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Multi-scale state-space dynamics of near-wall turbulence

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TURW04 - Wall-bounded turbulence: beyond current boundaries

Over the past decade, there has been a significant amount of evidence that coherent structures in wall-bounded shear flows emerge in the form of a hierarchy (or a fractal), as was hypothesized by Townsend (i.e. attached eddy hypothesis) in 1950s. In this talk, a numerical experiment, designed to simulate only two scale dynamics (i.e. large and small), will be introduced, and I will present three newly discovered scale interaction dynamics: 1) non-equilibrium energy cascade modulated by self-sustaining process; 2) enhanced small-scale turbulence production driven by energy cascade of large scale; 3) energy feeding from small to large scale. 28 invariant solutions are subsequently computed for this system, and they are classified into 1) large scale state; 2) small scale state; 3) scale interaction state. An exhaust examination with many physical relevant state-space visualisations revealed that none of the invariant solutions appear near the chaotic turbulent state, suggesting that the notion of the state space from the dynamical systems theory may not be very useful for multi-scale turbulence. Instead, each of the solutions is found to represent only part of the multi-scale processes. I will conclude this talk by addressing how we tackle this challenge in the dynamical systems description of turbulence.

This talk is part of the Isaac Newton Institute Seminar Series series.

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