Multidimensional Diagnostics of Turbine Cavitation

[+] Author and Article Information
Branko Bajic

Korto Cavitation Services–Korto GmbH, 12, rue Ste Zithe, L-2763 Luxembourg, Luxembourge-mail: korto@cavitation.de

J. Fluids Eng 124(4), 943-950 (Dec 04, 2002) (8 pages) doi:10.1115/1.1511162 History: Received December 01, 2000; Revised May 06, 2002; Online December 04, 2002
Copyright © 2002 by ASME
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The sensors placed on the 20 guide vanes react to cavitation in various locations around the spiral
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Typical power density spectra of noise picked up at different power values. There is no noticeable line at the revolution frequency, but the blade-passage frequency (BPF) lines are rather strong. The background noise, recorded in the turbine at rest while the other machinery in the plant was operating, is low enough to enable reliable estimation of the continuous spectrum component between 0.3 and 800 kHz.
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Overview of the normalized power spectra. The v=1 power density spectra recorded at different turbine power values are compared to the one recorded at 13.3 MW. The spectrum related to this reference value is thus represented by the zero-dB line.
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An example of modulation curves: M1(θ,f,P) in an octave band centered at f=125 kHz measured at different turbine power values
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Normalized spectra of Fig. 3(Po=13.3 MW) presented two dimensionally, seen from two perspectives
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Noise decomposition: contribution of the three cavitation mechanisms to the total noise
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The way used to determine the range of prevalence of a mechanism m,(f,P)m, in the total noise is illustrated here by the m=2 case. At the P-values between the pairs of curves the m=2 intensity is equal resp. 2, 5, or 10 times stronger than the rest of the intensity. There from the (f,P)2 denoted; the ratio 5 is assumed sufficiently high.
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Typical cases of noise modulation
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The fine-structure cavitation characteristics of the turbine: the most detailed description of cavitation that can be obtained by the multidimensional method. For each tested turbine-power value, P, there are 380 (number-of-runner-blades×number-of-guide-vanes) dimensionless values, Cvb, that stand for the intensity of cavitation caused by the interaction of a pair consisting of the runner blade b, and the guide vane v. The Cvb-values specify the relative intensity of cavitation. Their use in cavitation erosion estimation is discussed elsewhere (Bajic 1417). The data presented in the figure describe total cavitation. The method also enables identification of different segments of a cavitating flow—cavitation mechanisms—and yields data like this for each of them.
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Runner and wicket gate cavitation characteristics
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Global turbine characteristics without and with resolution with respect to cavitation mechanisms
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Check of (in)stationarity: variation of cavitation intensity at the (f,P)-values characteristic of the mechanisms



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