  We examine the process of particle capture by large deformable drops in
turbulent channel flow. We simulate the solid-liquid-liquid three-phase flow
with an Eulerian-Lagrangian method based on Direct Numerical Simulation of
turbulence coupled with a Phase Field Model, to capture the interface dynamics,
and Lagrangian tracking of small (sub-Kolmogorov) particles. Drops have same
density and viscosity of the carrier liquid, and neutrally-buoyant solid
particles are one-way coupled with the other phases. Our results show that
particles are transported towards the interface by jet-like turbulent motions
and, once close enough, are captured by interfacial forces in regions of
positive surface velocity divergence. These regions appear to be well
correlated with high-enstrophy flow topologies that contribute to enstrophy
production via vortex compression or stretching. Examining the turbulent
mechanisms that bring particles to the interface, we have been able to derive a
simple mechanistic model for particle capture. The model can predict the
overall capture efficiency and is based on a single turbulent transport
equation in which the only parameter scales with the turbulent kinetic energy
of the fluid measured in the vicinity of the drop interface. The model is valid
in the limit of non-interacting particles and its predictions agree remarkably
well with numerical results.
