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Scalar gradient statistics in isotropic turbulence in the presence of a mean scalar gradient

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We investigate the origin of the non-vanishing scalar gradient skewness in isotropic turbulence on which a mean-scalar gradient is imposed. The problem of the advection of an anisotropic scalar field is reformulated in terms of the advection of an isotropic vector field. It is shown how the scaling of the scalar gradient skewness depends on the choice of the time-scale used for the Lagrangian decorrelation of the vector field. The persistent anisotropy in the small scales for the third order statistics is shown to be perfectly compatible with Corrsin-Obukhov scaling for second order quantities.

Author(s):

Wouter Bos    
LMFA - CNRS - Ecole Centrale de Lyon
France