Place: 8th International Conference on Mesoscopic Methods in Engineering and Science (ICMMES) 2011, Lyon, France
We investigate a lattice Boltzmann model which can be applied for the simulation of foams as a multiphase system. In order to decrease the surface tension and increase the lifetime of bubbles, we use the multirange pseudopotential scheme proposed in . Here, the interactions of a given site with single-range neighbors xi + ckΔt, as well as with the double-range ones xi +2ckΔt are taken into account with coefficients G1k and G2k, respectively. Such scheme allows one to vary independently both the pressure from the equation of state which is determined by G1 +2G2, and the surface tension proportional to G1 +8G2 . Particularly, setting G1 +8G2 = 0 significantly increases the decay time of the foam. Unlike the scheme of , the method used preserves the isotropy. To simulate arbitrary equation of state, we apply the method proposed in .
This scheme stabilizes the stationary foam. Under shear, however, the bubbles begin to coalesce, and the foam decays rather fast. In order to overcome this effect, we introduce into the LB equation a second component which acts like a surfactant. It is attracted to the interfaces (regions where the gradient of the density of the main components is large). We introduce an interaction force which is proportional to ∇|∇ρ|2 and also to the density of surfactant. The relative motion of the surfactant and the main component produces a friction force proportional to ρρs(u − us). We use van der Waals equation of state for the main component, and the ideal gas one for the surfactant. Introduction of the surfactant leads to a significant increase of the foam lifetime for a certain range of parameters.
In order to further stabilize the foam (and to get closer to the reality), we introduce one more component which represents the gas filling the bubbles. To prevent the dissolution of the gas, a repulsion force between it and the main component is used, which hinders the collapse of bubbles.
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