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Research Papers: Gas Turbines: Turbomachinery

Experimental/Numerical Investigation on the Effects of Trailing-Edge Cooling Hole Blockage on Heat Transfer in a Trailing-Edge Cooling Channel

[+] Author and Article Information
M. E. Taslim

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

X. Huang

Mechanical and Industrial
Engineering Department,
Northeastern University,
Boston, MA 02115
e-mail: huang.x@husky.neu.edu

Contributed by the Heat Transfer Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received January 6, 2014; final manuscript received January 9, 2014; published online February 28, 2014. Editor: David Wisler.

J. Eng. Gas Turbines Power 136(8), 082603 (Feb 28, 2014) (15 pages) Paper No: GTP-14-1003; doi: 10.1115/1.4026845 History: Received January 06, 2014; Revised January 09, 2014

Hot and harsh environments, sometimes experienced by gas turbine airfoils, can create undesirable effects such as clogging of the cooling holes. Clogging of the cooling holes along the trailing edge of an airfoil on the tip side and its effects on the heat transfer coefficients in the cooling cavity around the clogged holes is the main focus of this investigation. Local and average heat transfer coefficients were measured in a test section simulating a rib-roughened trailing edge cooling cavity of a turbine airfoil. The rig was made up of two adjacent channels, each with a trapezoidal cross sectional area. The first channel 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, impinged on eleven radial ribs and exited from a second row of race-track shaped slots on the opposite wall that simulated the cooling holes along the trailing edge of the airfoil. Tests were run for the baseline case with all exit holes open and for cases in which 2, 3, and 4 exit holes on the airfoil tip side were clogged. All tests were run for two crossover jet angles. The first set of tests were run for zero angle between the jet axis and the trailing-edge channel centerline. The jets were then tilted towards the ribs by five degrees. Results of the two set of tests for a range of 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 and ribs 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. The realizable k-ε turbulence model in combination with enhanced wall treatment approach for the near wall regions were 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 crossover and each exit hole from the total flow for different geometries. The major conclusions of this study were: (a) clogging of the exit holes near the airfoil tip alters the distribution of the coolant mass flow rate through the crossover holes and changes the flow structure. Depending on the number of clogged exit holes (from 3 to 6, out of 12), the tip-end crossover hole experienced from 35% to 49% reductions in its mass flow rate while the root-end crossover hole, under the same conditions, experienced an increase of the same magnitude in its mass flow rate. (b) Up to 64% reduction in heat transfer coefficients on the tip-end surface areas around the clogged holes were observed which might have devastating effects on the airfoil life. At the same time, a gain in heat transfer coefficient of up 40% was observed around the root-end due to increased crossover flows. (c) Numerical heat transfer results with the use of the realizable k-ε turbulence model in combination with enhanced wall treatment approach for the near wall regions were generally in a reasonable agreement with the test results. The overall difference between the CFD and test results was about 10%.

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References

Figures

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Fig. 1

Schematics of the rig

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Fig. 2

Detail of the test section

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Fig. 3

A typical 12-million-mesh CFD model representing the entire test section with the crossover and exit holes

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Fig. 4

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

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Fig. 5

Typical CFD contours of velocity magnitude on the rig midplane for inline arrangement with 0 deg tilt angle and for staggered arrangement with 5 deg tilt angle

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Fig. 6

Typical CFD contours of velocity magnitude on the rig midplane for 0, 2 and 4 blocked exit holes, inline flow arrangement and 0 deg tilt angle

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Fig. 7

Percentage of mass flow rate through the crossover holes for all flow arrangements

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Fig. 8

Percentage of mass flow rates through the exit holes for all flow arrangements

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Fig. 9

Typical CFD contours of static pressure (gauge) variations on the rig midplane for 0 deg and 5 deg tilt angles and inline flow arrangements

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Fig. 10

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

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Fig. 11

Contours of velocity magnitude on the planes cutting the crossover and exit holes in the middle of the trailing-edge channel for the inline and staggered flow arrangements

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Fig. 12

Effects of exit hole blockage on the Nusselt numbers for the case of zero degree tilt angle and inline flow arrangement

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Fig. 13

Effects of exit hole blockage on the Nusselt numbers for the case of zero degree tilt angle and staggered flow arrangement

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Fig. 14

Effects of exit hole blockage on the Nusselt numbers for the case of five degree tilt angle and inline flow arrangement

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Fig. 15

Effects of exit hole blockage on the Nusselt numbers for the case of five degree tilt angle and staggered flow arrangement

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Fig. 16

Effects of exit hole blockage on areas 8, 9, 10, and 11 Nusselt numbers for the case of zero degree tilt angle and inline flow arrangement

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Fig. 17

Effects of exit hole blockage on areas 8, 9, 10, and 11 Nusselt numbers for the case of zero degree tilt angle and staggered flow arrangement

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Fig. 18

Effects of exit hole blockage on areas 8, 9, 10, and 11 Nusselt numbers for the case of five deg tilt angle and inline flow arrangement

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Fig. 19

Effects of exit hole blockage on areas 8, 9, 10, and 11 Nusselt numbers for the case of five degree tilt angle and staggered flow arrangement

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Fig. 20

CFD and test results comparisons for the four geometries when all exit holes are open

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Fig. 21

CFD results of the Nusselt number variation along the channel for 0, 3, 4, 5, and 6 blocked exit holes, 0 deg tilt angle, staggered flow arrangement

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Fig. 22

CFD results of the Nusselt number variation along the channel for 0, 3, 4, 5, and 6 blocked exit holes, 5 deg tilt angle, staggered flow arrangement

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Fig. 23

Comparison of the k-ε, k-ω and v2f turbulence models with the test results for the 5 deg tilt angle, staggered flow arrangement and four blocked exit holes

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Fig. 24

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

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