Gas turbine exhaust having reduced jet noise

A gas turbine engine comprising an engine core and an annular by-pass duct defined between the engine core and a surrounding nacelle, the nacelle having an exhaust nozzle at an aft end thereof through which exhaust gas flow exits, the nacelle exhaust nozzle having a selectively deployable noise-reducing component therewithin, the noise-reducing component including an annular perforated sleeve positioned to coincide with the inner nacelle loft line and circumscribing a mixed exhaust gas flow exiting the nacelle, the annular perforated sleeve being disposed radially inwardly of a displaceable inner wall of an inflatable envelope, the inner wall being radially displaceable between a deployed position wherein noise-reduction is active and a retracted position wherein noise-reduction is inactive, the inner wall being displaced from the retracted position to the deployed position when the inflatable envelope is pressurized thereby forcing portions of the inner wall to project through openings in the perforated sleeve and into the exhaust gas flow to form a rough surface at the loft line of the nacelle exhaust nozzle, causing a reduction in the noise level of the gas turbine engine.

A gas turbine engine comprising an engine core and an annular by-pass duct defined within a surrounding nacelle, the nacelle having an exhaust nozzle which includes a selectively deployable noise-reduction section on an inner surface thereof, the noise-reduction section defining an inflatable envelope comprising a fixed outer wall, a displaceable inner wall radially inward of the fixed outer wall, and an annular perforated sleeve radially inward of the inner wall and facing an exhaust gas flow exiting the exhaust nozzle, at least a portion of the inner wall being radially inwardly displaced when the envelope is pressurized and retracted radially outwardly when the envelope is de-pressurized, wherein the inner wall including projections thereon that extend through openings in the perforated sleeve and extend into the exhaust gas flow to form a rough surface on the inner surface of the nacelle exhaust nozzle when the envelope is pressurized, thereby reducing a. level of jet noise produced, and wherein said projections being retracted upon depressurization of the envelope such that the inner surface is smooth thereby increasing the level of the jet noise but decreasing fuel consumption.

A method for reducing the level jet noise produced by a gas turbine engine having a engine nacelle from which an exhaust gas flows, comprising pressurizing an inflatable portion of an exit nozzle of the engine nacelle to displace an inner wall of the inflatable portion radially inwardly such that projecting portions thereof protrude into the exhaust gas flow at the loft line of the nacelle so as to form a rough surface at the loft line to thereby reduce the exhaust velocity as it mixes with ambient free air shear surrounding the nacelle and thus reduce the level of jet noise produced;

• restricting the pressurized air to the inflatable portion at a predetermined altitude so that flight will proceed with the projecting portions retracted from the loft line and withdraw within the exit nozzle of the engine nacelle;
• and initiating the pressurized fluid to the inflatable portion in preparation for landing thereby re-forming the rough surface within the exit nozzle of the engine nacelle to thereby reduce the level of jet noise produced during landing.