NASA’s Langley Research Center researchers have developed a novel noise reduction system for jet engines. Aircraft jet engine noise is a major issue for airports, the communities near airports, and, of course, for the jet engine designers. Even with the use of recent high-bypass-ratio jet engine designs, noise continues to be a major concern. The present innovation represents a significant advancement to the concept of using mechanically fixed chevrons on the trailing edge of jet engine nozzles to reduce noise. While the effect of chevrons on noise reduction is well known, commercial implementation has been limited. Unfortunately, the turbulence created with the chevrons, while useful for reducing noise upon takeoff, serves to reduce efficiency during cruising. The present innovation is a simple noise reduction system with effects similar to that of chevrons, yet it is active and controllable to maximize noise reduction while maintaining efficiency.
The noise-reduction system makes use of injectors placed on the inside trailing edge of a jet engine nozzle. The momentum of the injected water causes turbulence, much like a chevron, to induce mixing of the inner core nozzle flow with the outer flow (bypass fan stream or free stream) upon exit from the nozzle. Optimization and control of the injector noise reduction is possible through control variables such as injector angle, injector placement and distribution, injector port shape, and water flow. This innovation has been developed and tested at NASA Langley Research Center using scale wind tunnel testing.
This simple design does not employ any moving parts, and can be used as a standalone noise-reduction system or in complement with chevrons (hence the term wet chevrons). It increases the effectiveness of chevrons while minimizing chevron penetration into the flow stream and the resulting loss of engine efficiency. The system’s noise reduction exceeds that of mechanically fixed chevrons. Noise reduction can be maximized at takeoff or other periods of operation, and turned off as needed to maximize engine operating efficiency.
The technology offers commercial opportunities within the civilian and defense aerospace markets for jet engines. Jet engine builders can leverage this technology into next-generation aircraft jet engines for maximum efficiency and quiet operation.