The Lagrangian equation for the gradient of a passive scalar is modelled consistently with the approach for the velocity gradient tensor recently developed by Chevillard and Meneveau. In three-dimensional, isotropic turbulence general properties of the scalar gradient represented by alignment with strain principal axes and norm production are retrieved by the model. In addition, model results suggest the existence of special alignments of the scalar gradient which are defined by a local strain persistence parameter and are different from the directions given by the strain principal axes.
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