Experimental Comparison of Supersonic Jets Exhausting from Military Style Nozzles with Interior Corrugations and Fluidic Inserts

This paper describes the development and analysis of fluidic inserts for supersonic jet noise suppression. The study uses scale model experiments of jets that simulate the exhaust jets from typical lowbypass ratio military jet aircraft engines during takeoff. The fluidic inserts use distributed blowing in the divergent section of the nozzle to simulate mechanical corrugations, while having the advantage of being an active control method. Measurements with simulated forward flight are important early in the analysis of noise reduction methods. The current design of the delivery piping is not streamlined enough for forward flight measurements. Therefore, forward flight acoustic measurements were first conducted with hardwall corrugation nozzles. The noise reduction of the hardwall corrugation nozzles was not affected by simulated forward flight. Mean flow field measurements of the jet plume were conducted with both hardwall corrugation and fluidic insert nozzles. This led to the development of a newer fluidic insert nozzle fabrication technique. The new nozzles, along with supplying varying injection pressures to upstream and downstream injection ports, have produced the most noise reduction to date. Noise reduction has been optimized for two different overexpanded jet conditions and is near 5 dB in the peak noise emission direction at low polar angles and 3 dB off of the broadband shock associated noise in the sideline direction. These results were obtained with injection mass flow rates less than 4% of the core jet flow rate.