Abstract: Gas-liquid two-phase centrifugal pumps are widely used in agriculture, water environment, nuclear industry, and petroleum industry. Centrifugal pumps perform most efficiently when operating under single-phase flow conditions. However, the presence of gas causes head degradation, low efficiency, and low hydraulic performance; and surge is one of the most serious problems faced by gas-liquid two-phase centrifugal pumps. In this work, the commercial software ANSYS CFX 16.0 is adopted to calculate the three-dimensional turbulent flows in a centrifugal pump with a mid-low specific speed impeller. From the results, we can find out that at the pump inlet, gas gathering becomes increasingly obvious and the gathering area is growing larger with the increasing gas volume fraction at the inlet until a surge occurs. Subsequently, a large amount of gas gathers in the impeller channel and even blocks its passages completely, which is known as surge. To improve the hydraulic performance of the pump under surging conditions, we apply a cavity structure to the pump, and examine in detail its effects on the external characteristics and internal flow field. The results show that under low flow rates, the cavity structure can improve blade pressure distribution and uniform gas phase distribution in the impeller channel, effectively reducing the gas blockage of the pump. This study shows that the cavity structure cannot only balance the pump impeller and reduce the pump weight, but reduce the phenomenon of gas-liquid separation in the flow field.

Key words: gas-liquid two-phase centrifugal pump, computational fluid dynamics, cavity structure, surge, inlet gas volume fraction