# CFD and Energy Loss Model Analysis of High-Speed Centrifugal Pump with Low Specific Speed
## 3 Results and Discussion
### Flow Field Analysis of the High-Speed Centrifugal Pump  
The variations of the total pressure and static pressure in the main channel along the streamline are shown in Figure 6. At Mark 1 in Figure 6, the fluid flows into the inducer from the inlet section and the pressure increases under the pre-pressurization of the inducer. With the increasing flowrate, the increasing speed decreases continuously, even a drop occurs at \(Q=5\) m\({}^{3}\).h\({}^{-1}\). The fluid comes out of the inducer and flows into the impeller channel. As the blade does not cover the whole channel, the fluid first enters a leafless area, where the static pressure is bound to be reduced or even become negative and the cavitation is most likely to happen. It can be seen from Figure 6 that with the increase of flow, the negative pressure area expands and the minimum static pressure decreases. Moreover, the dynamic pressure loss in the vaneless diffuser increases. Under the small flowrate and the design flowrate, the pre-pressurization effect of the inducer is well and the static pressure value is reasonable.  
After the fluid enters the area with blades, the pressure rises rapidly and it fluctuates after rising at the junction of the impeller and the vaned diffuser, as shown in Mark 2 in Figure 6. This is because there is the reflux and hub leakage between the impeller and the vaned diffuser. The reflux will cause the total pressure fluctuation in some areas. The hub leakage is the result of the high-pressure fluid flow, which then flows into the impeller. As a result, the total pressure rises to a certain extent. It can be seen from Figure 7 that the distribution of streamline near the impeller outlet is relatively uniform. At \(Q=1\) m\({}^{3}\).h\({}^{-1}\), the flow is blocked by the blades when flowing into the vaned diffuser and forced to divert, resulting in a serious reflux area in the impeller on the pressure surface of the blade. As the flow increases, the flow velocity vector increases while the shock caused by the blade relatively decreases. Under the rated condition, there is still a slight disturbance in the streamline on the blade's leading edge. When the flowrate continues to increase, there is no more eddy current phenomenon. According to the above analysis, the reflux phenomenon on the interface gradually disappears and the dynamic pressure loss accordingly decreases, resulting in the alleviation of the \"fluctuation\" phenomenon of total pressure. The liquid flows into the vaneless diffuser after flowing out of the curved vaned diffuser, whose hydraulic loss increases as the flow increases, as shown in Mark 3 in Figure 6. The pressure distribution of the vaneless diffuser is reasonable under the small flowrate and the design flowrate. The drastic change in the cross-sectional area at the interface between the diffuser outlet and motor flow channel leads to the loss of various reflux and secondary flow. At Mark 4 and Mark 5 in Figure 6, which indicates the inlet of the bearing channel, the total pressure fluctuates slightly as the flowrate is three orders of magnitude smaller than the mainstream, so the disturbance is particularly small.  
Figure 6: Pressure distribution of centrifugal pump fluid along streamline. (**a**) Total pressure distribution of centrifugal pump fluid along streamline; (**b**) static pressure distribution of centrifugal pump fluid along streamline.