Fluid layer acoustic shield for turbofan jet propulsion engine

Details Fluid layer acoustic shield for turbofan jet propulsion engine Fluid layer acoustic shield for turbofan jet propulsion engine

1975-07-02

1977-05-17

Franklin, Lawrence R.

Acoustics

Auditorium

137 151, 181 33HC, 181 51, 244 53B, 415119, F02C 724

Patent

active

040236447

ABSTRACT:
Noise generated by the tips of the fan blades in a turbofan jet propulsion engine is suppressed by generating an annular fluid layer or wake in the inlet of the turbofan engine forwardly from the fan blades and spaced inwardly from the inner wall of the inlet and by lining the inner wall of the inlet with an acoustically absorbent layer of material. Sound waves generated by the fan blades are reflected outwardly by the fluid layer and are absorbed in the acoustic absorbent layer on the inner wall of the inlet. In order for the wake to reflect sound waves, either the local fluid velocity in the wake must be lower than the fluid velocity of the surrounding airstream traveling through the inlet or the acoustic speed in the wake must be greater than or equal to the acoustic speed in the surrounding airstream. It is preferred that both conditions be met. The fluid layer can be created by an annular bluff body positioned in the inlet or by injecting a fluid from an annular plenum in a direction opposite to the flow of the airstream through the inlet.

REFERENCES:
patent: 2636666 (1953-04-01), Lombard
patent: 2647366 (1953-08-01), McCann
patent: 2783008 (1957-02-01), Bodine
patent: 3481427 (1969-12-01), Dobbs et al.
patent: 3533486 (1970-10-01), Paulson
patent: 3535928 (1976-01-01), Shah

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