Large Eddy simulation of a supersonic starting impinging jet

Supersonic impinging jets have wide applications in many directions, such as rocket exhaust, supersonic combustor mixing, and accidental leakage of pressurized fluids. The steady processes of impinging jets have been extensively studied, but there is little research on the starting impinging jets. Considering the important applications of starting jet in rocket launches, car's airbags, and pulse jets, the under-expanded round jet impinging on a flat plate normally with a nozzle pressure ratio of 2.7 has been investigated using large eddy simulations. The distance between the impinging plate and the nozzle outlet is set to 5 times the nozzle diameter. The simulation results agree well with the experimental data. The variations of flow structures and dominant frequencies of the acoustic resonance at the starting process are presented. The radiation directions of the dominant frequencies exhibit notable variations at different stages of the starting process, and the explanation for this distinction is explored by the two-dimensional correlation analysis. The wavenumber spectra and dispersion relations are employed, showing that at different stages, the upstream-propagating guided jet modes are excited by the interaction between the Kelvin–Helmholtz wavepacket and shock cells of distinct wavenumbers. Finally, based on the instantaneous pressure distribution, the dynamic evolution characteristics of the flow structures at different stages are analyzed.