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Research Papers: Multiphase Flows

Unsteady Cavitation at the Tongue of the Volute of a Centrifugal Pump

[+] Author and Article Information
Rudolf Bachert1 n2

 AUMA Riester GmbH & Co. KG, Aumastrasse 1, 79379 Muellheim, Germanyrudolf.bachert@auma.com

Bernd Stoffel

Laboratory for Turbomachinery and Fluid Power, Darmstadt University of Technology, Magdalenenstrasse 4, 64289 Darmstadt, Germanybernd.stoffel@fst.tu-darmstadt.de

Matevž Dular2

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

1

Corresponding author.

2

Previous address: Laboratory for Turbomachinery and Fluid Power, Darmstadt University of Technology, Magdalenenstr. 4, 64289 Darmstadt, Germany.

J. Fluids Eng 132(6), 061301 (May 19, 2010) (6 pages) doi:10.1115/1.4001570 History: Received October 15, 2009; Revised March 23, 2010; Published May 19, 2010; Online May 19, 2010

The paper deals with unsteady effects of cavitation at the tongue of the volute of a centrifugal pump. For the investigations parts of the volute casing, including the tongue and the hub of the impeller, were made of acrylic glass. Experiments were carried out at a flow rate above optimal value (slight overload) and at 3% head drop conditions. In this operating point there was no cavitation present in the impeller of the pump, hence, the whole 3% head drop resulted from cavitation on the tongue of the volute. By use of particle image velocimetry combined with special fluorescent particles it was possible to obtain information about the velocity field outside and inside the cavitating zone. An additional camera provided information about the location and extent of cavitation. The results imply that cloud cavitation similar to the one seen on single hydrofoils appears on the tongue. Periodical evolution of cavitation structures, from incipient to developed, with cavitation cloud shedding, is seen during each passing of a blade. The Results imply that greater consideration should be given to the possibility of cavitation appearance on the tongue of the volute as it is possible that this cavitation location alone causes the 3% head drop. Moreover, the appearance of unsteady cavitation in a higher-pressure region, such as the volute of the pump, can cause severe erosion to the solid surfaces.

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Copyright © 2010 by American Society of Mechanical Engineers
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Figures

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Figure 1

Schematic representation of the flow field in the vicinity of the volute tongue

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Figure 2

Impeller of the test pump with transparent front shroud

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Figure 3

Cross-section through the pump installation with noted view point of cameras

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Figure 4

Test loop for pump tests

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Figure 5

Integral characteristics of the pump(q-H diagram at NPSH=4 m—left and NPSH-H diagram at q=1.17—right)

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Figure 6

View into the impeller at the investigated operating point (q=1.17,  NPSH=4 m)

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Figure 7

Cavitation on the tongue of the volute (front view—left and side view—right)

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Figure 8

A sequence showing evolution of the cavitation structure as the blade passes the tongue

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Figure 9

Time averaged velocity field in the vicinity of the tongue with notated average incidence

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Figure 10

A sequence showing the velocity field near the tongue as the impeller blade passes it

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Figure 11

Evolution of the incidence angle as a function of impeller blade position

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