Supersonic jet noise source distributions.

Abstract

The purpose of this work is to examine the noise source distributions of shock-containing supersonic jets at various pressure ratios corresponding to fully expanded Mach numbers ranging from 1.0 to 1.4 in intervals of 0.2 for various nozzle exit diameters. Source location measurements using a phased array (beamforming), farfield jet noise measurements, and schlieren flow visualization are presented. It is found that supersonic noise source distributions are more complex than those of subsonic jets. The source distributions for supersonic jets can be divided into three different Strouhal regions. At low Strouhal numbers ( fD/U≤0.3), the noise source distributions appear very similar to those of a subsonic jet, as reported in open literature. This Strouhal region is dominated by jet-mixing noise associated with small-scale turbulence mixing. At high Strouhal numbers ( fD/U≥1.0), the noise source distributions are comprised of several repetitive sources at various discrete downstream jet locations that produce noise at all frequencies. The locations of these sources roughly correspond to the shock cells in the jet, and thus, vary with jet Mach number. Another region exists at Strouhal numbers between these two regions ( 0.3<fD/U<1.0) for which the precise location of the sources as a function of Strouhal number was determined to be ambiguous due to a limitation of the phased array used. This region roughly corresponds to the frequencies of noise where jet-mixing noise and shock noise are of similar levels. The spacing of the shock sources in this region are smaller than the beam width of the array measuring them. Their locations can no longer can be separately recorded; and instead, they are averaged together and their centroid location is plotted.