Research Papers

Heat Transfer and Pressure Drop Measurements in High Solidity Pin Fin Cooling Arrays With Incremental Replenishment

[+] Author and Article Information
Mitch L. Busche

e-mail: mitch.busche@my.und.edu

Leolein P. Moualeu

e-mail: leoleinpatrikmoual@my.und.edu

Nafiz Chowdhury

e-mail: nafiz.und@gmail.com

Clement Tang

e-mail: clement.tang@engr.und.edu

Forrest E. Ames

e-mail: forrest.ames@engr.und.edu
University of North Dakota,
Mechanical Engineering Department,
Grand Forks, ND 58202

1Corresponding author.

Contributed by the International Gas Turbine Institute of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received July 3, 2012; final manuscript received July 16, 2012; published online June 5, 2013. Assoc. Editor: David Wisler.

J. Turbomach 135(4), 041011 (Jun 05, 2013) (9 pages) Paper No: TURBO-12-1120; doi: 10.1115/1.4007581 History: Received July 03, 2012; Revised July 16, 2012

Leading edge heat loads on turbine airfoils can be reduced by increasing the diameter of the leading edge. The lower external heat transfer and more generous curvature may allow for cooling this region internally. Large diameter leading edge regions are expected to exhibit a relatively broad region with nearly constant heat transfer. However, the ability of internal passages to cool a surface diminishes with distance as cooling air picks up thermal energy within the passage. Two novel internal cooling geometries have been designed and tested, which incrementally replenish cooling air by using impingement holes distributed along the array. These cooling methods have been compared to a baseline high solidity passage in terms of both array heat transfer and pressure drop. Heat transfer rates and pressure drop have been determined on a row by row basis to provide a means to assess their ability to sustain adequate cooling levels across the entire leading edge region. The authors believe turbine airfoil designs integrating large diameter leading edge regions with properly designed internal passages have the potential to eliminate showerhead cooling arrays in many industrial gas turbine applications. This change is especially beneficial in environments where fuel or air impurities have the potential to clog leading edge showerhead cooling arrays. Heat transfer and pressure drop measurements were acquired in a bench scale test rig. Reynolds numbers ranged from approximately 5000 to 60,000 for the constant height channel arrays based on the pin diameter and the local maximum average velocity across a row. The high solidity pin fin arrays have an axial spacing (X/D) of 1.074 and a cross channel spacing (S/D) of 1.625. The constant section pin fin arrays have channel height to diameter ratios of 0.5. Each array has eight rows of pins with six pins per row in a staggered arrangement. Heat transfer testing was conducted using a constant temperature boundary condition.

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Fig. 1

Schematic of internal cooling array heat transfer and flow rig

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Fig. 2

Schematic of side view of heat transfer rig plenum with cooling array installed

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Fig. 3

(a) Photo of top and bottom surfaces for baseline high solidity pin fin array with inlet impingement holes. (b) Photo of top and bottom plates for configuration 1 of incremental impingement high solidity pin array. (c) Photo of top and bottom plates for configuration 2 of incremental impingement array with high solidity pin fins.

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Fig. 4

Photo shows the serpentine thermal isolation grooves, the thermocouple instrumentation and the thermofoil heaters on the back side of high solidity pin fin array

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Fig. 5

Top plate and total array hole discharge coefficient measurements versus Reynolds number

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Fig. 6

Baseline array averaged Nusselt number versus diameter Reynolds number based on VMAX, includes impingement row and Ref. [4] data for comparison

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Fig. 7

Flow friction factor comparing correlation from Ref. [4] with present baseline configuration data

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Fig. 8

Row by row internal cooling effectiveness as a function of Reynolds number, baseline configuration

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Fig. 9

Internal cooling parameter by row as a function of Reynolds number for the baseline configuration

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Fig. 10

Comparison of area averaged Nusselt number as a function of Reynolds number comparing the high solidity pin fin array with configurations 1 and 2

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Fig. 11

Row by row internal cooling effectiveness as a function of Reynolds number, cooling configuration 1

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Fig. 12

Row by row internal cooling effectiveness as a function of Reynolds number, cooling configuration 2

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Fig. 13

Cooling parameter as a function of row location and Reynolds number for cooling configuration 1

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Fig. 14

Cooling parameter as a function of row location and Reynolds number for cooling configuration 2

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Fig. 15

Overall pressure drop parameter for baseline and two leading edge cooling configurations as a function of Reynolds number




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