Causality of energy-containing eddies in wall turbulence

Abstract

Turbulent flows in the presence of walls may be apprehended as a collection of momentum- and energy-containing eddies (energy-eddies), whose sizes differ by many orders of magnitude. These eddies follow a self-sustaining cycle, i.e., existing eddies are seeds for the inception of new ones, and so forth. Understanding this process is critical for the modelling and control of geophysical and industrial flows, in which a non-negligible fraction of the energy is dissipated by turbulence in the immediate vicinity of walls. In this study, we examine the causal interactions of energy-eddies in wall-bounded turbulence by quantifying how the knowledge of the past states of eddies reduces the uncertainty of their future states. The analysis is performed via direct numerical simulation (DNS) of turbulent channel flows in which time-resolved energy-eddies are isolated at a prescribed scale. Our approach unveils, in a simple manner, that causality of energy-eddies in the buffer and logarithmic layers is similar and independent of the eddy size. We further show an example of how novel flow control and modelling strategies can take advantage of such self-similar causality.

even more improved wording and typos corrected, format changed

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• Life-cycle of streaks in the buffer layer of wall-bounded turbulence
• Causality analysis of large-scale structures in the flow around a wall-mounted square cylinder
• Informative and non-informative decomposition of turbulent flow fields
• CEBoosting: Online Sparse Identification of Dynamical Systems with Regime Switching by Causation Entropy Boosting
• Causal features in turbulent channel flow
• Identifying causal significance in three-dimensional isotropic turbulence
• Unsteady large-scale wake structure behind levitated freestream-aligned circular cylinder
• Mode-to-mode nonlinear energy transfer in turbulent channel flows
• Alternative physics to understand wall turbulence: Navier-Stokes equations with modified linear dynamics