In this paper, a new irreducible dynamic nonlinear tensor diffusivity model based on Noll's formulation is proposed for representing the subgrid-scale (SGS) heat flux. In contrast to the conventional eddy diffusivity type models, the proposed model does not require the alignment between the SGS heat flux and the resolved scalar gradient, and therefore allows for a more realistic geometrical representation of the SGS heat flux. Due to the inclusion of nonlinearity, the new SGS heat flux model improves the numerical stability of the simulations and can be applied locally in the flow without resorting to plane averaging for stable computation of the model coefficients.
