Effect of Cooling Air on Swirl Combustor

This paper presents the numerical study of the turbulent swirling flow in a combustor and the effect of cooling air, which has practical applications in industrial furnaces and jet engines. Cooling air is used to protect the combustor wall from burnout, while allowing the combustion to occur at higher temperature. The governing differential equations using k - ε turbulence model closure are solved by a control-volume based iterative finite difference technique. Computations are done for constant vane angle type swirl generation at inlet. Different swirl numbers up to 1.5 are considered. To study the effect of cooling air on the combustor performance, calculations are repeated for two different velocities of the cooling air jet. The predicted distribution of the mean axial and tangential velocities, turbulence kinetic energy and streamline plots are discussed in the article. With the increase of swirl strength, secondary on-axis recirculation due to swirl is observed. The swirl produces larger turbulence kinetic energy and enhances mixing rate, thus require shorter combustor length. The interaction between the non-swirling cooling air and swirling core flow also increases the generation of turbulence kinetic energy and mixing rate. The capability of the computational model for predicting recirculating flows is tested by comparing the results with available experimental data and found to have reasonable matching.Journal of Mechanical Engineering Vol.37 June 2007 pp.1-9doi:10.3329/jme.v37i0.811