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Research Papers: Flows in Complex Systems

Effect of J-Groove on the Suppression of Swirl Flow in a Conical Diffuser

[+] Author and Article Information
Junichi Kurokawa

Faculty of Engineering, Yokohama National University, 79-5 Tokiwadai, Hodogaya-ku, Yokohama 240-8501, Japan

Hiroshi Imamura

 Wind Energy Institute of Tokyo Inc., 4-29-6 Shimbashi, Suite 801, Minato-ku, Tokyo 105-0004, Japan

Young-Do Choi1

Department of Mechanical Engineering, Mokpo National University, 560 Muan-ro, Chunggye-myun, Muan-gun, Jeonnam 534-729, Koreaydchoi@mokpo.ac.kr

1

Corresponding author.

J. Fluids Eng 132(7), 071101 (Jun 29, 2010) (8 pages) doi:10.1115/1.4001899 History: Received April 28, 2009; Revised May 30, 2010; Published June 29, 2010; Online June 29, 2010

The purpose of this study is to examine the validity of J-grooves in controlling and suppressing the swirl flow in a conical diffuser, for draft surge suppression in a Francis turbine, which is caused by the swirl flow from the runner outlet into the draft tube. “J-groove” composed of shallow grooves and mounted parallel to the pressure gradient on the diffuser wall is a very simple passive device to suppress several abnormal phenomena in turbomachinery. The experimental study has been performed using the conical diffuser with a divergent angle of 20 deg. The measured results of the velocity distribution in the diffuser show that a considerable reduction in the swirl intensity is attained by using J-grooves. Besides, the amplitude of pressure fluctuation caused by the rotation of the vortex core around the dead water region near the diffuser inlet is reduced by J-grooves.

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Copyright © 2010 by American Society of Mechanical Engineers
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Figures

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Figure 2

Definition of J-groove

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Figure 3

Pressure distribution of conical diffuser for different swirl intensities without J-groove

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Figure 4

Axial (white symbols) and tangential (black symbols) velocity distributions for each swirl intensity without J-groove: (a) m0=0.01, (b) m0=0.24, and (c) m0=1.70

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Figure 5

Comparison of nondimensional velocity distributions in the case of m0=1.70 with J-groove of type D (black symbols) and without groove (white symbols): (a) axial and (b) tangential velocities

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Figure 6

Comparison of velocity distribution for different types of groove in the case of m0=1.70: (a) inlet and (b) outlet regions

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Figure 7

Suppression of instability and efficiency drop: (a) swirl intensity; (b) axial momentum; (c) angular momentum

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Figure 8

Comparison of the swirl reduction coefficient Cr

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Figure 9

Comparison of the total pressure loss in the case of m0=1.70

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Figure 10

Pressure fluctuation on the diffuser wall at each position without J-groove in the case of m0=1.70: (a) z/R0=1.0; (b) z/R0=2.4; (c) z/R0=3.4

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Figure 11

Pressure fluctuation on the diffuser wall at each position with J-groove type D+E in the case of m0=1.70: (a) z/R0=1.0; (b) z/R0=2.4; (c) z/R0=3.4

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Figure 12

Comparison of the power spectrum of pressure fluctuation in the case of m0=1.70 (arrows show the prevailing frequency fn): (a) z/R0=1.0; (b) z/R0=2.4; (c) z/R0=3.4

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Figure 13

Comparison of the Strouhal number St for various inlet swirl intensities m0

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Figure 14

Comparison of the amplitude of pressure fluctuation at each axial position in the case of m0=1.70

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