Investigation of base drag in gun launched shell projectile

Abstract

A typical shell projectile geometry was studied both numerically and experimentally for the possible base drag reduction using a novel passive technique called Inward Turning Base Bleed (IWTB). It is well known that the base drag arises due to low pressure acting at the base surface. The contribution of base drag in overall drag would be in the order of 30 to 40% at transonic and supersonic free stream Mach numbers. If any effort is made to reduce the contribution of this base drag it would eventually increase the range of the object. In this novel IWTB approach a small quantity of relatively high-pressure air is naturally drawn from the outer surface of the shell projectile and directed towards low pressure area at the base surface in order to increase the base pressure. For implementing the IWTB a cavity at the base needs to be created. Based on previous studies and available space, a few variations were carried out based on cavity optimization parameters such as lip thickness, ratio of cavity lip height to caliber diameter of 0.1, 0.15, 0.175 and 0.2 and depth thickness ratio, ratio of cavity depth to caliber diameter of 0.08, 0.12, 0.15 and 0.2. The outcome of the numerical simulation gave the highest cavity depth ratio of 0.2 and the lowest lip thickness ratio of 0.08 contributing to the highest base drag reduction among all variations. Further for implementing the IWTB method there are various parameters such as bleed hole inward turning angle or entry angle, exit angle, diameter of the bleed hole, the location of bleed holes at the base and number of bleed holes that are needs to be investigated in detail. newline