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Research Papers

Experimental Study on Effects of Internal Ribs and Rear Bumps on Film Cooling Effectiveness

[+] Author and Article Information
Eiji Sakai

e-mail: e-sakai@criepi.denken.or.jp

Toshihiko Takahashi

e-mail: tosihiko@criepi.denken.or.jp

Yukiko Agata

e-mail: agata@criepi.denken.or.jp
Central Research Institute of Electric
Power Industry, Japan,
2-6-1 Nagasaka, Yokosuka-shi,
Kanagawa-ken 240-0196, Japan

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the Journal of Turbomachinery. Manuscript received July 2, 2012; final manuscript received July 29, 2012; published online March 25, 2013. Editor: David Wisler.

J. Turbomach 135(3), 031025 (Mar 25, 2013) (14 pages) Paper No: TURBO-12-1116; doi: 10.1115/1.4007546 History: Received July 02, 2012; Revised July 29, 2012

This paper reports the detailed measurement of the film cooling effectiveness for a scaled up film-cooling hole with an expanded exit fed by a smooth and ribbed secondary flow channel, which is an arrangement typical of turbine blades. The experiments are carried out at blowing ratios ranging from 0.4 to 1.25, and ten different rib patterns, including forward oriented ribs and inverse oriented ribs, are evaluated. Furthermore, in order to develop an efficient film-cooling technique, several kinds of bumps are installed downstream of the hole exits and the effects of the bumps on the film cooling effectiveness are investigated. The bump structures tested here are semicircular, hemispherical, and cylindrical bumps. The results show that the rib orientation strongly affects the film cooling effectiveness. When the blowing ratio is comparatively low, the forward oriented ribs afford a higher film cooling effectiveness. On the contrary, when the blowing ratio is comparatively high, the inverse oriented ribs afford a higher film cooling effectiveness. The cylindrical bump provides a better spreading of the ejected secondary flow than the other bumps, leading to a higher film cooling effectiveness. To clarify how the bumps improve the film cooling effectiveness, computational simulations are performed. The simulations indicate that a longitudinal vortex, formed at the trailing edge of the cylindrical bump, improves the film cooling effectiveness by generating downward velocity vectors.

Copyright © 2013 by ASME
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References

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Renze, P., Schroder, W., and Meinke, M., 2008, “Large-Eddy Simulation of Film Cooling Flows With Variable Density Jets,” Flow, Turbul. Combust., 80, pp. 119–132. [CrossRef]
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Figures

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Fig. 3

Film cooling hole geometry

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Fig. 8

Film cooling effectiveness of the shaped hole (left: BR = 0.4, right: BR = 0.75)

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Fig. 9

Film cooling effectiveness of the cylindrical hole (left: BR = 0.4, right: BR = 0.75)

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Fig. 10

Relationship between ηspa and BR

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Fig. 11

Nondimensional temperature distribution (BR = 0.4) (left: shaped hole, right: cylindrical hole)

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Fig. 12

Relationship between ηspa and BR

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Fig. 13

Relationship between ηspa and BR

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Fig. 14

Effects of bumps on ηspa (Rib 5)

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Fig. 15

Film cooling effectiveness distribution (Rib 5, BR = 1.0)

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Fig. 16

Plane view of the nondimensional temperature (Rib 5, BR = 1.0)

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Fig. 17

Effects of the bumps on ηspa (Rib 2)

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Fig. 18

Film cooling effectiveness distribution (Rib 2, BR = 1.0)

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Fig. 19

Plane view of the nondimensional temperature (Rib 2, BR = 1.0)

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Fig. 20

Effects of the bumps on the ηspa of the cylindrical hole (Rib 5)

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Fig. 21

Discharge coefficient (shaped hole)

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Fig. 1

Experimental apparatus

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Fig. 5

Measurement grids for the temperature

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Fig. 6

Detailed view of the wall block for Grid A

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Fig. 7

Location of the pressure taps

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Fig. 22

Effect of the bumps on the discharge coefficient (shaped hole)

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Fig. 23

Numerical grids (Grid 1)

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Fig. 24

Grid dependency check

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Fig. 25

Velocity profile at the inlet of the main flow channel

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Fig. 26

Comparison of the film cooling effectiveness

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Fig. 27

Comparison of the nondimensional temperature at x/d = 1 (left: BR = 0.5, right: BR = 1.0)

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Fig. 28

Nondimensional temperature and film cooling effectiveness (BR = 1.0, Rib 5)

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Fig. 29

Laterally averaged film cooling effectiveness (BR = 1.0)

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Fig. 30

Cross-sectional velocity vectors and film cooling effectiveness (Rib 5)

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Fig. 31

Nondimensional temperature and film cooling effectiveness (BR = 1.0, Rib 2)

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Fig. 32

Laterally averaged film cooling effectiveness (BR = 1.0)

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Fig. 33

Streamlines colored by u and the film cooling effectiveness

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Fig. 34

Overall losses (BR = 1.0)

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Fig. 35

Skin-friction coefficient (BR = 1.0)

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Fig. 36

Film cooling effectiveness distribution (Rib 5, BR = 1.0)

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Fig. 37

Laterally averaged film cooling effectiveness (BR = 1.0)

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Fig. 38

Cross-sectional temperatures (left: w/o bump, right: Bump B)

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