Joint RANS/LES approach to premixed flames modelling in the context of the TFC combustion model

摘要

We present an original time-saving joint RANS/LES approach to simulate premixed combustion simulation in strong turbulence, which is intended mainly for industrial applications. It is based on successive RANS/LES numerical modeling where part of the information (stationary average fields) is achieved by RANS simulations and part (instantaneous nonstationary image of the process) by LES. This is performed using the fields of turbulent energy and dissipation rate, obtained from the RANS simulations, to model turbulent scalar transport and combustion rate. This approach has been developed using the TFC combustion model. This is based on a generalization of Kolmogorov's idea (equilibrium not only of small-scale turbulent structures but also of small-scale structures of the reaction zones), which is employed to express the combustion rates both for RANS and LES problems in terms of turbulent characteristics (described by the model equations) and the chemical time. It permits to overcome in some way well known fundamental difficulty of modeling (so called "challenge of turbulent combustion") connected with the fact that the reaction rates strongly depend on unresolved small-scale coupling of turbulence and chemistry. In this work we present results of simulations carried out employing the joint RANS/LES approach described above and compare them with predictions obtained from a classic LES approach where the sub-grid scale terms are closed according to the Smagorinsky model.