Experimental Study of Endwall Film Cooling and Heat Transfer for Different Upstream Slot and Hole Geometries in an Annular Sector Cascade Under High-Speed and Low-Speed Conditions, Part 1: Film Cooling Effectiveness

Abstract

Endwall film cooling in dry-low emission (DLE) gas turbines is crucial due to increased thermal loads from flat temperature profiles. Cooling strategies typically employ discrete holes or utilize purge air that exits from the gaps between adjacent turbine components. The downstream propagation of coolant, whether from discrete holes or component gaps, is significantly influenced by secondary flow patterns. To investigate these cooling mechanisms under engine-representative conditions, tests were performed in a high-speed annular sector cascade with four axisymmetrically contoured nozzle guide vanes (NGVs) at the University of Kaiserslautern-Landau. The study examined slot geometries, varying in width, axial location, and exit angle, as well as different hole configurations, including variations in shape (e.g., cylindrical, fan-shaped, Nekomimi), arrangement (single row, double row), and exit angle. To account for the influence of Mach and Reynolds numbers, experiments were conducted at pressure ratios between 1.48 and 1.05, with additional variation of the density ratio between unity and engine-like conditions. Film cooling effectiveness was measured using the pressure-sensitive paint (PSP) technique. Results show that inclined slots and shaped hole designs provide superior cooling performance, particularly at high blowing ratios. While low-speed testing proves valid for most configurations, shaped holes exhibit sensitivity to operating conditions near the leading edge. The present article focuses on film cooling effectiveness, with heat transfer and aerodynamic effects addressed in Part II of this paper series.