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Research Papers

Gill Slot Trailing Edge Aerodynamics: Effects of Blowing Rate, Reynolds Number, and External Turbulence on Aerodynamic Losses and Pressure Distribution

[+] Author and Article Information
J. D. Johnson

518 Combat Sustainment Squadron, United States Air Force, Hill AFB, UT 84056

N. J. Fiala

Energy and Environmental Research Center, University of North Dakota, Grand Forks, ND 58202

F. E. Ames

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

J. Turbomach 131(1), 011016 (Nov 06, 2008) (11 pages) doi:10.1115/1.2813002 History: Received June 20, 2007; Revised September 12, 2007; Published November 06, 2008

Gill slots (also called cutbacks) are a common method to cool the trailing edge of vanes and blades and to eject spent cooling air. Exit surveys detailing total pressure loss, turning angle, and secondary velocities have been acquired for a gill slot vane in a large-scale, low speed cascade facility. These measurements are compared with exit surveys of the base (solid) vane configuration. Exit surveys have been taken over a four to one range in chord Reynolds numbers (500,000, 1,000,000, and 2,000,000) based on exit conditions and for low (0.7%), grid (8.5%), and aerocombustor (13.5%) turbulence conditions with varying blowing rate (50%, 100%, 150%, and 200% design flows). Exit loss, angle, and secondary velocity measurements were acquired in the facility using a five-hole cone probe at two stations representing axial chord spacings of 0.25 and 0.50. Differences between losses with and without the gill slot for a given turbulence condition and Reynolds number are compared providing evidence of coolant ejection losses and losses due to the separation off the gill slot lip. Additionally, differences in the level of losses, distribution of losses, and secondary flow vectors are presented for the different turbulence conditions and at the different Reynolds numbers. The turbulence condition has been found to have only a small effect on the increase in losses due to the gill slot. However, decreasing Reynolds number has been found to produce an increasing increment in losses. The present paper, together with a companion paper (2007, “Gill Slot Trailing Edge Heat Transfer—Effects of Blowing Rate, Reynolds Number, and External Turbulence on Heat Transfer and Film Cooling Effectiveness  ,” ASME Paper No. GT2007-27397), which documents gill slot heat transfer, is intended to provide designers with the heat transfer and aerodynamic loss information needed to compare competing trailing edge designs.

Copyright © 2009 by American Society of Mechanical Engineers
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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 aeroderivative combustor turbulence generator used in place of nozzle

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Figure 3

Schematic of four vane, 11 times scale cascade test section

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Figure 4

Schematic of vane cross section showing coolant feed tube, location of pressure taps, pin fin arrays, and gill slot geometry

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Figure 5

Measured solid vane pressure distribution compared with calculated pressure distributions for incompressible and compressible vanes (FLUENT (27))

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Figure 6

Comparison between measured gill slot vane at design flow rate, measured base line vane, and predicted (FLUENT (27)) base line vane pressure distributions

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Figure 7

Trailing edge pressure distributions for the aerocombustor condition and 1,000,000 Reynolds numbers at four different mass flow rates

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Figure 8

(a) Total pressure loss contours Ω with secondary velocity vectors, base vane, 1∕4Cax, low turbulence, ReC=1,000,000. (b) Total pressure loss contours Ω with secondary velocity vectors, gill slot vane, 1∕4Cax, low turbulence, ReC=1,000,000, design flow. (c) Total pressure loss contours Ω with secondary velocity vectors for the base vane, 1∕4Cax, grid turbulence, ReC=1,000,000. (d). Total pressure loss contours Ω with secondary velocity vectors, gill slot vane, 1∕4Cax, grid turbulence, ReC=1,000,000, design flow. (e) Total pressure loss contours Ω with secondary velocity vectors, base vane, 1∕4Cax, aerocombustor turbulence, ReC=1,000,000. (f). Total pressure loss contours Ω with secondary velocity vectors, gill slot vane, 1∕4Cax, aerocombustor turbulence, ReC=1,000,000, design flow.

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Figure 9

Cross-passage averaged total pressure loss coefficient Ω for the gill slot vane and base vane, 1∕4Cax, low turbulence, ReC=1,000,000, design flow

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Figure 10

Cross-passage averaged total pressure loss coefficient Ω, gill slot vane, 1∕4Cax, comparing turbulence conditions, ReC=1,000,000 at design flow

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Figure 11

Cross-passage averaged turning angle β gill slot vane, 1∕4Cax, comparing turbulence conditions, ReC=1,000,000 at design flow

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Figure 12

Cross-passage averaged total pressure loss coefficient Ω for the gill slot vane, 1∕4Cax, aerocombustor turbulence showing effect of Reynolds number

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Figure 13

Increase in mass-averaged total pressure loss coefficient ΔΩ from base to gill slot vane versus Reynolds number, 1∕4Cax, varying turbulence conditions

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Figure 14

Cross-passage averaged turning angle β for the gill slot vane at 1∕4 axial chord, aerocombustor turbulence showing effect of Reynolds number

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Figure 15

Cross-passage averaged total pressure loss coefficient Ω, gill slot vane, 1∕4Cax, aerocombustor turbulence showing effect of discharge flow rate, ReC=1,000,000

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Figure 16

Mass-averaged total pressure loss coefficient Ω as a function of gill slot flow rate, 1∕4Cax, aerocombustor turbulence, ReC=1,000,000

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Figure 17

Cross-passage averaged turning angle β for the gill slot vane at 1∕4 axial chord, aerocombustor turbulence showing effect of discharge flow rate

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