A Comparison of Modal Decomposition Methods Applied to Hypersonic Schlieren Video

The modal decomposition methods formulate the governing equations of a system as a linear combination of the various modes to provide a powerful means for examining the influence of any individual or combined modes of interest. They are commonly used to characterize complex signal dominated fluid flows and their control. Three modal decomposition techniques, namely, the proper orthogonal decomposition (POD), dynamic mode decomposition (DMD), and higher-order dynamic mode decomposition (HODMD), are studied to understand their ability to analyze a high-speed schlieren video for Mach 6 flow over a cone. The video is focused on the base of the cone and the base flow region. The data-driven modal analysis techniques are used to analyze the interference generated by the sting on the base flow region. The basic characteristics of the base flow were under investigation in the experiment, so it was desirable to gain insight into the impact that the presence of the sting has on the base flow. The POD, DMD, and HODMD methods give different insights into the sting interference, but all three methods appear to show that the disturbance originating from the sting appears in the base region of the cone.