Impact of Heat on the Pressure Skewness and Kurtosis in Supersonic Jets

Abstract

Mach wave radiation and crackle are dominant noise components from high-speed jets, found in both high-power engines and scale nozzles. The statistics of the pressure signal and its time derivative () have been widely studied to identify and quantify crackle. In this paper, we investigate the impact of operating condition on the overall sound pressure level, skewness, and kurtosis of the pressure and signals of a jet issuing from an converging–diverging conical nozzle. The effect of temperature and nonideal expansion were independently investigated. An increase in convective Mach number , achieved by increasing either jet temperature or nozzle pressure ratio, proved to be related to elevated values of overall sound pressure level, skewness, and kurtosis, in both the near and far fields. The peak values of overall sound pressure level, skewness levels, and kurtosis levels were found to propagate at different angles for cold jets, but at elevated temperature, the directivity was more similar. From here, it was concluded that the intense levels of the high-order statistics appear to be generated at different locations in the shear layer of the jet and strengthen away from the jet by nonlinear propagation effects.