PERFORMANCE AND VIBRATION OF A DOUBLE VOLUTE CENTRIFUGAL PUMP - EFFECT OF IMPELLER TRIMMING

摘要

The fluid-structure interaction phenomenon, as manifested by the pressure pulsation excited by rotor-stator interaction, is the main cause of flow-induced vibrations at the blade passing frequency in large and high pressure centrifugal pumps. This phenomenon is strongly influenced by the clearance gap between impeller and volute diffusers/tongues and the geometry of impeller blade at exit. One way to reduce the effects of this interaction is to increase the effective gap by trimming the impeller. However, trimming the impeller will affect the pump performance and the flow pattern inside the pump volute. In the present work, experiments are carried out using a single stage, double-volute centrifugal model pump to investigate the effect of increasing the clearance gap by trimming the impeller on pump performance and vibration. Pressure fluctuations around the impeller inside pump volute are monitored and recorded. The clearance gap was increased three times by trimming the impeller radius by 1 mm, 2 mm, and 3 mm; respectively. Results showed that trimming the impeller reduces the pump vibration at the expense of the developed pump head. The minimum vibration was measured at the best efficiency point of the pump and the vibration amplitude increases when the pump operates at off-design conditions. Impeller trimming is more effective at flow rates equal to and higher that the design flow rate.