Supersonic active noise reduction in small- and moderate-scale nozzles

Supersonic tactical aircraft engines create a high amplitude noise environment. Penn State has developed an on-demand noise reduction method that uses fluidic inserts. These inserts inject steady secondary air into the diverging section of a converging-diverging nozzle. The fluidic inserts generate streamwise vortices that break up the large scale turbulence structures that are the primary source of noise. In addition shock noise is reduced by the effective area ratio change of the nozzle. The fluidic insert noise reduction method has shown up to a 5 dB noise benefit in the peak noise direction in laboratory small-scale testing. In preparation for eventual full-scale implementation, the fluidic insert noise reduction method was tested on a moderate-scale nozzle to demonstrate scalability and Reynolds number independence. The moderate-scale nozzle is five times larger than the small-scale nozzles tested at Penn State. The experiments at moderate-scale were conducted in collaboration with GE Aviation in The Cell 41 facility at Evendale, OH. Four different fluidic insert geometries were tested and compared for noise reduction between the two scale sizes.