Counter-gradient diffusion in a confined turbulent premixed flame

In the present study, we develop a full second order model and a new flamelet closure relation for the mean chemical source term to describe turbulent reactive flows with premixed reactants. This description ensures that non-gradient and counter-gradient diffusion which can appear In such flames, are taken into account in 2-D or 3-D geometries. 2-D calculations are performed in the case of a confined turbulent premixed flame stabilized by a backward Facing step, a configuration which reveals experimentally counter-gradient diffusion and combustion induced production of turbulence. Numerical results are found to be in excellent agreement with measurements of Shepherd et al, [Nineteenth Symposium (International) on Combustion (The Combustion Institute, Pittsburgh, 1982)]. The important Influence of counter-gradient diffusion on first order quantities, i.e,. mean velocity and length of the recirculation zone is shown. (C) 1997 American Institute of Physics.