The effect of temperature on subsonic jet noise

Abstract

The noise levels produced by hot and cold subsonic jets have beefi measured using a convergent circular nozzle in an anechoic chamber. This report presents the effects of jet temperature on the sound power, the overall sound-pressure levels and the spectra of the jet noise. The results show an unexpected increase in noise with increasing jet temperature at low jet velocities. The possibility of this observation arising from sources upstream of the nozzle exit is considered and discounted. It is concluded that both the spectral shapes and the overall sound-pressure level of a hot jet are significantly affected by refraction of the sound by the jet. The overall sound-pressure levels have been correlated to form the basis of a method for the prediction of the noise from static jets.