The pressure distribution on the head of a shell moving at high velocities

Abstract

§ 1. Introduction.-The pressure at any point of a body moving through a fluid may be considered to consist of two components-the static pressure, which would be the pressure at that point, if there were no relative motion between the body and the fluid-and the dynamic pressure due to the relative motion. The sum may be called the total pressure a t the point, and is, of course, always positive ; the dynamic pressure alone may be negative.Experiments, of an introductory kind, were undertaken by the authors, at the request of the Ordnance Committee, to attem pt to determine, as a function of the velocity of the shell, the dynamic pressure at various points on the head of a shell, whose axis of symmetry and direction of motion coincide or nearly coincide. The results appear to be not without general scientific interest, and are therefore presented in this paper by permission of the Ordnance Committee. The authors' best thanks are due to the officers of the Experimental Department, H.M.S. " Excellent," on whose range the firing trial was carried o u t; to the other officers of the Munitions Inventions Department, who shared the work of observation and computation ; to the Director of the National Physical Laboratory, where the comparative observations at low velocities were.m ade in a wind channel; and, above all, to Mr. W. J. Goudie, of University College, London, on whose determina tions of the rates of burning of powder-train time-fuzes at high rotational speeds the whole experiment was based.The fundamental idea of the experiments is the use of a service time-fuze as a manometer to determine the pressure under which the powder is burning.*The rate of burning of a service time-fuze is known from laboratory experiments to be affected by the total external pressure on the vents. Let us assume for the moment that this is the only factor that influences the rate of burning. A series of observations, for shells fired along the same * A service time-fuze contains a train of gunpowder, which is ignited by a detonator pellet on the shock of discharge from the gun. The " setting " of the fuze can be varied so that a length of powder train depending on the setting is burnt before the magazine of the fuze is ignited and the shell exploded. The setting is specified by a number which defines the length of composition burnt on an arbitrary scale. The time of burning is taken as equal to the time interval between the firing of the gun and the bursting of the shell.on May 11, 2018 http://rspa.royalsocietypublishing.org/ Downloaded from