Numerical investigation of supersonic nozzle flow separation

Separation of supersonic flow in a planar convergent-divergent nozzle with moderate expansion ratio is investigated by solving the Reynolds-averaged Navier-Stokes equations with a two-equation k-omega turbulence model. The focus of the study is on the structure of the fluid and wave phenomena associated with the flow separation. Computations are conducted for an exit-to-throat area ratio of 1.5 and for a range of nozzle pressure ratios. The results are compared with available experimental data in a nozzle of the same geometry. The flow separates by the action of a lambda shock, followed by a succession of expansion and compression waves. For 1.5 < NPR < 2.4, the computation reveals the possibility of asymmetric flow structure. The computationally obtained asymmetric flow structures are consistent with previous experimental flow visualizations studies. In addition, other flow features such as shock location and wall pressure distributions are also in good agreement with the experimental data. The present study provides new information that confirms earlier conjectures on the flow-wave structure relevant to the instability of the separated flow in convergent-divergent nozzles of moderate expansion ratio.