Subgrid-scale modeling of SGS scalar flux: a regularization of the gradient model

International audienceAccurate prediction of a scalar advected by a turbulent flow is needed for various applications. In the framework of large-eddy simulation (LES), a subgrid-scale (SGS) model for the subgrid-scale scalar flux has to be used. A gradient model derived from Taylor series expansions of the filtering operation is a well-known approach to model SGS quantities. This model is known to lead to high correlation levels between the un- known term and the model. However, this type of model can not be used in practical LES because it does not lead to sufficient global energy transfer from the large to the small scales. In this work, we propose a regularization of the gradient model based on a physical interpretation of this model. We compare the regularized gradient model with classic models through a priori tests. It is found that the new proposed model associ- ated with a dynamic procedure exhibits very good performances in comparison with the standard dynamic eddy diffusivity gradient models. To better evaluate the new dynamic procedure, we perform a posteriori (large-eddy simulation) tests, showing a substantial improvement for various scalar statistics predictions