Effect of inlet gas volume fraction on shafting vibration of multiphase pumps under low discharge conditions

Inlet gas volume fraction (IGVF) is one of the main factors that can influence the stability of multiphase pump. However, under low liquid phase discharge condition, the influence of IGVF on the stability of the shafting system of the multiphase pump is still not confirmed. In this study, a vibration test system is established. Then for different IGVF conditions at low liquid phase discharge, the vibration data of the shaft and bearing house of a three-stage multiphase pump are collected and analyzed. Images inside the impeller are also captured synchronously to illustrate the flow mechanism. The results indicate that the amplitude of the shaft vibration has a significant nonlinear relationship with the increase of IGVF. The internal flow mechanism that leads to the variation of the shaft vibration amplitude is the conversion of the gas-liquid flow pattern in the impeller. The vibration energy of the shaft under gas-containing conditions is enhanced compared to that under pure water conditions. The increase of IGVF not only results in the migration of shaft vibration energy from high frequency to low frequency, but also leads to more significant multifractal characteristics of the shaft vibration. All of these increase the risk of shaft resonance.