Interaction of Shear Layer Coherent Structures and the Stand-Off Shock of an Under-Expanded Circular Impinging Jet

This study looks specifically at the energy transformations that occur during the interaction of strong shear layer coherent structures with the stand off shock. Time resolved data has been produced from high fidelity large-eddy simulations at a nozzle pressure ratio of NPR = 3.4 and impingement surface stand-off distance of z = 5d. Two dominant instability modes have been analysed using the velocity fluctuation energy density in the shear layer. Stand-off shock position statistics have been found as a function of radial position. Comparison of the shear layer pressure fluctuations and shock position fluctuation through a magnitude squared coherence analysis has been performed. It has been shown that the correlation of the initial shear layer pressure fluctuations and shock position is moderate at the dominant mode Strouhal numbers.