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Passive scalar mixing in turbulent flow

Abstract : The mixing of a passive scalar in turbulent flow is studied. First, Direct Numerical Simulation (DNS), Large Eddy Simulation (LES) and dimensional arguments are used to investigate the scalar flux spectrum in isotropic turbulence with a mean scalar gradient. A scaling law allowing for inertial range slopes varying from -5/3 to -7/3 is derived. The LES results support a K^{-2} expression. Subsequently, using a two-point closure (EDQNM), we show that at very high Reynolds numbers, the scalar flux spectrum in the inertial range behaves as predicted by the classical dimensional analysis of Lumley (1967) and scales as K^{-7/3}. At Reynolds numbers corresponding to laboratory experiments the closure leads to a spectrum closer to K^{-2}. It is shown that the K^{-2} scaling in the LES is induced by large scale forcing. The closure is then applied to homogeneous shear flow and the spectra of cross-stream and streamwise scalar fluxes are investigated. The streamwise scalar flux spectrum is found to scale as K^{-23/9}. This result is in agreement with experiments but disagrees with classical dimensional analysis. Eventually, we show that the link between particle dispersion and scalar mixing allows to formulate a Markovian two-point closure for the velocity and scalar that does not involve any model constant.
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https://tel.archives-ouvertes.fr/tel-00199364
Contributor : Wouter Bos <>
Submitted on : Tuesday, December 18, 2007 - 6:06:30 PM
Last modification on : Wednesday, July 8, 2020 - 12:42:06 PM
Long-term archiving on: : Monday, April 12, 2010 - 8:24:32 AM

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  • HAL Id : tel-00199364, version 1

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Wouter J.T. Bos. Passive scalar mixing in turbulent flow. Fluid Dynamics [physics.flu-dyn]. Ecole Centrale de Lyon, 2005. English. ⟨tel-00199364⟩

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