Reynols Number and Temperature Effects on Jet Noise

Abstract

A detailed study has been undertaken to understand and quantify the effects of Reynolds number and temperature on jet noise. Da ta acquired at Boeing’s Low Speed Aeroacoustic Facility (LSAF) with nozzles of different diameters (1.5”, 2.45” and 3.46”) operating over a range of Mach number and temperature was used in this study. Detailed spectral and overall power level comparisons h ave been made to identify and isolate the effects of Reynolds number and temperature . It is well known that the jet mixing can be affected by the initial conditions which in turn can be affected by Reynolds number. It is also known that the jet mixing beco mes less sensitive to initial conditions as the jet diameter is increased. In this study , the initial conditions (boundary layer, etc.) were not measured to separate the effect of initial conditions versus the Reynolds number. However, it is shown that spe ctra from the smaller diameter jet is not significantly different from that of the larger diameter jets, especially in the low - to mid -frequency range. On the other hand, there is an increase in spectral levels at higher frequencies with increasing Reynold s number. This trend has been observed over all the angles and for a wide range of operating conditions. Comparisons of spectra at various angles of cold & heated jets at constant jet velocity clearly identified the effects of temperature on jet noise. It is shown that the effects of temperature depends on the jet vel ocity as observed by many other studies in the past. Comparisons of the overall sound pressure level at 90 0 , thereby minimizing refraction effects and convective amplification, as a function of velocity show a dependence of about V 8 j for cold jets and about V 6 j for hot jets suggesting the existence