A Study of the Aerodynamics and Acoustics of Super-BVI

Super-BVI was previously predicted during an aggressive right-turn maneuver. During this maneuver a substantial increase in noise was observed around the helicopter. This noise increase was found to be caused by the parallel interaction of a bundle of tip vortices with the rotor blades. Although this maneuver is aggressive in nature and somewhat uncommon during normal helicopter operation, it highlights the potential of tip-vortex bundling and the possibilities of creating substantial noise in certain flight maneuvers. Understanding this potential noise source could prove important in future helicopter quieting research. Based on this premise, further research into the conditions that cause super-BVI and its effects on rotor noise has been undertaken. It is concluded that the helicopter roll motion was the major contributor to super-BVI formation. To investigate the potential of the bundled tip vortices as a noise source in general helicopter operations, a roll oscillation maneuver is also discussed.