This thesis presents an experimental study on the effect of geometry on the flow structure of experimental swirl-stabilized gas turbine burners. The purpose of this project was to test a number of geometric changes to a burner and determine how these changes affected the flow field in order to evaluate how they might affect a combustion process.
Tests were initially conducted in a water channel on several full-scale experimental burner models, which included the use of elliptic outlet geometries and a vortex breakdown stabilizer. Velocity and phase-averaged PLIF measurements are presented for the different burner configurations. More extensive measurements were then conducted in a cold flow air channel on a series of one-quarter scale experimental swirlers. The scale models were designed with different geometries in order to test the effect of different blade angles and spacings. The models were also tested with a vortex breakdown stabilizer and a mixing section located between the swirler outlet and the sudden expansion. A scale model burner with an elliptic outlet was also tested. Stereo PIV measurements are presented for the different configurations.
Water channel measurements identified axial oscillation of the vortex breakdown bubble as the primary driving mechanism behind combustion instabilities. Tests showed that the elliptic geometry damped oscillation of the breakdown bubble and the vortex breakdown stabilizer physically anchored the breakdown bubble inside the burner cone. Tests in the air channel showed that wider blade spacing resulted in a reduced swirl number and a weaker vortex breakdown. A wider blade angle was observed to increase the swirl and the strength of the vortex breakdown. Certain configurations of the breakdown stabilizer were seen to increase the strength of the vortex breakdown while other configurations forced it to form in an unstable configuration. The use of a mixing section at the swirler outlet caused the vortex breakdown bubble to propagate upstream inside of the mixing tube. The elliptic swirler exhibited a very complex flow structure, indicative of axis-switching.