Turbulent Statistics of a Hot, Overexpanded Rectangular Jet

Abstract

The near-field dynamics of a rectangular heated overexpanded jet of aspect ratio two is examined with an implicit large-eddy simulation using experimental data for validation purposes. The conical nozzle, representative of practical configurations, results in multiple shock trains from the throat region as well as the overexpanded operating condition. Each train introduces unsteadiness that influences the external shock cell and plume structure. A detailed analysis of the terms contributing to the turbulent kinetic energy (TKE) is performed to examine the evolution of the plume. The major-axis shear layer experiences significant amplification of the TKE compared with the minor axis, particularly near the core collapse region, and thus pressure fluctuations in the near acoustic field are correspondingly larger in that direction. The most prominent source of TKE in this region is associated with strong mean flow gradients across the major-axis shear layer, and larger corresponding cross-correlations of velocity fluctuations. These effects are shown to be consistent with protrusions of vortical perturbations arising in the minor-axis shear layer into the potential core. The evolution of pressure perturbations from asymmetric to axisymmetric occurs relatively quickly, to achieve agreement with far-field experimental data.