Acoustic Mode Analysis of a Supersonic Jet

The dynamics of a supersonic jet emanating from a high-aspect-ratio rectangular nozzle is investigated using dynamic mode decomposition. In the analysis, dynamic mode decomposition is applied to flowfield data obtained from a large-eddy simulation and the significance of each extracted mode to the snapshot data series is determined using a sparsity-promoting method. Furthermore, in order to assess the validity of the resulting modes, they are compared with the unprocessed large-eddy simulation data in terms of frequency content, sound pressure levels, and space-time correlations. It is found that the accuracy of the modes predicted by the dynamic mode decomposition is sufficient and that the modes deemed as most important give a good representation of the jet flow dynamics. Moreover, the jet flow, at the simulated conditions, is known (from experiments) to be dominated by a screech mechanism. The dynamic mode decomposition methodology, as set up in the present study, is able to isolate the jet screech mode, and the frequency of the extracted mode is in excellent agreement with previous observations.