Influence of Nozzle Geometry on the Noise of High-Speed Jets

The effectiveness of jet noise reduction by the use of different nozzle exit geometry is examined. Because there will be thrust loss associated with a nozzle of complex geometry, consideration is confined to practical configurations with reasonably small thrust loss. Only jets with a single stream are considered. The nozzle configurations examined are circular, elliptic, and rectangular. Plug nozzles as well as a suppressor nozzle are included. It is shown that the measured turbulent mixing noise of the jets from these nozzles consists of two independent components. The noise spectrum of each component is found to fit the shape of a seemingly universal similarity spectrum. It is also found that the maximum levels of the fitted noise power spectra of the jets are nearly the same. This finding suggests that nozzle geometry modification may not be an effective method for jet noise suppression.