## 3 Results and Discussion
### Analysis of Flow Field in the Radial Inlet  
The results of three radial inlets under the design operation condition were used for the subsequent analysis. Among three radial inlets, the distinction of the flow field appeared behind the guide vanes, which was due to the TEB and SIS. To evaluate the effect of the SIS on the flow field and guide vane wake, we selected and depict sections A, B, C, and D in the radial inlet in Figure 6. Taking the impeller as a reference, we defined the left curve as the hub and the right curve as the shroud in the meridian plane. Figure 6 also illustrates the streamline in the self-induced slot. It was observed that there was a semicircle flow performance in each self-induced slot. Figure 7 shows the streamline in the self-induced slots and the velocity distribution at the slot's outlet under different angles in the SIS model. Particularly, Figure 7 reveals that the streamline in slots under different angles showed a similar flow phenomenon since the self-induced slots were set at the trailing edge of the guide vane, and the flow passed through the interface between the slot and main flow. Near the hub region, the flow akin to the semicircle flow moved into the slot, turned the flow direction, and finally flowed out of the slot near the shroud region. However, the detail of the streamline in each self-induced slot showed a slight difference. Figure 7 depicts the velocity distribution at the interface between the self-induced slot and the main flow. The ordinate represents the velocity, with the positive value meaning that the fluid flowed into the slot, and the negative value meaning that the fluid flowed out of the slot. As we can see, from 0 spanwise to 0.7 spanwise, the flow mainly flowed into the slot. Contrarily, from the 0.7 spanwise to 0.7 spanwise, the flow flow is also seen to be the same as the flow flow. Figure 5: Compressor characteristic performance comparison of the UGV, SIS, and TEB models. Figure 6: The sections and streamline in the self-induced slot. 1 spanwise, the flow mainly flowed out of the slot. Moreover, the fluid flowing into the slot at 180\({}^{\circ}\) was nearly up to 0.75 spanwise. A higher number means there is a more significant amount of fluid flowing into and out of the slot. Therefore, it is necessary to investigate the reason for the flow phenomenon in the self-induced slot. Figure 8 illustrates the pressure contour at different sections shown in Figure 6 and shows the pressure distribution at the inlet of different sections. It is well-known that the radial inlet is used to turn the flow direction. Therefore, the profile lines of the radial inlet contain the concave and convex arcs. The hub refers to the concave, and the shroud refers to the convex. Figure 8a illustrates that the flow pressure increases at the concave but decreases at the convex, which means that the radial inlet profile lines result in higher pressure near the hub and lower pressure near the shroud. As shown in Figure 8b, the pressure was the highest in section A, and the pressure was the lowest in section C. Moreover, there was a slight difference between sections B and D. Furthermore, section C showed the maximum difference value compared with the others. The pressure difference led to the flow phenomenon in the self-induced slot. The high pressure near the hub made the flow move into the slot, and the lower pressure near the shroud made the flow move out of the slot, as shown in Figure 8. Therefore, the higher pressure difference at section C raised the higher velocity at 180\({}^{\circ}\) in Figure 7b. Figure 8: The (**a**) pressure contour and (**b**) distribution in the SIS model. Figure 7: (**a**) The streamline in the self-induced slot and (**b**) the velocity distribution in the SIS model. Employing the self-induced slot, the flow phenomenon in the radial inlet changed. Figure 9 shows the locations of monitor lines to obtain the guide vane wake distribution.