Abstract
A computational investigation of the role of thermal nonuniformity on the development of instability modes in the shear-layer of a supersonic , jet is performed in this study. Cold fluid is injected at the axis of a heated jet to introduce radial nonuniformity and control the spatial development of shear layer. This is a companion investigation of an experimental study that observed a 2 dB reduction in peak narrowband sound pressure for centered injection. This investigation highlights the role of nozzle turbulence in changing the development of the noise-generating fluctuations by performing a separation of scales between boundary-layer turbulence and the coherent shear layer fluctuations. The mean flow is analyzed with an efficient Reynolds-averaged Navier–Stokes (RANS) approach. Different turbulence models are tested and compared with the experiments. The coherent perturbation is analyzed using linear parallel and parabolized stability equations (PSEs). PSEs agree with the experiments with regard to the small but consistent decrease in growth rate of forced modes with injection and identify the weakening of the first circumferential mode as the main contribution. Turbulence models for the base flow have a substantial effect on the perturbation development, and a compressibility correction of the RANS base flow is key to investigate jet-noise reduction strategies.
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