A study of rotorcraft noise prediction in maneuvering flight

The coupled flight simulation/noise prediction system (GENHEL-PSU-WOPWOP) has been partially validated for steady noise predictions in this paper. The noise predictions for a utility helicopter matched quite well with wind tunnel measurements of the isolated main rotor. The GENHEL-PSU-WOPWOP system is not capable of blade-vortex-interaction noise prediction, because GENHEL does not account for individual vortices. This limitation was mitigated in this work by choosing flight conditions that are not expected to be dominated by BVI noise. A flight simulation of a complex 80-second was performed. This maneuver, which included a climb, acceleration, 180° coordinated turn, and level flight, demonstrated the complexity of the radiated noise field during maneuvering flight. Care must be taken when interpreting the acoustic signal to account for changes in propagation distance, directivity changes due to aircraft attitude changes, and transient maneuver noise. In general maneuvering flight can be considered as a set of steady flight conditions connected by transient maneuvers. Transient maneuver noise, when present, may contribute dramatically to the radiated acoustic field. Transient maneuver noise is generated during short-duration maneuvers by a multiple sources: aperiodic rotor blade motions; aircraft attitude changes - especially rapid roll maneuvers; and unsteady transient aerodynamic loading on the rotor due to pilot control overshoots, and aerodynamic force overshoots. A more detailed understanding of transient maneuver noise was developed through a set of turn entry maneuvers of different durations.