Mitigation of blast waves as regards pyrotechnic security is of great concern for the CEA DAM. The objective of this thesis is to understand the physical mechanisms, which underlie the mitigation properties of the aqueous foams. Aqueous foam is a two-phase medium, which is built from an assembly of gaseous cells, which are separated by the liquid phase. The present study focuses on dry foams, having an expansion ratio (inverse of the volume fraction) higher than 20. Two experimental campaigns have been designed and achieved. At first, the behavior of the aqueous foam under shock loading has been studied in a Shock Tube at IUSTI Marseilles. Then, a database on blast characteristics has been obtained in the test field of the Polygone d'Expérimentation de Moronvilliers CEA. The experimental data have helped the development of the numerical modeling, which relies on an Eulerian multiphase formalism, solved by the Discrete Equation Method. The analysis of the Shock Tube data has shown that under high shock loading, the liquid films are prone to rupture and as a consequence, the foam collapses into a spray of liquid ligaments. The Plateau Borders deform and are atomized into a cloud of droplets. The two-phase shock wave structure can be decomposed into two parts. The first one is relative to the foam fragmentation and consists of a precursor shock of amplitude of hundreds of millibar. The relaxation zone then follows where the momentum and energy transfer bring the states of the two phases towards dynamic and thermal equilibrium. The experimental data from the pyrotechnic campaign have also confirmed these findings. Finally, the numerical modeling has also shown that the expansion ratio was the main parameter of the mitigation of the blast wave. The complex structure of the two-phase blast wave from the model compares favorably with the experimental data.
Experimental study and numerical modeling of shock and blast waves in aqueous foams