones at the blade passing frequency, furthermore, quasi-tonal and broadband acoustic components were also obtained. In order to quantify the installation effects on the measurements and source generation mechanisms, high-fidelity Very Large Eddy Simulations (VLES) with the Lattice Boltzmann method were performed at a single operating condition. This is achieved by simulating the complete experimental setup, e.g. the anechoic room and the tail rotor geometry. A good agreement in the overall mean performances, such as torque and mass flow, is achieved between the VLES simulations and the measurements. Furthermore, direct far-field acoustic spectra computations show a good agreement with the experimental measurements. Cross correlation between the near-field and far-field pressure was performed in order to reveal possible locations of noise generation and propagation on the tail rotor.