Analysis of shock-wave propagation in aqueous foams using shock tube experiments

Abstract

International audienceThis paper reports experimental results of planar shock waves interacting with aqueous foams in a horizontal conventional shock tube. Four incident shock wave Mach numbers are considered, ranging from 1.07 to 1.8, with two different foam columns of one meter thickness and expansion ratios of 30 and 80. High-speed flow visualizations are used along with pressure measurements to analyse the main physical mechanisms that govern shock wave mitigation in foams. During the shock/foam interaction, a precursor leading pressure jump was identified as the trace of the liquid film destruction stage in the foam fragmentation process. The corresponding pressure threshold is found to be invariant for a given foam. Regarding the mitigation effect, the results show that the speed of the shock is drastically reduced and that wetter is the foam, slower are the transmitted waves. The presence of the foam barrier attenuates the induced pressure impulse behind the transmitted shock, while the driest foam appears to be more effective, as it limits the pressure induced by the reflected shock off the foam front. Finally, it was found that the pressure histories in the two-phase gas-liquid mixture are different from those previously obtained within a cloud of droplets. The observed behavior is attributed to the process of foam fragmentation and to the modification of the flow topology past the shock. These physical phenomena occurring during the shock/foam interaction should be properly accounted for when elaborating new physical models. (C) 2015 AIP Publishing LLC

Modeling of particle cloud dispersion in compressible gas flows with shock waves

“…Other applications concern explosion in the confinement building, where the shock waves can be initiated accidentally. In order to mitigate their effects, an aqueous foam [12][13][14][15] or a water spray system 16 can be used. In this case, the shock-spray interaction can change dramatically the dispersion of droplets, leading to the change in the mitigation capacity of the spray system.…”

Blast Suppression Foam, Aqueous Gel Blocks, and their Effect on Subsequent Analysis of Forensic Evidence*

“…The authors proposed that the mitigation effects were likely due to internal reflections at the air-liquid interfaces, energy loss in breaking foam bubbles, and heating of the water component. These ideas were later experimentally confirmed by other researchers, further contributing insight that rupture of the foam films creates droplets, which absorb energy upon evaporation, elaborating the effect of expansion ratio and bubble size, and demonstrating the reduction in explosive noise that aqueous foams provide (16,(21)(22)(23)(24)(25). The presence of the foam reduces overpressure by a factor of 3-30 (26,27).…”

Pulsed Detonation Hydroramjet: Design Optimization

“…The averaged shock structure in one-dimensional calculations was shown to become less oscillatory and tending to monotonic when the bubble size distribution broadened. Jourdan et al [25] conducted a series of shock tube experiments on shock wave propagation through the columns of aqueous foam, focusing on the shock mitigation capability of the foam. The mitigation effect was shown to be more pronounced for shock waves having a blast-shaped profile due to attached rarefaction waves.…”