Foam flows in 2D porous media: intermittency and bubble fragmentation
Résumé
Flowing foams are used in many engineering and technical applications. A well-known application is oil recovery. Another one is the remediation of polluted soils: the foam is injected into the ground in order to mobilize chemical species present in the medium. Apart from potential interesting physico-chemical and biochemical properties, foams have peculiar flow properties that applications might benefit of. 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. In most experimental studies no local information of the foam structure is possible, and only global quantities such as the effective viscosity can be measured.Using two-dimensional transparent flow cells, we have previously shown that foam structural [1] and elastic [2] effects significantly impact the flow of foams in porous media. We now present an investigation of foam flow through a two-dimensional (2D) porous medium consisting of circular obstacles positioned randomly in a Hele-Shaw cell (see figure). The foam structure is recorded in time by a video camera and subsequently analyzed by image processing, which provides us with the velocity field and spatial distribution of bubble sizes. The flow exhibits a rich phenomenology, including flow irreversibility, preferential flow paths, local flow intermittency/non-stationarity (despite the imposed permanent global flow rate). Moreover, the medium impacts the nature of the flowing fluid by selecting the bubble size through bubble fragmentation. We investigate how preferential flow paths and intermittency depend on the imposed global flow rate and foam quality (the water content), and show that the spatial distribution of bubble sizes is to some extent correlated with the velocity field. We furthermore measure the evolution, along the flow direction, of the probability density function for bubble sizes, and present a fragmentation model to explain that evolution.References:[1] S. A. Jones, B. Dollet, Y. Méheust, S. J. Cox, I. Cantat, Phys. Fluids 25, 063101 (2013).[2] B. Dollet, S. A. Jones, Y. Méheust, I. Cantat, Phys. Rev. E, in Press (2014).