Aerodynamic tip desensitization in axial flow turbines
Abstract (Summary)iii The leakage flow near the tip of unshrouded rotor blades in axial turbines imposes significant thermal loads on the blade. It is also responsible for up to a third of aerodynamic losses in a turbine stage. The leakage flow, mainly induced by the pressure differential across the rotor tip section, usually rolls into a stream-wise vortical structure near the suction side of the blade tip. The current study uses several concepts to reduce the severity of losses introduced by the leakage vortex. Three tip desensitization techniques, both active and passive, are examined. Coolant flow from a tip trench is used to counter the momentum of the leakage jet. Next, a very short winglet obtained by slightly extending the tip platform in the tangential direction is investigated. Lastly, variations of the widely used concept of squealer tip are studied. The current investigation is performed in the Axial Flow Turbine Research Facility (AFTRF) of the Pennsylvania State University. Rotating frame five hole probe measurements as well as stationary frame phase averaged total pressure measurements downstream of a single stage turbine facility are taken. A method of studying the heat transfer coefficient on the blade tip is also developed. The study enables one to draw conclusions about the nature of the flowfield in the rotor tip region. It also shows that significant efficiency gains might be possible by using some of these techniques.
School Location:USA - Pennsylvania
Source Type:Master's Thesis
Date of Publication: