Large Eddy Simulation of ALSTOM's reheat combustor using tabulated chemistry and stochastic-fields combustion model

Large Eddy Simulations (LES) of natural gas ignition and combustion in turbulent flows are performed using a novel combustion model based on a composite progress variable, a tabulated chemistry ansatz and the stochasticfields turbulence-chemistry interaction model. It is a significant advantage of this approach that it can be applied to industrial configurations with multi-stream mixing at relatively low computational cost and modeling complexity. The computational cost is independent of the chemical mechanism or the type of fuel, but increases linearly with the number of streams. The model is validated successfully against the Cabra methane flame and Delft Jet in Hot Coflow (DJFC) flame. Both cases constitute fuel jets in a vitiated coflow. The DJFC flame coflow has a non-uniform mixture of air and hot gases. The model considers this non-uniformity by an additional mixture fraction dimension, emulating a ternary mixing case. The model not only predicts flame location, but also the temperature distribution quantitatively. The LES combustion model is further extended to consider four stream mixing. It has been successfully validated for ALSTOM's reheat combustor at atmospheric conditions. Compared to the past steady-state RANS (Reynolds Averaged Navier-Stokes) simulations [1], the LES simulations provide an even better understanding of the turbulent flame characteristics, which helps in the burner optimization.