Direct numerical simulation of turbulent mixing at very low schmidt number with a uniform mean gradient

P. K. Yeung, K. R. Sreenivasan

Research output: Contribution to journalArticle

Abstract

In a recent direct numerical simulation (DNS) study [P. K. Yeung and K. R. Sreenivasan, "Spectrum of passive scalars of highmolecular diffusivity in turbulent mixing," J. Fluid Mech. 716, R14 (2013)] with Schmidt number as low as 1/2048, we verified the essential physical content of the theory of Batchelor, Howells, and Townsend ["Small-scale variation of convected quantities like temperature in turbulent fluid. 2. The case of large conductivity," J. Fluid Mech. 5, 134 (1959)] for turbulent passive scalar fields with very strong diffusivity, decaying in the absence of any production mechanism. In particular,we confirmed the existence of the-17/3 power of the scalar spectral density in the so-called inertial-diffusive range. In the present paper, we consider the DNS of the same problem, but in the presence of a uniform mean gradient, which leads to the production of scalar fluctuations at (primarily) the large scales. For the parameters of the simulations, the presence of themean gradient alters the physics of mixing fundamentally at low Peclet numbers. While the spectrum still follows a -17/3 power law in the inertial-diffusive range, the pre-factor is non-universal and depends on the magnitude of the mean scalar gradient. Spectral transfer is greatly reduced in comparison with those for moderately and weakly diffusive scalars, leading to several distinctive features such as the absence of dissipative anomaly and a new balance of terms in the spectral transfer equation for the scalar variance, differing from the case of zero gradient. We use the DNS results to present an alternative explanation for the observed scaling behavior, and discuss a few spectral characteristics in detail.

Original languageEnglish (US)
Article number015107
JournalPhysics of Fluids
Volume26
Issue number1
DOIs
StatePublished - Jan 13 2014

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Schmidt number
turbulent mixing
Direct numerical simulation
direct numerical simulation
scalars
gradients
Fluids
Peclet number
Spectral density
Physics
diffusivity
fluids
Temperature
anomalies
scaling
conductivity
physics

ASJC Scopus subject areas

  • Condensed Matter Physics

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Direct numerical simulation of turbulent mixing at very low schmidt number with a uniform mean gradient. / Yeung, P. K.; Sreenivasan, K. R.

In: Physics of Fluids, Vol. 26, No. 1, 015107, 13.01.2014.

Research output: Contribution to journalArticle

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