## 4 Results and Discussion
### Two Types of Starting Processes under Different Lip Angles
\[\varphi\ =\ \dot{m}\Big{/}\rho_{\infty}v_{\infty}A \tag{4}\]  
\[\sigma\ =\ TP_{t}\Big{/}TP_{\infty} \tag{5}\]  
Next, the inlet with \(\delta\) = 10\({}^{\circ}\) is considered to analyze the second starting process, for which the Mach contour is shown in Figure 8. At Mach numbers of 3.0 and 4.2, an opened separation zone exists in the flow field, and the flow characteristics are the same as those of the inlet with \(\delta\) = 3\({}^{\circ}\). When the Mach number increases to 4.3, the separation zone greatly shrinks and moves downstream. At this time, the separation shock impinges on the cowl, and the spillage disappears completely. Under this state, the separation bubble forms a closed recirculation zone in the duct, therefore called a closed separation zone. With the further increase in the Mach number, the position of the closed separation zone  
Figure 6: Mach number contours during the first type of starting process (\(\delta\) = 3\({}^{\circ}\)). Figure 7: Distributions of the mass flow ratio and total pressure recovery coefficient during the first type of starting process (\(\delta\) = 3\({}^{\circ}\)). gradually travels downstream. When the Mach number reaches 4.7, the closed separation zone completely disappears and a supersonic flow forms in the duct. Figure 9 shows the changes in the mass flow ratio and total pressure recovery coefficient at the throat during the second type of starting process. When the Mach number is low, an opened separation zone exists, and the two parameters are both low as well. At Ma = 4.3, the closed separation zone is formed, the mass flow ratio increases significantly, and the total pressure recovery coefficient also rises sharply (as denoted by the arrows in Figure 9). With a further increase in the incoming velocity, the mass flow ratio increases linearly, and the total pressure recovery also improves. When the Mach number increases from 4.6 to 4.7, the inlet enters the fully-starting state. At this time, the mass flow ratio shows no significant increase; however, the total pressure recovery coefficient rises sharply again. In summary, the second type of starting process can be described as follows. When the incoming Mach number is low, the opened separation zone is formed in the flow field. When the Mach number increases to a certain value, the separation zone enters the internal contraction section and forms a closed one. With a further increase in the Mach number, the separation zone shrinks and moves downstream. As the Mach number increases further, the closed separation zone disappears, and the inlet enters the fully-starting state. In this starting process, the mass flow ratio rises sharply only when the closed separation zone is formed. In contrast, the total pressure recovery coefficient increases significantly at two separate instances: once, when the closed separation zone is formed, and for the second time, when the inlet enters the fully-started state. [PERSON] [3] reported that an inlet could be deemed to be in the starting state when the internal flow does not affect the flow capture ability. On this basis, the inlet with \(\delta=10^{\circ}\) can be considered as entering the starting state at Ma = 4.3. However, a large-scale separation bubble still exists in the duct. Moreover, the separation, reattachment, and reflected shock waves induced by the separation bubble dramatically increase the flow loss, which differs significantly from the fully-starting state. Generally, whether a flow field can be regarded as a starting one can be judged based on two aspects: the flow structure and the inlet  
Figure 8: Mach number contours during the second type of starting process (\(\delta=10^{\circ}\)). Figure 9: Distributions of mass flow ratio and total pressure recovery coefficient during the second type of starting process (\(\delta=10^{\circ}\)). aerodynamic performance.