ON THE INFLUENCE OF DIFFERENT MAPPING TECHNIQUES FOR A MULTISCALE APPROACH TO TURBULENT THREE-PHASE FLOWS

In this work we investigate a multiscale approach for high Stokes number, turbulent three phase flows. It is
widely proven that a straightforward application of Galerkin's method to problems characterized by
multiscale phenomena does not generally lead to robust numerical solutions. In this optic, multiscale methods
are commonly adopted in order to provide solutions for complex problems in an highly efficient way. In
certain problems it is convenient to identify multiple scales (more than 2), each characterized by its own
characteristic spatial and temporal length. For this kind of problems a possible approach consists in
completely resolving the coarse scales, partially resolving the middle scales, while analytically modeling the
smallest. In turbulent three phase flows with high Stokes number, those can be identified respectively as the
particle characteristic scale, the interface dynamic scale, and the turbulent fine scale.
The coarse scale is here resolved through an Eulerian-Lagrangian approach that enables us to track the
particle motion in a Lagrangian way.
We partially resolve the middle-scale through the usage of a supporting domain where semi local variables
are resolved. The solution of the middle-scale is based on the Volume of Fluid (VOF) technique in order to
capture the dynamic interface, while turbulent phenomena are solved with a Large Eddy Simulation (LES)
approach. The coarse-scale domain and the middle-scale domain must exchange informations and this
process is obtained by mapping variables between the two fields. We will here show how the choice of the
mapping technique largely affect the solution in therms of both accuracy and efficiency. A thoughtful study
about the optimal mapping strategy could therefore be extremely beneficial in order to discover the most
suitable scale-linking technique.
The aim of this work is to investigate the effect of the adopted mapping technique on the resolved scale.
Simulations with different Reynolds and Stokes number are proposed and compared, and conclusions about
the consistency of the mapping technique are drawn.