Effects of Blade Loading Distribution on Aerodynamic Performance of Ultra-High Lift LP Turbine Airfoils Under the Influences of Wake Passing and Freestream Turbulence

Abstract

This paper deals with studies on the flow field around three types of linear cascades of low pressure turbine (LPT) airfoils with different chordwise loading distributions, while keeping the aerodynamic loading index almost the same. The purpose of the low-speed linear cascade study is to clarify the performance of newly designed two ultra high-lift blade (UHL blade) and compare each of them to that of the conventional LPT blade (Base Model) with low solidity through the measurements of boundary layers accompanied by separation bubble for low Reynolds number conditions. Cylindrical bars on the timing belts work as wake generator to emulate upstream stator wakes that impact the boundary layer on the airfoil suction surface. Freestream turbulence is also enhanced by use of passive turbulence grid. In addition to the pneumatic probe measurements of the midspan loss characteristics of each of the cascades, hot-wire probe measurement is conducted over the blade suction surface to understand to what extent and how the interaction of incoming wakes as well as freestream turbulence affect the boundary layer and separation bubble. Computational Fluid Dynamics (CFD) analyses are also applied to the flow fields around the cascades, mainly using Large-Eddy Simulation (LES) with dynamic Smagorinsky subgrid scale model.