Simulation and stability analysis of a supersonic impinging jet at varying nozzle-to-wall distances

A model for an ideally expanded Mach 1.5 turbulent jet impinging on a at plate using unstructured high-fidelity large eddy simulations (LES) and hydrodynamic stability analysis is presented. The LES are repeated for two nozzle-to-wall distances as well as with and without the addition of sixteen microjets positioned uniformly around the nozzle lip. The Reynolds-Averaged Navier-Stokes (RANS) equations are also used to model the flow for five nozzle-to-wall distances without the microjets. Microjet control only substantially reduces the noise for some nozzle-to-wall distances according to experiments. Observations of substantial noise reduction are associated with a relative absence of large-scale coherent vortices in the jet shear layer. To better understand and predict the effectiveness of microjet control, the application of global stability analysis about LES and RANS mean fields is used to extract axisymmetric and helical instability modes revealing the complex interplay between the coherent vortices, shocks, and acoustic feedback.