The Aerodynamic Characteristics Of Supersonic Spinning Projectiles And Their Flow Separation Control

Precision strike is the general trend of the modern warfare.However,the boundary layer separation phenomenon will occur subsequently on the surface of the conventional projectile when it flies,which causes its vibration,even make it instable under certain conditions.Despite the boundary layer separation can be suppressed quite much by the rotation of the projectiles,it still occurs during the flight.Therefore,the researches on aerodynamic characteristics of spinning projectiles and the boundary separation control on their surface are great significant for the optimization and modification of the supersonic spinning projectiles.Based on Detached Eddy Simulation(DES)method,second order AUSM+ format and sliding mesh technique,numerical simulations were performed for the flow fields of the typical spinning projectiles,and numerical results obtained were agreed with the previous results.Further more,the mechanism of the Magnus phenomenon and its influence on the surface pressure of spinning projectile with the change of the angle of attack,Mach number and rotate speed was investigated.Then,the influence of boattail shape on the aerodynamic characteristics of the spinning projectile was studied by changing the boattail length and angle.In addition,the flow fields around the supersonic spinning projectile with passive vortex generators(PVG),such as micro ramp and micro vanes and active vortex generator(AVG),were simulated and discussed.It revealed the mechanism of vortex generator on the boundary layer fluid separation control of spinning projectiles,and it was found that the micro vortex generator(MVG)could improve the flight stability of conventional spinning projectile.The main work and achievements are descried as follows:The Magnus effect on a typical 6.37 diameter long tangential-ogive-cylinder type projectile was simulated and compared with the previous experimental and simulated results,which could verify the reliability of numerical methods in this paper.In order to further reveal the Magnus phenomenon of the spinning projectile,the flow field of a typical 6-cal SOCBT projectile was simulated numerically.The results show that there is a great influence of boattail geometry on the Magnus effects.Magnus force and moment coefficients increase gradually with the increase of the angle of attack,especially as the angle of attack is small,Magnus force and moment coefficients increase linearly.At the same rotate speed and angle of attack,the Magnus effect will decrease with the increase of Mach number.Magnus force and moment coefficients will increase linearly with the increase of the rotate speed as other conditions are same.Based onthe above numerical results,a set of simple and high precision engineering estimation formulas for Magnus force and moment coefficients were given.The previous research results show that there is a great influence of the boattail on Magnus force and moment,so as to study its principle,the long tangential-ogive-cylinder type projectile was used as the initial model,and the influence of the boattail shape on the aerodynamic characteristics of the spinning projectile was studied by changing the boattail angle and length.The results show that the pressure on the windward wall of warhead increases after adding the boattail,which results in the increase of the drag and lift coefficients,but the coefficients decrease with the increase of boattail length.The lift coeficient shows a decreasing trend with the increase of boattail angle,but the drag coefficient becames a slight periodic fluctuation with the increase of the boattail angle from 5° Magnus coefficients show an increasing trend with the increase of boattail length and boattail angle.In addition,according to the variatio?n trends of all aerodynamic coefficients,the reasonable range of boattail length is 0.8cal?1.2cal,and the reasonable range of boattail angle is 7 °?10°,which is in conformity with the present conventional spinning projectile.PVGs were mounted on the front of the shoulder of the standard 122mm finned projectile and 155mm projectile,and the flow fields were simulated to study the boundary layer separation control process of the PVGs.Then,two kinds of PVGs,micro ramps and micro vanes were applied to control the flow separation of the standard 155mm projectile,respectively.The flow fields of the projectile with two kinds of PVGs were simulated to discuss the differences of control mechanism.The results show that the streamwise vortex strings inducted by micro ramps are attached to the projectile surface,so as to inhibit flow separation of the boundary layer.In addition,the lift coefficient and pitching moment coefficient become stable obviously,and their vibrations over time are eliminated virtually after adding micro ramps on the projectile.As a result,the flight stability of projectile is improved.The wake vortexes structures of micro ramps and vanes are quite different,but control mechanisms of two kinds of PVGs are almost same.They both can inhibit the fluid separation of boundary layer on projectile surface effectively,and eliminate vibrations of lift and pitching moment coefficients.As a result,two kinds of PVGs both can improve the flight stability of supersonic spinning projectiles.The control effects of the AVG,jet vortex generator on boundary layer separation of 122mm finned projectile and 155mm projectile were studied numerically with the use of DES method.The simulations were performed on the flow fields of the projectile with and without jets.The fluid separation control mechanism of jet and the effect on aerodynamics characteristics of spinning projectile were discussed in detail.The influences of different parameters of the jet on the control effect were also investigated.The results show that jet control is conducive to inhibit the fluid separation on projectile surface,and reduce the vibration of aerodynamic coefficients.In addition,jet control can reduce the shake of projectile body and improve the flight stability of the projectile.For the finned projectile,jet control can make its lift coefficient and pitching moment coefficient increase obviously,thus the axis of the projectile can draw close to the direction of velocity vector much more quickly.As a result,the flight stability and shooting accuracy of the finned projectile can be improved.For the spinning projectile,jet control can increase the lift coefficient and make the drag coefficient unchanged,so as to extend firing range of the projectile.Meanwhile,the jet control can reduce the pitching moment coefficient,which can improve the static stability of the projectile.Finally,the influences of different parameters of the jet on the control effect are compared and discussed,and it comes to a conclusion that the effect of jet control is better when Mach number of jet Ma=1.5,pressure of jet Pj=latm and jet angle ?=30°.