A bluff-body stabilized lean premixed combustor has been numerically studied using Large Eddy Simulation (LES). Available experimental data from Pitz and co-workers at Sandia Labs and Vanderbilt University, including, spatially resolved mean temperature and emissions, were compared to the LES predictions. The combustion LES utilized various subgrid chemistry descriptions including simple 1-step, laminar assumptions to 5-step, Linear Eddy Mixing (LEM) models. The LEM model represents the state-of-the-art in resolving subgrid turbulencechemistry interactions since it captures molecular mixing and chemical reaction in 1D down to the molecular level and models the unresolved turbulent stirring using Kolmogorov cascade laws. It was shown that the LEM was needed to predict the turbulent reacting bluff-body flow. Laminar chemistry assumptions do not allow large-scale turbulent structures to form and the subsequent enhanced mixing downstream of the bluff-body. 3D modeling was also needed instead of 2D axisymmetric modeling since non-symmetric large scale motion strongly influenced the predictions resulting in better agreement with the data. As computers become continually faster and cheaper, is anticipated that LES with appropriate subgrid chemistry modeling will be used as a routine design tool for natural gas-fired combustion systems in the near future. LES is already being used to solve difficult instability challenges facing the lean premixed gas turbine combustor community.
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