关键词: 旋成体, 马格努斯效应, 船尾, 边界层厚度, 边界层位移厚度

Abstract: The pointed rotating body and boattail shape are common layout forms of projectiles such as bullets, cannons and rockets. Studies have shown that the boattail layout has the effect of reducing the bottom resistance and increasing the range, while on the other side it has an adverse effect on the motion stability owing to the increasing Magnus effects of rotating bodies. In order to explain this flow phenomena, the numerical simulation of the flow field of a three-dimensional spinning bullet is carried out to analyze the Magnus forces and moments from subsonic to supersonic, focusing on the comparison between the standard and the boattail bottom shape. The results indicate that the boattail shape has an effect of increasing the Magnus effect relative to the standard shape at all incoming flows, and the Magnus forces and movements are proportional to the boattail angle. In order to reveal the flow mechanism, a comparative analysis of the distributions of Magnus moment coefficients, boundary layer thickness and boundary layer displacement thickness for the two layouts is performed at selected incoming speeds. Results show that the stern Magnus effect at subsonic and transonic speeds is caused by the accelerated flow around the corner, which increases the local pressure coefficient amplitude. For supersonic flow, the Magnus effect is caused by the expansion of the flow at the stern, which increases the boundary layer displacement thickness distortion on both sides of the rotating body. Both of the effects increase the Magnus moment of rotating body, in terms of subsonic flow, this effect occurs at the joint between the column section and the stern section, while in supersonic flow, it occurs at the stern section after the joint. Both effects may play a role when the incoming velocity is around the acoustic velocity point, causing the Magnus effect of the boattail configuration to increase substantially.

Key words: rotating body, Magnus effect, boattail, boundary layer thickness, boundary layer displacement thickness