Cahn-Hilliard diffuse interface simulations of bubble-wall collisions

Abstract

The collision of a rising bubble with a superhydrophilic horizontal surface is studied numerically using the Cahn-Hilliard diffuse-interface method. For the studied systems, the Bond number, $Bo=\rho R^2 g/\sigma$, varies between 0.25 to 1.5, and the Galileo number, $Ga=\rho (R^3 g)^{1/2}/\mu$, changes between 8.5 to 50. We assume that the viscosity and density of the bubble are negligible compared to the surrounding medium. We show that our computations reproduce experimentally observed dynamics for the collision of a bubble with a solid surface. Furthermore, for the studied range of parameters, the bubble-wall collision is mainly in the inertial regime. Our simulations show that even in the absence of substantial viscous dissipation, the ratio of rebound-to-collision velocity, the so-called coefficient of restitution, is much smaller than one for the studied systems. More importantly, the coefficient of restitution best scales with the Froude number, $Fr=U_{t}/\sqrt{g R}$, the ratio of inertial to gravitational forces.