JET NOISE REDUCTION

We are working on innovative techniques, invented at UCI, to suppress noise from engines of a variety of jet aircraft. The fundamental principle is reduction of the convective Mach number of turbulent eddies that cause intense noise. In a turbofan engine, a very effective way to achieve this is by tilting sligtly downward the bypass plume relative to the core plume. Tilting can be done with vanes or fluidic injectors installed near the end of the bypass duct. Tests are conducted in UCI's Jet Aeroacoustic Facity, which uses small-scale jets to simulate the conditions of actual engine exhausts. The figures below show some illustrative examples.

Vanes installed inside the bypass duct of a simulated engine with bypass ratio BPR= 5. In general, the vanes can be installed inside or outside the bypass duct.

Measured velocity field of a jet similar to that shown on the left. The downward tilt of the bypass stream results in a thick layer of low-speed flow under the end of the primary potential core (end of dark brown region). This layer reduces the convective Mach number of the eddies there, hence suppresses sound radiated towards the ground.

Estimates of perceived noise level versus time for the BPR=5 engine without and with deflection. The effective perceived noise level (EPNL) is reduced by about 3 decibels. In supersonic turbofan engines, reductions up to 7 decibels have been recorded.

Further information is contained in several downloadable articles on eccentric nozzles and nozzles with fan flow deflection.