# Effect of Radial Height of Helical Static Blade on the Cavitation Performance of Inducer
## 4 Results Analysis
### Analysis of Simulation Results
#### 4.2.4. Cavitation Evolution Process  
Figure 11 shows the bubble volume distribution in the flow channel of the inducer and helical static blade under different cavitation numbers with different radial heights.  
Figure 10: Comparison of external characteristic under different radial heights.  
Figure 9: Static pressure distribution under different radial height. Static pressure distribution on suction surface (**a**). Static pressure distribution on pressure surface (**b**).  
When the cavitation number \(\sigma=0.16\), it can be seen in each case that bubbles appear first on the suction surface near the inlet side of the inducer. The analysis of flow field shows that here, the velocity increases dramatically on account of the blade rounding and the backflow vortex, and the local pressure is at its lowest, so that cavitation is most prone to generate in this area. Compared with the separate inducer, a larger scale of cavitation area exists on the suction surface of the inducer with helical static blades under the same  
Figure 11: Bubble volume distribution under different radial heights. (**a**) inducer, (**b**) \(k=0.05\), (**c**) \(k=0.1\), (**d**) \(k=0.15\), (**e**) \(k=0.2\).  
-cavitation number. As the radial height of the helical static blade increases, the cavitation area gradually enlarges, because the backflow vortex at the inlet enhances with the radial height. Then, the bubbles will collapse rapidly due to the effect of the high-pressure fluid behind, with no significant change in head.  
With the decrease in cavitation number, the cavitation becomes more serious, and the cavitation evolution process becomes different for the inducer with and without helical static blades:  
For the separate inducer, the cavitation area mainly extends towards the entrance along the axial direction, and at the same time, towards the hub along the radial direction. When the cavitation number decreases to 0.08, the thickness of the bubbles increases to affect the pressure face of the adjacent blade. At this time, the head of the inducer begins to decrease according to Figure 6. When the cavitation number decreases to \(\sigma_{10\%}\), it can be seen that the bubbles basically cover half of the suction surface, block the channel of the inducer, and cause the head to drop rapidly.  
For the inducer with helical static blades, take, for example, the radial height \(k=0.1\); the channel of the helical static blade is another way in which the cavitation area can extend. At the cavitation number 0.08, although the scale of cavitation area is larger than the same situation in the separate inducer, there are not enough bubbles within the inducer to affect the channel, and the head is manifested as a small increment, as shown in Figure 6. With the increase in the radial height, more space is provided in the channel of the helical static blade for the diffusion of bubbles. Nonetheless, because of the enlarged low-pressure zone, more bubbles generate in the situation of higher radial height under the same cavitation number, which limits the further improvement of cavitation performance.