Revealing the evolution of flow structure and pressure fluctuations in a multiphase pump under varying gas phase conditions

Multiphase pumps are vital for extracting oil and gas from deep-sea environments and transporting blended media in chemical processes. The gas phase significantly alters these pumps' flow structure and pressure fluctuations. Our study reveals that gas injection boosts axial and circumferential velocities, disrupts velocity matching between the impeller and diffuser, and leads to the backflow structure and pump surge. Further, the flow in the vaneless region is divided into six regions according to the influence of the mainstream, wake jet, clearance, and end wall, and summarizes four-speed triangle transition modes (VSFTM) in the vaneless region. The VSFTMs in the mainstream and end wall areas worsen flow. Moreover, the turbulent kinetic energy and pressure pulsation in these regions are also significantly enhanced. The VSFTM in the wake and gap zones helps with speed matching but reduces water head. Analysis of pressure fluctuation in the vaneless region shows that the standard deviation and the relative amplitude coefficient of pressure pulsation rise with inlet gas volume fraction (IGVF). A 10% IGVF increase results in a surge of 1.4–1.6 times in the peak relative amplitude coefficient. These findings advance our understanding of the gas phase effect and flow structure in multiphase pumps.