Effects of Upstream Platform Geometry on the Endwall Flows of a Turbine Cascade

Abstract

This paper describes the effect that the endwall geometry has on the endwall flows in the vicinity of the blade platform in a low-pressure turbine. The aim of this work is to assess the effect on blade performance of a step in hub diameter just ahead of the blade row. The blade profile under consideration is of high aspect ratio and characterized by a large pressure surface separation bubble. The tests are conducted on a linear cascade and the experimental results are supported by numerical simulations. Two different steps are employed, i.e., forward facing and backward facing steps. Furthermore, the size of the step and the thickness of the inlet endwall boundary layer are also varied. It was found that the presence of the step ahead of the blade row can significantly alter the structure and the strength of the endwall flows. A backward facing step gives rise to lower losses when compared with a flat endwall. However, the effect is found to be dependent on the step height and the thickness of the approaching boundary layer. A forward facing step, on the other hand, produces higher losses than a flat endwall.