## 4 The Flow Characteristics of Two Inlet Configurations under High Maneuver Condition
### Analysis of Transient Flow Characteristics
#### 4.2.1 Flow Characteristics of the Submerged Inlet with the Rapid Pitch Maneuver  
Let the mesh in the internal rotating region conduct a simple pitching maneuver around the y-axis at two angular velocities, and the calculated total pressure recovery coefficient of the outlet of the inlet is shown in Figure 14.  
Figure 12: Flow characteristics of inlet under typical sideslip angles. Figure 13: Two Motion Laws of Transient Maneuver. It can be seen from Figure 14 that the instantaneous total pressure recovery coefficient of two configurations of the inlet during pitching maneuver shows a trend of first increasing, then decreasing and then increasing with the increase of \(\alpha\), which is consistent with the trend of equivalent steady state calculation results. However, the value of \(\sigma\) calculated in the steady state is slightly higher than that calculated in the transient state. When the \(\alpha=-30^{\circ}\), the difference between the results calculated in the steady state and the results calculated in the transient state is the largest, about 0.05. The difference decreases with the increase of \(\alpha\). When \(\alpha\) reaches \(30^{\circ}\), there is almost no difference between the steady-state and transient results. It can be seen from Figure 14a that there is a certain hysteresis phenomenon in the pitching maneuver cycle. In the pitching up process (in the process of \(\alpha\) from \(-30^{\circ}\) to \(30^{\circ}\)), the total pressure recovery coefficient is slightly lower than that in the pitching down process (in the process of \(\alpha\) from \(30^{\circ}\) to \(-30^{\circ}\)), and the hysteresis phenomenon is obvious in the range of \(-10^{\circ}\) to \(0^{\circ}\). It can be seen from Figure 14b that \(\sigma\) of the distributed inlet configuration fluctuates significantly during the pitching maneuver period. In the range of \(\alpha\) from \(10^{\circ}\) to \(20^{\circ}\), it can be clearly observed that \(\sigma\) of the pitching up maneuver (in the process of \(\alpha\) from \(-30^{\circ}\) to \(30^{\circ}\)) is significantly lower than that of pitching down maneuver (in the process of \(\alpha\) from \(30^{\circ}\) to \(-30^{\circ}\)). This is because the submerged inlet is located in the belly of the missile, and the airflow has an upward velocity relative to the missile in the process of pitching down, which increases the included angle between the airflow and the plane where the submerged inlet opening is located, thus increasing the windward surface of the inlet to facilitate air intake. In contrast, the airflow has a downward velocity relative to the missile in the process of pitching up, which reduces the angle between the airflow and the plane of the submerged inlet opening, and thus reduces the windward surface of the inlet, which is not conducive to air intake. The hysteresis of the conventional submerged inlet configuration is more obvious in the range of \(-10^{\circ}\) to \(0^{\circ}\), while the hysteresis of the distributed submerged inlet configuration is more obvious in the range of \(10^{\circ}\) to \(20^{\circ}\). The reason for this difference is the different intake mechanism of the two configurations. Specifically, the conventional submerged inlet mainly relies on the suction vortex generated by the side edge at the inlet to drive the airflow into the inlet, so it is more sensitive to the angle between the airflow and the side edge when the airflow passes through the side edge. In addition to the entrained vortex generated by the side edges of the main inlet, the side edges of the auxiliary inlet distributed on both sides of the missile body are also generating entrained vortex beneficial to the intake. In the process of angle of attack change, the entrainment vortices intensity of the main inlet  
Figure 14: Total pressure recovery coefficient versus angle of attack. (**a**) Conventional submerged inlet, (**b**) Distributed submerged inlet.