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Research Papers: Flows in Complex Systems

Rotordynamic Moment on the Backshroud of a Francis Turbine Runner Under Whirling Motion

[+] Author and Article Information
Bingwei Song

School of Hydraulic Engineering, Faculty of Infrastructure Engineering, Dalian University of Technology, Dalian 116024, China; Department of Mechanical Science and Bioengineering, Graduate School of Engineering Science, Osaka University, 1-3 Machikaneyama, Toyonaka, Osaka 560-8531, Japan

Hironori Horiguchi1

Department of Mechanical Science and Bioengineering, Graduate School of Engineering Science, Osaka University, 1-3 Machikaneyama, Toyonaka, Osaka 560-8531, Japanhoriguti@me.es.osaka-u.ac.jp

Zhenyue Ma

School of Hydraulic Engineering, Faculty of Infrastructure Engineering, Dalian University of Technology, Dalian 116024, China

Yoshinobu Tsujimoto

Department of Mechanical Science and Bioengineering, Graduate School of Engineering Science, Osaka University, 1-3 Machikaneyama, Toyonaka, Osaka 560-8531, Japan

1

Corresponding author.

J. Fluids Eng 132(7), 071102 (Jul 08, 2010) (9 pages) doi:10.1115/1.4001802 History: Received May 11, 2009; Revised May 12, 2010; Published July 08, 2010; Online July 08, 2010

This paper addresses the rotordynamic instability of an overhung rotor caused by a hydrodynamic moment due to whirling motion through the structural coupling between whirl and precession modes. First, the possibility of instability is discussed based on a vibration model in which the hydrodynamic forces and moments are assumed to be smaller than structural forces with the structural coupling being represented by a structural influence factor. Then, the fundamental characteristics of rotordynamic moment on the backshroud of a Francis turbine runner under whirling motion were studied using model tests and numerical calculations. The runner is modeled by a disk positioned close to a casing with a small radial clearance at the outer periphery. The moment is caused by an inward leakage flow that is produced by an external pump in the model test. The experiments were designed to measure the rotordynamic fluid force moments under various leakage flow rates with various preswirl velocities and various axial clearances between the backshroud and casing. The computation was carried out based on a bulk flow model. It was found that the fluid force moment is generally destabilizing, except for a small region of positive whirling speed ratios.

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Copyright © 2010 by American Society of Mechanical Engineers
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Figures

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Figure 1

Force and moment acting on the rotor: (a) coordinate system and (b) definition of the force and moment on complex plane z=x+iy

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Figure 2

Schematic of experiment facility: (a) whirl generator and (b) cross section of sleeve

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Figure 3

Details of the test section

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Figure 4

Steady pressure distribution in the clearance: (a) effect of flow rate (C2=4 mm, UJ=0), (b) effect of preswirl flow (C2=4 mm, vl/UT=0.170), and (c) effect of clearance (UJ=0, vl/UT=0.170; uncertainty in ψs±0.01)

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Figure 5

Fluid force moment at various flow rates in the case of C2=4 mm and UJ/UT=0: (a) normal moment and (b) tangential moment (uncertainty in Mn/M0Ω and Mt/M0Ω±0.03)

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Figure 6

Fluid force moment at various flow rates in the case of C2=4 mm and UJ/UT=0: (a) normal moment and (b) tangential moment (uncertainty in Mn/M0ω and Mt/M0ω±0.01)

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Figure 7

Fluid force moment at various preswirl velocities in the case of C2=4 mm and vl/UT=0.170: (a) normal moment and (b) tangential moment (uncertainty in Mn/M0ω and Mt/M0ω±0.01)

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Figure 8

Fluid force moment in the cases of C2=2 mm, 4 mm, and 6 mm at vl/UT=0.170, UJ/UT=0: (a) normal moment and (b) tangential moment (uncertainty in Mn/M0ω and Mt/M0ω±0.01)

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Figure 9

Fluid force moments obtained by the force sensor, the steady pressure, and the computation in the case of C2=4 mm, vl/UT=0.170, and UJ/UT=0: (a) normal moment and (b) tangential moment (uncertainty in Mn/M0ω and Mt/M0ω±0.01)

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Figure 10

Unsteady components of pressure and velocity in the clearance for Ω/ω=1.2 in the case of C2=4 mm, vl/UT=0.170, and UJ/UT=0: (a) pressure (Exp.), (b) pressure (Calc.), and (c) velocity (Calc.)

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Figure 11

The same as Fig. 1, for Ω/ω=0.3

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Figure 12

The same as Fig. 1, for Ω/ω=−0.3

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Figure 13

The same as Fig. 1, for Ω/ω=−1.2

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