Conclusion
On the basis of pressure measurements and frame photography, we examined breakup of a dry foam in shock waves with MS<1.4.
It was established, that in a polyhedral dry foam a wave forms with 1) a leading pressure jump, which propagates through gas phase, and 2) a relaxation zone of pressure increase to a maximum level. The shockwave propagation process is accompanied by breakup of the foam structure.
The initial stage of foam breakup is related to the deformation of the foam cells, their displacement in the direction of wave motion, and breakup of the cell walls. Subsequent break-up of the cell edges and the formation of a gas-droplet suspension follows a mechanism analogous to the stripping of the surface layer of a droplet by gas flow around it. Measured induction times and droplet breakup times are in satisfactory agreement with values calculated from formulas for droplets, if the radius of curvature of the cell edge is taken as the characteristic dimension.
The breakup of foam cells is the initial stage of the interaction of the shock wave with the foam. The formation of a gas-droplet medium and energy transfer between the droplecs and the flow ends much later under the conditions investigated and can take from 300 to 600 usec.
The authors thank B. I. Palamarchuk and B. E. Gel'fand for useful discussions and constructive comments on the contents of this work.
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Moscow. Translated from Fizika Goreniya i Vzryva, Vol. 28, No. 5, pp. 108–116, September–October, 1992.
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Britan, A.B., Zinovik, I.N. & Levin, V.A. Breaking up foam with shock waves. Combust Explos Shock Waves 28, 550–557 (1992). https://doi.org/10.1007/BF00755733
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DOI: https://doi.org/10.1007/BF00755733