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Research Papers

Letterbox Trailing Edge Heat Transfer: Effects of Blowing Rate, Reynolds Number, and External Turbulence on Heat Transfer and Film Cooling Effectiveness

[+] Author and Article Information
N. J. Fiala, I. Jaswal, F. E. Ames

Department of Mechanical Engineering, University of North Dakota, Grand Forks, ND 58202

J. Turbomach 132(1), 011017 (Sep 18, 2009) (10 pages) doi:10.1115/1.3106703 History: Received January 06, 2009; Revised January 29, 2009; Published September 18, 2009

Heat transfer and film cooling distributions have been acquired for a vane trailing edge with letterbox partitions. Additionally, pressure drop data have been experimentally determined across a pin fin array and a trailing edge slot with letterbox partitions. The pressure drop across the array and letterbox trailing edge arrangement was measurably higher than for the gill slot geometry. Experimental data for the partitions and the inner suction surface region downstream from the slot have been acquired over a four-to-one range in vane exit condition Reynolds number (500,000, 1,000,000, and 2,000,000), with low (0.7%), grid (8.5%), and aerocombustor (13.5%) turbulence conditions. At these conditions, both heat transfer and adiabatic film cooling distributions have been documented over a range of blowing ratios (0.47M1.9). Heat transfer distributions on the inner suction surface downstream from the slot ejection were found to be dependent on both ejection flow rate and external conditions. Heat transfer on the partition side surfaces correlated with both exit Reynolds number and blowing ratio. Heat transfer on partition top surfaces largely correlated with exit Reynolds number but blowing ratio had a small effect at higher values. Generally, adiabatic film cooling levels on the inner suction surface are high but decrease near the trailing edge and provide some protection for the trailing edge. Adiabatic effectiveness levels on the partitions correlate with blowing ratio. On the partition sides adiabatic effectiveness is highest at low blowing ratios and decreases with increasing flow rate. On the partition tops adiabatic effectiveness increases with increasing blowing ratio but never exceeds the level on the sides. The present paper, together with a companion paper that documents letterbox trailing edge aerodynamics, is intended to provide engineers with the heat transfer and aerodynamic loss information needed to develop and compare competing trailing edge designs.

Copyright © 2010 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Schematic of large-scale incompressible flow vane cascade wind tunnel

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Figure 2

Schematic of four-vane, 11-times scale cascade test section

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Figure 3

Measured pressure distributions for 11-times scale vane compared with computational fluid dynamics (CFD) predictions for incompressible and compressible vanes

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Figure 4

Schematic of heat transfer vane cross-section showing coolant feed tube, location of thermocouples, pin fin arrays, and letterbox geometry

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Figure 5

Cross-sectional view of five-row aluminum pin fin array showing location of letterbox partitions and thermocouple (TC) instrumentation

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Figure 6

Schematic of conduction model in trailing edge region

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Figure 7

Aluminum heat transfer partition used to acquire partition side heat transfer coefficients and adiabatic effectiveness

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Figure 8

Balsa wood partition with active aluminum heat transfer surface used to acquire partition top heat transfer coefficients and adiabatic effectiveness measurements

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Figure 9

Letterbox and gill slot vane surface pressure distributions compared with fluent prediction for base vane

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Figure 10

Comparison between pressure distribution downstream from gill slot ejection with distribution downstream from letterbox ejection

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Figure 11

Comparison of pressure distribution downstream from letterbox ejection for various flow rates, ReC=1,000,000

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Figure 12

Comparison of normalized pressure drop across the pin fin array to the vane exit for the gill slot and letterbox vanes with Vmax defined for the last row in the converging pin fin array

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Figure 13

Letterbox partition side heat transfer levels with ReDmax based on the last row of pin fin array and ReC the exit chord Reynolds number

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Figure 14

Letterbox partition top Stanton number levels with ReDmax based on the last row of pin fin array showing the effect of exit chord Reynolds number with no upstream heating

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Figure 15

Letterbox partition adiabatic effectiveness for side (open symbols) and top (solid symbols) surfaces as a function of local blowing ratio, ReC=500,000

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Figure 16

Letterbox partition adiabatic effectiveness for side (open symbols) and top (solid symbols) surfaces as a function of local blowing ratio, ReC=2,000,000.

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Figure 17

Letterbox partition adiabatic effectiveness for side (open symbols) and top (solid symbols) surfaces as a function of local blowing ratio; ReC=500,000, 1,000,000, and 2,000,000

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Figure 18

Comparison of gill slot and letterbox inner suction surface heat transfer levels for 500,000 and 2,000,000 Reynolds numbers at relative design flow with aerocombustor turbulence

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Figure 19

Comparison of gill slot and letterbox inner suction surface adiabatic effectiveness as a function of distance from pin array exit over a four-to-one range in chord Reynolds number at relative design flow and aerocombustor turbulence

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Figure 20

Adiabatic effectiveness distributions at the near-partition location with varying coolant flow rates at each Reynolds number for the aerocombustor turbulence condition

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