Study On Aerodynamic Characteristics And Store Safety Separation For Internal Weapon Bay

The internal weapon bay system can reduce the radar cross section and drag of the fighter significantly,which is beneficial for the fighter to achieve stealth and supersonic cruise.Thus,the new generation fighters tend to replace external stores with internal weapon bay.However,there are also some serious aerodynamic issues accompanied with the internal weapon bay,such as shear-layer instability,vortex generation and shedding,shock waves/shock waves,and shock waves/shear-layer interactions.Serious pressure oscillation induced by these flow phenomena will cause fatigue damage to equipments in the weapon bay.During the launching process,the store needs to cross the shear-layer.The strong unsteady flow field will change separation trajectories and attitude angles of the store,which may lead to decreasing the hit rate of store or even colliding with the fighter.Therefore,it is significant to study on aerodynamic characteristics and store safety separation of the internal weapon bay system.The high accurate numerical simulation method is implemented to study aerodynamic characteristics,flow control methods,strong interaction between weapon bay and store,and store safety separation problems.Essential research progresses are as follow:1.Two main near field noise simulation methods were compared synthetically.The results demonstrate that the detached eddy simulation method is more suitable for mechanism research of internal weapon bay flow.Then,the influence of boundary layer thickness on weapon bay flow characteristics and aero-acoustic characteristics was obtained by using this method.The physical implication of the empirical constant was clarified by proposing an improved Rossiter formula derivation method.The relationship between the value of the empirical constant and boundary layer thickness was found,which is helpful to reveal the mechanism of noise frequency shift caused by increasing in boundary layer thickness.2.A new flow control approach to suppress the noise with combination of a porous rear wall and a dissipative cavity was proposed.Noise reduction mechanism of“piston type”and“circulation type”flow inside the dissipative cavity was analysed and efficient dissipative cavity size was obtained.This method can effectively buffer shedding vortex impinge strength,terminate the self-sustained oscillation loop and suppress the aerodynamic noise inside the weapon bay.The impinging frequency and strength of shedding vortices are changed by modifying the leading edge shape,and the aerodynamic characteristic inside the weapon bay was altered.3.To study the strong interaction between the weapon bay and store,a new research and analysis approach was built,which succeeded in solving the store separation and aero-acoustic noise problem simultaneously.By using joint time-frequency analysis method,non-stationary aero-acoustic characteristics of the weapon bay during the store crossing the shear-layer were obtained.Compared with the external separation,it reveals the impact of the unsteady flow field and the shear-layer on the aerodynamic force and separation trajectory of the store.4.Under supersonic inflow condition,complex flow field includes interaction of shock waves caused by the falling store and the bay door,and reflection of shock wave/shear-layer was simulated.The influence of complex flow field on aerodynamic characteristics and motion rule of the store was found.It clarifies the impact mechanism of bay door and door open states on the store separation quality.The separation trajectory varying with inflow Mach numbers,launching speed and initial angular velocities was obtained.This research can enrich the aero-acoustic mechanism of internal weapon bay,provide innovative ideas for flow control method.It will provide reliable references for design of the weapon bay door and store arrangement for the new generation fighters,and offer technical support for the development of store separation strategy.