Numerical research on the rotor “super blade/vortex interaction noise” generation mechanism in helicopter roll maneuver state

To explore the evolution law of rotor vortex and aeroacoustic characteristics during helicopter roll maneuver flight, numerical simulations were conducted in different roll rates based on the high-precision computational fluid dynamics method and the Ffowcs Williams-Hawkings equation. Initially, we verified the collective pitch increased test and the blade/vortex interaction (BVI) test cases. The comparison results show that the constructed method can capture the aerodynamic characteristics of rotor transient maneuvering states and has reliable predictive capability for BVI noise. Then, the aeroacoustic characteristics analyses of different right roll rates was performed. It was found that in the right roll state, multiple vortices merge and develop into a higher-intensity “supervortex system” near the 75° azimuth angle, triggering “superblade/vortex interaction noise” (Super-BVI) upon collision with the subsequent blade, with a maximum increase in the overall sound pressure level (OASPL) of approximately 16 dB. Next, numerical simulations were carried out for different left roll rates, and it was found that the maximum sound pressure (pmax) and maximum OASPL (OASPLmax) have linear and logarithmic relationships with roll rate, respectively. This law holds for both left- and right-roll states. Finally, four cases of specific roll angles were conducted for comprehensive comparison studies. It was found that transient roll maneuvers intensify the interaction strength on the rolling side while weakening the interaction strength on the other side, which is closely linked to the formation mechanism of “Super-BVI noise.”