Eddies, understood as regions of the flow, which maintain spatial and temporal coherence, are widely used by the turbulence community as a conceptual model to organize and understand the flow. However, are they really there? Can they be identified and tracked in time? The present talk deals with the temporal evolution of vortices and eddies responsible for the momentum transfer in turbulent channels studied via time-resolved direct numerical simulation at high Reynolds numbers in a five hundred Terabytes database.
Eddies are identified as connected regions of the flow above a prescribed threshold, and tracked in time with a novel method specifically designed for the task. Once the evolutions are properly organized, they provide all the necessary information to test the coherence of the eddies and to characterize their lives from birth to death with a level of detail never achieved before. Finally, all the new information is compiled to build a structural model for the logarithmic layer of wall-bounded turbulence based on self-similar sweep-ejection pairs embedded within streamwise rolls. It is shown that these eddies act as the fundamental dynamical units of the flow and provide a great insight into the Turbulence physics.