Darryl E. Metzger Memorial Session Paper: A Summary of the Cooled Turbine Blade Tip Heat Transfer and Film Effectiveness Investigations Performed by Dr. D. E. Metzger

Abstract

The clearance gap between the stationary outer air seal and blade tips of an axial turbine allows a clearance gap leakage flow to be driven through the gap by the pressure-to-suction side pressure difference. The presence of strong secondary flows on the pressure side of the airfoil tends to deliver air from the hottest regions of the mainstream to the clearance gap. The blade tip region, particularly near the trailing edge, is very difficult to cool adequately with blade internal coolant flow. In this case, film cooling injection directly onto the blade tip region can be used in an attempt to directly reduce the heat transfer rates from the hot gases in the clearance gap to the blade tip. The present paper is intended as a memorial tribute to the late Professor Darryl E. Metzger, who made significant contributions in this particular area over the past decade. A summary of this work is made to present the results of his more recent experimental work, which was performed to investigate the effects of film coolant injection on convection heat transfer to the turbine blade tip for a variety of tip shapes and coolant injection configurations. Experiments are conducted with blade tip models that are stationary relative to the simulated outer air seal based on the result of earlier works that found the leakage flow to be mainly a pressure-driven flow, which is related strongly to the airfoil pressure loading distribution, and only weakly, if at all, to the relative motion between blade tip and shroud. Both heat transfer and film effectiveness are measured locally over the test surface using a transient thermal liquid crystal test technique with a computer vision data acquisition and reduction system for various combinations of clearance heights, clearance flow Reynolds numbers, and film flow rates with different coolant injection configurations. The present results reveal a strong dependency of film cooling performance on the choice of the coolant supply hole shapes and injection locations for a given tip geometry.

Influence of Different Rim Widths and Blowing Ratios on Film Cooling Characteristics for a Blade Tip

“…Yang and Diller [4] reported local heat transfer coefficients on a squealer tip experimentally, using a single point measurement on the cavity bottom. Kim et al [5] presented the results of Metzger's important experimental work, which showed the heat transfer and film cooling effectiveness with a rectangular tip model. Bunker and Bailey [6,7] experimentally investigated the heat transfer coefficient and leakage flow.…”

Turbine Blade Film Cooling Using PSP Technique

“…A review of the work done on tip-gap film cooling by Dr. Metzger's group is available in Kim et al (1995). More recently, Kwak and Han (2003a,b) and Christophel et al (2005) used thermal imaging techniques (Liquid crystal and IR thermography respectively) to measure detailed film cooling effectiveness contours on the tip with holes on the tip region of the pressure side and on the tip.…”