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TECHNICAL PAPERS

Steady and Unsteady Radial Forces for a Centrifugal Pump With Impeller to Tongue Gap Variation

[+] Author and Article Information
José González

 Universidad de Oviedo, Área de Mecánica de Fluidos, Campus de Viesques, 33271 Gijón (Asturias), Spainaviados@uniovi.es

Jorge Parrondo, Carlos Santolaria, Eduardo Blanco

 Universidad de Oviedo, Área de Mecánica de Fluidos, Campus de Viesques, 33271 Gijón (Asturias), Spain

J. Fluids Eng 128(3), 454-462 (Sep 29, 2005) (9 pages) doi:10.1115/1.2173294 History: Received May 18, 2004; Revised September 29, 2005

Experimental and numerical studies are presented on the steady and unsteady radial forces produced in a single volute vaneless centrifugal pump. Experimentally, the unsteady pressure distributions were obtained using fast response pressure transducers. These measurements were compared with equivalent numerical results from a URANS calculation, using the commercial code FLUENT . Two impellers with different outlet diameters were tested for the same volute, with radial gaps between the blade and tongue of 10.0% and 15.8% of the impeller radius, for the bigger and smaller impeller diameters, respectively. Very often, pump manufacturers apply the similarity laws to this situation, but the measured specific speeds in this case were found to be slightly different. The steady radial forces for the two impellers were calculated from both the measured average pressure field and the model over a wide range of flow rates in order to fully characterize the pump behavior. Again, a deviation from the expected values applying the similarity laws was found. The data from the pressure fluctuation measurements were processed to obtain the dynamic forces at the blade passing frequency, also over a wide range of flow rates. Afterwards, these results were used to check the predictions from the numerical simulations. For some flow rates, the bigger diameter produced higher radial forces, but this was not to be a general rule for all the operating points. This paper describes the work carried out and summarizes the experimental and the numerical results, for both radial gaps. The steady and unsteady forces at the blade passing frequency were calculated by radial integration of the pressure distributions on the shroud side of the pump volute. For the unsteady forces, the numerical model allowed a separate analysis of the terms due to the pressure pulsations and terms related to the momentum exchange in the impeller. In this way, the whole operating range of the pump was studied and analyzed to account for the static and dynamic flow effects. The unsteady forces are very important when designing the pump shaft as they can produce a fatigue collapse if they are not kept under a proper working value.

Copyright © 2006 by American Society of Mechanical Engineers
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Figures

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Figure 1

Experimental setup for the pump measurements (dimensions in m)

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Figure 2

View of the piezoelectric transducers mounted on the shroud side of the pump

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Figure 3

Pressure spectrum as a function of flow rate (D2=0.2m). Position: 20deg from volute tongue in the rotating direction.

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Figure 4

Sketch of the pump unstructured mesh. (Inlet and outlet pipe portions are added).

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Figure 5

Static pressure around the volute for three flow rates (comparison of the numerical and experimental results)

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Figure 6

Experimental comparison of the static pressure force for the two impellers

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Figure 7

Comparison of the static contribution for the force angle around the volute (angles referred to the rotation center to volute tongue direction). Impeller with D2=200mm.

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Figure 8

Comparison of the static contribution for the force magnitude around the volute. Impeller with D2=200mm.

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Figure 9

(a) Comparison of the pressure fluctuations at the blade-passing frequency for the two impellers Q<QN. Experimental measurements. (b) Comparison of the pressure fluctuations at the blade-passing frequency for the two impellers Q⩾QN. Experimental measurements.

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Figure 10

Comparison of the pressure fluctuations at the blade-passing frequency for Q=1.5QN on a shroud plane (z=0.0). Tongue at φ=0deg and D2=200mm.

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Figure 11

Nondimensional pressure fluctuation at the blade-passing frequency for three axial positions at the volute (numerical values). The tongue is at φ=0deg and Q=0.5QN.

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Figure 12

Vector diagram of unsteady radial pressure force from experiments. A blade-passing period for D2=190mm.

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Figure 13

Vector diagram of unsteady radial pressure force from experiments. A blade passing period for D2=200mm.

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Figure 14

Vector diagram of unsteady radial force numerically calculated during a blade passing period for D2=200mm

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Figure 15

Comparison of the vector diagram of unsteady radial force due to the pressure fluctuations during a blade-passing period for D2=200mm. Q=0.6QN.

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Figure 16

Comparison of the vector diagram of unsteady radial force due to the pressure fluctuations during a blade-passing period for D2=200mm. Q=QN.

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Figure 17

Comparison of the vector diagram of unsteady radial force due to the pressure fluctuations during a blade-passing period for D2=200mm. Q=1.5QN.

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Figure 18

Comparison of the vector diagram of unsteady radial force due to the pressure fluctuations and total force during a blade-passing period for D2=200mm. Q=0.5QN.

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