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TECHNICAL PAPERS

An Investigation of the Relationship Between Acoustic Emission, Vibration, Noise, and Cavitation Structures on a Kaplan Turbine

[+] Author and Article Information
Tomaž Rus

 Turboinštitut d.d., Rovšnikova 7, 1210 Ljubljana-Šentvid, Sloveniatomaz.rus@turboinstitut.si

Matevž Dular1

Laboratory for Water and Turbine Machines,  University of Ljubljana, Aškerčeva 6, 1000 Ljubljana, Sloveniamatevz.dular@fs.uni-lj.si

Brane Širok

Laboratory for Water and Turbine Machines,  University of Ljubljana, Aškerčeva 6, 1000 Ljubljana, Sloveniabrane.sirok@fs.uni-lj.si

Marko Hočevar

Laboratory for Water and Turbine Machines,  University of Ljubljana, Aškerčeva 6, 1000 Ljubljana, Sloveniamarko.hocevar@fs.uni-lj.si

Igor Kern

 Turboinštitut d.d., Rovšnikova 7, 1210 Ljubljana-Šentvid, Sloveniaigor.kern@turboinstitut.si

1

Corresponding author.

J. Fluids Eng 129(9), 1112-1122 (Apr 02, 2007) (11 pages) doi:10.1115/1.2754313 History: Received June 21, 2006; Revised April 02, 2007

The goal of the study was to explain the relationship between different acoustic signals and visual appearance of cavitation. Measurements of acoustic emission, vibration, and noise were performed on a Kaplan turbine model, with only two blades, in a cavitating condition. Since a model with only two blades was used, most of the side effects were eliminated, and it was concluded that the cavitation itself is the source of the recorded signal. Results showed an interesting relationship between the extent of the cavitation and the recorded data from sensors. At a decreasing cavitation number, the recorded amplitudes from all measurements first rose, experienced a local maximum, then fell to a local minimum, and finally rose again. The cavitation was also visually observed. It was concluded from the measurements that there are distinct correlations between acoustic emission, vibration, and noise on one side and the topology, extent, and type of cavitation structures on the other side. A physical explanation for the phenomenon was introduced and included in a semi-empirical model that links the visual appearance of cavitation on the blade of the turbine to the generated noise and vibration.

Copyright © 2007 by American Society of Mechanical Engineers
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Figures

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Figure 1

Low head closed-loop test rig for Kaplan turbine testing: 1, model turbine; 2, motor-generator; 3, circuit pumps; 4, pressure tank; 5, suction tank; 6, flowmeters; and 7 and 8, regulation and by-pass valves, respectively

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Figure 2

Experimental setup: 1, accelerometer; 2, hydrophone; 3, AE sensor; 4, stroboscopic light; 5, CCD camera; 6, trigger; 7, stroboscopic main unit; 8, PC with video grabber card; and 9, PC with data acquisition

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Figure 3

Two-bladed impeller model efficiency at various cavitation numbers

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Figure 4

Results of measurements with acoustical emission sensor

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Figure 5

Results of measurements with a hydrophone

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Figure 6

Results of measurements with accelerometer

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Figure 7

A typical image with noted places of cavitation occurrence on the blade

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Figure 8

Typical images of vapor structures at different cavitation numbers

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Figure 9

Image from the series (left), mean value of gray level μ (middle), and standard deviation of gray level s (right) for three cavitation numbers

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Figure 10

A typical diagram of acoustical measurements with noted corresponding cavitation types and positions

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Figure 11

Principle on which the model is based

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Figure 12

Positions of masks that define different positions of cavitation occurrence

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Figure 13

Evolution of values of parameter k2 during iterations

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Figure 14

Graphical representation of the model structure

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Figure 15

Results of noise measurements and model predictions of the pressure wave amplitude

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Figure 16

Predicted pressure wave contributions of each cavitation region

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