UNSTABLE OPERATION OF A MIXED-FLOW PUMP AND THE INFLUENCE OF TIP CLEARANCE

摘要

Many mixed-flow and axial flow pumps exhibit a so-called unstable head curve. Due to the risk of instabilities this flow region is usually avoided during pump operation. This paper presents experimental and numerical research on the relation between the instability in the head curve and the magnitude of unsteady hydraulic forces. It is found that there is a strong influence of the extend of the clearance gap between impeller blades and casing. The spectral content of the forces shows evidence of rotating instabilities. It indicates that not only instability of the head curve and unsteady forces are interrelated, but also rotating instabilities play a role in this phenomenon. Results of CFD calculations are presented as well, showing the difficulties in simulating the flow under such conditions.