A coupling framework for modeling the non-constant-velocity approach of
two fluid particles and the curved film drainage was developed, and an
improved model was presented to predict the variable-velocity approach.
Using this framework, the effect of the constant-velocity and
variable-velocity approach on liquid film drainage was investigated. Two
film drainage models based on immobile interface and fully mobile
interface were adopted. The simulation results showed that the film
thinning rate of the former is much less than that of the latter. In the
case of constant-velocity approach, the immobile interface model showed
a relatively flat curved film, while in the case of variable-velocity
approach, three types of film, wimple, pimple and dimple, can be found.
The different combinations of the drainage models and the approach
velocity boundary conditions were compared with the experiments. The
fully mobile interface model with variable-velocity approach can
reasonably predict the coalescence and rebound of bubbles.