New interpretations of shock-associated noise with and without screech

Abstract

SUMMARYAnomalous trends in present convergent nozzle (Mach 1) shock-associated noise analyses and predictions, with parttoular znphasis on the roles of screech and ,jet temperature, are discussed. Experimentally measured values of shock-associated noise are usedto reassess data trends, including both frequency and sound pressure level. The data used Includes model-scale o% nozzles, varying in nominal diameter from 5 cm to 13 cm, and Cull-scale engine nozzles up to 48 cm. All data were obtained at static conditions. From this sM reassessment of the measured data, now empirical methods for the prediction of shock-associated noise are developed. Separate procedures are presented for screech-free and screech-contaminated shock-asnociatod noise. In the present approach, shock-associated noise spectra are developed from considerations thatInclude the peak sound pressure Level and its frequency, the loan frequency sound pressure level slope, and the high frequency ;sound pressure level, slape or roll-off; the latter is shown to vary with directivity angle.