The effect of nozzle inlet shape, lip thickness, and exit shape and size on subsonic jet noise

Abstract

Far field noise data were taken for convergent nozzles of various shapes and sizes at subsonic velocities exceeding 400 feet per second. For a circular nozzle, the nozzle inlet shape and lip thickness had no effect on the noise level, directivity, or spectra when compared at the same nozzle exit diameter and peak exhaust velocity. A sharp edged orifice was one exception to this statement. Coannular nozzles can produce additional high frequency noise. Blunt ended centerbodies, where there is significant base drag, also generate significant additional noise.The total noise power generation was essentially the same for cirpular, slot, and plug nozzles of good aerodynamic shape. The noise radiation patterns were essentially the same for these nozzle shapes except°° near the nozzle exhaust axis. These patterns were well described by "7 '(1 -M C cos 9j)~3, except near the nozzle exhaust axis. w

Lip noise generated by flow separation from nozzle surfaces

“…1, taken from Ref. 3, it is clearly shown that for coaxial nozzles the velocity ratio, VR, across the core nozzle lip has a strong effect on flow separation lip noise. When the velocity ratio was below 0.5 the lip noise was less than the broadband jet noise.…”

“…The noise from the nozzles listed above, all of which have regions of flow separation, will be discussed herein in order to tie in the Ref. 3 results with the new data contained. It is hoped that these few examples will impress upon the reader the importance of using nozzle designs that have no flow separation in jet noise experiments.…”

“…Some examples, which were described very briefly in Ref. 3, are flow separation off the plug of a plug nozzle and flow separation off the core nozzle lip of a coaxial nozzle. In the lattar case, a thin flow sepa ration zone occurs downstream of the core nozzle lip which causes intense high frequency noise.…”

“…1 (taken from Ref. 3) shows an example of flow se paration noise from a mode'.-scale coaxial nozzle. The flow separation region that occurs downstream of the 0.25 cm thick blunt core nozzle lip of this coaxial nozzle caused the intense narrow band high frequency noise that is as much as ZU dB above the jet noise.…”

Jet noise from coaxial nozzles over a wide range of geometric and flow parameters

“…In Ref. 6, some of the single stream jet noise spectral data obtained from this facility were compared to scaled up data taken by Lush in an anechoic chamber(7); the agreement was within the day to day repeatability.…”