International Journal of Modern Manufacturing Technologies ISSN 2067–3604, Vol. II, No. 1 / 2010 49 EXPERIMENTAL DETERMINATION OF BLAST WAVES PARAMETERS GENERATED BY FIRING OF LARGE-CALIBER GUN SYSTEMS Liviu-Cristian Matache 1 , Teodora Zecheru 1 , Adrian Rotariu 2 & Tudor Cherecheş 2, 3 1 NBC Defence and Ecology Scientific Research Center, Aeroportului Street, No. 16, CP19 OP Bragadiru, 077025 Ilfov 2 Military Technical Academy, Blvd. George Cosbuc No. 81-83, sector 5, 050141 Bucharest, Romania 3 S.C. MNA PRODCOM IMPEX SRL, Blvd. Iuliu Maniu No.220, sector 6, 061126 Bucharest, Romania Corresponding author: Liviu-Cristian Matache, mliviucris@yahoo.com Abstract: In order to evaluate the effects of the blast waves generated by firing of large-caliber gun systems against humans and ammunition or other objects placed next to the guns, it is necessary to determine the phenomena generated. The present study presents a qualitative assessment methodology, through high speed shooting procedure, and a quantitative one, using data acquisition systems, for the phenomena that occur when firing of large-caliber gun systems. The data recorded are useful for validating the Computational Fluid Dynamics (CFD) models conceived, and their application for various weapon systems configurations (located on different fighting devices on board ships, etc.), are necessary for the establishment of safety distances for the participant staff and materials and for new weapon systems implementation. Keywords: blast wave, gun system, measurement techniques, slow motion analysis, CFD. 1. INTRODUCTION Without considering a particular weapon system, its operating principle is based on energy transfer. Through deflagration, a propelling charge transforms into gaseous reaction products at high temperatures and pressures, able to effectuate mechanical work, in order to propel projectiles and rockets. They act on the projectile, transferring some of their energy as kinetic energy. The propulsion is achieved shortly after the projectile leaves the barrel. A brief description of a gun system, consisting in ammunition (propellant and projectile) and a barrel (gun or launcher), shows that the main destination of the system is to shoot a projectile or a rocket through the intermediary of different powders or propergols deflagration. Initial rate and kinetic energy of the projectile is necessary for the motion on a trajectory that finally crosses the target selected. Additionally, during the firing of weapon systems, other phenomena associated occur, such as flame, smoke, noise, and blast waves in the air. These undesirable events represent a direct consequence of the projectile propelled by the gases resulted from the powder or propellant deflagration. Since the topic of this study is represented mainly by blast waves generated by shooting bore weapons systems, in the present paper we will focus to these phenomena. The blast waves generated during firing are generally classified by indicating the source of their occurrence: - primary blast waves – they occur due to rapid discharge of propellant gases, after the projectile leaves the barrel; - secondary blast waves – they are a consequence of the unburnt powder particles released from the barrel in the atmosphere; the presence of the oxygen conducts to the rapid afterburning of the propellants, generating the so-called “gun muzzle flashes”. The blast waves generated are characterized by specific pulses and rapid evolution of their state parameters into the external environment in which they propagate (pressure, temperature, density). The generation of the blast waves in the air is followed by transmission and direct wave propagation in various media or objects nearby. These pulses transmit, on their turn, a part of their energy and they induce some important state and kinematic parameters modifications to the environment in which they propagate, with harmful or destructive consequences. The gun muzzle blast or muzzle flowfield apparition begins with the expulsion from the barrel of the air compressed by the projectile accelerated movement and, after that, the propellant flows, rapidly displacing the nearby environment and forming a strong blast wave (the primary blast wave). The blast wave initially constrains the free-flow expansion until it decouples from the flow field. As a result, unique flow features develop in the gun muzzle flow fields (Stiefel, 1988). Generally, the muzzle flow field of a gun exhibits the structure of a supersonic under-expanded jet flow encapsulated by an outer blast wave. Due to the high in-bore gas pressure, the jet flow rapidly exits the muzzle and is severely impeded by the blast wave, during the direct interaction with the blast jet flow. This interaction results in the formation of a turbulent