Abstract:
Fuel-lean combustion is an area of significant interest in the domain of numerical combustion
modelling as it results in the lowering of the emissions of pollutants like CO and NOx from the
combustion chamber. However, the application of fuel-lean combustion also leads to flame
blowout, which is why flame stabilization mechanisms like the imparting of swirling motion
to the reactants are important to bring the instabilities resulting from lean combustion under
control. This work presents the numerical simulation of a benchmark experimental analysis of
lean combustion in a dual swirl partially premixed combustor using the Flamelet/Progress
Variable (FPV) and Eddy Dissipation Concept (EDC) combustion modelling techniques along
with the Detached Eddy Simulations turbulence modelling approach. Performance of each
model is analyzed based on its accuracy in capturing time-averaged parameters like axial, radial
and swirl velocities, temperatures, mixture fractions and species mass fractions, along with
important flow features like the development of recirculation zones. The numerical simulations
were set up and executed in the ANSYS Fluent CFD solver, and the reaction kinetics for the
Eddy Dissipation Concept were modelled using the GRI Mech 2.11 chemical kinetic
mechanism. The FPV approach achieved a considerably higher level of accuracy in capturing
the thermochemical parameters compared to EDC, which significantly overpredicted the fuel
consumption rate and time-averaged temperatures, while also predicting an unconventional
inner recirculation zone profile. Following the validation analysis, a parametric analysis was
performed using three combustor configurations featuring distinct inner swirler angles of 60,
62, and 64 degrees respectively. The major differences between the predicted flow features of
the three geometries included a broadened inner recirculation zone for the 62 degrees
configuration and a considerably narrow inner recirculation zone for the 64 degrees
configuration, which also predicted a highly pronounced outer recirculation zone where mixing
and reactions dominated as opposed to the inner recirculation zone.
