Session: 12-02: End-wall and Tip Film Cooling

Paper Number: 153364

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 

In the context of today's dry-low emission (DLE) gas turbines, the demand for efficient endwall cooling has surged, given that the flat temperature distribution amplifies the thermal stress. 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, which arise from the interaction between the endwall boundary layer and the vane surface. To account for the effects of Reynolds- and Mach numbers but also for the influence of the radial pressure gradient, experiments were conducted on various slot and hole designs in an annular sector cascade. This cascade, comprising four axisymmetrically designed nozzle guide vanes, was set up in the high-speed turbine test facility at the Institute of Fluid Mechanics and Fluid Machinery, University of Kaiserslautern-Landau, Germany.

The experimented slot configurations differed in attributes like their width, axial placement, and exit angle. In contrast, the hole designs were varied based on their shape (e.g., cylindrical, laidback, fan-shaped), spatial arrangement (e.g., single row, double row), diameter, and exit angle. Every design underwent testing across a broad range of blowing ratios, under both unity and engine-like density ratios. To further examine how Mach and Reynolds numbers affect the interaction between coolant and secondary flow, the study investigated three different pressure ratios (1.48, 1.15, and 1.05).

Part 2 of this study addresses the effects of film cooling on heat transfer with respect to local and averaged heat transfer coefficients. The measurements were conducted with an internally cooled endwall insert that was covered with an insulation layer of constant thickness. The temperature distribution of the flow-facing surface was measured by IR thermography, with the heat flux being calculated by assuming 1D heat conduction within the insulation layer. Additionally, five-hole probe measurements were performed in the endwall region of the cascade outlet to assess the aerodynamic impact of coolant injection.

Presenting Author: Moritz Klappenberger University of Kaiserslautern-Landau

Presenting Author Biography: Studied mechanical engineering at the University of Kaiserslautern-Landau, currently doing his PhD Institute of Fluid Mechanics and Fluid Machinery (SAM), research focus: film cooling in highly loaded nozzle guide vanes.

Authors:

Christian Landfester German Aerospace Center
Moritz Klappenberger University of Kaiserslautern-Landau
Martin Böhle University of Kaiserslautern-Landau
Robert Krewinkel Graz University of Technology