  In recent years the Smoothed Particle Hydrodynamics (SPH) approach gained
popularity in modeling multiphase and free-surface flows. In many situations,
due to certain reasons, interface and free-surface fragmentation occurs. As a
result single SPH particle solids/droplets of one phase can appear and travel
through other phases. In this paper we investigate this issue focusing on a
movement of such single SPH particles. The main questions we try to answer here
are: is movement of such particles physically correct? What is its physical
size? How numerical parameters affect on it? With this in mind we performed
simple simulations of solid particles falling due to gravity in a fluid.
Considering three different diameters of a single particle, we compared values
of the drag coefficient and the velocity obtained through the SPH approach with
the experimental and the analytical reference data. In the way to accurately
model multiphase flows with free-surfaces we proposed and validated a novel SPH
formulation.
