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Flow of an aqueous foam through a two-dimensional porous medium: structure-dynamics couplings

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Foams and Minimal Surfaces

Co-authors: Sin A. Jones (Universit Paris 11), Baudouin Graud (Universit Rennes 1), Simon J. Cox (Aberystwyth University), Yves Mheust (Universit Rennes 1), Isabelle Cantat (Universit Rennes 1)

Flowing foams are used in many engineering and technical applications. They have peculiar flow properties that might be beneficial in applications involving porous media. In particular, viscous dissipation arises mostly from the contact zones between the soap films and the walls, which results in peculiar friction laws allowing the foam to invade narrow pores more efficiently than Newtonian fluids would. We investigate experimentally the flow of a two-dimensional foam in three geometrical configurations. We first consider a medium consisting of two parallel channels with different widths. The flow behavior is highly dependent on the foam structure within the narrowest of the two channels [Jones et al., Phys. Fluids 25, 063101 (2013)]; consequently, the flux ratio between the two channels exhibits a non-monotonic dependence on the ratio of their widths. We then consider two parallel channels that are respectively convergent and divergent. The resulting flow kinematics imposes asymmetric bubble deformations in the two channels; these deformations strongly impact the foam/wall friction, and consequently the flux distribution between the two channels. We quantitatively predict the flux ratio as a function of the channel widths by modeling pressure drops of both viscous and capillary origins. This study reveals the crucial importance of boundary-induced bubble deformation on th e mobility of a flowing foam. We then study the flow of a foam in a two-dimensional porous medium consisting of randomly-positioned cylindrical grains. Irreversibility, intermittency and non-stationarity characterize the velocity field under permanently imposed inlet flow. In this grain geometry, flow channeling appears to be different from what would be expected for a Newtonian fluid, which allows a different part of the pore population to be visited. The influence of the ratio of the typical pore size to the bubble size is also addressed.

This talk is part of the Isaac Newton Institute Seminar Series series.

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