Purge–Mainstream Interactions in a Turbine Stage With Rotor Endwall Contouring

Abstract

Purge flows are prevalent in modern gas turbine design, allowing for increased turbine entry temperatures. The purge flow passes through a rim seal and interacts with the mainstream flow, modifying the blade secondary flow structures and reducing stage efficiency. These structures may be controlled using end wall contouring (EWC), though experimental demonstration of their benefit is seldom reported in the literature. The optically accessible turbine at the University of Bath was designed to directly measure and visualize the flow field within the blade passage for a rotor with EWC. The single-stage turbine enables phase-locked flow field measurements with volumetric particle image velocimetry (PIV). Purge flow was supplied to investigate a range of operating conditions in which the secondary flow structures were modified. The modular turbine rotor allowed for expedient change of a bladed ring, or bling, featuring non-axisymmetric EWC. The identified secondary flow structures were the pressure-side leg of the horse shoe vortex (PS-HSV) and an egress vortex (EV) of concurrent rotational direction. An increase in purge flowrate monotonically shifted the EV toward the suction-side (SS) of the adjacent blade. The migration of the PS-HSV toward the SS caused the two aforementioned vortices to merge. The EWC rotor design included a leading-edge (LE) feature to alter the PS-HSV and a trough to guide the EV low spanwise in the passage and maintain displacement from the adjacent suction-side. The EWC rotor was found to be effective at altering the formation and positioning of the secondary flow structures at a range of purge flow conditions.