Abstract: An aircraft cavity acoustic resonance suppression system is described which comprises a small diameter, substantially cylindrically shaped member disposed substantially parallel to and spaced up to a distance corresponding to about three airflow boundary layer thicknesses from the surface of the aircraft near the leading edge of the cavity and substantially transverse of airflow thereacross, and an actuator operatively connected to the member providing selective adjustment of the spacing between the member and the aircraft surface.

Abstract: An apparatus for and method of suppressing noise generated by the primary exhaust gas flow from jet engine nozzles or the like without significantly affecting thrust. A secondary jet stream is provided exteriorly of the primary exhaust gas flow for interacting at the boundary between the exhaust gas flow and the ambient air immediately adjacent the exit end of the nozzle to preclude the formation and propagation of noise generating phenomena. The pressure of the secondary jet stream can be varied in accordance with noise levels sensed at the nozzle exit end to provide optimum noise suppression under essentially all conditions of exhaust gas flow.