Controlling secondary flows in very highly-loaded low-pressure turbine cascades

This thesis documents experimental and computational results of a research program investigating the aerodynamic losses generated by extremely highly loaded low-pressure turbine blades, with particular focus on the three-dimensional flow near the endwall. The study identifies the physical mechanisms associated with loss generation and documents changes in the flow field that result from the application of passive flow control techniques. The experimental study was conducted in Carleton University's low-speed, linear cascade wind tunnel. Quantitative results include seven-hole pneumatic probe pressure measurements downstream of the cascade to assess blade row losses, as well as detailed measurements within the blade passage to track the development of flow structures. Qualitative results in the form of oil surface flow visualization on the endwall and blade suction surface are used to assist in the interpretation of the physics. The complementary computational studies were performed using Reynolds-averaged Navier-Stokes (RANS) simulations, providing detailed resolution of the various vortical structures comprising the endwall flow.;The work examined two passive flow control techniques for mitigating endwall loss. The techniques were applied to very high-lift, low-pressure turbine airfoils with the goal of expanding the design space. The airfoils and both flow control techniques were designed by Pratt & Whitney Aircraft (PWA) using proprietary tools. It was found that endwall loss could be significantly reduced and the mechanisms of loss reduction were identified. The loss measurements have allowed plausible limits to be defined for a high-lift replacement of the baseline airfoil used in the study.