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Prandtl number effects in decaying homogeneous isotropic turbulence with a mean scalar gradient

type de publication      article dans une revue internationale avec comité de lecture
date de publication 2017
auteur(s) Briard Antoine; Gomez Thomas
journal (abréviation) Journal of Turbulence (Journal of Turbulence)
volume (numéro) 18 (5)
  
pages 418 – 442
résumé Decaying homogeneous isotropic turbulence with an imposed mean scalar gradient is investigated numerically, thanks to a specific eddy-damped quasi-normal Markovian closure developed recently for passive scalar mixing in homogeneous anisotropic turbulence (BGC). The present modelling is compared successfully with recent direct numerical simulations and other models, for both very large and small Prandtl numbers. First, scalings for the cospectrum and scalar variance spectrum in the inertial range are recovered analytically and numerically. Then, at large Reynolds numbers, the decay and growth laws for the scalar variance and mixed velocity–scalar correlations, respectively, derived in BGC, are shown numerically to remain valid when the Prandtl number strongly departs from unity. Afterwards, the normalised correlation ρwθ is found to decrease in magnitude at a fixed Reynolds number when Pr either increases or decreases, in agreement with earlier predictions. Finally, the small scales return to isotropy of the scalar second-order moments is found to depend not only on the Reynolds number, but also on the Prandtl number.
mots clés Homogeneous turbulence, scalar gradient, cospectrum, EDQNM
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