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Title: Optimization of endwall film-cooling in axial turbines
Author: Thomas, Mitra
Awarding Body: University of Oxford
Current Institution: University of Oxford
Date of Award: 2014
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Considerable reductions in gas turbine weight and fuel consumption can be achieved by operating at a higher turbine entry temperature. The move to lean combustors with flatter outlet temperature profiles will increase temperatures on the turbine endwalls. This work will study methods to improve endwall film cooling, to allow these advances. Turbine secondary flows are caused by a deficit in near-wall momentum. These flow features redistribute near-wall flows and make it difficult to film-cool endwalls. In this work, endwall film cooling was studied by CFD and validated by experimental measurements in a linear cascade. This study will add to the growing body of evidence that injection of high momentum coolant into the upstream boundary layer can suppress secondary flows by increasing near-wall momentum. The reduction of secondary flows allows for effective cooling of the endwall. It is also noted that excess near-wall momentum is undesirable. This leads to upwash on the vane, driving coolant away from the endwall. A passive-scalar tracking method has been devised to isolate the contribution of individual film cooling holes to cooling effectiveness. This method was used to systematically optimize endwall cooling systems. Designs are presented which use half the coolant mass flow compared to a baseline design, while maintaining similar cooling effectiveness levels on the critical trailing endwall. By studying the effect of coolant injection on vane inlet total pressure profile, secondary flows were suppressed and upwash on the vane was reduced. The methods and insight obtained from this study were applied to a high pressure nozzle guide vane endwall from a current engine. The optimized cooling system developed offers significant improvement over the baseline.
Supervisor: Povey, Thomas; Gillespie, David Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Aerodynamics and heat transfer ; aerodynamics ; heat transfer ; film cooling ; turbine endwall cooling