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Research Papers

Experimental and Numerical Cross-Over Jet Impingement in an Airfoil Trailing-Edge Cooling Channel

[+] Author and Article Information
M. E. Taslim, A. Nongsaeng

Department of Mechanical and Industrial Engineering, Northeastern University, Boston, MA 02115

J. Turbomach 133(4), 041009 (Apr 20, 2011) (10 pages) doi:10.1115/1.4002984 History: Received June 28, 2010; Revised June 29, 2010; Published April 20, 2011; Online April 20, 2011

Trailing edge cooling cavities in modern gas turbine airfoils play an important role in maintaining the trailing-edge temperature at levels consistent with airfoil design life. In this study, local and average heat transfer coefficients were measured in a test section, simulating the trailing-edge cooling cavity of a turbine airfoil using the steady-state liquid crystal technique. The test rig was made up of two adjacent channels, each with a trapezoidal cross-sectional area. The first channel, simulating the cooling cavity adjacent to the trailing-edge cavity, supplied the cooling air to the trailing-edge channel through a row of racetrack-shaped slots on the partition wall between the two channels. Eleven crossover jets issued from these slots entered the trailing-edge channel and exited from a second row of race-track shaped slots on the opposite wall in staggered or inline arrangement. Two jet angles were examined. The baseline tests were for zero angle between the jet axis and the trailing-edge channel centerline. The jets were then tilted toward one wall (pressure or suction side) of the trailing-edge channel by 5 deg. Results of the two set of tests for a range of local jet Reynolds number from 10,000 to 35,000 were compared. The numerical models contained the entire trailing-edge and supply channels with all slots to simulate exactly the tested geometries. They were meshed with all-hexa structured mesh of high near-wall concentration. A pressure-correction based, multiblock, multigrid, unstructured/adaptive commercial software was used in this investigation. Standard high Reynolds number kε turbulence model in conjunction with the generalized wall function for most parts was used for turbulence closure. Boundary conditions identical to those of the experiments were applied and several turbulence model results were compared. The numerical analyses also provided the share of each cross-over and each exit hole from the total flow for different geometries. The major conclusions of this study were (a) except for the first and last cross-flow jets which had different flow structures, other jets produced the same heat transfer results on their target surfaces, (b) jets tilted at an angle of 5 deg produced higher heat transfer coefficients on the target surface. The tilted jets also produced the same level of heat transfer coefficients on the wall opposite the target wall, and (c) the numerical predictions of impingement heat transfer coefficients were in good agreement with the measured values for most cases; thus, computational fluid dynamics could be considered a viable tool in airfoil cooling circuit designs.

Copyright © 2011 by American Society of Mechanical Engineers
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Figures

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Figure 1

Schematics of the rig

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Figure 2

Details of the test section

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Figure 3

A typical mesh for the entire test section with the cross-over and exit holes

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Figure 4

Details of the mesh around a cross-over and a trailing-edge slot for inline and staggered flow arrangements

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Figure 5

Typical CFD contours of velocity magnitude on the rig midplane for inline and staggered flow arrangements and 0 deg tilt angle

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Figure 6

Typical CFD contours of velocity magnitude on the rig midplane for zero, two, and four blocked exit holes, inline flow arrangements, and 0 deg tilt angle

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Figure 7

Percentage of mass flow rate through the cross-over holes with all exit holes open

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Figure 8

Percentage of mass flow rate through the cross-over holes when two or four exit holes are blocked

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Figure 9

Percentage of mass flow rate through the exit holes

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Figure 10

Measured Nusselt number variation with local jet Reynolds number on area 6, no blocked exit hole

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Figure 11

Contours of Nusselt number and temperature on area 6 for inline and staggered arrangements, and for 5 deg tilt angle

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Figure 12

Measured Nusselt number variation with local jet Reynolds number on areas 1–5 for the 0 deg tilt angle, two blocked exit holes, and open end hole

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Figure 13

Measured Nusselt number variation with local jet Reynolds number on areas 1–5 for the 0 deg tilt angle, four blocked exit holes, and open end hole

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Figure 14

Measured Nusselt number variation with local jet Reynolds number on areas 1–5 for the 5 deg tilt angle, two blocked exit holes, and open end hole

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Figure 15

Measured Nusselt number variation with local jet Reynolds number on areas 1–5 for the 5 deg tilt angle, four blocked exit holes, and open end hole

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Figure 16

Comparison of the CFD and test results for the 0 deg tilt angle and inline arrangement

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Figure 17

Comparison of the CFD and test results for the 0 deg tilt angle and staggered arrangement

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Figure 18

Comparison of the CFD and test results for the 5 deg tilt angle and inline arrangement

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Figure 19

Comparison of the CFD and test results for the 5 deg tilt angle and staggered arrangement

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Figure 20

Comparison of the CFD and test results for the 5 deg tilt angle, staggered arrangement, and two blocked exit holes

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Figure 21

Comparison of the CFD and test results for the 5 deg tilt angle, staggered arrangement, and four blocked exit holes

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Figure 22

Comparison of the CFD and test results on the target and opposite walls for the 5 deg tilt angle, inline, and staggered arrangements

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Figure 23

Contours of velocity magnitude on the planes cutting the cross-over and exit holes in the middle of the trailing-edge channel for the inline and staggered geometries

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Figure 24

Comparison of the k−e, v2f, and k−w turbulence models with the test results for the 0 deg tilt angle staggered arrangement and two blocked exit holes

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Figure 25

Measured pressure ratios across the cross-over holes and across the trailing-edge channel for all geometries and flow arrangements

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