The effect of corrugations on the crackle noise in under-expanded 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 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 increases with an increase 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 at a skewness value of 0.1391, which is less than that of the free jet.