## 4 Results and Discussion
### Single-Phase Flow Characteristics and Internal Flow Characteristics
#### 4.1.1 Internal Flow under Different Flow Rates  
Figure 10 presents the effects of three different flow rates on various parameters within the hydraulic components (inducer, impeller, and vaned diffuser) at the designed rotating speed. As shown in Figure 10a, the static pressure coefficient (\(\varphi\) = 0.0506) increases from 0 at the inlet of the inducer to 0.0118 at the trailing edge of the inducer blades. Due to the suction effect of the impeller, the static pressure coefficient decreases to 0.00274 in the gap between the inducer outlet and the impeller inlet. It slightly reduces to 0.00156 at the leading edge of the impeller blades. Subsequently, the pressure rapidly rises to 0.635 under the boosting effect of the rotating blades. The static pressure in the gap between the impeller blades and the vaned diffuser blades slightly increases due to the sudden increase in flow cross-sectional area. After the fluid flows into the vaned diffuser, as the cross-sectional area rapidly decreases from the inlet to the throat, part of the kinetic energy converts into static pressure, and the static pressure coefficient reaches 1.01 at the throat. Under different flow coefficient conditions, the static and total pressure coefficient trends along the streamlines are generally consistent. The variations in static pressure coefficient remain similar under other flow coefficient conditions, with higher static pressure coefficients along the central streamline at lower flow coefficients. Equal to the static pressure coefficient, As shown in Figure 10b, the fluid total pressure coefficient increases with the rotation of the inducer and the impeller. The average liquid temperature gradually increases along the central streamline, as presented in Figure 10c, with a rapid increase in temperature within the impeller due to the viscous dissipation of the working fluid. The maximum temperature appears at the throat of the vaned diffuser. The temperature rises at the three flow coefficient conditions with increasing flow coefficient, 0.606 K, 0.326 K, and 0.284 K, respectively. Figure 11 depicts the pressure distribution of single-phase R134a refrigerant at different flow coefficient conditions. As the inducer rotates at high speed, a low-pressure region attaches to the leading edge of the inducer blade on the suction side. This low-pressure region gradually diminishes from the hub to the shroud direction and decreases when the flow rate increases. When the value of the low-pressure area, generated by the rapid flow, falls below the saturation pressure corresponding to the local temperature of the liquid-phase R134a refrigerant, cavitation starts to occur in the region. The cavitation part will be discussed in Section 4.2. In conjunction with Figure 10a, the boosting pressure effect of the inducer decreases with increasing flow rate. Under low flow rate conditions (\(\varphi\) = 0.0217), the inducer provides a static pressure rise of approximately 50 kPa for R134a refrigerant. However, as the flow rate increases, the static pressure rise supplied by the inducer decreases to 31 kPa and 16 kPa, respectively. Figure 10: Effects of different degrees of flow rate on (**a**) static pressure, (**b**) total pressure, and (**c**) temperature along the direction of streamline (\(n\) = 7500 rpm). Figure 12 presents the streamlined chart of relative velocity at the designed rotating speed. Figure 12a shows that when the flow rate is below the design condition, the deviation between the fluid velocity and the inlet blade angle is too large. A pronounced vortex and flow separation occur in the middle region between the pressure and suction sides of the impeller blades. The strong flow separation phenomenon is due to the significant deviation between the flow angle on the impeller outlet and the vaned diffuser inlet blade angle. After being accelerated by the blades, the fluid impacts and rebounds on the blade surface at the vaned diffuser blades.