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

Abstract

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.

Investigation of unsteady flow-induced impeller oscillations of a single-blade pump under off-design conditions

“…Several steps were included in the measurement procedure: the ''slow rotation without water (slow-dry)'' measurement to register the existing bearing clearances and the deviations from the roundness of the outer impeller suction diameter, the ''test speed without water (dry)'' measurement to confirm that the mechanical balance of the rotor was sufficient; and the ''test speed with water (wet)'' measurement. Details about the three steps can be found in the former work by Benra (2006). To obtain the test oscillation value induced by the hydraulic force, the possible mechanical rest unbalances and the deviations from the roundness of the outer impeller suction were subtracted from the wet measurement.…”

“…In the research area of fluid machinery, some numerical research was conducted with a coupled method, but only a few studies considered the vibration problems of pump machinery in which water was the operational medium, such as the works by Benra (2006), Benra et al (2006), Benra and Dohmen (2007), Campbell and Paterson (2011), Gnesin and Rzadkowski (2002), Kato et al (2005), Langthjem andOlhoff (2004), andMuench et al (2010). These numerical and experimental studies offer insight on flow-induced vibration and noise phenomenon in fluid machinery; however, only a few considered the integrated interaction between the fluid and solid with a strongly coupled analysis.…”

Effect of Blade Outlet Angle on Unsteady Hydrodynamic Force of Closed-Type Centrifugal Pump with Single Blade

“…In addition, the relationship between the hydrodynamic forces acting on the impeller and the whirling of the impeller has been investigated [5,[8][9][10]. We have also proposed a design method for single-blade centrifugal impellers and have discovered, for a closed-type centrifugal impeller with a single blade that was designed using this design method as a basis, how the performance characteristics relate to the radial thrust [11].…”

Numerical Analysis of Pressure Fluctuation Intensity for a Low-Speed Sewage Centrifugal Pump

“…However, a severe problem caused by strong rotor-stator interaction is faced with this hydrodynamic unbalanced impeller structure, especially when the sewage pumps are developed for large scale and high power nowadays. The strong unsteady flow and pressure fluctuations caused by RSI in the pump generally cause the periodically hydrodynamic force acting on the impeller surface and result in strong rotor vibrations [1,2]. The reliability of the pump, therefore, will be decreased obviously, and the pump users will face the high maintenance cost of the pump and other severe problems.…”