In this talk the reconstruction of sub-grid velocity and scalar fields in large eddy simulation (LES) of turbulent flows will be addressed. The approach is based on the assumption of fractality of these fields.  The characteristics of the reconstructed signal depend on the stretching parameter d, which is related to the fractal dimension of the signal. In many previous studies the parameter d was assumed to be constant in space and time. As it will be discussed, such a model is too limited to describe the turbulence properties of interest in a satisfactory manner. Improved results can be obtained after the variability of the stretching parameter is accounted for.