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Research Papers

Film Cooling Effectiveness Improvements Using a Nondiffusing Oval Hole

[+] Author and Article Information
Emin Issakhanian

Department of Mechanical Engineering,
Loyola Marymount University,
Los Angeles, CA 90045
e-mail: emin.issakhanian@lmu.edu

Christopher J. Elkins, John K. Eaton

Department of Mechanical Engineering,
Stanford University,
Stanford, CA 94305

1Corresponding author.

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received October 17, 2015; final manuscript received November 5, 2015; published online December 29, 2015. Editor: Kenneth C. Hall.

J. Turbomach 138(4), 041004 (Dec 29, 2015) (6 pages) Paper No: TURBO-15-1229; doi: 10.1115/1.4032045 History: Received October 17, 2015; Revised November 05, 2015

The need for improvements in film cooling effectiveness over traditional cylindrical film cooling holes has led to varied shaped hole and sister hole designs of increasing complexity. This paper presents a simpler shaped hole design which shows improved film cooling effectiveness over both cylindrical holes and diffusing fan-shaped holes without the geometric complexity of the latter. Magnetic resonance imaging measurement techniques are used to reveal the coupled 3D velocity and coolant mixing from film cooling holes which are of a constant oval cross section as opposed to round. The oval-shaped hole yielded an area-averaged adiabatic effectiveness twice that of the diffusing fan-shaped hole tested. Three component mean velocity measurements within the channel and cooling hole showed the flow features and vorticity fields which explain the improved performance of the oval-shaped hole. As compared to the round hole, the oval hole leads to a more complex vorticity field, which reduces the strength of the main counter-rotating vortex pair (CVP). The CVP acts to lift the coolant away from the turbine blade surface, and thus strongly reduces the film cooling effectiveness. The weaker vortices allow the coolant to stay closer to the blade surface and to remain relatively unmixed with the main flow over a longer distance. Thus, the oval-shaped film cooling hole provides a simpler solution for improving film cooling effectiveness beyond circular hole and diffusing hole designs.

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Figures

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Fig. 1

Cross-sectional view of tunnel contraction, development section, test section, feed plenum, hole insert, and outlet. All dimensions are in mm.

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Fig. 2

Schematic side view of plenum, hole, and test section. Gray area denotes MRV measurement volume.

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Fig. 3

Schematic of tested hole shapes: oval- (top) and fan-shaped (bottom). Dimensions are in mm unless otherwise stated.

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Fig. 4

Adiabatic surface effectiveness, η, map for the oval-shaped hole. Plot values have been filtered.

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Fig. 5

Adiabatic surface effectiveness, η, map for the fan-shaped hole. Plot values have been filtered.

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Fig. 6

Laterally averaged adiabatic surface effectiveness, η¯, versus streamwise position for the oval-shaped hole (top) and the fan-shaped hole (bottom). Plot values have been filtered.

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Fig. 7

Ratio of laterally averaged adiabatic surface effectiveness, η¯, of the oval-shaped hole to that of the fan-shaped hole plotted against streamwise position

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Fig. 8

Isostreamwise vorticity surfaces at threshold levels of 0.5 (bottom) and −0.5 (top) for oval-shaped hole

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Fig. 9

Midhole secondary flow velocity vectors for oval-shaped hole

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Fig. 10

Contours of streamwise vorticity and in-plane velocity vectors at x/D = 4 for fan-shaped hole

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Fig. 11

Contours of streamwise vorticity and in-plane velocity vectors at x/D = 4 for oval-shaped hole

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Fig. 12

Contours of normalized streamwise velocity overlaid with in-plane velocity vectors and lines of isonormalized temperature for the fan-shaped hole

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Fig. 18

Revised cooling hole feed plenum. Nonessential geometry is suppressed for clarity. Dimensions are in mm unless otherwise stated.

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Fig. 17

Contours of velocity ratio magnitude at oval hole exit plane

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Fig. 16

θ = 0.25 isosurfaces for the fan-shaped hole (green) and oval hole (orange), see online version for color

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Fig. 15

Contours of normalized temperature in the symmetry plane for the oval-shaped hole. Streamlines originating at windward and leeward edges of hole overlaid.

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Fig. 14

Contours of normalized temperature in the symmetry plane for the fan-shaped hole. Streamlines originating at windward and leeward edges of hole overlaid.

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Fig. 13

Contours of normalized streamwise velocity overlaid with in-plane velocity vectors and lines of isonormalized temperature for the oval-shaped hole

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