Tactical aircraft noise reduction using fluidic nozzle inserts

Abstract

The noise levels generated by tactical aircraft pose health hazards to personnel working in the vicinity of the aircraft (such as on an aircraft carrier deck) and are annoying to communities close to airbases. The engine exhausts are hot and supersonic and generally operate in an off-design condition, where the nozzle exit and ambient pressures are unequal. This results in shock cells in the jet plume. The interaction between the jet turbulence and the shock cells generates broadband shock-associated noise. The dominant noise radiation is in the downstream direction and is associated with the supersonic convection of turbulence in the jet. This paper describes the development of a technology to reduce both noise sources and involves the controlled injection of air into the diverging section of the nozzle to generate flow corrugations. This enables the jet to operate closer to its design condition and also breaks up the large scale turbulent structures that are responsible for the dominant noise radiation. Both flow and acoustic measurements are described. In addition, steady RANS computations provide information on the flow upstream of the nozzle exit and the effect of injector operating conditions on the flow field. Estimates of nozzle performance are also described.