An original model for numerical simulation of turbulent premixed and partially premixed combustion at large Re and Da numbers is described. A quantitative description of the coupling between turbulence and chemistry by the flamelet mechanism is proposed, based on the generalized Kolmogorov concept of small scale equilibrium structures in developed turbulence. A model equation for premixed combustion is described in the terms of a reaction progress variable. This model has been implemented in the commercial code FLUENT5, and is validated against the experients by V. Karpov (spherical flames in a well stirred reactor) and P.Moreau (high velocity combustion in a channel). Partially premixed combustion is modeled by transport equations for the PDF of passive concentration and the conditional progress variable. Results of numerical simulations with turbulence-chemistry coupling by equilibrium and laminar flamelet chemistry are compared with experimental data by Barlow and Frank
