Spatiotemporally-resolved multiscale interactions between attached eddies in turbulent channel flows

Wall-bounded turbulent shear flows are conceptually decomposed into attached and detached eddies, with the attached ones primarily carrying the energy and momentum. Within this framework, multiscale interactions between the attached eddies are often neglected when making statistical predictions, despite experimental observations of phenomena such as inner-outer modulation. We characterize these multiscale interactions in a semi-Lagrangian sense by tracking the attached eddies in the flow at multiple scales, as well as the interscale energy fluxes between them, in both space and time. To achieve this, we employ a bandpass filtering approach and a multispecies structure tracking algorithm (Elnahhas et al., J. Phys. Conf. Ser. 2024). By tracking both the attached eddies and the multiscale contributions to the energy fluxes between them, we characterize the degree of locality of the interscale interactions between the attached eddies over their Lagrangian lifetimes. By encoding all interscale interaction events in a multilayer network, we extract conditionally averaged flow fields around multiscale events by restricting our analysis to eddies that belong to specific subsets of the network, e.g., those with strong non-local/local interactions between specific scales. The analysis is conducted using the temporally resolved turbulent channel flow datasets of Vela-Martín et al. (J. Comput. Sci., 2021).