High Temperature Turbine First Stage Vane Wake to Stator Heat Shield Interaction on Outer Casing

Emission reduction and efficiency increase are key targets for gas turbine design. One way to reduce emissions is to get a lower peak temperature, e.g. to replace a parabolic inlet temperature profile protecting edge areas (platforms, heatshields) by a flat temperature profile. Another possibility is to design compact turbines with smaller spacing between blade rows to reduce hot gas wetted areas. Both solutions result in higher thermal load on endwalls. At part interfaces, gaps need to be purged to prevent hot gas ingestion. Cooling air consumption leads to lower efficiencies. A better understanding of the thermal load on endwalls will offer cooling air reduction potential. This paper focuses on the purging gap between first stage vane and the downstream outer diameter heatshield. The requirements for the gap purge air depend on the vane wake. A generic, realistic geometry including the interfacial gap is studied. Computational fluid dynamic is used to understand the flow structure, the film cooling effectiveness and heat transfer coefficient. Film-cooling effectiveness are measured on a cascade bench by a steady-state thermochromic liquid crystal technique. Results are compared to CFD. A parametric study on the influence of blowing ratio is included.