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Research Papers

Film-Cooled Trailing Edge Measurements: 3D Velocity and Scalar Field

[+] Author and Article Information
Michael Benson

U.S. Military Academy
West Point, NY 10996
e-mail: michael.benson@usma.edu

Gregory Laskowski

GE Global Research Center
Niskayuna, NY 12309
e-mail: laskowsk@ge.com

Chris Elkins

e-mail: celkins@stanford.edu

John K. Eaton

e-mail: eatonj@stanford.edu
Stanford University
Stanford, CA 94305

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received August 4, 2011; final manuscript received August 10, 2011; published online October 30, 2012. Editor: David Wisler.

This material is declared a work of the U.S. Government and is not subject to copyright protection in the United States. Approved for public release, distribution is unlimited.

J. Turbomach 135(1), 011030 (Oct 30, 2012) (7 pages) Paper No: TURBO-11-1176; doi: 10.1115/1.4006425 History: Received August 04, 2011; Revised August 10, 2011

Aircraft turbine blade trailing edges commonly are cooled by blowing air through pressure-side cutback slots. The surface effectiveness is governed by the rate of mixing of the coolant with the mainstream, which is typically much faster than predicted by CFD models. Three-dimensional velocity and coolant concentration fields were measured in and around a cutback slot using a simple uncambered airfoil with a realistic trailing edge cooling geometry at a Reynolds number of 110,000 based on airfoil chord length, which is lower than practical engines but still in the turbulent regime. The results were obtained using magnetic resonance imaging (MRI) techniques in a water flow apparatus. Magnetic resonance concentration (MRC) scans measured the concentration distribution with a spatial resolution of 0.5 mm3 (compared to a slot height of 5 mm) and an uncertainty near 5%. Magnetic resonance velocimetry (MRV) was used to acquire 3D, three-component mean velocity measurements with a resolution of 1.0 mm3. Coupled concentration and velocity measurements were used to identify flow structures contributing to the rapid mixing, including longitudinal vortices and separation bubbles. Velocity measurements at several locations were compared with an unsteady RANS model. Concentration measurements extrapolated to the surface provided film cooling effectiveness and showed that the longitudinal vortices decreased effectiveness near the lands and reduced the average film cooling effectiveness.

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References

Figures

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Fig. 1

Cross-sectional top view of flow apparatus, with flow from left to right. Dimensions in millimeters.

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Fig. 2

Side and top view of airfoil. Flow is left to right, with the y coordinate axis highlighted.

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Fig. 3

Key features of the trailing edge region

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Fig. 4

CFD mesh for airfoil and channel simulation

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Fig. 5

Velocity profiles for CFD (dashed) and MRV (solid) at 3 streamwise locations

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Fig. 6

Iso-surfaces of fast (red) and reverse (purple) flow for the trailing edge. U 1.3*Umain are shown in red. Streamlines in black depict freestream flow from positions centered above the slot and land.

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Fig. 7

Concentration flux at each streamwise position

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Fig. 8

The 10% concentration iso-surface

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Fig. 9

Surface effectiveness for the three slots; 90% effectiveness contour highlighted

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Fig. 10

Spanwise averaged surface effectiveness variation downstream of slot exit

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Fig. 11

Wake dispersion from the middle of the center slot jet. Lines added to highlight airfoil exterior edges.

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Fig. 12

Measured coolant field 4 slot heights downstream of the trailing edge

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Fig. 13

Experimental concentration contours and velocity vectors for a slot centerplane. Lines added to emphasize airfoil surfaces.

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Fig. 14

Multiple planes of concentration contours with tangential velocity vectors

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Fig. 15

Coolant distribution at 8 slot heights downstream of slot exit

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