Gas turbine exhaust having reduced jet noise

Abstract

A gas turbine engine has an engine core and an annular by-pass duct, within a surrounding nacelle. An exhaust nozzle of the nacelle includes a selectively deployable noise-reduction section on an inner surface thereof. The noise-reduction section includes an inflatable envelope comprising a fixed outer wall and a displaceable inner wall. At least projections on the inner wall are inwardly displaced when the envelope is pressurized and retracted radially outwardly when the envelope is de-pressurized. When the envelope is pressurized, the inner wall includes portions that project to form a rough surface on the inner surface of the nacelle exhaust nozzle. This thickens the boundary layer and reduces the speed of the gas flow at the outer radius of the nozzle, thus reducing the differential velocity with the ambient air, which reduces the gradient throughout the shear layer thus reducing the noise level of the engine.