We demonstrate that a similar type of large-scale coherent structures, elongated and low-speed features, that are found in subsonic experiments, are present in our supersonic and hypersonic turbulent boundary layer datasets from direct numerical simulation (DNS). Contour plots of the reconstructed streamwise velocity fluctuation from the most energetic proper orthogonal decomposition (POD) modes show the existence of very long low-momentum regions in the logarithmic layer. Furthermore, the 'superstructure' in the logarithmic layer is found to have a modulating effect on the small-scale motions in the viscous sublayer. Also, we present a physically based automated technique to track and study hairpin packets, as well as their wall signatures and their association with superstructures. Statistical correlations and a geometric algorithm are combined to identify the hairpin packets and their wall signatures. In addition, an activity tracking algorithm that is developed based on feature-Petri net, a mathematical modeling language for the description of distributed systems, is employed to track individual packets and their wall signatures over space and time.
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