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The muzzle blast field generated by a gun-launched high-velocity projectile is characterized by a highly underexpanded supersonic exhaust plume, which terminates at a strong shock (the Mach disk), an expanding front of exhaust gases (the contact surface), and an expanding, nearly spherical outer shock (the blast wave). The present study is directed toward theoretical description of the inviscid gas dynamics of the blast field. The rioted features are discussed in terms of well-established theories for spherical blast waves with variable energy release and for steady underexpanded plumes, from which their interaction can be qualitatively described. To obtain a quantitative representation, a finite difference solution is developed for the unsteady compressible flow between the Mach disk and the blast wave, assuming spherical symmetry. The results obtained are in good agreement with experimental measurements of the motion of the blast wave, the contact surface and Mach disk for a 3200 fps round fired from an M16 rifle. V2 = a constant related to energy content of blast field = specific heat at constant pressure = bore diameter = energy = an index: / = 1 for propellant gas, / = 2 for air = an index: y = 0 for planar symmetry, j= 1 for axial symmetry, andy = 2 for spherical symmetry k = arbitrary constant M -Mach number n = exponent of time in blast wave theory for shock position p = pressure r = radial distance S = entropy t = time u = gas velocity z = axial distance Z 0 = origin of a spherical coordinate system /? = exponent of time for description of energy variation in blast wave theory 7 = ratio of specific heats, C p /C v 6 = polar angle p = gas density X = independent variable in blast wave theory Subscripts c = contact surface e = nozzle exit p = projectile r = reference condition s = shock (Mach disk or blast wave) oo = ambient (freestream) value projectile. 1 The acoustic and optical (i.e., flash) characteristics of muzzle blast are also of practical concern. Definition and modeling of the unsteady gas-dynamic processes that occur within the blast field are necessary prerequisites to analysis of these and other related problems, and constitute the subject of the present paper.Descriptions of the gas dynamic processes that generate the muzzle blast field are available elsewhere 2 ' 3 and the details will be only briefly reviewed here in relation to the analytical models to be described. Two blast fields are generated by each round fired; the first, or precursor, is due to the expulsion of a column of air driven out of the barrel ahead of the round, and the second is due to the release of propellant gases from the barrel after the round exits the muzzle. The visible features of these flowfields are exhibited in the shadowgraphs shown in Figs. 1 and 2, from Refs. 3 and 4. The spherical blast wave Fig. 1 Precursor blast field generated by explusion of air from the barrel by the projectile-M16 round fired from Mann barrel at 3200 fps muzzle velocity.

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