Numerical Study On Drag Reduction Of The Projectile With Base Cavity

In this paper,the commercial sofware Fluent is used to simulate the unsteady flow field of two dimensional projectile with different base cavity in subsonic transonic and supersonic speed.We also simulate two dimensional projectile with different base cavity numbers in subsonic.The reason why we do that is due to the fact that we want to know the effect the base cavity on the base flow field.We analyze the similarities and differences of the base flow field with / without base cavity in the subsonic speed,and the base cavity effect on the vortex formation,vortex shedding frequency and drag coefficient,explaining why the base cavity can reduce drag.In addition,the base flow field of the projectile in supersonic flow is analyzed and its drag coefficient is compared to see if there is a drag reduction effect.Finally,the numerical simulation of the different base cavity number is carried out under the condition of Mach number 0.4 with base cavity depth of 0.5D.The results show that there is a certain difference in the formation of vortices in the subsonic flow and low transonic with different base cavity depth.When the projectile is blunt,the vortex is periodically shedding and the vorticity is strong.But with the increase of the base cavity depth,the part of the vortex structure or the complete vortex will be at some time into the base cavity,and with other vortex fusion,expansion,and then weaker vortex will fall off from above.However,in the high transonic and supersonic flow,there is no vortex shedding.In addition,the simulation results also show that the vortex shedding frequency decrease with the increase of base cacity depth.When the Mach number is 0.4,the shedding frequency of the vortex shows a decrease trend with little change in the value.When monitoring the drag coefficient of each cases,we find that the base cavity reduces the drag coefficient of projectile in the subsonic and transonic flow;meanwhile increases the drag coefficient of projectile in the supersonic flow.In the numerical simulations of the different number of base cavity in the subsonic speed,it is found when the number of base cavity is one,the effect of drag reduction is the best.