Flow Statistics and Noise of Ideally Expanded Supersonic Rectangular and Circular Jets

Abstract

Simulations of an ideally expanded supersonic jet for two operating temperatures are conducted with a low aspect ratio of two rectangular nozzle, and an equivalent diameter circular nozzle of the same design Mach number. The emphasis is on accurately resolving the near-field data, capturing the far-field acoustics, and examining the flow asymmetry of the rectangular jets. The simulated acoustic data of the cold and heated jets are validated against experimentally recorded sound-pressure-level spectra with very good agreement. Rectangular nozzle metrics are calculated in two orthogonal, axial spanning planes to determine the impact of the nozzle exit asymmetry, and then they are compared with the circular jet. The shock cell structure, the jet core length, and the axial distribution of the flow at similar radial distances (normalized by the major, minor, or circular radial lengths) are observed to be different between the two planes of the rectangular jet and relative to the circular jet. The dynamics of the large-scale coherent structures differ between the rectangular and the circular jets, in the near-nozzle region, with streamwise vorticity and corner effects being a factor in the rectangular jets, leading to enhanced entrainment. The upstream counter rotating streamwise vortex pairs and their subsequent interaction inhibits axis switching for the rectangular jet cases presented. Overall, far-field noise in the major and minor axis planes is lower than the circular jet for the cold case; however, the noise spectra collapses in the heated case, despite dissimilarities in the near-field flow structures between rectangular and circular jets.