Acoustic Characteristics of Jets Emanating from Curved Triangular Topologies

Abstract

Noise generated from two geometrically contrasting jet flow topologies – concave and convex triangular jets are considered in the present work. Jets are generated from disk-nozzles made by cutting out the requisite concave/convex geometries on thin plates. The areas as well as the radii of curvature of concave and convex jets are maintained the same. Acoustic characteristics of the curved jets are measured and compared with those of a regular equilateral triangular jet. Experiments are conducted for underexpanded conditions for pressure ratios ranging from 2 to 7, corresponding to fully expanded jet Mach numbers of 1.04 ≤ Mj ≤ 1.92. Acoustic characterization has been carried out in terms of overall sound pressure levels, spectra, and directivity. The results show that mid-edge planes are noisier than vertex planes. The initial jet perimeter is found to be a key parameter influencing the noise emission of curved jets. Along the mid-edge planes, the concave jet is the noisiest, followed by regular equilateral triangular jet and then by the convex triangular jet. Curvature brings about a reduction in the shock-cell length – the equilateral triangular jet has the highest shock cell length followed by the convex and concave triangular jets.