JET NOISE REDUCTION FOR HIGH SPEED EXHAUST SYSTEMS

Jet noise has been an environmental issue since the advent of jet aircraft. The past five decades have seen much research into solving this very difficult challenge for a variety of applications. The Supersonic Transport (SST), High Speed Civil Transport (HSCT), and a variety of supersonic business jet (SSBJ) applications all face significant jet noise challenges. Jet noise from high performance military aircraft has also received growing attention. The continuous drive to higher specific thrust results in increasing jet noise levels. Compounding this is that many military bases, Naval in particular, are located in desirable locations on the coast, and surrounding communities are encroaching closer to these bases. In this paper we will conduct a survey of some jet noise reduction technologies for high-speed exhaust systems investigated in the past, as well as some of the implementation issues associated with them. Specific technologies aimed at changing the mixing characteristics of the jet plume after it leaves the nozzle will be discussed in detail, including chevrons and fluidic injection. Other noise reduction technologies, such as the inverted velocity profile, and fluid shield can also change the mixing characteristics of the jet plume. This includes the added benefit of noise reflection or shielding. Measured data will be presented to show the effect these technologies have on high-speed jets.