Acoustic Characteristics of Non-Circular Slot Jets

Abstract

Experimental investigations on the acoustic characteristics of non-circular jets are carried out. Non-circular geometries include triangular, rounded triangular, square, and elliptic configurations, with a circular jet serving as the baseline case. Acoustic characteristics in terms of the spectra, directivity of sound pressure, tonal properties, and broadband shock associated noise are obtained to unravel the basic differences in these jets. Experiments are carried out for various pressure ratios ranging from 2 to 6, corresponding to fully expanded jet Mach numbers ranging from 1.04 to 1.82. The reduced effects of screech and broadband shock associated noise in triangular and square jets render them quieter than circular jet by up to 10 dB. The broadband shock associated noise levels are higher along flat edge planes than vertex planes, at all pressure ratios. Tonal analysis of the acoustic radiation from elliptic jet reveals that the screech tones along the major axis plane are more intense than those along minor axis plane.