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Research Papers: Multiphase Flows

Numerical Analyses of Cavitating Flow in a Pelton Turbine

[+] Author and Article Information
A. Rossetti

University of Padua,
Department of Industrial Engineering,
Via Venezia 1,
Padova (PD) 35131, Italy
e-mail: antonio.rossetti@unipd.it

G. Pavesi

University of Padua,
Department of Industrial Engineering,
Via Venezia 1,
Padova (PD) 35131, Italy
e-mail: giorgio.pavesi@unipd.it

G. Ardizzon

University of Padua,
Department of Industrial Engineering,
Via Venezia 1,
Padova (PD) 35131, Italy
e-mail: guido.ardizzon@unipd.it

A. Santolin

Tamanini Hydro S.r.l.,
sal. Dossi 5,
Mattarello (TN) 38123, Italy
e-mail: alberto.santolin@tamanini.it

1Corresponding author.

Contributed by the Fluids Engineering Division of ASME for publication in the JOURNAL OF FLUIDS ENGINEERING. Manuscript received March 26, 2013; final manuscript received March 3, 2014; published online June 2, 2014. Assoc. Editor: Edward M. Bennett.

J. Fluids Eng 136(8), 081304 (Jun 02, 2014) (10 pages) Paper No: FE-13-1195; doi: 10.1115/1.4027139 History: Received March 26, 2013; Revised March 03, 2014

Erosion and wear of hydraulic surfaces are frequent problems in hydraulic turbines, which lead to a decrease of the performance in time and/or in extreme cases to the rotor mechanical failure. These circumstances have negative repercussions on the annual produced power due to the decay of the efficiency, the delivered power, and to the off line periods as result of ordinary and extraordinary hydraulic profiles maintenances. Consistently, the study of this wearing process is an important step to improve the impeller design, and to avoid or minimize the rise of extraordinary maintenance. While mechanical damages are well documented and studied, little information can be found on cavitation in Pelton turbines. In this paper, a CFD model was applied to study the cavitation mechanics on a Pelton turbine. A Pelton runner affected by pitting cavitation was taken as a test case. The bucket geometry was modeled and analyzed using unsteady Reynolds averaged Navier-Stokes (RANS) multiphase analyses. Numerical results allowed us to highlight the different vapor productions during the cut-in water jet processes by the bucket. Furthermore, a simple procedure to identify the locations of higher damage risk was presented and verified in the test case runner.

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References

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Figures

Grahic Jump Location
Fig. 1

Location of hydraulic damage on a Pelton bucket

Grahic Jump Location
Fig. 2

Cavitation damage on the test case runner (a) cavitation pitting on the splitter tip back (b) front face of the bucket

Grahic Jump Location
Fig. 3

Relative jet flow and bucket profile on the symmetry plane of the model

Grahic Jump Location
Fig. 4

Numerical domains (a) rotating and stationary domains (b) detail of boundary condition at the jet inlet

Grahic Jump Location
Fig. 5

Numerical model mesh. (a) Sketch of the mesh of the whole numerical model. (b) Detail of the three bucket and the nozzle. (c) Detail of the refinements on the cut-out of the bucket. (d) Close up of the bucket cut-out.

Grahic Jump Location
Fig. 6

Time evolution of water vapor volume around the reference bucket

Grahic Jump Location
Fig. 7

Location characterized by vapor volume fraction in the CFD model

Grahic Jump Location
Fig. 8

Time evolution of water vapor volume on the front of the cut-out

Grahic Jump Location
Fig. 9

Relative streamline at different instants in the plane z* = 20%; n water

Grahic Jump Location
Fig. 10

Sheet cavitation in the front face of the cut-out

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Fig. 11

Development of water–water vapor for different cut-in position view from the bucket symmetry plane

Grahic Jump Location
Fig. 12

Torque normalized as a fraction of the maximum net torque versus time and time step

Grahic Jump Location
Fig. 13

Relative streamline on the symmetry plane, n water, n water vapor

Grahic Jump Location
Fig. 14

Relative streamline at t = 2.06 ms at different planes: (a) symmetry z* = 0, (b) z* = 20%, (c) z* = 50%, (d) z* = 75%, and (e) z* = 90%, n water, n water vapor

Grahic Jump Location
Fig. 15

Water vapor volume near the cut-out back during the cut-in

Grahic Jump Location
Fig. 16

Development of water–water vapor for different cut-in positions

Grahic Jump Location
Fig. 17

Relative streamline at t = 2.47 ms, z = 20%; n water; n water vapor; n air

Grahic Jump Location
Fig. 18

Cavitation damage on the test case runner (a) compared to the predicted point of damage in CFD analyses (b)

Grahic Jump Location
Fig. 19

Vapor (a) and air (b) volume fraction for three points of Fig. 7

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