Numerical and Experimental Investigation on the Flow Induced Oscillations of a Single-Blade Pump Impeller

[+] Author and Article Information
F.-K. Benra

 University of Duisburg-Essen, Faculty of Engineering Sciences, Institute of Energy and Environmental Engineering, Turbomachinery, P. O. Box 1629, 47048 Duisburg, Germanybenra@uni-duisburg.de

J. Fluids Eng 128(4), 783-793 (Dec 22, 2005) (11 pages) doi:10.1115/1.2201629 History: Received November 01, 2004; Revised December 22, 2005

This contribution is addressed to the periodically unsteady flow forces of a single-blade sewage water pump, which affect the impeller and produce radial deflections of the pump shaft. The hydrodynamic excitation forces were calculated from the time dependent flow field, which was computed by numerical simulation of the three-dimensional, viscous, time-dependent flow in the pump. A commercial computer code was used to determine the time accurate Reynolds averaged Navier-Stokes equations. The transient radial flow forces at all time steps for a complete impeller revolution affect the rotor of the single-blade pump and stimulate it to strong oscillations. To determine the influence of the vibration stimulation forces on the dynamic behavior of the pump rotor, an investigation of the rotor’s structural dynamics was accomplished. A dynamic time analysis for the pump rotor provided the dynamic answer from the structural model of the rotor under the influence of the flow forces. The hydrodynamic forces, which were calculated before, were defined as external forces and applied as the load on the rotor. The resulting impeller deflections were calculated by a transient analysis of the pump rotor system using the commercial finite element method software PROMECHANICA . To verify the results obtained by standard numerical methods, the radial deflections of the impeller of a commercial sewage water pump, which has been investigated numerical in advance, were measured for the horizontal and for the vertical coordinate direction by proximity sensors. The measured data were compared to the computed amounts for a wide range of pump operation. The results show a good agreement for a strong part of an impeller revolution for all investigated operating points. The simultaneous measurement of vibration accelerations at the outer side of the pump casing showed the effects of the time-dependent flow, which produce hydrodynamic forces acting at the impeller of the pump and stimulating it to strong oscillations.

Copyright © 2006 by American Society of Mechanical Engineers
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Figure 2

Numerical model of a single-blade pump

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Figure 3

Calculated static pressure distributions at several impeller positions (half blade height)

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Figure 4

Calculated radial hydrodynamic forces for several operating points without taking impeller side chamber flow into account

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Figure 15

(a) Rotor orbits for n=1000min−1, (b) rotor orbits for n=1250min−1, (c) rotor orbits for n=1440min−1

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Figure 16

(a) Radial accelerations at the pump casing, (b) axial accelerations at the pump casing

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Figure 5

(a) Averaged hydrodynamic forces depending on flow rate, (b) averaged hydrodynamic forces depending on rotational speed

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Figure 6

Coupling model of a fluid-solid problem

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Figure 7

Calculated natural frequencies of the single-blade pump rotor

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Figure 8

Hydrodynamic forces obtained by numerical simulation for nominal speed of rotation

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Figure 9

Computed deflections due to hydrodynamic forces for four operating points (nominal speed of rotation)

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Figure 10

Calculated impeller orbit curves

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Figure 11

Calculated rotor oscillations due to hydrodynamic forces for different speeds of rotation

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Figure 1

Measured head characteristics and vibration amplitudes of a single-blade sewage water pump

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Figure 13

(a) Application of proximity sensors, (b) sensor calibration curve

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Figure 14

Measured raw signals of sensors for the operating point: n=1440min−1, Q=11L∕s

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Figure 17

(a) Frequency spectra of radial accelerations (n=1440min−1), (b) frequency spectra of axial accelerations (n=1440min−1)

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Figure 18

Influence of impeller side chamber flow on hydrodynamic forces

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Figure 19

(a)–(c) Comparison of calculated and measured rotor orbit curves for three flow rates

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Figure 12

CAD volume model of test facility for the single-blade centrifugal pump




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