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 2: Heat Transfer and Aerodynamics

Abstract

Endwall film cooling strategies typically involve the employment of discrete holes or harness purge air that exits from the gaps between adjacent turbine components. Whichever the technique, the propagation of the coolant is predominantly governed by the secondary flows. To investigate these effects, experiments were conducted on various slot and hole designs in a high-speed annular sector cascade at the University of Kaiserslautern-Landau, Germany. The configurations included slots of different widths, axial placement, and exit angles, as well as hole designs varying in shape (e.g., cylindrical, fan-shaped, Nekomimi), spatial arrangement, and exit angle. All designs were tested across a broad range of blowing ratios at three different pressure ratios (1.48, 1.15, and 1.05) to examine Mach and Reynolds number effects. This study consists of two parts. The first was concerned with film cooling effectiveness. Part II addresses the effects of film cooling on heat transfer and aerodynamics, combining IR thermography measurements on the endwall with five-hole probe investigations at the passage outlet. The results show that coolant injection significantly influences both aerodynamics and heat transfer, with the specific impact depending strongly on injection geometry and operating conditions. While perpendicular injection leads to increased secondary flow losses and heat transfer, inclined injection provides better aerodynamic and thermal performance. Most notably, the heat transfer characteristics exhibit strong Mach number sensitivity in the passage throat, underlining the importance of high-speed testing.