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Research Papers

Aerothermal Investigation of Backface Clearance Flow in Deeply Scalloped Radial Turbines

[+] Author and Article Information
Ping He

Graduate University of Chinese Academy of Sciences,
Beijing, 100190, China;
Institute of Engineering Thermophysics,
Chinese Academy of Sciences,
Beijing, 100190, China
e-mail: heping@mail.etp.ac.cn

Zhigang Sun

e-mail: sunsonofjilin@126.com

Baoting Guo

e-mail: guobt@mail.etp.ac.cn

Haisheng Chen

e-mail: chen_hs@mail.etp.ac.cn

Chunqing Tan

e-mail: tan@mail.etp.ac.cn
Institute of Engineering Thermophysics,
Chinese Academy of Sciences,
Beijing, 100190, China

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received July 28, 2011; final manuscript received December 4, 2011; published online October 31, 2012. Assoc. Editor: Ricardo F. Martinez-Botas.

J. Turbomach 135(2), 021002 (Oct 31, 2012) (12 pages) Paper No: TURBO-11-1165; doi: 10.1115/1.4006664 History: Received July 28, 2011; Revised December 04, 2011

A numerical investigation of flow structure and heat transfer in the backface clearance of deeply scalloped radial turbines is conducted in this paper. It is found that the leakage flow is very strong in the upper radial region whereas in the lower radial region, the scraping flow dominates over the clearance and a recirculation zone is formed. Pressure distributions are given to explain the flow structure in the backface clearance, and it is found that due to the sharp reduction of radial velocity and Coriolis force, the pressure difference in the lower radial region is reduced drastically, which is the mechanism for the domination of the scraping flow and the corresponding recirculation zone. There are two high heat transfer coefficient zones on the backface surface. One is located in the upper radial region due to the reattachment of the leakage flow and the other is located in the lower radial region caused by the impingement of the scraping flow. Increase of the clearance height reduces the high heat transfer coefficient caused by the impingement of the scraping flow, although it increases the leakage loss. On the other hand, the high heat transfer coefficient in the upper radial region can be reduced remarkably by using the suction side squealer geometry.

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Figures

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Fig. 1

Deeply scalloped radial turbine rotors: (a) turbine A and (b) turbine B

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Fig. 2

Meridional view of the flow passage for turbine A

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Fig. 3

Different squealer geometries for turbine A: (a) PSS, (b) SSS, and (c) PS + SS

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Fig. 4

Meshes for the three turbines: (a) turbine A, (b) turbine B, (c) the rotor of turbine A with SSS backface, and (d) the blade of turbine C with SSS tip

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Fig. 5

Comparisons of outlet parameter distribution for turbine B: (a) total pressure, (b) total temperature, (c) flow angle, and (d) efficiency

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Fig. 6

Comparisons of H on the flat tip for turbine C: (a) H contour on the tip and (b) distribution of H along the axial distance

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Fig. 7

Comparison of H on the SSS tip for turbine C

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Fig. 8

Comparison of the overall H on the flat and SSS tips for turbine C

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Fig. 9

Streamlines in the backface clearance at different radial locations: (a) RL = 50%, (b) RL = 10%, and (c) RL = 5%

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Fig. 10

Radial variations of mass flow in the backface clearance

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Fig. 11

Limiting streamlines on the blade backface

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Fig. 12

Streamlines at the mid clearance height plane

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Fig. 13

Schematic of the backface clearance flows

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Fig. 14

H contour on the blade surfaces (the pressure and suction surfaces are unfolded)

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Fig. 15

Interaction of the flows in the backface clearance

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Fig. 16

Flow near the scallop rim of the deeply scalloped radial turbine: (a) 3D view and (b) meridional view

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Fig. 17

Pressure at hub without backface clearance: (a) turbine A and (b) turbine B by Simonyi [5]

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Fig. 18

Pressure contour on the backface casing surface

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Fig. 19

Pressure difference across the clearance

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Fig. 20

Net mass flows for different clearance heights

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Fig. 21

H contours for different clearance heights (the pressure and suction surfaces are unfolded): (a) BC = 2%, (b) BC = 4%, (c) BC = 8%, and (d) BC = 10%

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Fig. 22

Distribution of average H on the blade surfaces for different clearance heights: (a) backface surface and (b) suction surface

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Fig. 23

Streamlines in the backface clearance for different squealer geometries (RL = 50%): (a) PSS, (b) SSS, and (c) PS + SS

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Fig. 24

H contours for different squealer geometries: (a) flat, (b) PSS, (c) SSS, and (d) PS + SS

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Fig. 25

Distribution of average H on the backface surface for different squealer geometries

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