Numerical Modeling of Fuel/Air Mixing in a Dry Low-Emission Premixer

Large-eddy simulation of turbulent fuel/air mixing in a combustor that is a close approximation of a full-scale General Electric gas turbine combustor has been carried out to quantify the efficiency of the premixer of this combustor. Experimental studies show that the swirling fuel/air mixture generated by the dual annular counter-rotating premixer has significant spatial variation in the local equivalence ratio in the near field. This unmixedness can impact the emission characteristics of the combustor. The present study focuses on determining if this observed phenomenon can be simulated using a large-eddy simulation methodology that captures the dynamics of scalar mixing within the context of a new linear-eddy subgrid mixing model as well as a gradient-diffusion based subgrid closure. Results demonstrate that unmixedness observed in the experiments can be simulated with reasonable accuracy on a relatively coarse grid.

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