The effect of corrugation on the crackle noise in underexpanded impinging jets.

The present study investigates crackle noise of the impinging jet over the flat and corrugated plate. The experiments are conducted using a 10 mm diameter (d) orifice for jet production. The standoff distance is varied from 1.5d to 6d, incrementing 0.5d. The nozzle pressure ratio (NPR) is varied from 4 to 5.6 with a step size of 0.2. Results are discussed by plotting the probability density function of normalized pressure data and its derivative and the measured skewness values. For the flat plate, the positive skewed pressure data associated with strong compression and expansion is observed for all NPRs, and the skewness value fluctuates with the change in NPR. The crackle noise is absent in the corrugated plate for most NPRs and standoff distances, although it is observed within a short duration at some NPRs. In contrast, the crackle noise is persistent for the flat plate throughout the time range and is observed even the skewness of the normalized acoustic pressure exceeds the skewness of the derivative of acoustic pressure data. [ABSTRACT FROM AUTHOR]