Jet Noise Reduction by Fluidicly Enhanced Chevrons on Separate Flow Exhaust Systems

Abstract

This paper investigates the potential for using fluidic injection to enhance the acoustic performance of conventional chevron exhaust nozzles for separate flow exhaust systems. Fluidic injection consists of small jets of air strategically injected around the nozzle exit. This injection can induce stream-wise vorticity in the flow, which entrains air between the streams and yields greater mixing relative to conventional configurations without fluidic injection. When applied to chevron nozzles, the fluidic injection can also strengthen the vortices generated by the chevrons, delaying vortex breakdown and increasing the mixing across the shear layer. Enhanced mixing has been shown to reduce the mean jet velocity and temperature, thereby reducing jet noise. The experimental testing reported here was performed in two stages. The first stage was conducted at the University of Cincinnati Aeroacoustic Test Facility in single-stream flow. The success of these tests led to the second stage, which was conducted on a dual flow nozzle with simulated external flow, at the GE Aviation Anechoic Free-Jet Test Cell 41 Facility. Test results demonstrated overall sound pressure level jet noise reductions of 1 to 2 dB at each directivity angle for a single-stream exhaust, and approximately 1 dB of reduction for a dual-stream exhaust with a simulated external flow.