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Research Papers

Direct Measurement of Heat Transfer Coefficient Augmentation at Multiple Density Ratios

[+] Author and Article Information
Emily J. Boyd

Department of Mechanical Engineering,
The University of Texas at Austin,
204 E. Dean Keeton Street,
Austin, TX 78712
e-mail: emily.june.boyd@gmail.com

John W. McClintic

Department of Mechanical Engineering,
The University of Texas at Austin,
204 E. Dean Keeton Street,
Austin, TX 78712
e-mail: jmcclintic@utexas.edu

Kyle F. Chavez

Department of Mechanical Engineering,
The University of Texas at Austin,
204 E. Dean Keeton Street,
Austin, TX 78712
e-mail: kyle.f.chavez@utexas.edu

David G. Bogard

Department of Mechanical Engineering,
The University of Texas at Austin,
204 E. Dean Keeton Street,
Austin, TX 78712
e-mail: dbogard@mail.utexas.edu

1Present address: Department of Mechanical Engineering & Materials Science, Washington University in St. Louis, St. Louis, MO 63130.

2Corresponding author.

3Present address: Williams International, Commerce Township, MI 48390.

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received June 21, 2016; final manuscript received July 1, 2016; published online September 8, 2016. Editor: Kenneth Hall.

J. Turbomach 139(1), 011005 (Sep 08, 2016) (11 pages) Paper No: TURBO-16-1120; doi: 10.1115/1.4034190 History: Received June 21, 2016; Revised July 01, 2016

Knowing the heat transfer coefficient augmentation is imperative to predicting film cooling performance on turbine components. In the past, heat transfer coefficient augmentation was generally measured at unit density ratio to keep measurements simple and uncertainty low. Some researchers have measured heat transfer coefficient augmentation while taking density ratio effects into account, but none have made direct temperature measurements of the wall and adiabatic wall to calculate hf/h0 at higher density ratios. This work presents results from measuring the heat transfer coefficient augmentation downstream of shaped holes with a 7 deg forward and lateral expansion at DR = 1.0, 1.2, and 1.5 on a flat plate using a constant heat flux surface. The results showed that the heat transfer coefficient augmentation was low while the jets were attached to the surface and increased when the jets started to separate. At DR = 1.0, hf/h0 was higher for a given blowing ratio than at DR = 1.2 and DR = 1.5. However, when velocity ratios are matched, better correspondence was found at the different density ratios. Surface contours of hf/h0 showed that the heat transfer was initially increased along the centerline of the jet, but was reduced along the centerline at distances farther downstream. The decrease along the centerline may be due to counter-rotating vortices sweeping warm air next to the heat flux plate toward the center of the jet, where they sweep upward and thicken the thermal boundary layer. This warming of the core of the coolant jet over the heated surface was confirmed with thermal field measurements.

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References

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Figures

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Fig. 1

Diagram of wind tunnel test section

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Fig. 2

Shaped hole geometry

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Fig. 3

Diagram of insulation beneath the heat flux foil

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Fig. 4

η¯ at (a) DR = 1.2 and (b) DR = 1.5

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Fig. 5

Laterally averaged hf/h0 at (a) DR = 1.0, (b) DR = 1.2, and (c) DR = 1.5

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Fig. 6

Laterally averaged hf/h0 comparison between the current study and Saumweber and Schulz [10]

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Fig. 7

hf/h0 comparison at DR = 1.0, 1.2, and 1.5 and M = 1.5 and 2.5

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Fig. 8

Lateral temperature and hf/h0 profiles at x/d = 5, DR = 1.0, 1.2, and 1.5, and M = 1.5 and 2.5

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Fig. 9

Comparison of hf/h0 when M is matched

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Fig. 10

Comparison of hf/h0 when I is matched

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Fig. 11

Comparison of hf/h0 when VR is matched

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Fig. 12

Contours of dimensionless temperature, θ, at x/d = 4.66, M = 2.0, and DR = 1.2 with the heat off (left) and the heat on (right)

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Fig. 13

Thermal profiles of a jet at x/d = 4.66, M = 2.0, and DR = 1.2 with the heat flux plate on and off at (a) z/d = 0 and (b) z/d = 0.44

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Fig. 14

Thermal field measurements in the centerline of the jet at M = 2.0 and DR = 1.2

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Fig. 15

Comparison of thermal field profiles with the heat flux plate off at M = 2.0 and 3.0 at DR = 1.2 and (a) x/d = 3, (b) x/d = 5, (c) x/d = 10, and (d) x/d = 14.66

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Fig. 16

Comparison of thermal field profiles at M = 2.0, x/d = 5 and DR = 1.2 and 1.5 with the heat flux plate (a) off and (b) on

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