Numerical study of nozzle exit condition effects on jet development

Numerical predictions of the influence of nozzle exit conditions on the development of an ideally expanded supersonic rectangular jet are performed. The effects of these conditions on the jet's development have been found to be significant in experimental investigations. A model for the initial conditions is developed. A higher-order accurate finite difference algorithm for the solution of the full three-dimensional Navier-Stokes equations is used to generate results that isolate the impacts of excitation amplitude, modal excitation, and corner vortices on the jet character. Time-averaged, cross-correlation, and cross-spectral data are gathered from the simulation and compared to experimental data. The results indicate that, over the range of operating conditions considered here, the excitation amplitude does not significantly alter the jet development. The corner vortices, although prescribed in a sense that should anticipate axis switching (as determined by experimental subsonic results), are found to delay it. This appears to be caused by the dominance of flow instabilities in supersonic jets and the observed tendency of the corner vortices to reduce the mixing associated with this instability. Finally, independent of modal excitation, the lowest-order modes (of the large-scale turbulence structure) are found to consist of a combination of flapping in the minor axis plane with varicose motion in the major axis plane.