Abstract:
The quest for greater pump efficiency and improved reliability has focused
research topics in the understanding of pump hydraulic and dynamic behaviours.
On-Design pump performance has been optimised utilising modern design
strategies incorporating Computational Fluid Dynamics technology to predict and
simulate the fluid flow in a pump.
The fluid conditions within the arrangement of an impeller and collector present
a complex unsteady flow phenomenon, which give rise to fluid structure
interaction. Periodic hydraulic excitation forces are generated as a consequence.
The interaction forces increase as the flow recirculation grows; the flow becomes
less uniform at the impeller periphery. Thus, the highest magnitude of forces is
observed at low flow and high flow operating conditions. They are impacted onto
the rotor and transmitted to the bearing housing, although the forces are not
quantitatively known.
Lateral analysis of a pump rotor can demonstrate the rotor will not traverse or
operate within a region of a critical speed, however, bearing housing vibration
can be excessive and outside acceptable limits when operating at part load.
The rationale of the project was therefore to employ a numerical modelling
technique to capture hydraulically induced vibration caused by the interaction of
the rotor and stator. A series of transient numerical analyses were carried out to
investigate the unsteady fluctuating pressure field within a single stage pump for
five operating conditions. The hydraulic excitation forces were captured and
incorporated into a rotordynamic model where the corresponding displacement
vibration were evaluated. It was shown that the highest estimated displacement
vibration was at the low flow operating condition and at the cutwater region. An
experimental campaign of the single stage pump validated the unsteady pressure
fluctuations within an acceptable margin of two percent for nominal flow and five
percent for low flow operating point. Greater variations were found when
comparing the numerical and experimental approximations to the displacement
vibration.