14th European Conference on Turbomachinery Fluid dynamics & Thermodynamics
In order to understand the flow characteristic of centrifugal pumps under air-entrained condition, a flow visualization test stand was set up. Pump performance, pressure pulsation and visualized flow behavior of a unshroud impeller centrifugal pump were analyzed under different air-water two-phase flow void. Performance at low flow rates is more sensitive to air content. Upon entering the air, the pressure pulsing frequency domain signal appear a lot of low frequency components. Using the example of air void fraction equal to 2%, axial frequency becomes an important frequency for all flow rates. With increasing inlet void fractions and decreasing flow rates, the bubbles increase in size and tend to agglomerate near the impeller suction side shroud at mid-chord and close to the pressure side close to the impeller outlet plane. The starting point of pump break down is related to a strong inward reverse flow that occurs in the vicinity of the shroud gap of the impeller and volute tongue area.