Abstract: An active control device for reducing blade-vortex interactions (BVI) noise generated by a rotorcraft, such as a helicopter, comprises a segmented trailing edge flap located near the tip of each of the rotorcraft's rotor blades. The various flap segments may be independently actuated according to flap deflections schedules which are tailored to address a particular operating regime with maximum efficiency and effectiveness. Through the careful azimuth-dependent independent actuation of the flap segments, blade tip vortices which are the primary source for BVI noise are (a) made weaker and (b) pushed farther away from the rotor disk (that is, larger blade-vortex separation distances are achieved), resulting in lower BVI noise.

Abstract: Porous surfaces on an aerodynamic structure driven with positive and negative pressures are used in an active control system for attenuating shock waves responsible for high-speed impulsive (HSI) noise. The control system includes an array of apertures in the outer skin of the structure providing fluid communication between the exterior flow stream and an interior volume of the structure. A movable diaphragm within the structure pushes air out of and pulls air in through the apertures under the action of a drive mechanism within the structure, thus creating oscillating air jets. The drive mechanism may be actuated by a controller based on information supplied by a sensor in the leading edge of the aerodynamic structure. The array of apertures may be spaced apart along the outer skin of the aerodynamic structure so as to span a distance of about 15% of the chord length. The oscillating airjets may be provided on multiple surfaces of the aerodynamic structure, including the upper and lower surfaces.

Abstract: An active control device for reducing blade-vortex interactions (BVI) noise generated by a rotorcraft, such as a helicopter, comprises a trailing edge flap located near the tip of each of the rotorcraft's rotor blades. The flap may be actuated in any conventional way, and is scheduled to be actuated to a deflected position during rotation of the rotor blade through predetermined regions of the rotor azimuth, and is further scheduled to be actuated to a retracted position through the remaining regions of the rotor azimuth. Through the careful azimuth-dependent deployment and retraction of the flap over the rotor disk, blade tip vortices which are the primary source for BVI noise are (a) made weaker and (b) pushed farther away from the rotor disk (that is, larger blade-vortex separation distances are achieved).

Abstract: An active control device for reducing blade-vortex interactions (BVI) noise generated by a rotorcraft, such as a helicopter, comprises a trailing edge flap located near the tip of each of the rotorcraft's rotor blades. The flap may be actuated in any conventional way, and is scheduled to be actuated to a deflected position during rotation of the rotor blade through predetermined regions of the rotor azimuth, and is further scheduled to be actuated to a retracted position through the remaining regions of the rotor azimuth. Through the careful azimuth-dependent deployment and retraction of the flap over the rotor disk, blade tip vortices which are the primary source for BVI noise are (a) made weaker and (b) pushed farther away from the rotor disk (that is, larger blade-vortex separation distances are achieved).