Investigation of supersonic projectile drag reduction using base injection and free stream combustion

Abstract

Base drag accounts for nearly half the total drag of a supersonic projectile. A review is presented of early base flow studies. By relating rate of entropy generation to projectile drag, it is demonstrated that the trailing shock dominates "base drag. Base injection was selected as the means of weakening this shock. Base pressure, as a function of injectant flow rate, was obtained by means of a free jet wind tunnel with a coaxial, Mach 2.0 nozzle. Base pressure ratio (P(β)/P ͚) increases of 13 percent at an effective I(SP) of 465 seconds were achieved with cold nitrogen. Free stream combustion was simulated by nozzle contour. Base pressure increases due to free stream combustion and base injection were shown not to be additive effects.