Review of pressure flow losses reduction methods in axial turbines

This paper investigates the methods that enhance the aerodynamic performance of axial turbine stages by addressing pressure-based flow losses. Considering the latest requirements for turbine blade performance, the main focus is centered on minimizing the formation of vortices from secondary flows and tip leakage losses, which are the main factors contributing to efficiency reductions. This study explores various passive, active, and mixed flow control techniques to highlight the cases with the most notable improvements that have the potential to be implemented. As a classification, the methods are categorized based on a common specific criterion, as there are fixed geometry configurations such as winglets and suction slots, film cooling enhancements, or the integration of plasma actuators for controlling flow disturbances and enhancing cooling efficiency. Furthermore, unique concepts within these categories were also reviewed with the intention of creating a more open perspective in the realm of improving turbine flow losses. It was noted that similar outcomes are achieved through different approaches, and the most outstanding performances in pressure losses were obtained with oscillatory blowing and plasma actuators mounted at the tip, whereas suction side slots demonstrated the best behavior of vortices. None of these can be classified as a mixed method as expected, reinforcing the fact that it is not so relevant what type of method is used, but rather what breakthroughs can be obtained from it.