EFFECT OF SECONDARY AIR ON THE FLOW FIELD INSIDE A GAS TURBINE COMBUSTOR

In the present work, the air flow pattern inside a gas turbine combustor is studied. The effect of primary air swirl, secondary to primary air ratio and secondary air direction on the flow field is investigated. For this purpose, a test rig was constructed including a vertical combustor provided with an air swirler, primary and secondary air lines. Four air swirlers having the same blockage ratio of 0.72 were used. The swirlers have different vane angles of 15o, 30o, 45o, and 60o which generate swirl numbers of 0.23, 0.50, 0.87 and 1.5, respectively. A three dimensional model was used to simulate the flow characteristics by using the computational fluid dynamics package Fluent 6.3. The measured and the calculated reverse flow zone sizes inside the combustor show a good agreement. Using the combustor with restricted end, the boundaries of the reverse flow zone for different swirl numbers up to 1.5, are performed completely inside the combustor. Increasing the swirl number, the size of the reverse flow zone is also increased in its length and width. Using the secondary air in tangential direction with secondary to primary air ratio of unity and swirl number of 0.87 produces minimum size of the  reverse flow zone. The size of the reverse flow zone for forward direction is larger than that of backward one. Increasing the swirl number and the secondary to primary air mass ratio, the turbulence intensity level also increased. This level is higher for tangential direction than the other ones.