Measurement and analysis of the shear-layer instabilities in supersonic impinging jets using dual-time velocity data

The flow unsteadiness in supersonic impinging jets due to the aero-acoustic feedback loop phenomenon can lead to practical problems like ground erosion in short take-off and vertical landing (STOVL) aircrafts, high noise levels and high unsteady structural loading. The shear-layer instabilities of the jet play an important role in the flow dynamics and their investigation is carried out in the present work using dual-time data. The study of the instabilities is usually conducted with the time derivatives of the velocity field. However, time resolved experimental data acquisition using particle image velocimetry (PIV) techniques has its challenges for high-speed flows due to the requirements of high spatial and temporal resolution. An alternate approach using dual-time PIV measurements is presented in the current study which involves the data acquisition using two parallel PIV systems, offset by a very small time scale. Samples of velocity field pairs are obtained by such measurements which contain additional information of the instantaneous time derivatives. Using analysis techniques like dynamic mode decomposition (DMD) and proper orthogonal decomposition (POD), valuable information about the dominant structures along with their frequency can be obtained. Numerical data generated using large eddy simulations (LES) and sampled like a double PIV data was used for the analysis. The quantifiable information regarding the flow dynamics that can be obtained using dual-time data along with a rigorous validation is shown in the current work.