Abstract:
This paper presents a comparison of multi-fidelity approaches for the HART-II rotor noise prediction using the high-fidelity and multi-disciplinary rotorcraft analysis software suite CREATE™-AV Helios. The acoustic simulations are performed using the noise prediction tools AARON/ANOPP2 and PSU-WOPWOP. Both permeable and impermeable formulations of the Ffowcs Williams and Hawkings equation are considered for noise predictions. The HART-II baseline and 3/rev high harmonic control (HHC) minimum vibration cases are simulated and validated against test measurements. Compared with the free-wake simulation, the high fidelity CFD/CSD loose coupling simulations agree better with the measured data but still under-predict the advancing side airloads. Both impermeable and permeable surface approaches show better noise predictions than the free-wake approach in terms of noise directivity and amplitude. As the finest wake-grid resolution reduces from 7.5% to 5% chord, the impermeable surface strategy shows an increment of 3 dB in maximum mid-frequency sound pressure level (SPL) on the advancing side of the mid-frequency SPL contour. The maximum mid-frequency SPL on the retreating side of the vehicle is only increased by 1 dB. At a finer wake-grid resolution, the permeable surface approach does not show improvement in blade-vortex interaction (BVI) noise prediction on the advancing side of the rotor disk.