Large eddy simulation of a turbulent reacting jet with conditional source-term estimation

Abstract

The Conditional Source-term Estimation (CSE) method was recently proposed to close the chemical source terms occurring in the spatially filtered transport equations of species and enthalpy for Large Eddy Simulation (LES) of nonpremixed reacting flows [W. K. Bushe and H. Steiner, Phys. Fluids 11, 1896 (1999)]. The model is based on the Conditional Moment Closure hypothesis, which provides fairly accurate predictions for the conditional averages of the chemical reaction rates as functions of the conditionally averaged composition vector and temperature with the mixture fraction being an appropriate conditioning variable. In CSE the conditionally averaged composition vector and temperature are obtained by mapping the corresponding spatially filtered scalar fields resolved by the LES into the conditioning (i.e., mixture fraction) space. After the conditional averages of the chemical reaction rates are approximated in mixture fraction space, these are mapped into the physical space to close the source terms in the LES transport equations for the reactive scalars. The present simulation of a turbulent reacting jet is the first test of this new closure in a self-sustained predictive LES. A two-step reduced chemical kinetic mechanism for methane–air flames was used. The results of the simulation, which are in reasonable agreement with available experimental data, prove the model’s predictive capabilities as well as its robustness and feasibility for LES.