  The effect of swirl, premixedness and geometry has been investigated for
hydrogen enriched premixed flame using Large Eddy Simulation (LES) with a
Thickened Flame (TF) model. Swirl strength has been varied to study the effects
of swirl on flame behavior in a laboratory-scale premixed combustor operated
under atmospheric conditions. In addition, the levels of premixedness and
geometry have also been changed to study the role of these quantities on flame
behavior. The turbulent flow field and the chemistry are coupled through TF
model. In the LES-TF approach, the flame front is resolved on the computational
grid through artificial thickening and the individual species transport
equations are directly solved with the reaction rates specified using Arrhenius
chemistry. Good agreement is found when comparing predictions with the
published experimental data including the predicted RMS fluctuations. Also, the
results show that higher swirl strength and increase in level of premixedness
make the system more susceptible to upstream flame movement due to higher
combustibility of hydrogen, which increases the reaction along the flame front,
thereby raises temperature in the reaction zone and leads to combustion induced
vortex breakdown (CIVB). Moreover, upstream flame movement is always observed
at higher swirl strength irrespective of level of premixedness and burner
geometry, whereas the premixed systems exhibit stable behavior while operating
at low swirl.
