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TECHNICAL PAPERS

Frequencies in the Vibration Induced by the Rotor Stator Interaction in a Centrifugal Pump Turbine

[+] Author and Article Information
C. G. Rodriguez1

Department of Mechanical Engineering, University of Concepcion, Casilla 160-C, Concepcion, Chilecristian.rodriguez@udec.cl

E. Egusquiza

Center of Industrial Diagnostics and Fluid Dynamics, Technical University of Catalonia, Avenida Diagonal 647, 08028 Barcelona, Spainegusquiza@mf.upc.edu

I. F. Santos

Department of Mechanical Engineering, Technical University of Denmark, DK-2800 Kongis Lyngby, Denmarkifs@mek.dtu.dk

1

Formerly at the Center of Industrial Diagnostics and Fluid Dynamics, Technical University of Catalonia.

J. Fluids Eng 129(11), 1428-1435 (May 26, 2007) (8 pages) doi:10.1115/1.2786489 History: Received February 09, 2006; Revised May 26, 2007

The highest vibration levels in large pump turbines are, in general, originated in the rotor stator interaction (RSI). This vibration has specific characteristics that can be clearly observed in the frequency domain: harmonics of the moving blade passing frequency and a particular relationship among their amplitudes. It is valuable for the design and condition monitoring to count on these characteristics. A CFD model is an appropriate tool to determine the force and its characteristics. However, it is time consuming and needs highly qualified human resources while usually these results are needed immediately and in situ. Then, it is useful to determine these characteristics in a simple, quick, and accurate method. At present, the most suitable method indicates a large amount of possible harmonics to appear, without indicating the relative importance of them. This paper carries out a theoretical analysis to predict and explain in a qualitative way these frequencies and amplitudes. The theoretical analysis incorporates the number of blades, the number of guide vanes, the RSI nonuniform fluid force, and the sequence of interaction. This analysis is compared with the method currently in use, and both methods are applied to a practical case. The theoretical analysis gives a resulting force over the pump turbine, which corresponds well to the measured behavior of a pump turbine in terms of its frequencies and the relationship between their amplitudes. A corrective action is proposed as a result of the analysis and after it is carried out in one of the units, the vibration levels are reduced. The vibration induced by the RSI is predicted considering the sequence of interaction and different amplitudes in the interactions between the same moving blade and different stationary blades, giving a different and original interpretation about the source of the vibration characteristics. A successful corrective action is proposed as a consequence of this new interpretation.

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Copyright © 2007 by American Society of Mechanical Engineers
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Figures

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Figure 1

Scheme of the forces over the runner at the reference initial time t=0

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Figure 2

Time between interactions

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Figure 3

Phase for a signal of frequency ZVΩ

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Figure 7

Graphical explanation of the zero amplitude components

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Figure 8

Nonuniform distribution of the RSI. Cut water and static eccentricity.

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Figure 9

Excitation force over a blade considering (a) an eccentricity and (b) the cut water

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Figure 10

Frequency content of the resultant excitation considering (a) an eccentricity and (b) the cut water

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Figure 11

Spectrum of vibration measured in the rotating shaft. Spots indicate harmonics of blade passing frequency.

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Figure 12

Resulting force over a blade

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Figure 4

Blade and guide vane interaction in the inertial system of reference for a combination of five guide vanes and (a) 2, (b) 3, and (c) 4 blades

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Figure 5

Blade and guide vane interaction in the rotating system of reference for a combination of five guide vanes and (a) 2, (b) 3, and (c) 4 blades

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Figure 6

Time between the interactions of two consecutive blades

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