Time-Dependent Simulation of Fuel-Flexible Gas-Turbine Burners
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Time-dependent computational fluid dynamics (CFD) and combustion modeling is used to predict burning velocity of fuel-air mixtures in a closed vessel and swirl-stabilized reacting flow in a representative turbine engine fuel nozzle. The purpose of the modeling is the development of analysis techniques for studying the effect of fuel flexibility in gas turbine engines. In the closed-vessel case, the fuel burning velocity is computed from the spherically propagating flame in the same way that an equivalent experiment would be performed using premixed gases. This model can be used as a guide for designing and performing flame speed experiments at gas turbine conditions. In the turbine engine fuel nozzle, an experimentally characterized, swirl-stabilized reacting flow is investigated with regard to ignition, piloting, flame stability, and pollutant emissions. Simulations using both unsteady Reynolds-averaged Navier-Stokes' (URANS) and Large-Eddy Simulation (LES) techniques, together with accurate geometry modeling, establish the aerodynamic and combustion flow environment and provide good agreement with experimental data for pollutant emissions. It was found that modeling the full geometry of the fuel injector produced the best agreement with available data and was superior than assuming an axisymmetric geometry with premixed fuel and air. The model can be used as a starting point for parametric studies related to fuel flexibility simulations.
