NP Division Campfire: On the concept of energy cascades in turbulence: from Richardson/Kolmogorov picture to multifractal and beyond

Turbulent flows are characterized by a self-similar energy spectrum, signature of fluid movements at all scales. This organization has been described for more than 70 years by the phenomenology of “Kolmogorov/Richardson cascade”: the energy injected on a large scale by the work of the force that moves the fluid (e. g. a turbine) is transferred to smaller and smaller scales with a constant dissipation rate, up to the Kolmogorov scale, where it is transformed into heat and dissipated by viscosity. Such cascade phenomenology is at the basis of most turbulent models.

I will discuss in this talk how progresses in numerical simulations and laboratory experiments gradually changed such simple vision (starting from Landau objection in the 50’s), leading to a new picture where quasi-singularities living beyond Kolmogorov scale play a central role. This has important impact on resolution requirement of numerical simulations and call for new models of turbulence.

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