Numerical simulation of air blast waves

Spherical divergent blast wave consecutive to the detonation of an explosive charge is only an ideal representation of most realistic cases. It is observed that the influence of the shape of the charge on the blast wave is negligible in far field. However, in short range, the initial shape of the charge plays an important role in the blast wave formation. Data for spherical propagation are not sufficient to describe the blast wave engendered by the non spherical charge. Thus, a corrective model is required for estimating the pressure at a given distance. This study is based on an approach with a commercial code using the Finite element method with an explicit scheme. Cylindrical charges have been considered taking the aspect ratio as a parameter. The location of the initiation of the charge is also taken into account. The JWL equation of state has been used to simulate the detonation of the charge. Calculations have been performed in Arbitrary Lagrangian Eulerian (ALE) mode. Results have been compared with a series of experiments performed with explosive emulsions and conventional explosives at short range (0.75 m.kg−1/3 < Z < 1.5 m.kg−1/3). The numerical simulation, in agreement with experiments, shows first that the shape of the blast wave depends indeed on the initial shape of the charge but also on the position of the initiation of the detonation. Thus, it is then possible to deduce a local TNT-equivalent along the shock front at a given distance. The evolution of the overpressure generated by the blast wave is plotted versus the scaled distance. A comparison with known data for spherical charges is given and a corrective fit is proposed.

The Author

Dr. Michel Arrigoni
Assistant Professor
ENSTA-Bretagne
2 rue françois verny
29806 Brest, France

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