Oscillating air jets on aerodynamic surfaces

An active control device for reducing blade-vortex-interaction (BVI) noise generated by a rotorcraft, the active control device being adapted to be installed into a rotor blade of the rotorcraft, the rotor blade having a skin forming an aerodynamic surface of the rotor blade and surrounding an inner volume of the rotor blade, the active control device comprising:

• a diaphragm disposed within the inner volume, the diaphragm having a center point, a perimeter, a first surface, and a second surface opposite to the first surface;
• a wall coupled to the second surface of the diaphragm, the wall having a center and a perimeter, whereby the centers of the diaphragm and the wall are placed into proximity when the wall is coupled to the second surface of the diaphragm, and whereby the perimeter of the wall does not extend beyond the perimeter of the diaphragm when the wall is coupled to the second surface of the diaphragm;
• a coil wound around the wall;
• and
• a magnetic field producing member disposed around both the wall and the coil, whereby the wall and the coil are movable within the magnetic field producing member to thereby facilitate movement of the diaphragm.

An active control device for use on an aerodynamic structure having an outer skin and an interior volume, the outer aerodynamic skin surrounding the interior volume, the active control device comprising:

• at least one aperture disposed in the outer aerodynamic skin, the at least one aperture connecting the outer aerodynamic skin to the interior volume;
• and
• a diaphragm disposed in the interior volume, the diaphragm having an outer periphery and an inner periphery, the outer periphery being adapted to be coupled to the skin of the rotor blade;
• a rigid piston connected to the inner periphery of the diaphragm;
• a wall coupled to the rigid piston;
• and
• a wire wound around the wall;
• wherein the rigid piston is movable between a first position and a second position, wherein movement of the rigid piston from the first position to the second position pushes air through the at least one aperture and out of the interior volume;
• and
• wherein movement of the rigid piston from the second position to the first position draws air through the at least one aperture and into the interior volume.

An active control device for reducing blade-vortex-interaction (BVI) noise generated by a rotorcraft, the active control device comprising:

• a rotor blade including an outer skin, a leading edge, and a trailing edge;
• a plurality of apertures disposed in the outer skin of the rotor blade;
• and
• a plurality of oscillating piston assemblies disposed within the rotor blade, each of the oscillating piston assemblies being movable between a first position and a second position, whereby movement of each piston assembly from the first position to the second position pushes air out of at least one of the plurality of apertures, and whereby movement of each piston assembly from the second position to the first position draws air into at least one of the plurality of apertures, each piston assembly comprising a diaphragm having an inner periphery and an outer periphery that is adapted to be coupled to the outer skin, a rigid piston connected to the inner periphery of the diaphragm, a wall coupled to the rigid piston and a wire wound around the wall.

An active control device for use on an aerodynamic structure having an outer skin and an interior volume, the outer aerodynamic skin surrounding the interior volume, the active control device comprising:

• at least one aperture disposed in the outer aerodynamic skin, the at least one aperture connecting the outer aerodynamic skin to the interior volume;
• and
• an electromagnetically-driven rigid piston disposed in the interior volume, the electromagnetically-driven rigid piston being movable between a first position and a second position, wherein movement of the electromagnetically-driven rigid piston from the first position to the second position pushes air through the at least one aperture and out of the interior volume at a peak velocity greater than about 120 ft/sec;
• and
• wherein movement of the electromagnetically-driven rigid piston from the second position to the first position draws air through the at least one aperture and into the interior volume at a peak velocity greater than about 120 ft/sec.