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Show respectively. The domain is filled with a propane-air mixture with an equivalence ratio of 0.75. The inlet velocity V 0 is equal to 50 m/s and the fresh gas temperature T 0 is 300 K. Figure 14 shows calculation prediction of the flame surface density field. The presence of five reaction zones and six hot gas recirculating zones can be observed. Compared to Figure 12, where the same furnace is equipped with only one injector, Figure 14 shows also the importance of flame confinement due to the reaction zones issued from the neighbooring injectors and also due walls. The influence of inlet velocity can be deduced from comparison of case 5 (Vo= 100 m/s) and case 6 (Vo = 50 m/s). In case 5, the flame is longer than in case 6. Case 7 : Gas turbine This case corresponds to a simplified two-dimensionnal gas turbine combustor. This configuration is similar to that of a recent numerical study carried out by Fricker et al. [6] at the Nasa Lewis Research Center using the new code ALLSPD-3D. This combustion chamber is called GE-E3 (General Electric-E3) combustor. Note that due to the absence of dimensions of the GE-E3 combustor in Fricker et al., we have taken the height and lenght of the combustion chamber (Figure 15) to be respectively 160 and 300 m m . The computational grid used has 71 x 52 nodes in the longitudinal and transversal directions, respectively. The domain is filled with a propane-air mixture with an equivalence ratio of 0.7. The inlet velocity V 0 is equal to 100 m/s and the fresh gas temperature T 0 is 300 K. The results that follow are not to be compared directly with those of Fricker et al. [6], since the geometry is not the same. However, they are presented to show that our model can be adapted to arbitrary geometries and give logical results. The ignition is done by imposing a fixed value of flame surface density behind the obstacle separating the two entries of the combustor. The flame surface predicted by our model (Figure 16) takes place in the two stages of the combustor and more intensely in the upper one. Note that numerical results from the code ALLSPD-3D gives an unrealistic temperature maximum of 3200 K (The fresh gas temperature is 760 K ) just behind the entries of the two stages combustor. Our model gives 1860 K (the fresh gas temperature is 300 K ) at the combustor exit (Figure 17) and 2230 K if the fresh gas temperature is 760 K. In reality, the exit temperature is lower due to dilution by fresh gas (by-pass) which acts as a combustor cooler. Howerver, it is a reasonable prediction owing to the absence of dilution by fresh air in our calculations. CONCLUSION A new turbulent premixed combustion model is briefly reviewed in this paper. The mean flame surface density and heat release rate determined numerically are compared to experimental measurements of the light emission from the reaction zone for various combustors. The agreement is qualitatively and quantitatively good. The main features are retrieved in most cases where experimental results are available. The model may be completed to include flame curvature and propagation effects on the production/destruction mechanisms of the flame area. REFERENCES 1- Blint, J. 'The relationship of laminar flame width to flame speed" Combustion Science and technology, 49, p.79-92, 1986. 2- Candel, S.M., and Poinsot, T. " Flame strech and the balance equation for flame area" Combustion Science and technology, 70, 1-15, 1990. 3- Candel, S., VeynanteJJ)., Lacas, F., Maistret, E., Darabiha, N. and Poinsot, T. "Coherent Flame Model : applications and recent extensions". In Advances in combustion modelling, Larrouturou, B. Singapore : World Scientific, 19-64, 1991. 4- Cant, R.S., Pope, S.B. and Bray, K.N.C. "Modelling of flamelet surface to volume ratio in turbulent premixed combustion"23/tf Symposium (International) on Combustion. Pittsburgh: The Combustion Institute, 809-815, 1990. 5- Duclos, J.M., Veynante, D., and Poinsot, T. "A comparison of flamelets models for premixed turbulent combustion" Combustion and Flame, 95, 101-107, 1993. 6- Fricker, D. M., Chen, K.H., Duncan, B., Lee, J., Moder, J.P. and Quearly, A. "ALLSPD-3D a new combustion code from Nasa Lewis Research Center", A G T S R Combustion III workshop, March 1996., 7 |
