# Effects of the Damping Parameters on the Opening and Closing Characteristics of Vent Valves
## 1 Introduction  
The instability of the aero engine flow field seriously affects engine performance and even endangers the safety of the engine and aircraft [1, 2, 3]. A surge is an unstable flow characterized by air flow interruption in a compression system. After the compression system enters a surge, the flow through the system and the pressure at the compressor outlet both oscillate at a low frequency over time, resulting in flow blockage or backflow. A number of studies indicated that intake distortion plays a decisive role in the engine stability margin, and intake distortion is an important factor of engine surge [4]. Inlet distortion widely occurs in aero engines, and it is mainly caused by an asymmetric inlet passage and an uneven distribution of pressure, velocity, temperature and density in the compressor inlet flow field [5, 6]. A two-stage pressure control vent valve is a kind of pneumatic valve in aero engines. The main function of the vent valve is to discharge part of the compressed air into the outer duct, improving the surge margin of the engine and achieving a compromise in balancebetween engine performance and safety [7]. The absolute velocity at the inlet of the working impeller is adjusted by way of a mid-stage air release so as to change the angle of attack of the gas velocity relative to the rotor blade and prevent compressor surge. Therefore, the opening and closing characteristics of the vent valve have important consequences for the anti-surge control of aero engines. Many scholars have carried out relevant research on the valve's opening and closing performance. [PERSON] et al. [8] simulated the opening and closing process of the safety valve. The change in spring force and the medium force on the disc were analyzed, the structure of the safety valve was optimized, and the vibration of the valve was reduced. [PERSON] et al. [9] analyzed the movement of the valve spool over time and the pressure distribution of the medium inside the valve. [PERSON] et al. [10] conducted a qualitative analysis on the risk of the influence of abnormal opening of the VBV mechanism on the engine function of a high bypass ratio turbofan engine. [PERSON] et al. [11] conducted a dynamic simulation on the magneto flow variable valve mechanism and concluded that adjusting the valve opening to reduce the valve overlap angle can effectively improve the volumetric efficiency of the engine at low speeds. The valve's opening and closing is mainly controlled by pressure. Some scholars have carried out in-depth studies on the pressure of hydraulic valves and piping systems. [PERSON] et al. [12] studied the optimal design of annular gap pressure-regulating valves by intermittent wind tunnel testing and analyzed its pressure characteristics. [PERSON] et al. [13] proposed a microfluidic gas damper that can provide stable fluid driving pressure and studied the influence of the gas volume and pressure frequency on pressure fluctuation. [PERSON] et al. [14] used computational fluid dynamics to obtain the aerodynamic parameters of solenoid valves and analyze their response characteristics. [PERSON] et al. [15] proposed a hybrid model predictive control method to achieve multi-objective optimization and optimize the pressure-tracking accuracy and valve switching. [PERSON] et al. [16] analyzed the pressure characteristics and frequency response of a decompression method with an outlet of 31.5 MPa. [PERSON] et al. [17] studied the pressure characteristics of high-pressure pneumatic clearance and fixed cavities. [PERSON] et al. [18] studied the pressure-regulating characteristics of four kinds of automatic pressure-regulating valves. The damping hole and pipeline diameter are important components of pneumatic valves which affect the improvement of the valve pressure characteristics and opening and closing characteristics. [PERSON] et al. [19] proposed a method of actively adjusting the variable damping holes to suppress hydraulic shock. [PERSON] et al.