Mixed-derivative skewness for high Prandtl and Reynolds numbers in homogeneous isotropic turbulence

The mixed-derivative skewness S uθ of a passive scalar field in high Reynolds and Prandtl numbers decaying homogeneous isotropic turbulence is studied numerically using eddy-damped quasi-normal Markovian closure, for Re λ ≥ 103 up to Pr = 105. A convergence of S uθ for Pr ≥ 103 is observed for any high enough Reynolds number. This asymptotic high Pr regime can be interpreted as a saturation of the mixing properties of the flow at small scales. The decay of the derivative skewnesses from high to low Reynolds numbers and the influence of large scales initial conditions are investigated as well.