The unstable cavitation flow and the dynamic characteristics of oil-gas multiphase pumps usually lead to vibration, noise, and even pump damage. The multiphase flow mixture model and the full cavitation model were used to simulate the transient flow and dynamic features of the pump. The results show that cavitation changes the inflow conditions, aggregates the unstable flow, and generates large pressure pulsations. It also accelerates the variation frequency of axial force and intensifies the uneven distributions of internal flow and circumferential pressure. Both the radial force on the impeller and its variation amplitude are enlarged. Understanding the characteristics of unsteady excitation induced by cavitation can provide references for studying the mechanism of vibration and noise in multiphase pumps.

The flow inside axial-flow type multi-phase pumps is unstable at the conditions of high-speed and high gas volume fractions. The transient dynamic characteristics induced by the unstable flow will lead to pump vibration. Using the standard k-e turbulence model, the standard wall equation, and the structured grid division technology, the transient dynamic characteristics of the pump at different gas volume fractions were computed by the SIMPLEC algorithm. The axial force and radial force on the pump were calculated by applying integral to the surface area of the computational domain. The results show that the pressurizing performance of the impeller degrades, the dynamic reaction on the blades decreases, while the force acting on the hub increases with the increasing of gas volume fractions. If the gas volume fraction reaches to a certain value, the direction of axial force on the multi-phase pump will change. The radial forces on the first-and last-stage impellers are non-uniformly distributed, and the pressure fluctuation is obvious, while the radial forces on the second-stage impeller and guide vanes are uniformly distributed, and the fluctuation amplitude is small. With the increasing of gas volume fractions, the radial forces on various components decrease gradually.

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