High pressure turbines are nowadays designed to a point where most design enhancements only yield marginal efficiency improvements. This challenges research facilities to reliably resolve ever smaller differences in efficiency caused by individual design changes. In recent years, immense efforts towards such highly accurate delta-efficiency measurements have been undertaken at the Large Scale Turbine Rig (LSTR). This paper comprises an overview of the applied methodology and the achievements on the basis of various validation cases.
By thoroughly controlling the operation point and accounting for all variables affecting the efficiency η, the rig can resolve efficiency-differences Δη of ±0.1 % for a single day measurement. Four benchmark cases are investigated to validate the rig’s capabilities. First, the influence of tip clearance is investigated for a squealer-type geometry for swirling inflow. It is found that for an increase in tip clearance of 1 %, η is decreased by 2.68 %. Then, it is shown that a winglet-type tip geometry may improve the efficiency by Δη 0.33% in comparison to the squealer tip. Third, it is shown that these trends are similar for plain inflow, however swirl decreases efficiency by up to 1.25 % in comparison to plain inflow. Finally, the clocking-position of the combustor-module relative to the nozzle guide vanes is varied leading to efficiency differences of up to 0.52 %.