## 6 Conclusions  
The essence of the self-start of hypersonic inlets is the vanishment of separations near or in the inlet. Experiments were conducted to reveal the self-start characteristics of three distinct types of unsstart modes of the hypersonic inlet (flow modes SSB, LSB, and DSBL). After that, a \"Flow Field Reconstruction Method\" was used to improve the self-start ability of the DSBL flow mode (which is the most difficult to self-start). Finally, the intrinsic flow  
Figure 30: Spatial streamlines from body-side and lip-side separations—Model/SB-1 at the status of M\({}_{0}=4/\)alpha = 8\({}^{\circ}\). Figure 29: Flow structures of different longitudinal sections—Model/SB-1 at the status of M\({}_{0}=4/\)alpha = 8\({}^{\circ}\), DSBL flow mode. (**a**) Mach number contours. (**b**) Pressure contours (d1 \(>\) d2 \(>\) d3 \(>\) d4 \(>\) d5). mechanism of the poor self-start performance of the DSBL unsstart form was revealed via CFD calculation. The main achievements of this study are as follows:  
1. Shock boundary-layer interaction is the main factor inducing the SSB flow mode. This flow mode appears when at a small alpha, and self-start is achieved as the alpha is increased. This kind of self-start takes about 4-5 ms, and the small body-side separation noticeably dwindles as it approaches the transition point. 2. The combined action of congestion in the inlet throat and shock boundary-layer interaction is thought to be the cause of the LSB unsstart mode. Both acceleration and a decreasing alpha contribute to the vanishing of LSB, which takes about 2 ms. If LSB vanishing occurs at a small alpha, a remnant of LSB may form the SSB flow mode, and self-start can subsequently be achieved by increasing the alpha. Conversely, self-start can be achieved directly. 3. Separations of the DSBL unsstart mode are difficult to vanish directly. Thus, self-start is hard to achieve only through acceleration. Because a decreasing alpha contributes to the flow mode transformation from DSBL to LSB (the time consumed is about 2 ms), self-start may be achieved via the following path: the prompt flow mode being converted into the intermediate form of LSB at first, and then achieving self-start. 4. The stable flow structure of DSBL at M\({}_{0}\) = 5/alpha = 4\({}^{\circ}\) (Model/SB-1) was eliminated by blocking the downstream channel, and then the LSB flow mode was reconstructed. Self-start was subsequently achieved in the process of releasing the downstream channel. This self-start improvement method is named the \"Flow Field Reconstruction Method\". 5. Detailed flow characteristics of the LSB and DSBL flow modes were revealed via the CFD calculation, from which the reason for the poor self-start performance of the DSBL flow mode was deduced: the vanishment of lip-side separation cannot benefit from broadwise spillage with the resistance of sideboards. Regardless, large-scale separation on the lip side is very difficult to vanish only by swallowing downstream. Because of a strong shock boundary-layer interaction and significant three-dimensional flow, the flow problems of a hypersonic inlet are very complex. Thus, multiple unsstart modes were induced, which made the self-start characteristics of hypersonic inlets extremely intricate, and classical double-solution theory was no longer applicable. Based on this, the self-start characteristics of a hypersonic inlet with the existence of multiple unsstart modes were revealed in this study. As for the worst unsstart form, the DSBL flow mode, the mechanisms of this mode's poor self-start performance and self-start improving method were explored. Therefore, this study is very innovative; it not only expands the theory of start problems but also has great significance in guiding the engineering design of hypersonic inlets. X.T. : Investigation (lead); Formal analysis (lead); Methodology (lead); Writing--original draft (lead); Writing--review and editing (lead). B.X.