Blast waves from an e xplosion in air can cause si gnifkant structural damage. As an example, cylindrically-shaped charges have been used for over a century as dynamite sticks for mining, excavation, and demolition. Near the charge, the effects of geometry, standoff from the ground, the proximity to other objects, confinement (tamping), and location of the detonator can significantly affect blast wave characteristics. Furthermore, nonuniformity in the surface characteristics and the density of the charge can affect fireball and Shockwave structure. Currently, the best method for predicting the shock structure near a charge and the dynamic loading on nearby structures is to use a multidimensional, multimaterial shock physics code. However, no single numerical technique curren tly exists for predicting secondary combustion, especially when particulates from the charge are propelled through the fireball and ahead of the leading shock lens. Furthermore, the air within the thin shocked layer can dissociate and ionize. Hence, an appropriate equation of state for air is needed in these extreme environments. As a step towar ds predicting this complex phenomenon, a technique was developed to provide the equilibrium species composition at every computational cell in a n air blast simulation as an initial condition for hand-off to other analysis codes for combusti on fluid dynamics or radiation transport. Her e, a bare cylindrical charge of TNT detonated in air is simulated using CTH, an Eulerian, finite volume, shock propagation code developed and maintained at Sandia National Laboratories. The shock front propagation is computed at early times, including the detonation wave structure in the explosi ve and the subs equent air shock up to 100 microseconds, where ambient air entr ainment is not sig nificant. At each computational cell, which could have TNT detonation products, air, or both TNT and air, the equilibrium species concentration at the density-energy state is computed using the JCZS2i database in the thermochemical code TIGER. Thi s extensive database of 1267 gas (including 189 ioniz ed species) an d 490 condensed species can predict thermodynamic states up to 20,000 K. The res ults of these calculations provide the detailed three-dimensional structure of a thin shock front, and spatial species concentrations including free radicals and ions. Further more, air shock predictions are compared with experi mental pressure gage data from a right circul ar cylinder of pressed TNT, detonated at one end. These complime ntary predictions show excellent agreement with the data for the primary wave structure.
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