Apparatus and method for reducing aircraft noise and acoustic fatigue

A passive treatment area for reducing unsteady pressure fluctuations of high velocity exhaust mass flow exiting from an aerospace vehicle to reduce fatigue, the passive treatment area comprising:

• means for attenuating the unsteady pressure fluctuations caused by the high velocity exhaust mass flow existing from an exhaust nozzle of the aerospace vehicle to reduce fatigue, the means also attenuating reflected noise, said means comprising:
• a layer of sound absorptive material to provide noise attenuation;
• a plurality of roughness elements positioned adjacent said sound absorptive layer, wherein said roughness elements comprise at least one of elements of varying sizes, elements of irregular shapes, and elements of both varying sizes and irregular shapes;
• and
• a covering positioned over said passive treatment area operable for permitting sound waves to pass through to said roughness elements and sound absorption material.

A method of reducing acoustic fatigue of an aerospace vehicle having high velocity exhaust mass flow exiting from the aerospace vehicle, the method comprising:

• positioning a passive treatment area in a path of the high velocity exhaust flow exiting from the aerospace vehicle, wherein said passive treatment area comprises at least one roughness element comprising at least one of a plurality of elements of varying sizes, elements of irregular shapes, and elements of both varying sizes and irregular shapes;
• attenuating unsteady pressure fluctuations generated by said high velocity exhaust flow, and further attenuating sound waves;
• reflecting said attenuated pressure and sound waves omni-directionally from said passive treatment area;
• and
• impinging said attenuated pressure fluctuations on said aerospace vehicle.

A method of attenuating and reflecting unsteady pressure fluctuations and sound waves of an aerospace vehicle having high velocity exhaust mass flow existing from the aerospace vehicle using a passive treatment area located on an aircraft support platform, the method comprising:

• forming a passive treatment area adjacent said platform, in which said forming further comprises:
• positioning a layer of sound absorption material in said passive treatment area;
• embedding at least one roughness element in said sound absorbing layer, wherein said at least one roughness element comprises at least one of a plurality of elements of varying sizes, elements of irregular shapes, and elements of both varying sizes and irregular shapes;
• and
• directing high velocity exhaust flow from an engine of the aerospace vehicle toward said passive treatment area.