Fast Prediction of Full-Scale Helicopter Rotor Noise using Acoustic Modal Analysis

A state-of-the-art, rapid global rotor noise prediction method in the acoustic modal domain has been established and verified. Given its potential for speed-up compared to the traditional Ffowcs Williams-Hawkings equation solver for rotor noise solutions, it has potential to be used in real-time noise prediction. This study aims to assess the capability of the acoustic modal analysis (AMA) towards predicting noise of a full-scale Bo 105 helicopter rotor with elastic blades. The AMA method operates by converting the exact frequency domain noise solution of the monopole and the dipole point source into the acoustic modal domain, where the acoustic modal coefficients are identified based on aerodynamic loading obtained using a mid-fidelity comprehensive analysis code. The noise prediction results are compared with a Ffowcs Williams-Hawkings equation solver, PSU-WOPWOP, to quantify the accuracy of the proposed method as well as compare execution times. It was found in the study that, in comparision to PSU-WOPWOP, the AMA model is able to give the noise prediction results at least two orders of magnitude faster while maintaining moderate accuracy.