The initial flow structures and oscillations of an underexpanded impinging jet

A numerical investigation into an underexpanded round jet impinging vertically onto a flat plate is conducted using large-eddy simulation (LES). The impinging jet features a Mach number of 1.0 at the nozzle exit, a nozzle-pressure ratio of 4.03 and a nozzle-to-plate spacing of 2.08. Three levels of mesh refinement, two temporal discretization schemes and two subgrid-scale (SGS) models are compared. The mean velocity profiles and the dominant impinging tone frequency of the current simulation match the experimental data and the LES results available in the literature. The initial flow structures of the impinging jet are presented to investigate the formation of the flow field and the establishment of the feedback loop. The main processes of the feedback loop are investigated in detail. The oscillations of the Mach disk and the evolutions of the annular shocks and vortex structures are studied. It is observed that the periods of these evolvement processes are identical to that of the acoustic wave generations. (C) 2021 Elsevier Masson SAS. All rights reserved.