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Article Dans Une Revue Journal of Turbulence Année : 2023

An EDQNM study of the dissipation rate in isotropic non-equilibrium turbulence

Le Fang
  • Fonction : Auteur
Wouter J.T. Bos

Résumé

The energy cascade from large to small scales is a robust feature of three-dimensional turbulence. In statistically steady turbulence, the average dissipation is in equilibrium with the energy injected in the system. A global quantity measuring the deviations from such a flux equilibrium is the normalised dissipation rate C_eps , corresponding to the viscous dissipation, normalised by quantities associated with the largest scales of the system. Recent investigations have pointed out how this normalised dissipation rate varies in unsteady flows. We focus on two test-cases to assess non-equilibrium in isotropic turbulence. These cases are, respectively, turbulence in the presence of a large-scale periodic forcing and turbulence with reversed initial conditions. We show, using the Eddy-Damped Quasi-Normal Markovian closure, that for turbulence in the presence of periodic forcing, a C_eps ∼ R_lam^ −15/14 scaling is reproduced (R_lam indicating the Taylor-scale Reynolds number) when the forcing-frequency is adjusted to be of the order of the inverse of the integral timescale. It is shown that the spectrum can be decomposed into an equilibrium spectrum, governed by Kolmogorov scaling in the inertial range, and a perturbation spectrum, proportional to k^ −7/3 , k being the wavenumber. For reversed turbulence, a novel procedure is introduced to prescribe initial conditions for the nonlinear transfer. Subsequently a clear transient with a scaling C_eps ∼ R_lam^ −2 is observed in the dynamics.
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hal-04271732 , version 1 (06-11-2023)

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Le Fang, Wouter J.T. Bos. An EDQNM study of the dissipation rate in isotropic non-equilibrium turbulence. Journal of Turbulence, 2023, 24 (6-7), pp.217-234. ⟨10.1080/14685248.2023.2189731⟩. ⟨hal-04271732⟩

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