Gokulakrishnan et al. (2009): Turbulence-Chemistry interaction in Blow-out

Title

Influence of Turbulence-Chemistry Interaction in Blow-out Predictions of Bluff-Body Stabilized Flames

Authors

Ronnuthurai Gokulakrishnan, Ravi Bikkani, Michael S. Klassen, Richard, J. Roby, and Barry V. Kiel

Summary

LES were performed to investigate the effect of turbulence-chemistry interaction on flame instability and flame-vortex interaction in bluff-body stabilized premixed flames (propane-air flames).

The tested models were followings:

1. Semi-global reduced mechanism vs. Skeletal mechanisms
2. Laminar chemistry (LC) vs. Eddy Dissipation Concept (EDC)

The simulations were performed at 0.6 and 0.45 equivalence ratios. LES predictions with the EDC model show that the blow-out occurs at 0.6 of equivalence ratio as observed experimentally.

• LES with Skeletal Propane mechanism (EDC vs. LC)
  1. When the chemical source term was resolved with the EDC model the flame starts to break-up at 0.6 of \(\phi\).
  2. Further reduction of \(\phi\) to 0.45 shows a complete blow-out of the flame.
  3. But when the simulation with LC model where the sub-grid scale fluctuations in the chemical source were ignored, complte blow-out was not observed.
  4. With the LC model, no significant difference in the flame structure between the two equivalence ratios: This can be attributed to the absence of the sub-grid scale turbulence-chemistry interactions.
  5. When the EDC is used, the effect of turbulence has dissipated the flame in the wake region.
  6. With the LC model, the asymmetric Von-Karman vortex shedding is suppresed in the vicinity of the V-gutter: This is due to the expansion of fluid caused by the heat-release which reduce the vorticity magnitude.
  7. The instantaneous vorticity profiles demonstrate that the EDC results exhibit an asymmertical Von-Karman vortex shedding consistently for two \(\phi\) cases.
• LES with 44-step Reduced Propane mechanism (EDC vs. LC)
  1. Same result as (7) above was observed with this test.
  2. The flame instability leading to the blow-out conditions observed in LES-EDC modeling results can be attributed to asymmetrical Von-Karman vortex shedding due to the weakening of the dilatation effects.

In conclusion, the flame structure predicted by the LES is same for both kinetics models when the LC combustion model is used. However, when the sub-grid scale turbulence chemistry interactions were resolved using the EDC, more detailed Skeletal mechanism exhibit different flame structure at 0.6 equivalence ratio from the other.