On the Penetrator Nose Drag Measurements

Abstract

In the current study, a rigid body penetrator nose shape that is optimized for minimum penetration drag [1] has been tested to determine the aerodynamic drag of such a penetrator in comparison to three additional nose shapes. Other nose shapes tested were an ogive cylinder, a 3/4 power series nose, and a standard cone. Fineness ratio for the studied nose geometries was chosen as l/d = 1 to maximize variation of the aerodynamic drag forces acting on the nose shapes. This paper discusses the measurements carried out in the University of Alabama’s 6″ × 6″ supersonic wind tunnel, using a 4 component force balance system. In separate experiments, drop tests were made in a viscous fluid to determine the skin-friction effects on these nose shapes. Supersonic wind-tunnel experiments were performed on each of the nose shapes at nine different Mach numbers ranging from 2 to 3.65. Results show that the nose shape optimized for penetration has the lowest drag coefficient of all the shapes at each Mach number within an uncertainty of 5.75%. In the viscous flow drop-test experiments, each nose shape was dropped from rest through water and then separately through viscous fluid (Nu-Calgon vacuum pump oil) under freefall conditions. Each drop was recorded via videotape, and the video was then analyzed to find the terminal velocity of each individual nose shape. Using classical dynamics equations, the weight, buoyant force, and experimentally determined terminal velocity are used to determine the drag force applied to each nose cone shape. Results indicate that while the optimal shape has a lesser drag coefficient than tangent ogive and the cone, the 3/4 power series shape is observed to have the least drag coefficient. In addition to the experiments performed, results on further investigation of the optimal nose shape for penetration are presented. The nose shape has been split into a series of line segments, and a program written has been utilized to search through numerical space for the combination of line segment slopes that produces the nose geometry with the lowest nose shape factor. The results of the numerical analysis in this study point to a different nose shape than the “optimal nose” shape tested in the current study.