AN ALTERNATIVE APPROACH TO MODELING TURBULENT PREMIXED COMBUSTION

We develop an alternative approach to the turbulent premixed combustion theory that permits to eliminate well known challenge of modelling of p redominantly counter-gradient scalar flux and the stress tensor, which must describe, in part icular, observed in experiments abnormal increasing in the premixed flame of the velocity fl uctuations. We analyse two combustion mechanisms: instantaneous combustion takes place in wrinkled laminar or microturbulent flame. The approach is based on derived in the pape r conditionally averaged momentum equations instead of traditionally used for modelli ng Favere averaged one. We state not only a system of the unclosed equations where requiring modelling unknowns are the conditional turbulent stresses in the unburned and burned gases b j i u j i u u u u ) ( , ) ( ′ ′ ′ ′ and the mean chemical source W ρ , but also develop model equations in the terms of these unknowns. Turbulence in model equations is characterized by conditional kin etic energies b u k k , and dissipation rates b u e e , , the stresses are described b j i u j i u u u u ) ( , ) ( ′ ′ ′ ′ in the standard gradient form using conditional turbulent viscosity coefficients u t , ν , b t , ν . We state the model W ρ using the theoretical expression for the turbulent flame spee d, which we derive using Kolmogorov type assumptions of statistical equilibrium of the small -scale reaction structures and at the same time nonequilibrium large-scale ones. The scalar fl ux and stress tensor do not require special modelling as the former is described in terms of th e conditional mean velocities u u r and b u r ,