In a recently developed and widely used premixed turbulent flame model, the so-called G-equation is averaged and combined with a balance equation for the variance G 2 G G ( ) 2 , where G is an averaged G-field. The goal of this communication is to discuss certain basic issues relevant to the G -and 2 G -equations and, in particular, to stress that the latter equation is ill defined, because the G-and G -equations are physically meaningful at different surfaces. Moreover, by analyzing simple

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... ples, it is shown that a widely accepted association of the scalar G with the so-called distance function does not allow us to consider the G-equation to be physically meaningful in the entire flow field.