Effects of Tip Clearance Gap and Exit Mach Number on Turbine Blade Tip and Near-Tip Heat Transfer

This study focuses on local heat transfer characteristics on the tip and near-tip regions of a turbine blade with a flat tip, tested under transonic conditions in a stationary, 2-D linear cascade with high freestream turbulence. The experiments were conducted at the Virginia Tech transonic blow-down wind tunnel facility. The effects of tip clearance and exit Mach number on heat transfer distribution were investigated on the tip surface using a transient infrared thermography technique. In addition, thin film gages were used to study similar effects in heat transfer on the near-tip regions at 94% height based on engine blade span of the pressure and suction sides. Surface oil flow visualizations on the blade tip region were carried-out to shed some light on the leakage flow structure. Experiments were performed at three exit Mach numbers of 0.7, 0.85, and 1.05 for two different tip clearances of 0.9% and 1.8% based on turbine blade span. The exit Mach numbers tested correspond to exit Reynolds numbers of 7.6 × 105, 9.0 × 105, and 1.1 × 106 based on blade true chord. The tests were performed with a high freestream turbulence intensity of 12% at the cascade inlet.Results at 0.85 exit Mach showed that an increase in the tip gap clearance from 0.9% to 1.8% translates into a 3% increase in the average heat transfer coefficients on the blade tip surface. At 0.9% tip clearance, an increase in exit Mach number from 0.85 to 1.05 led to a 39% increase in average heat transfer on the tip. High heat transfer was observed on the blade tip surface near the leading edge, and an increase in the tip clearance gap and exit Mach number augmented this near-leading edge tip heat transfer. At 94% of engine blade height on the suction side near the tip, a peak in heat transfer was observed in all test cases at s/C = 0.66, due to the onset of a downstream leakage vortex, originating from the pressure side. An increase in both the tip gap and exit Mach number resulted in an increase, followed by a decrease in the near-tip suction side heat transfer. On the near-tip pressure side, a slight increase in heat transfer was observed with increased tip gap and exit Mach number. In general, the suction side heat transfer is greater than the pressure side heat transfer, as a result of the suction side leakage vortices.Copyright © 2013 by ASME

[1]  Thomas E. Diller,et al.  Simultaneous Heat Flux and Velocity Measurements in a Transonic Turbine Cascade , 2005 .

[2]  Nicole L. Key,et al.  Comparison of Turbine Tip Leakage Flow for Flat Tip and Squealer Tip Geometries at High-Speed Conditions , 2006 .

[3]  P. R. Dodge,et al.  Rotor-Tip Leakage: Part I—Basic Methodology , 1982 .

[4]  M. L. G. Oldfield,et al.  The theory of advanced multi-layer thin film heat transfer gauges , 1987 .

[5]  Je-Chin Han,et al.  Heat Transfer and Flow on the Squealer Tip of a Gas Turbine Blade , 2000 .

[6]  Steen A. Sjolander,et al.  Measurements of the Flow in an Idealized Turbine Tip Gap , 1995 .

[7]  T. V. Jones,et al.  Heat-transfer measurements in short-duration hypersonic facilities , 1973 .

[8]  John E. LaGraff.  Unsteady Heat Transfer on the Turbine Research Facility at Wright Labs , 2000 .

[9]  Srinath V. Ekkad,et al.  A Transient Infrared Thermography Method for Simultaneous Film Cooling Effectiveness and Heat Transfer Coefficient Measurements From a Single Test , 2004 .

[10]  Steen A. Sjolander,et al.  Measurements of the Flow in an Idealized Turbine Tip Gap , 1994 .

[11]  Je-Chin Han,et al.  Heat-Transfer Coefficients of a Turbine Blade-Tip and Near-Tip Regions , 2002 .

[12]  Karen A. Thole,et al.  The Effects of Freestream Turbulence, Turbulence Length Scale, and Exit Reynolds Number on Turbine Blade Heat Transfer in a Transonic Cascade , 2011 .

[13]  R. Cress.  Turbine Blade Heat Transfer Measurements in a Transonic Flow Using Thin Film Gages , 2006 .

[14]  Karen A. Thole,et al.  Effects of Large Scale High Freestream Turbulence and Exit Reynolds Number on Turbine Vane Heat Transfer in a Transonic Cascade , 2009 .

[15]  Wing Ng,et al.  Experimental Measurements and Modeling of the Effects of Large-Scale Freestream Turbulence on Heat Transfer , 2007 .

[16]  Li He,et al.  Overtip Shock Wave Structure and Its Impact on Turbine Blade Tip Heat Transfer , 2011 .

[17]  D. E. Metzger,et al.  HEAT TRANSFER AT THE TIP OF AN UNSHROUDED TURBINE BLADE , 1982 .

[18]  Robert J. Moffat,et al.  Describing the Uncertainties in Experimental Results , 1988 .

[19]  Srinath V. Ekkad,et al.  Effect of Tip Gap and Squealer Geometry on Detailed Heat Transfer Measurements Over a High Pressure Turbine Rotor Blade Tip , 2004 .

[20]  Zhenping Feng,et al.  Investigation of Leakage Flow and Heat Transfer in a Gas Turbine Blade Tip With Emphasis on the Effect of Rotation , 2008 .

[21]  O. Popp,et al.  An Investigation of Heat Transfer in a Film Cooled Transonic Turbine Cascade: Part I — Steady Heat Transfer , 2000 .

[22]  Richard J. Anthony,et al.  Showerhead Film Cooling Performance of a Turbine Vane at High Freestream Turbulence in a Transonic Cascade , 2012 .

[23]  Ali Ameri,et al.  Heat Transfer and Flow on the First-Stage Blade Tip of a Power Generation Gas Turbine: Part 1—Experimental Results , 2000 .

[24]  Je-Chin Han,et al.  Heat Transfer and Flow on the Squealer Tip of a Gas Turbine Blade , 2000 .

[25]  John Moore,et al.  Tip leakage flow in a linear turbine cascade , 1987 .