Numerical Investigations On The Missile Separation And Its Flow Control

When the missile separates from an aircraft,the unsteady aerodynamic phenomenon between them become complex and highly transient.Especially for modern supersonic fighters,the separation of missile from aircraft is much more dangerous due to the increase of flighter speed and the modification of its shape.Generally speaking,the modern fighter basically adopts the internal weapons bay.When the door of the internal weapons bay is opened,a series of complex flow phenomena are generated,such as the interaction between shock wave and shear layer,which are not conducive to the missile separation appear.Therefore,it is of great significance to study the missile separation and control its trajectory.Based on the coupling of the computational fluid dynamics/rigid body motion equations of six degree of freedom(CFD/6DOF),with the use of the dynamic mesh technique and the AUSM+scheme,and the high precision detached eddy simulation(DES)method,the three-dimensional flow fields of misslie separation process are solved numerically.Moreover,based on the computational fluid dynamics/computational structure dynamics(CFD/CSD)fluid-solid two-way coupling method,a classical missile separation problem is numerically simulated,the feasibility of the numerical method for missile separation is verified.The main work and results are described mainly as follows:(1)The numerical results of two kinds of numerical simulation methods of CFD/6DOF method and CFD/CSD method are compared.It is found that the flow fields of the two numerical methods have the same wave structures,and the difference of centroid displacement and velocity of the missile during separation of the two numerical methods are very small.The elastic deformation of the missile has little influence on the flow fields and the translational motion of the missile,but has some effects on the angular motion of missile.Moreover,the CFD/CSD method can analyze the structural response of missile.Therefore,the CFD/CSD method has more comprehensive application value.However,since this method needs huge computational resources,it is not applied widely in engineering fields,therefore,we mainly uses the CFD/6DOF method to carry out the simulation investigations on the missile separation and flow control.(2)Based on the CFD/6DOF method,the missile separating processes of a typical air-to-air missile with different angles of attack have been calculated numerically.The results show that when the angle of attack is small,it has little influence on the flow fields,and the missile can move away from the aircraft quickly.However,with the increase of the angle,pressure on the lower side of the wing increases,which has great influence on the separation process.The processes of missile separation at large angles of attack pose a serious threat to the safety of missile and aircraft.(3)The separation processes of a missile from an internal weapons bay with the effect of passive control devices are numerically studied.The flow field and trajectory parameters of the missile are compared and discussed for four different conditions(free separation,and rectangle,prism and wedge control).The mount of control devices in front of internal weapons bay makes the shear layer under the internal weapons bay wider,which facilitates the missile to pass through the shear layer smoothly.At the front of the control device,the typical bow shock wave appears,and a high-pressure region is formed behind the control device.When the missile leaves the bay,high pressure of shock wave acts on the upper side of the missile makes the missile head nose-down,and accelerates the separation process.Under the computational conditions of this paper,the movement of missile is accelerated in all the three cases with control device.The variations of attitude angles of the missile are relatively small and slow for the case of wedge control device,which has the best separation motion.The pitch motion of the missile is relatively large with the other two kinds of control devices.For the case with wedge control device,the center of gravity(CG)displacement of the missile in the z direction decreases with the increase of the wedge length,but increases with the increase of the height,and the same with that of the pitch angle.The variation of wedge height has strong effect than that of its length on the missile separation.(4)The separation processes of a missile from an internal weapons bay with the effect of active control are numerically studied.The influence of a jet flow on the missile separation process is analyzed with the example of a jet in the front of the bay.High pressure jet flow can accelerate the separation of missile and change the angular motion of missile.The smaller the pressure of the jet is,the worse the missile separation becomes.The stronger the pressure under the jet is,the greater the separation distance between the missile and the bay.When the angle of the jet is small(60°),the missile will nose-up after leaving the internal weapons bay and threaten the safety of the aircraft.When the angle of the jet is 90°,the separation movement of the missile is the most stable.The displacement of the missile is larger when the angle of the jet flow is within 120°?130°.