Experimental investigation of nonlinear properties of crackle and screech in supersonic jets

Supersonic crackle, an irritable component of aircraft jet noise, was investigated using model scale measurements. Near-field results showed Gaussian distribution but far-field had high skewness and even higher in its derivative. Skewness, a measure of asymmetry in the waveform, was compared to screech arising from shock associated noise which was also high but in contrast to crackle its skewness derivative had dropped to a much smaller value than its waveform. Both crackle and screech are nonlinear but their nonlinear properties are entirely different. Crackle is quantified when its derivative skewness becomes larger than its waveform skewness which should exceed 0.3.