Multiphase flows are ubiquitousin nature and industry. Examples include oil extraction/ separation in the oil & gas industry, airborne particles or aerosols, sediment-laden flows, fiber suspensions, but also swimming microorganisms, biopolymers and blood rheology. The numerical description of multiphase flows is a complex task that requires an accurate representation of the mutual interaction between the involved phases, which can be solid particles, liquid/gas layers or droplets/bubbles depending on the specific application. Even in the idealized scenario of dilute suspensions of pointlike particles, inertia leads to non-trivial behaviors, such as multiscale clustering typically observed in the turbulent regime. With increasing levels of concentration, the two-way coupling between the phases becomes manifest, for both momentum and energy. This coupling can be enhanced by collective effects, e.g. leading to cluster-induced turbulence, or by finite-size effects, when particles are significantly larger than the Kolmogorov scale of the flow. Shape effects may represent an important source of bias that adds to inertia in determining the macroscopic flow behavior.
Difficulties in modeling and simulation arise also in the presence of an interface between the continuous and dispersed phases, which may produce sub-Kolmogorov length and time scales near the interface. In this case, two main approaches can be adopted: The first one exploits deformable, boundary-fitted grids that adapt to the dynamics of the interface (but require definition of appropriate boundary conditions on it); the second one makes use fixed grids to describe the dynamics of the entire flow field, plus the addition of an independent representation of the interface, via both Lagrangian or Eulerian methods, such as Front-Tracking, Volume-Of-Fluid (VOF), Level-Set (LS), Phase- Field (PF) or Smoothed Particle Hydrodynamics (SPH). In this latter case, a redistribution of interface forces/effects on the background fixed grid is necessary.
In this course, we will present and discuss the numerical models/ methods currently available for the accurate simulation of turbulent multiphase flows. In particular, we will consider: Lagrangian methods for particle dispersion in turbulence (with and without finite-size effects), boundary-fitted methods for deformable gas and liquid layers, and commonly-used approaches such as VOF, LS, PF and SPH approaches. A comprehensive ensemble of applications, extracted from the lecturers’ own research field and covering areas of applied physics and engineering, will also be provided together with a hands-on computer session by Dr. Alessio Roccon and Dr. Giovanni Soligo.
The course will be particularly attractive to graduate students, PhD candidates, young researchers and faculty members in applied physics and chemical/mechanical engineering. The advanced topics and the presentation of current progress will also be of considerable interest to many senior researchers, as well as industrial practitioners having a strong interest in understanding the complex multiscale flow behavior, with particular emphasis on their modeling and simulation.