Shock-Induced Flow Separation in an Overexpanded Supersonic Planar Nozzle

Abstract

Shock-induced flow separation in an overexpanded supersonic planar nozzle is investigated numerically by means of three-dimensional wall-modeled large-eddy simulations (LES). The objective of this study is to identify the origin of the low-frequency shock oscillations (LFO) and the associated side-loads generation in planar nozzles. The computational results are compared with the experimental data for validation. The promise of the near-wall LES modeling approach, adopted in this study, is supported by its satisfactory performance in correctly predicting the shock-induced flow separation and offering a major advantage of being 30–40 times faster than the wall-resolved LES counterpart, allowing thereby the capture of very–low-frequency shock oscillations with much better statistics convergence. The simulations bring clear evidence of the existence of broadband and energetically significant LFO in the vicinity of the separated shock, whose forward and backward movements are mainly driven by changes in the downstream flow conditions. The complex interactions between the backflow, the separation bubbles, and the large-scale turbulent structures developing in the shear-layer region strongly influence the shock unsteadiness, which in turn drives the LFO. A scenario of the LFO, confirming conclusions from earlier studies, is described in this work.