NUMERICAL STUDY OF NOZZLE EXIT CONDITION EFFECTS ON JET DEVELOPMENT

Numerical predictions of the influence of nozzle exit conditions on th e development of an ideally expanded supersonic rectangular jet are pe rformed. 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 finit e difference algorithm for the solution of the full three-dimensional Navier-Stokes equations Is used to generate results that isolate the i mpacts of excitation amplitude, modal excitation, and corner vortices on the jet character. Time-averaged, cross-correlation, and cross-spec tral data are gathered from the simulation and compared to experimenta l data. The results indicate that, over the range of operating conditi ons considered here, the excitation amplitude does not significantly a lter the jet development. The corner vortices, although prescribed in a sense that should anticipate axis switching las determined by experi mental subsonic results), are found to delay it. This appears to be ca used by the dominance of flow instabilities in supersonic jets and the observed tendency of the corner vortices to reduce the mixing associa ted with this instability. Finally, independent of modal excitation, t he Lowest-order modes (of the large-scale turbulence structure) are fo und to consist of a combination of flapping in the minor axis plane wi th varicose motion in the major axis plane.