Investigation of wall-bounded turbulence dynamics using spatiotemporal tracking and network-centric methods

Wall-bounded turbulence has long been characterized by coherent structures or eddies such as hairpins and streaks (Robinson 1991 ARFM). The kinematics and time-averaged statistical properties of these eddies have been extensively studied using techniques such as proper orthogonal decomposition (POD), conditional averaging, and flow visualization. However, the dynamical properties and spatiotemporal interactions of eddies remain less explored. We employ a spatiotemporal tracking algorithm capable of simultaneously tracking multiple sets of eddies to study their dynamics and interactions. The algorithm results in a large network whose properties are analyzed using node-level and higher-order organizational measures, referred to as network motifs. The mechanistic importance of the motifs, e.g., contribution to production/dissipation cycles, are quantified. Both minimal flow units and large domain channel flows are examined, where the ejection/sweep and low/high-speed-streak side-by-side pairing emerged as the lowest form of spatiotemporal organization. The application of the methodology to higher Reynolds number flows and to the study of other sets of eddies is discussed.