Pump as turbine is a device for energy conversion. To master the characteristics of energy transformation, especially within impeller, plays important roles for further optimum design of pump as turbine. In order to analyze the energychanging features in detail using computational fluid dynamics, the impeller is divided into six regions by the radius. Under different operating conditions, the variations of power in the different radial cross-section of the impeller, the input net energy in different regions of the impeller, and the energy from the fluid to the impeller were demonstrated. The results show that the pressure energy of fluid is primary for impeller work, instead of the kinetic energy; the front and middle regions of the impeller (about the area of (0.6-1.0) D 2 ) are important parts for energy conversion; in the rear area of the impeller, it acquires little energy from fluid relatively, what's more, the fluid not only does not work to impeller, but also consumes the impeller mechanical energy under the large flow conditions. So this research may point out the direction for optimization design of the impeller blade.

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The internal flow is very complex in the multiphase pump, especially in the static impeller, where the flow is more disorganized than that in the impeller wheel, and it will cause greater hydraulic losses. In order to investigate deeply the flow rules within the static impeller, all kinds of the flow losses are analyzed quantificationally in the multiphase pump. Based on the standard SST k-ω turbulence model, selected the helical axial flow multiphase pump as the research object, used the three-dimensional modeling software for the three-dimensional modeling of the flow through parts of the multiphase pump, such as impeller wheel, the static impeller, the suction chamber, and the extrusion chamber. The ANSYS software is used to simulate the three-dimensional flow in static impeller, and the ICEM software was used to divide the mesh of suction chamber, press outlet chamber, moving impeller and static impeller respectively. The results show that the flow within the impeller wheel is more uniform than the static impeller, and larger axial vortexes appear in the static impeller. Compared with the impeller wheel, the effect of the flow rate on the flow within the first static impeller is greater. The friction loss is the largest among all kinds of losses in the static impeller, followed by the turbulence dissipation loss. What’s more, the shock loss and the contraction loss are the smallest, they are all less than 20%, and the main loss within the static impeller are the turbulent dissipation loss and friction loss. The proportion of energy losses in the first and second static impeller is almost the same, which is around 50%, respectively. The results can be used as a reference for the improvement of the hydraulic performance of the multiphase pump.