Reducing Secondary Flow Losses in Low-Pressure Turbines With Blade Fences. Part I: Design in an Engine-Like Environment

This paper deals with the design of passive control devices for reducing the impact of secondary flows on the aerodynamics of low-pressure turbine (LPT) stages. A novel kind of device is introduced which consists of shelf-like fences to be added to the blade surface. Such a device is intended to harm the development of secondary flows, thus reducing losses and flow turning devi-ation with respect to the naked blade. The first part of this work is devoted to the design of the blade fences, whereas the second part addresses the experimental validation of the device. The blade fences are designed on a LPT stator vane, in an engine-like environment. As secondary flows generated by one blade row produce their major effects on the downstream one, and hence on the stage performance, the assess-ment is performed on a stator-rotor configuration. Steady calcu-lations are considered for the design, then the optimal geometry is verified via unsteady calculations to include the effects of the actual interaction. The geometry and layout of the blade fences are effectively handled by means of a parametric approach, which enables the fast generation of several configurations. An optimization procedure, based on Artificial Neural Networks (ANNs) is exploited to drive the fences design. The analysis of the relative merit of each solution is carried out using a state-of-the-art CFD approach. Finally, a detailed comparison between the naked blade and the one equipped with fences is presented, and the physical mechanisms responsible for the mitigation of secondary flow losses are discussed in detail.