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Research Papers

Crossover Jet Impingement in a Rib-Roughened Trailing-Edge Cooling Channel

[+] Author and Article Information
Mohammad E. Taslim

Mechanical and Industrial
Engineering Department,
Northeastern University,
Boston, MA 02115
e-mail: m.taslim@northeastern.edu

Fei Xue

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

1Corresponding author.

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received November 4, 2016; final manuscript received November 23, 2016; published online February 28, 2017. Editor: Kenneth Hall.

J. Turbomach 139(7), 071007 (Feb 28, 2017) (12 pages) Paper No: TURBO-16-1289; doi: 10.1115/1.4035570 History: Received November 04, 2016; Revised November 23, 2016

Airfoil trailing-edge cooling is the main focus of this study. The test section was made up of two adjacent trapezoidal channels, simulating the trailing-edge cooling cavity of a gas turbine airfoil and its neighboring cavity. Eleven racetrack-shaped holes were drilled on the partition wall between the two channels to produce 11 cross-over jets that impinged on the rib-roughened wall of the trailing-edge channel. The jets, after impinging on their respective target surface, turned toward the trailing-edge channel exit. Smooth target wall, as a baseline case, as well as four rib angles with the flow of 0 deg, 45 deg, 90 deg, and 135 deg are investigated. Cross-over holes axes were on the trailing-edge channel center plane, i.e., no tilting of the cross-over jets. Steady-state liquid crystal thermography technique was used in this study for a range of jet Reynolds number of 10,000–35,000. The test results are compared with the numerical results obtained from the Reynolds-averaged Navier–Stokes and energy equation. Closure was attained by k–ω with shear stress transport (SST) turbulence model. The entire test rig (supply and trailing-edge channels) was meshed with variable density hexagonal meshes. The numerical work was performed for boundary conditions identical to those of the tests. In addition to the impingement heat transfer coefficients, the numerical results provided the mass flow rates through individual cross-over holes. This study concluded that: (a) the local Nusselt numbers correlate well with the local jet Reynolds numbers, (b) 90 deg rib arrangement, that is, when the cross-over jet axis was parallel to the rib longitudinal axis, produced higher heat transfer coefficients, compared to other rib angles, and (c) numerical heat transfer results were generally in good agreement with the test results. The overall difference between the computational fluid dynamics (CFD) and test results was about 10%.

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References

Figures

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Fig. 1

Sketches of the test rig

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Fig. 2

Details of the crossover holes and ribs

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Fig. 4

A CFD model with about 12 × 106 all-hexa elements representing the entire test section with the crossover holes and ribs

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Fig. 5

Mesh details around a crossover hole for 0 deg and 45 deg ribs

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Fig. 6

Velocity magnitude contours on the rig midplane for smooth and rib-roughened target wall with 0 deg, 45 deg, 90 deg, and 135 deg ribs, Rejet = 20,600, CFD results

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Fig. 7

Velocity magnitude contours on a plane cutting the middle crossover hole and target area (sixth area), Rejet = 20,400

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Fig. 8

Vorticity magnitude contours on the rig midplane for smooth and rib-roughened target walls Rejet = 20,600

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Fig. 9

Mass flow percentage rates through the 11 crossover holes for all target wall geometries

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Fig. 10

Static pressure (gauge) contours on the rig midplane for the smooth and rib-roughened target walls

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Fig. 11

Test results for the variation of Nusselt number along the channel at Rejet = 10,300 and 15,100

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Fig. 12

Test results for the variation of Nusselt number along the channel at Rejet = 20,400 and 25,600

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Fig. 13

Test results for the variation of Nusselt number along the channel at Rejet = 31,200 and 35,100

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Fig. 14

Test result contours of constant Nusselt numbers (iso-Nu lines) on the sixth target surface for the five target surface geometries at Rejet = 20,400

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Fig. 15

Comparison of CFD and test results of Nusselt numbers on all target areas for the smooth target wall geometry: (a) average jet Reynolds numbers and (b) local jet Reynolds numbers

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Fig. 16

Comparison of CFD and test results of Nusselt numbers on all target areas for the 0 deg-rib target wall geometry: (a) average jet Reynolds numbers and (b) local jet Reynolds numbers

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Fig. 17

Comparison of CFD and test results of Nusselt numbers on all target areas for the 45 deg-rib target wall geometry: (a) average jet Reynolds numbers and (b) local jet Reynolds numbers

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Fig. 18

Comparison of CFD and test results of Nusselt numbers on all target areas for the 90 deg-rib wall geometry: (a) average jet Reynolds numbers and (b) local jet Reynolds numbers

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Fig. 19

Comparison of CFD and test results of Nusselt numbers on all target areas for the 135 deg-target wall geometry: (a) average jet Reynolds numbers and (b) local jet Reynolds numbers

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Fig. 20

Comparison of the test and CFD results of the k–ω and realizable k–ε with the enhanced wall treatment turbulence models for: (a) smooth target wall and (b) 135 deg ribs

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Fig. 21

Measured Nusselt number variation with respect to the rib angle (with the axial flow direction) for the average jet Reynolds number of (a) 10,300 and (b) 35,100

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Fig. 22

Measured data and CFD pressure ratios across the crossover holes and across the trailing-channel for smooth and rib-roughened target walls

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