Small scale simulation of multiphase flows
Résumé
Editorial The following issue of Computers and Fluids has been compiled to highlight the spirit of the Euromech colloquium 555 held in 2013 in Pessac France, concerning ''Small-scale numerical methods for multi-phase flows''. During the three days of the colloquium, three sessions were proposed dealing with direct numerical simulation (DNS) of interfacial flows, DNS of particulate flows and numerical modeling of multiphase flows. Halle. The scope of the colloquium was the numerical simulation of multiphase flows at small scale, i.e. characteristic interfacial scales such as those of bubbles or drops are larger than the simulation mesh size. The numerical simulation of such multi-phase flows involving immiscible phases generally considers the interaction between an ambient fluid and another phase (such as solid particles , droplets, bubbles, films, sprays, jets). Either deformable grids, which are adapted to the interface, or fixed grids, with an independent representation of the interface, as in the case of front-tracking , volume-of-fluid, level-set and phase-field methods, can be used to investigate these flows. The direct numerical simulation of multi-phase flows can be achieved with different mathematical models (Navier–Stokes, Boltzmann, Saint–Venant, Smooth-Particle Hydrodynamics) with emphasis on different physical aspects of the flow (representation of the capillary force with constant or variable surface tension, phase change, wettability and contact lines, and more complex phenomena involving electric and magnetic fields). Other topics of interest to the colloquium were the large-eddy simulation and the multi-scale modeling of multi-phase flows. The main goal of this colloquium has been to bring together developers and users of different numerical approaches and codes to share their experience in the development and validation of the algorithms and discuss the difficulties and limitations of the different methods and their pros and cons. The focus has been mainly on fixed-grid methods, however adaptive and unstructured grids have been also welcomed with the aim to compare and validate the different approaches. Researchers from 6 countries (France, Germany, Turkey, USA, Italy, Canada) have participated to the sessions with 54% communications on DNS of multiphase flows, 27% on the DNS of flows interacting with particles and 19% on numerical modeling of multiphase flows. Among the wide variety of models and numerical methods devoted to the small scale simulation of multiphase flows, the statistics of the scientific topics can be summarized as follows: – The modeling of mass and momentum conservation was mainly achieved by Navier–Stokes equations (70% of the presentations) while Euler/Euler models (10%), smooth particle hydrodynamics (SPH, 7%), phase field approaches (3%), Boltzmann models (7%) and boundary element techniques (3%) were also represented. – For interfacial flows, the interface tracking was investigated mainly by means of volume of fluid methods (50%), with also level set techniques (10%) and front tracking approaches (3%). – Among the wide variety of numerical methods that are required to handle the presence of interfaces in multiphase flows, we can notice that 20% of the presentations were devoted to fictitious domains, immersed boundary and DLM methods and penalty approaches. Adaptive mesh refinement was the concern of 10% works, discrete element methods (DEM) and body fitted grids for 3% of the talks. – The physical topics that have been predominantly treated during the colloquium were fluid–structure interaction (30%), drops and bubbles (30%), particle flows (27%), turbulence (23%), transport of species (10%), fluidized beds (7%), compressible flows (7%), porous media (7%), liquid films and atomization (6%) and viscoelastic fluids (3%). The organizers were very happy to welcome researchers and specialists of the CFD development and modeling of multiphase flows. This colloquium was a success with a lot of discussions and projects that are under development as a continuation of the Euromech colloquium.