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Research Papers

Heat Transfer Coefficient Measurements on the Film-Cooled Pressure Surface of a Transonic Airfoil

[+] Author and Article Information
Paul M. Kodzwa

e-mail: pmkodzwa@hotmail.com

John K. Eaton

Department of Mechanical Engineering,
Flow Physics and Computation Division,
Stanford University,
Stanford, CA 94305

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received July 4, 2011; final manuscript received January 26, 2013; published online September 13, 2013. Assoc. Editor: Je-Chin Han.

J. Turbomach 135(6), 061011 (Sep 13, 2013) (16 pages) Paper No: TURBO-11-1097; doi: 10.1115/1.4023620 History: Received July 04, 2011; Revised January 26, 2013

This paper presents isoenergetic temperature and steady-state film-cooled heat transfer coefficient measurements on the pressure surface of a modern, highly cambered transonic airfoil. A single passage model simulated the idealized two-dimensional flow path between blades in a modern transonic turbine. This set up offered a simpler construction than a linear cascade but produced an equivalent flow condition. Furthermore, this model allowed the use of steady-state, constant surface heat fluxes. We used wide-band thermochromic liquid crystals (TLCs) viewed through a novel miniature periscope system to perform high-accuracy (±0.2 °C) thermography. The peak Mach number along the pressure surface was 1.5, and maximum turbulence intensity was 30%. We used air and carbon dioxide as injectant to simulate the density ratios characteristic of the film cooling problem. We found significant differences between isoenergetic and recovery temperature distributions with a strongly accelerated mainstream and detached coolant jets. Our heat transfer data showed some general similarities with lower-speed data immediately downstream of injection; however, we also observed significant heat transfer attenuation far downstream at high blowing conditions. Our measurements suggested that the momentum ratio was the most appropriate variable to parameterize the effect of injectant density once jet lift-off occurred. We noted several nonintuitive results in our turbulence effect studies. First, we found that increased mainstream turbulence can be overwhelmed by the local augmentation of coolant injection. Second, we observed complex interactions between turbulence level, coolant density, and blowing rate with an accelerating mainstream.

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Figures

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Fig. 1

Schematic of single passage experiment

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Fig. 2

Grid used to produce high turbulence condition

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Fig. 3

Measurements of Mis and K∞ compared to infinite cascade standard for low and high turbulence conditions

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Fig. 8

Plots of spanwise-averaged Tiso measurements elucidating effects of blowing ratio

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Fig. 10

Plots of spanwise-averaged Tiso showing the effect of turbulence levels

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Fig. 9

Plots of spanwise-averaged Tiso showing the effect of injectant density

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Fig. 11

Plot of spanwised-averaged St comparing drilled and undrilled surface heat transfer measurements. Note that there is no blowing with the drilled surface (variable error bars).

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Fig. 12

Measured spatially-resolved maps of St (left) with Θ = 8.00(10)-5 and Stc,° (center) Θc=8.76(10)-5 and Stc,°/St at low turbulence conditions. Flow is from top to bottom.

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Fig. 13

Spatially-resolved maps of Stc: BL1 = 0.775 and BL2 = 0.917 (left), BL1 = 2.004 and BL2 = 1.073 (center), and BL1 = 5.207 and BL2 = 5.803 (right). Flow is from top to bottom.

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Fig. 14

Plots of St¯c showing effect of blowing ratio (variable error bars)

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Fig. 15

St¯c at specific sc locations and St¯c/St¯c,° curves with varying blowing rates

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Fig. 7

Photographs of undrilled pressure surface with and without constant heat flux surface and completed drilled pressure heat transfer measurement surface

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Fig. 6

Schematic of assembled heat flux surface

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Fig. 5

Sample spatially-resolved temperature map (at Tset=26.2 °C) and TLC-painted copper calibrator surface for comparison

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Fig. 4

Q curves for two calibration cells in zone 1 and T¯-Tset curves at Tset=26.2 °C, 28.1 °C, 30.0 °C, and 34.0 °C

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Fig. 16

Plots of St¯c showing effect of density ratio (variable error bars)

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Fig. 17

St¯c values at specific s'c positions holding BL and I constant (variable error bars)

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Fig. 18

Spatially-resolved map of Stc showing effects of density ratio; BL1 = 2.613 and BL2 = 1.396. Flow is from top to bottom.

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Fig. 19

St¯c curves with varying turbulence levels and injectant densities (variable error bars)

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Fig. 20

St¯c values at specific s'c positions with varying turbulence levels and injectant densities (variable error bars)

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Fig. 21

St¯c curves with varying turbulence levels and injectant densities (variable error bars)

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