Swirling flow effect on film cooling performance downstream of a sudden expansion

Experiments are performed to study and obtain the film cooling effectiveness in a film cooled circular pipe downstream of an abrupt 2.4:1 expansion with the presence of weak swirling flow in the mainstream. The swirling flow is generated by a flat-vaned swirler situated upstream before expansion. The radial temperature measurements are used to infer the flow structure and the rate of mixing of film jet with swirling flow. Experiments demonstrate that the size of the recirculation zone and the location of the reattachment point are significantly affected by the swirl and the film jet velocity. The recirculation zone has a very slow rate of mixing with film jet and results in a higher film cooling effectiveness. However, the reattachment of flow can impinge and destroy severely the film jet structure and results in a significant reduction in film cooling effectiveness. The system of governing equations and boundary conditions are used to derive the dimensionless parameters that affect the film cooling performance. In the experiments, the blowing parameter ranged from 0.5 to 2.0, and the swirl number from 0 to 0.6. Correlations for film cooling effectiveness are presented.