## 3 Results and Discussion
### Analysis of Flow Field in the Radial Inlet
At different spans of the guide vane (0.1 span, 0.5 span, and 0.9 span), the monitor lines were set behind the guide vanes, and the distance between the lines and the guide vane trailing edge was about 1/4 of the guide vane chord length. Figure 10 shows the velocity distribution at the monitor lines for different radial inlets. It was observed that there were 18 low-velocity regions corresponding to 18 guide vanes along the circumference direction in the radial inlet, i.e., guide vane's wake. In the SIS model, the self-induced slot made the flow move into the slot near the hub region and move out of the slot near the shroud region in the radial inlet. The hub and shroud correspond to the 0.1 and 0.9 spans, respectively. Figure 10 shows the wake velocity of the guide vanes at 0.1 span. The SIS model showed a lower velocity at the wake than the UGV model, which was about 2 m/s to 3 m/s. It means the self-induced slot enhanced the wake intensity near the hub region. As for the streamline in the slot, there was no apparent influence at the middle span. Therefore, the wake velocity of the guide vanes in SIS and UGV were almost the same, as shown in Figure 10. Contrarily, the wake velocity in the SIS model was higher than that in the UGV model at 0.9 span, which was about 10 m/s in Figure 10. Since the flow moved out of the slot, it compensated for the wake deficit, similar to the trailing edge blowing. It indicated that the self-induced slot weakened the wake intensity near the shroud region. According to the judgment criterion of wake, Table 5 reports the non-dimensionalized momentum thickness \(\theta/d\) distribution in different radial inlets. The velocity of the guide vane's wake corresponds to \(\theta/d\approx 0\) in the TEB model and \(\theta/d>0\) in the UGV model. Compared with the UGV model, the \(\theta/d\) in the SIS model was more significant at 0.1 span, and it became more minor at 0.9 span. Compared with the TEB model, wherein the blowing velocity at 0.9 span was about 60 m/s, the velocity in the SIS model was about 20 m/s. Compared with the TEB model, although the self-induced slot method could not improve the wake style to the momentumless wake style, it changed the wake style from the pure wake to the weak wake near the shroud region. However, the price of the self-induced slot method enhanced the wake intensity near the hub region. The changed wake style further affected the downstream flow field. Figure 9: The locations of monitor lines. Figure 11 shows the total pressure comparison of radial inlets at cross-section 1-1, i.e., the outlet of the radial inlet and inlet of the impeller, see Figure 1a. When the flow passed through the guide vane, it flowed from the radial direction to the axial direction. In the UGV model, there were 18 low total pressure regions at cross section 1-1 due to the guide vane wake. See Figure 11a. The difference between the UGV and SIS models around the shroud in the guide vane wake region was that the region of the low total pressure in the SIS model was reduced, particularly in the red circle region, as shown in Figure 11b. However, the SIS model showed lower total pressure near the hub, particularly in the blue circle region in Figure 11b. The total pressure distribution was due to the flow phenomenon in the self-induced slot, which reduced the wake intensity near the shroud and increased the wake intensity near the hub. Because of the extra blowing flow, the  
Figure 10: The velocity distributions of the guide vane’s wake at (**a**) 0.1 span, (**b**) 0.5 span, and (c) 0.9 span. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Momentum Thicknesses \(\theta\)/\(d\)** & **0.1 Span** & **0.5 Span** & **0.9 Span** \\ \hline UGV & 0.404 & 0.332 & 0.370 \\ SIS & 0.444 & 0.326 & 0.266 \\ TEB & \(-\)0.018 & 0.018 & 0.015 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: The non-dimensionalized momentum thickness \(\theta/d\) distribution in different radial inlets. wake region almost disappeared in the TEB model, see Figure 11c.