Aeroacoustic Prediction and Validation of Variable RPM Rotors and Rotor-Airframe Interactions for Advanced Air Mobility Applications

Aeroacoustic prediction of the tonal noise sources for rotors operating with time-varying rotor rotation rate (RPM) is explored. Enhancements to the CHARM analysis and CHARM/PSU-WOPWOP interface software are described that are required to support acoustic predictions of time-varying RPM multiple rotor and rotor + strut configurations. Predictions are compared with acoustic test data from (Ref. 1) and (Ref. 2) for both constant and time-varying RPM. The configuration with time-varying RPM was considered to understand the tonal noise sources with a focus on loading noise. The effect of change in RPM on aerodynamic interaction between rotor and strut and its effect on loading noise was studied. A comparison between NASA wind tunnel test data and predictions for an isolated ideally twisted rotor is carried out with time-varying rotor RPM data. Sound pressure spectrum plots are generated for raw test data, filtered test data (frequency range 250-1500 Hz), and acoustic pressure time history to perform validation at in-plane and out-of-plane microphones.