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Research Papers

The Effect of Area Ratio Change Via Increased Hole Length for Shaped Film Cooling Holes With Constant Expansion Angles

[+] Author and Article Information
Shane Haydt

Mechanical and Nuclear Engineering
Department,
The Pennsylvania State University,
University Park, PA 16802
e-mail: shane.haydt@psu.edu

Stephen Lynch

Mechanical and Nuclear Engineering
Department,
The Pennsylvania State University,
University Park, PA 16802
e-mail: splynch@psu.edu

Scott Lewis

Turbine Durability,
United Technologies—Pratt & Whitney,
400 Main Street,
East Hartford, CT 06108
e-mail: Scott.Lewis@pw.utc.com

1Corresponding author.

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received October 4, 2017; final manuscript received October 19, 2017; published online February 27, 2018. Editor: Kenneth C. Hall.

J. Turbomach 140(5), 051002 (Feb 27, 2018) (13 pages) Paper No: TURBO-17-1183; doi: 10.1115/1.4038871 History: Received October 04, 2017; Revised October 19, 2017

Shaped film cooling holes are used as a cooling technology in gas turbines to reduce metal temperatures and improve durability, and they generally consist of a small metering section connected to a diffuser that expands in one or more directions. The area ratio (AR) of these holes is defined as the area at the exit of the diffuser, divided by the area at the metering section. A larger AR increases the diffusion of the coolant momentum, leading to lower average momentum of the coolant jet at the exit of the hole and generally better cooling performance. Cooling holes with larger ARs are also more tolerant of high blowing ratio conditions, and the increased coolant diffusion typically better prevents jet lift-off from occurring. Higher ARs have traditionally been accomplished by increasing the expansion angle of the diffuser while keeping the overall length of the hole constant. The present study maintains the diffuser expansion angles and instead increases the length of the diffuser, which results in longer holes. Various ARs have been examined for two shaped holes: one with forward and lateral expansion angles of 7 deg (7-7-7 hole) and one with forward and lateral expansion angles of 12 deg (12-12-12 hole). Each hole shape was tested at numerous blowing ratios to capture trends across various flow rates. Adiabatic effectiveness measurements indicate that for the baseline 7-7-7 hole, a larger AR provides higher effectiveness, especially at higher blowing ratios. Measurements also indicate that for the 12-12-12 hole, a larger AR performs better at high blowing ratios but the hole experiences ingestion at low blowing ratios. Steady Reynolds-averaged Navier–Stokes simulations did not accurately predict the levels of adiabatic effectiveness, but did predict the trend of improving effectiveness with increasing AR for both hole shapes. Flowfield measurements with particle image velocimetry (PIV) were also performed at one downstream plane for a low and high AR case, and the results indicate an expected decrease in jet velocity due to a larger diffuser.

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References

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Figures

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Fig. 1

7-7-7 baseline shaped film cooling hole, developed by Schroeder and Thole

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Fig. 2

Schematic of the wind tunnel facility used in the current study

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Fig. 3

Range of ARs for the 7-7-7 and 12-12-12 holes

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Fig. 4

PIV setup for measurements at an x/D = 10 crossplane

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Fig. 5

7-7-7 AR2 and AR6 holes both at M = 3.0, showing periodicity within experimental uncertainty in the adiabatic effectiveness contours (a) and in the laterally averaged effectiveness plot (b)

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Fig. 6

CFD domain with boundary conditions and a depiction of the centerline mesh resolution

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Fig. 7

Contours of measured adiabatic effectiveness for all 7-7-7 ARs, all at M = 1.0

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Fig. 8

Laterally averaged effectiveness for all 7-7-7 ARs, all at M = 1.0

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Fig. 9

Contours of measured adiabatic effectiveness for all 7-7-7 ARs, all at M = 3.0

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Fig. 10

Contours of measured adiabatic effectiveness for all 7-7-7 ARs, all at M = 6.0

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Fig. 11

Laterally averaged effectiveness for all 7-7-7 ARs, all at M = 6.0

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Fig. 12

Contours of measured adiabatic effectiveness for the 7-7-7 AR2 case at all blowing ratios

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Fig. 13

Contours of measured adiabatic effectiveness for the 7-7-7 AR4 case at all blowing ratios

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Fig. 14

Contours of measured adiabatic effectiveness for the 7-7-7 AR6 case at all blowing ratios

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Fig. 15

Laterally averaged effectiveness for the largest and smallest AR at a range of blowing ratios

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Fig. 16

Adiabatic effectiveness comparison between AR2, AR4, and AR6 of the 7-7-7 (left) and 12-12-12 (right) holes, all at M = 3.0

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Fig. 17

Laterally averaged effectiveness for AR2, AR4, and AR6 of the 7-7-7 and 12-12-12 holes, all at M = 3.0

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Fig. 18

Adiabatic effectiveness comparison between AR2, AR4, and AR6 of the 7-7-7 (left) and 12-12-12 (right) holes, all at M = 6.0

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Fig. 19

Laterally averaged effectiveness for AR2, AR4, and AR6 of the 7-7-7 and 12-12-12 holes, all at M = 6.0

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Fig. 20

Area-averaged effectiveness for all experimental cases versus blowing ratio. 7-7-7 with solid symbols, 12-12-12 with open symbols

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Fig. 21

Area-averaged effectiveness normalized by breakout width versus effective blowing ratio

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Fig. 22

Area-averaged effectiveness normalized by breakout width versus M/AR, including data from Gritsch et al. [7]

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Fig. 23

Predicted and measured adiabatic effectiveness contours for AR2, AR4, and AR6 of the 7-7-7 hole, all at M = 3.0

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Fig. 24

Area-averaged effectiveness for the simulations of all AR cases of the 7-7-7 and 12-12-12 holes

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Fig. 25

Predictions of centerline planes contoured by nondimensional temperature, for AR2 cases at M = 6.0

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Fig. 26

Normalized area-averaged effectiveness plotted versus effective blowing ratio for all simulated cases of the 7-7-7 and 12-12-12 holes

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Fig. 27

Predicted contours of jet velocity at the exit plane for a case at the optimal effective blowing ratio of M/AR = 0.5, and the same AR at a higher blowing ratio

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Fig. 28

Diffuser efficiency plotted versus blowing ratio for all simulated cases

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Fig. 29

Downstream plane at x/D = 10, contoured with x-velocity and overlaid with in-plane vectors, for the AR2 hole at (a) M = 1.0 and (b) M = 6.0

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Fig. 30

Downstream plane at x/D = 10, contoured with x-velocity and overlaid with in-plane vectors, for the AR6 hole at (a) M = 1.0 and (b) M = 6.0

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