Cooling the Tip of a Turbine Blade Using Pressure Side Holes—Part II: Heat Transfer Measurements

2005 ◽  
Vol 127 (2) ◽  
pp. 278-286 ◽  
Author(s):  
J. R. Christophel ◽  
K. A. Thole ◽  
F. J. Cunha
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Turbine Blade ◽  
Suction Side ◽  
Leakage Flow ◽  
Pressure Side ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Net Heat Flux ◽  
Blade Tip

The clearance gap between a turbine blade tip and its associated shroud allows leakage flow across the tip from the pressure side to the suction side of the blade. Understanding how this leakage flow affects heat transfer is critical in extending the durability of a blade tip, which is subjected to effects of oxidation and erosion. This paper is the second of a two-part series that discusses the augmentation of tip heat transfer coefficients as a result of blowing from film-cooling holes placed along the pressure side of a blade and from dirt purge holes placed on the tip. For the experimental investigation, three scaled-up blades were used to form a two-passage, linear cascade in a low-speed wind tunnel. The rig was designed to simulate different tip gap sizes and film-coolant flow rates. Heat transfer coefficients were quantified by using a constant heat flux surface placed along the blade tip. Results indicate that increased film-coolant injection leads to increased augmentation levels of tip heat transfer coefficients, particularly at the entrance region to the gap. Despite increased heat transfer coefficients, an overall net heat flux reduction to the blade tip results from pressure-side cooling because of the increased adiabatic effectiveness levels. The area-averaged results of the net heat flux reduction for the tip indicate that there is (i) little dependence on coolant flows and (ii) more cooling benefit for a small tip gap relative to that of a large tip gap.

Cooling the Tip of a Turbine Blade Using Pressure Side Holes: Part 2 — Heat Transfer Measurements

2004 ◽  
Author(s):  
J. R. Christophel ◽  
K. A. Thole ◽  
F. J. Cunha
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Turbine Blade ◽  
Suction Side ◽  
Coolant Flow ◽  
Total Power ◽  
Leakage Flow ◽  
Pressure Side ◽  
Transfer Coefficients ◽  
Blade Tip

The clearance gap between a turbine blade tip and its associated shroud allows leakage flow across the tip gap from the pressure side to the suction side of the blade. Understanding how this leakage flow affects heat transfer is critical in extending blade tip durability in terms of oxidation, erosion, clearance, and overall turbine performance. This paper is the second of a two part series that discusses the augmentation of tip heat transfer as a result of blowing from the pressure side of the tip as well as dirt purge holes placed on the tip. For the experimental investigation, three scaled-up blades were used to form a two-passage linear cascade in a low speed wind tunnel. The rig was designed to simulate different tip gap sizes and coolant flow rates. Heat transfer coefficients were quantified by measuring the total power supplied to a constant heat flux surface placed on the tip of the blade and measuring the tip temperatures. Results indicate that increased blowing leads to increased augmentations in tip heat transfer, particularly at the entrance region to the gap. When combined with adiabatic effectiveness measurements, the coolant from the pressure side holes provides an overall net heat flux reduction to the blade tip but is nearly independent of coolant flow levels.

Measured Adiabatic Effectiveness and Heat Transfer for Blowing From the Tip of a Turbine Blade

2005 ◽  
Vol 127 (2) ◽  
pp. 251-262 ◽  
Author(s):  
J. R. Christophel ◽  
E. Couch ◽  
K. A. Thole ◽  
F. J. Cunha
Keyword(s):  
Heat Transfer ◽  
Turbine Blade ◽  
Suction Side ◽  
Leakage Flow ◽  
Transfer Coefficients ◽  
Forward Region ◽  
Cooling Effectiveness ◽  
Combustion Gas ◽  
Blade Tip ◽  
Blade Alloy

The clearance gap between the tip of a turbine blade and the shroud has an inherent leakage flow from the pressure side to the suction side of the blade. This leakage flow of combustion gas and air mixtures leads to severe heat transfer rates on the blade tip of the high-pressure turbine. As the thermal load to the blade increases, blade alloy oxidation and erosion rates increase thereby adversely affecting component life. The subject of this paper is the cooling effectiveness levels and heat transfer coefficients that result from blowing through two holes placed in the forward region of a blade tip. These holes are referred to as dirt purge holes and are generally required for manufacturing purposes and expelling dirt from the coolant flow when operating in sandy environments. Experiments were performed in a linear blade cascade for two tip-gap heights over a range of blowing ratios. Results indicated that the cooling effectiveness was highly dependent on the tip-gap clearance with better cooling achieved at smaller clearances. Also, heat transfer was found to increase with blowing. In considering an overall benefit of cooling from the dirt purge blowing, a large benefit was realized for a smaller tip gap as compared with a larger tip gap.

Comparison of Heat Transfer Measurement Techniques on a Transonic Turbine Blade Tip

2009 ◽  
Author(s):  
Devin O’Dowd ◽  
Qiang Zhang ◽  
Phil Ligrani ◽  
Li He ◽  
Stefan Friedrichs
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Turbine Blade ◽  
Transfer Coefficients ◽  
Adiabatic Wall ◽  
Steady State Condition ◽  
Heat Transfer Coefficients ◽  
Measure Surface Temperature ◽  
Blade Tip ◽  
Processing Techniques

The present study considers spatially-resolved surface heat transfer coefficients and adiabatic wall temperatures on a turbine blade tip in a linear cascade under transonic conditions. Six different measurement and processing techniques are considered and compared, including transient infrared thermography and thin-film heat flux gauges. Three methods use the same experimental setup, using a heater mesh to provide a near-instantaneous step-change in mainstream temperature, employing an infrared camera to measure surface temperature. The three methods use the same data but different processing techniques to determine the heat transfer coefficients and adiabatic wall temperatures. Two methods use different processing techniques to reconstruct heat flux from the temperature time trace measured. A plot of the heat flux versus temperature is used to determine the heat transfer coefficients and adiabatic wall temperatures. The third uses the classical solution to the 1-D non-steady Fourier equation to determine heat transfer coefficients and adiabatic wall temperatures. A fourth method uses regression analysis to calculate detailed heat transfer coefficients for a quasi-steady state condition using a thin-foil heater on the tip surface. The fifth method uses the infrared camera to measure the adiabatic wall temperature surface distribution of a blade tip after a quasi-steady state condition is present. Finally, the sixth method employs thin-film gauges to measure surface temperature histories at four discreet blade tip locations. With this approach, heat flux reconstruction is used to calculate the transient heat transfer coefficients and adiabatic wall temperatures. Overall, the present study shows that the infrared thermography technique with heat flux reconstruction using the Impulse method, is the most accurate and reliable method to obtain detailed, spatially-resolved heat transfer coefficients and adiabatic wall temperatures on a turbine blade tip in a linear cascade.

Heat Transfer Coefficients on the Squealer Tip and Near Tip Regions of a Gas Turbine Blade With Single or Double Squealer

2003 ◽  
Author(s):  
Jae Su Kwak ◽  
Jaeyong Ahn ◽  
Je-Chin Han ◽  
C. Pang Lee ◽  
Robert Boyle ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Gas Turbine ◽  
Pressure Ratio ◽  
Suction Side ◽  
Pressure Side ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Blade Tip

Detailed heat transfer coefficient distributions on a gas turbine squealer tip blade were measured using a hue detection based transient liquid crystals technique. The heat transfer coefficients on the shroud and near tip regions of the pressure and suction sides of a blade were also measured. Squealer rims were located along (a) the camber line, (b) the pressure side, (c) the suction side, (d) the pressure and suction sides, (e) the camber line and the pressure side, and (f) the camber line and the suction side, respectively. Tests were performed on a five-bladed linear cascade with a blow down facility. The Reynolds number based on the cascade exit velocity and the axial chord length of a blade was 1.1×106 and the overall pressure ratio was 1.2. Heat transfer measurements were taken at the three tip gap clearances of 1.0%, 1.5% and 2.5% of blade span. Results show that the heat transfer coefficients on the blade tip and the shroud were significantly reduced by using a squealer tip blade. Results also showed that a different squealer geometry arrangement changed the leakage flow path and resulted in different heat transfer coefficient distributions. The suction side squealer tip provided the lowest heat transfer coefficient on the blade tip and near tip regions compared to the other squealer geometry arrangements.

Comparison of Heat Transfer Measurement Techniques on a Transonic Turbine Blade Tip

2010 ◽  
Vol 133 (2) ◽  
Author(s):  
D. O. O’Dowd ◽  
Q. Zhang ◽  
L. He ◽  
P. M. Ligrani ◽  
S. Friedrichs
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Turbine Blade ◽  
Infrared Camera ◽  
Transfer Coefficients ◽  
Adiabatic Wall ◽  
Steady State Condition ◽  
Heat Transfer Coefficients ◽  
Blade Tip ◽  
Processing Techniques

The present study considers spatially resolved surface heat transfer coefficients and adiabatic wall temperatures on a turbine blade tip in a linear cascade under transonic conditions. Five different measurement and processing techniques using infrared thermography are considered and compared. Three transient methods use the same experimental setup, using a heater mesh to provide a near-instantaneous step-change in mainstream temperature, employing an infrared camera to measure surface temperature. These three methods use the same data but different processing techniques to determine the heat transfer coefficients and adiabatic wall temperatures. Two of these methods use different processing techniques to reconstruct heat flux from the temperature time trace measured. A plot of the heat flux versus temperature is used to determine the heat transfer coefficients and adiabatic wall temperatures. The third uses the classical solution to the 1D nonsteady Fourier equation to determine heat transfer coefficients and adiabatic wall temperatures. The fourth method uses regression analysis to calculate detailed heat transfer coefficients for a quasi-steady-state condition using a thin-foil heater on the tip surface. Finally, the fifth method uses the infrared camera to measure the adiabatic wall temperature surface distribution of a blade tip after a quasi-steady-state condition is present. Overall, the present study shows that the infrared thermography technique with heat flux reconstruction using the impulse method is the most accurate, computationally efficient, and reliable method to obtain detailed, spatially resolved heat transfer coefficients and adiabatic wall temperatures on a transonic turbine blade tip in a linear cascade.

Measured Adiabatic Effectiveness and Heat Transfer for Blowing From the Tip of a Turbine Blade

2004 ◽  
Author(s):  
J. Christophel ◽  
E. Couch ◽  
K. A. Thole ◽  
F. J. Cunha
Keyword(s):  
Heat Transfer ◽  
Turbine Blade ◽  
Suction Side ◽  
Leakage Flow ◽  
Transfer Coefficients ◽  
Forward Region ◽  
Cooling Effectiveness ◽  
Combustion Gas ◽  
Blade Tip ◽  
Blade Alloy

The clearance gap between the tip of a turbine blade and the shroud has an inherent leakage flow from the pressure side to the suction side of the blade. This leakage flow of combustion gas and air mixtures leads to severe heat transfer rates on the blade tip of the high pressure turbine. As the thermal load to the blade increases, blade alloy oxidation and erosion rates increase thereby adversely affecting component life. The subject of this paper is the cooling effectiveness levels and heat transfer coefficients that result from blowing through two holes placed in the forward region of a blade tip. These holes are referred to as dirt purge holes and are generally required for manufacturing purposes and expelling dirt from the coolant flow when operating in sandy environments. Experiments were performed in a linear blade cascade for two tip gap heights over a range of blowing ratios. Results indicated that the cooling effectiveness was highly dependent upon the tip gap clearance with better cooling achieved at smaller clearances. Also, heat transfer was found to increase with blowing. In considering an overall benefit of cooling from the dirt purge blowing, a large benefit was realized for a smaller tip gap as compared with a larger tip gap.

Heat Transfer Coefficients on the Squealer Tip and Near-Tip Regions of a Gas Turbine Blade With Single or Double Squealer

2003 ◽  
Vol 125 (4) ◽  
pp. 778-787 ◽  
Author(s):  
Jae Su Kwak ◽  
Jaeyong Ahn ◽  
Je-Chin Han ◽  
C. Pang Lee ◽  
Ronald S. Bunker ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Gas Turbine ◽  
Pressure Ratio ◽  
Suction Side ◽  
Pressure Side ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Blade Tip

Detailed heat transfer coefficient distributions on a gas turbine squealer tip blade were measured using a hue detection based transient liquid-crystals technique. The heat transfer coefficients on the shroud and near tip regions of the pressure and suction sides of a blade were also measured. Squealer rims were located along (a) the camber line, (b) the pressure side, (c) the suction side, (d) the pressure and suction sides, (e) the camber line and the pressure side, and (f) the camber line and the suction side, respectively. Tests were performed on a five-bladed linear cascade with a blow down facility. The Reynolds number based on the cascade exit velocity and the axial chord length of a blade was 1.1×106 and the overall pressure ratio was 1.2. Heat transfer measurements were taken at the three tip gap clearances of 1.0%, 1.5%, and 2.5% of blade span. Results show that the heat transfer coefficients on the blade tip and the shroud were significantly reduced by using a squealer tip blade. Results also showed that a different squealer geometry arrangement changed the leakage flow path and resulted in different heat transfer coefficient distributions. The suction side squealer tip provided the lowest heat transfer coefficient on the blade tip and near tip regions compared to the other squealer geometry arrangements.

Turbine Airfoil Net Heat Flux Reduction With Cylindrical Holes Embedded in a Transverse Trench

2007 ◽  
Author(s):  
Katharine L. Harrison ◽  
John R. Dorrington ◽  
Jason E. Dees ◽  
David G. Bogard ◽  
Ronald S. Bunker
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Heat Flux ◽  
Film Cooling ◽  
Suction Side ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Heat Transfer Augmentation ◽  
Net Heat Flux ◽  
Cylindrical Holes

Film cooling adiabatic effectiveness and heat transfer coefficients for cylindrical holes embedded in a 1d transverse trench on the suction side of a simulated turbine vane were investigated to determine the net heat flux reduction. For reference, measurements were also conducted with standard inclined, cylindrical holes. Heat transfer coefficients were determined with and without upstream heating to isolate the hydrodynamic effects of the trench and to investigate the effects of the thermal approach boundary layer. Also the effects of a tripped versus an un-tripped boundary layer were explored. For both the cylindrical holes and the trench, heat transfer augmentation was much greater with no tripping of the approach flow. A further increase in heat transfer augmentation was caused by use of upstream heating, with as much as a 150% augmentation with the trench. With a tripped approach flow the heat transfer augmentation was much less. The net heat flux reduction for the trench was found to be significantly higher than for the row of cylindrical holes.

Turbine Airfoil Net Heat Flux Reduction With Cylindrical Holes Embedded in a Transverse Trench

2008 ◽  
Vol 131 (1) ◽  
Author(s):  
Katharine L. Harrison ◽  
John R. Dorrington ◽  
Jason E. Dees ◽  
David G. Bogard ◽  
Ronald S. Bunker
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Heat Flux ◽  
Film Cooling ◽  
Suction Side ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Heat Transfer Augmentation ◽  
Net Heat Flux ◽  
Cylindrical Holes

Film cooling adiabatic effectiveness and heat transfer coefficients for cylindrical holes embedded in a 1d transverse trench on the suction side of a simulated turbine vane were investigated to determine the net heat flux reduction. For reference, measurements were also conducted with standard inclined, cylindrical holes. Heat transfer coefficients were determined with and without upstream heating to isolate the hydrodynamic effects of the trench and to investigate the effects of the thermal approach boundary layer. Also, the effects of a tripped versus an untripped boundary layer were explored. For both the cylindrical holes and the trench, heat transfer augmentation was much greater for the untripped approach flow. A further increase in heat transfer augmentation was caused by use of upstream heating, with as much as a 180% augmentation for the trench. The tripped approach flow led to much lower heat transfer augmentation than the untipped case. The net heat flux reduction for the trench was found to be significantly higher than for the row of cylindrical holes.

Effect of Blade Tip Geometry on Tip Flow and Heat Transfer for a Blade in a Low Speed Cascade

2003 ◽  
Author(s):  
Vikrant Saxena ◽  
Hasan Nasir ◽  
Srinath V. Ekkad
Keyword(s):  
Heat Transfer ◽  
Wind Tunnel ◽  
Flow Direction ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Transfer Coefficients ◽  
Wake Effect ◽  
Low Speed ◽  
Heat Transfer Coefficients ◽  
Blade Tip

A comprehensive investigation of the effect of various tip sealing geometries is presented on the blade tip leakage flow and associated heat transfer of a scaled up HPT turbine blade in a low-speed wind tunnel facility. The linear cascade is made of four blades with the two corner blades acting as guides. The tip section of a HPT first stage rotor blade is used to fabricate the 2-D blade. The wind tunnel accommodates an 116° turn for the blade cascade. The mainstream Reynolds number based on the axial chord length at cascade exit is 4.83 × 105. The upstream wake effect is simulated with a spoked wheel wake generator placed upstream of the cascade. A turbulence grid placed even farther upstream generates the required free-stream turbulence of 4.8%. The center blade has a tip clearance gap of 1.5625% with respect to the blade span. Static pressure measurements are obtained on the blade surface and the shroud. The effect of crosswise trip strips to reduce leakage flow and associated heat transfer is investigated with strips placed along the leakage flow direction, against the leakage flow and along the chord. Cylindrical pin fins and pitch variation of strips over the tip surface are also investigated. Detailed heat transfer measurements are obtained using a steady state HSI-based liquid crystal technique. The effect of periodic unsteady wake effect is also investigated by varying the wake Strouhal number from 0. to 0.2, and to 0.4. Results show that the trip strips placed against the leakage flow produce the lowest heat transfer on the tips compared to all the other cases with a reduction between 10–15% compared to the plain tip. Results also show that the pitch of the strips has a small effect on the overall reduction. Cylindrical pins fins and strips along the leakage flow direction do not decrease the heat transfer coefficients and in some cases enhance the heat transfer coefficients by as much as 20%.

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