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Accueil > Actualités > Séminaires > Archives 2020

Carlo Cossu, CNRS - LHEEA, Nantes, France

Why Reynolds stresses should be modelled in resolvent analyses of wall-bounded turbulent flows

Vendredi 31 janvier 2020, 11h, salle Archipel, bât. H10, ECL

Why Reynolds stresses should be modelled in resolvent analyses of wall-bounded turbulent flows

Recent research suggests that wall-bounded turbulence is associated with a whole family of self-sustaining motions with scales ranging from those of buffer-layer streaks to those of large-scale and very-large-scale motions in the outer layer. These motions, associated with coherent streaks and quasi-streamwise vortices, are able to sustain themselves at each relevant scale in the absence of forcing from larger- or smaller-scale motions by extracting energy from the mean flow via a coherent lift-up effect. In this context, it has been recently proposed that the analysis of the resolvent operator could be used to predict the most energetic structures in these flows. We will show that, indeed, good predictions of turbulent correlations can be obtained when the resolvent operator includes the modelling of turbulent Reynolds stresses. This is not the case when the standard approach, which does not include Reynolds stresses in the resolvent, is followed.

(source : Morra et al. J. Fluid Mech. vol. 867, pp. 969-984, 2019)
Caption : comparison of the root-mean-square streamwise velocity profiles (square-root of the spatio-temporal spectral correlation Suu) computed by direct numerical simulation (DNS) of a turbulent plane channel flow at Reτ = 1007 with the 6-modes expansions on the optimal spectral proper orthogonal decomposition (SPOD) of the power spectral density computed by DNS (SPOD) and on the optimal resolvent modes including (Res-νt) or not (Res-ν) a model of Reynolds stresses for (a) near-wall structures with λx+= 450, λz+=100 at the peak frequency ω = 4.3 and (b) large-scale structures with λx = 3, λz = 1.5 at the peak frequency ω = 1.4.


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