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Research Papers: Fundamental Issues and Canonical Flows

Numerical and Experimental Analysis of Cavitating Flow in a Low Specific Speed Centrifugal Pump With Different Surface Roughness

[+] Author and Article Information
Phillip Limbach

Chair of Hydraulic Fluid Machinery,
Ruhr Universität Bochum,
Universitätsstr. 150,
Bochum 44801, Germany
e-mail: phillip.limbach@ruhr-uni-bochum.de

Romuald Skoda

Chair of Hydraulic Fluid Machinery,
Ruhr Universität Bochum,
Universitätsstr. 150,
Bochum 44801, Germany
e-mail: romuald.skoda@ruhr-uni-bochum.de

Contributed by the Fluids Engineering Division of ASME for publication in the JOURNAL OF FLUIDS ENGINEERING. Manuscript received September 21, 2016; final manuscript received April 18, 2017; published online July 6, 2017. Assoc. Editor: Matevz Dular.

J. Fluids Eng 139(10), 101201 (Jul 06, 2017) (8 pages) Paper No: FE-16-1619; doi: 10.1115/1.4036673 History: Received September 21, 2016; Revised April 18, 2017

Three-dimensional (3D) simulations with ansys cfx 16.1 as well as measurements of the cavitating flow in a low specific speed centrifugal pump (nq = 12 min−1) are performed for different operation conditions and varying surface roughness. Surface roughness is considered by wall functions in the flow simulations. Good agreement between measured and calculated head is achieved for noncavitating flow. Net positive suction head (NPSH3%) rises toward overload due to incidence, flow separation, and vapor zones at the volute tongue. The NPSH3% rise is slightly higher for rough walls according to measurements and significantly overestimated by the wall function approach, irrespective of the roughness level in the simulation. A low-Reynolds number approach at the volute tongue leads to a more accurate prediction of NPSH3% than wall functions, at the cost of high computational effort.

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Figures

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Fig. 1

Closed-circuit centrifugal pump test rig: 1—tank, 2—closed ball valves, 3—pressure transducers, 4—flow meter, 5—throttle, 6—connection to vacuum pump, 7—vacuum pump, CP1, 2—centrifugal pumps

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Fig. 2

Measured head drop curves for several flow rates

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Fig. 3

Computational domain and grid at the volute tongue

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Fig. 4

Head characteristics dependent on grid resolution and wall treatment

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Fig. 5

Head characteristics dependent on the surface roughness

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Fig. 6

Snapshot of the TKE at the volute tongue for grids CWF, FWF, and FLR at an arbitrary impeller position, which is the same for all grids

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Fig. 7

Snapshot of the cavitation zones illustrated by isosurfaces of the vapor volume fraction (αv=0.1): Sim_CWF_smooth (a) 0.7 φ2,opt, (b) 1.0 φ2,opt, (c) 1.4 φ2,opt, and (d) Sim_FLR_smooth, 1.4 φ2,opt

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Fig. 8

Assignment of the pressure losses leading to a 3% head drop to impeller and volute

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Fig. 9

σ3% characteristics dependent on surface roughness, grid resolution, and wall treatment

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Fig. 10

Time sequence of cloud cavitation at the volute tongue for one impeller blade cycle at 1.4 φ2,opt and ∼σ3%

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