Comparisons of Endwall Overall Effectiveness From Two Film Hole Distribution Patterns at Low and High Exit Mach Numbers

Abstract

In this paper, detailed overall cooling effectiveness and associated flow patterns are presented for two distinct film hole distribution patterns over a turbine endwall: an axial-row pattern and an iso-Mach number line row pattern. Measurements, in combination with numerical simulations, are performed in a scaled-up cascade. Thermal protection for the endwall is achieved by jet-array impingement on the cold side and discrete film cooling on the hot-gas side, combined with purge air from an inclined slot that simulates the upstream seal cavity. Infrared (IR) thermography techniques are used to obtain overall effectiveness in a wide range of coolant flow ratios of 1.5–3.8%. Mach numbers at the exit of the vane cascade are 0.25 and 0.70, representing the variations of engine operating conditions. Overall effectiveness measurements and computational flowfields show that the iso-Mach number line hole pattern outperforms the hole pattern with axial rows of holes in terms of overall effectiveness levels and thermodynamic energy losses, regardless of coolant flow ratios. Increasing Mach number increases overall effectiveness levels on the endwall and higher Mach numbers generate higher effectiveness improvement for the iso-Mach number line arrangement, relative to the axial-row configuration. Additionally, adding purge air to the endwall considerably improves the overall effectiveness levels and purge air performs better for the axial-row pattern due to no direct interactions with downstream discrete coolant injection.