Toward the predictive simulation of bouncing versus coalescence in binary droplet collisions

Turbulent Flows With Drops and Bubbles: What Numerical Simulations Can Tell Us—Freeman Scholar Lecture

“…For these reasons, the adoption of analytic and semi-analytic models appears to be a promising option to improve the numerical simulation of coalescence events. To determine whether two colliding interfaces should merge, two different approaches are usually adopted, the first is based on the contact (or interaction) time [231], while the second is based on the minimum film thickness [232,233]. In the first case, interfaces are merged if the contact time exceeds the time required for a complete drainage of the liquid film; if the contact time is smaller, interfaces rebound before merging takes place.…”

“…Regardless of the particular approach chosen (contact time or film thickness), in both cases the interfaces are artificially merged as soon as the criterion for interface coalescence is met. Some of these lubrication models account also for rarefied flow effects [231][232][233][234]: when the Knudsen number (ratio of the mean free path over a reference length scale, taken in this case as the film thickness) approaches unity, the continuum hypothesis breaks down and suitable corrections for the friction (slip models) have to be included [234]. Alternative to the use of lubrication models, a possible solution is to employ macroscopic models.…”

Bouncing off the Walls: The Influence of Gas-Kinetic and van der Waals Effects in Drop Impact

“…In particular, one would like to predict the transitions from drop bouncing to contact-induced wetting and, in doing so, address discrepancies between Kolinski et al's [13] experiments, where the air film height reaches ∼2 nm before contact, compared to de Ruiter et al's [14,15], where heights below 100-200 nm are never observed. Notably, there are similarities to the collision of droplets, where transitions between bouncing and coalescence are pressure dependent and have been captured by a computational model developed by Li [28] that incorporates GKE [29], and are further explored in [30]. Interestingly, there have been no equivalent studies, experimental or computational, investigating the pressure effect in the transition between bouncing and wetting for drops impacting solids.…”

Special issue on finite-size particles, drops and bubbles in fluid flows: advances in modelling and simulations

“…However, alternative approaches are available that are also reported in the present issue: in particular, implicit viscous penalty methods [4,26] and Lattice Boltzmann methods (LBM) [21]. As far as fluid particles are concerned, two contributions [18,22] rely on the one-fluid model [15,23], which is the most widely used approach in the literature as it only requires to adapt density and viscosity at the interface without changing the numerics of the single-phase solver. In addition, one contribution [7] makes use of a Boltzmann approach, which allows an easy parallel implementation of particulate flows, while another contribution [13] exploits the IBM, to track non-deformable bubbles in a way similar to what is typically done with solid particles.…”

“…Among the contributions that deal with drops and bubbles, Liu and Bothe [18] from the Technische Universität Darmstadt (Germany) use an incompressible simulation tool with VOF-based tracking of the deformable interfaces. A multiscale modelling approach is considered to deal with bouncing or coalescing droplets.…”