## 2 Distributed Submerged Inlet Design  
### Flow Characteristics Analysis of Submerged Inlet  
In order to avoid the engine surge or even engine shutdown caused by the sharp deterioration of the inlet distortion characteristics of the submerged inlet at high angle of attack and large sideslip angle maneuver, it is necessary to discuss the intake mechanism of the submerged inlet under different flight conditions. Figure 1 is a schematic diagram of the mechanism of submerged air intake under different flight conditions. From Figure 1a, it can be seen that when the angle of attack and the sideslip angle are small, the external airflow is mainly driven into the inlet by the entrainment vortices generated by the side edge. As the sideslip angle gradually increases, the side edge with the same direction of the incoming flow can no longer produce a suction vortex that is beneficial to the intake. Although the side edge opposite to the incoming flow can still produce a suction vortex that is beneficial to the intake, the effect of driving the external airflow into the inlet is weakened a lot because the airflow changes the angle of the side edge during the flow around the body, as shown in Figure 1b.  
It can be seen from Figure 1c that the submerged inlet has a windward surface during the flight at a positive angle of attack, which is conducive to improving the inlet efficiency, and the airflow directly flows into the inlet, which experiences less drag from the boundary layer on the surface of the projectile, and the total pressure loss of the airflow is less. It can be seen from Figure 1d that the submerged inlet also has a windward surface during the flight with a negative angle of attack, which is beneficial to improve the intake efficiency, but there is certain energy loss when the airflow is dragged by the boundary layer on the surface of the projectile when it bypasses the surface of the projectile. At the same time, the angle of airflow around the body changes, so the effect of driving the external airflow into the inlet is somewhat weakened.  
From the above analysis, it can be seen that the inlet efficiency of the submerged inlet is low when the sideslip angle and attack angle are large, and some flow control measures should be adopted to improve its inlet performance. However, the use of commonly used passive flow control methods, such as ridge vortex generators, will increase the projected area of the incoming flow direction and increase the resistance while destroying the stealth performance. If the commonly used active flow control methods, such as jet, blowing, and suction flow control methods, are used, they will need to consume additional mass and energy, and need an external drainage pump and other equipment, which is more complex.  
Figure 1: Intake mechanism intention of submerged inlet under different flight conditions.(**(a)** Intake mechanism intention when sideslip angle and angle of attack are small, **(b)** Intake mechanism intention when sideslip angle is large and angle of attack is small, **(c)** Intake mechanism intention when the sideslip angle is small and the angle of attack is positive and large, **(d)** Intake mechanism intention when sideslip angle is small, angle of attack is negative and large).  
Therefore, according to the characteristics of the submerged inlet and the characteristics of the large sideslip maneuver flight, the distributed submerged inlet configuration applied to the large maneuver state is proposed in this paper.