Assessment of numerical methods for fully resolved simulations of particle-laden turbulent flows

This work was granted access to the HPC resources of CALMIP and the National Center for Atmospheric Researchs (NCAR) supercomputing centers. P. Costa acknowledges the funding from the Portuguese Foundation for Science and Technology under grant no. SFRH/BD/85501/2012. L.-P. Wang acknowledges the funding from the U.S. National Science Foundation (NSF) under grants CBET-1706130.Peer reviewedPostprin

Numerical study of an unsteady confined jet. Application to crossflow filtration

This paper deals with the influence of a new flow unsteadiness on the permeate flux in crossflow filtration. A pneumatically controlled valve generates intermittent jets from the main flow, leading to the formation of large vortices moving downstream along the tubular membrane. A numerical calculation of this flow is achieved using a finite difference scheme. Influences of tube diameter and jet velocities are discussed. Application of this technique is carried out by filtering a bentonite suspension through an ultrafiltration membrane. / L'article traite d'un nouveau procédé hydrodynamique destiné à améliorer les débits de filtrat en filtration tangentielle. Une vanne pneumatique génère des jets intermittents dans l'écoulement principal. Il en résulte la formation de tourbillons se déplaçant le long de la membrane de filtration. La simulation numérique de l'écoulement instationnaire ainsi généré a été conduite à l'aide d'un code de calcul aux différences finies. On étudie l'effet du passage des tourbillons sur les vitesses et les concentrations près de la paroi filtrante. Le mécanisme de balayage hydrodynamique de la paroi est analysé. Les influences relatives de la vitesse de jet et des rapports de diamètre (jet/tube filtrant) conduisent à conseiller des dimensionnements différents suivant la nature du colmatage prévisible. L'efficacité du procédé est vérifiée expérimentalement par ultrafiltration d'une suspension de bentonite

Direct numerical simulation of a freely decaying turbulent interfacial flow

International audienceWhereas Large Eddy Simulation (LES) of single-phase flows is already widely used in the CFD world, even for industrial applications, LES of two-phase interfacial flows, i.e. two-phase flows where an interface separates liquid and gas phases, still remains a challenging task. The main issue is the development of subgrid scale models well suited for two-phase interfacial flows. The aim of this work is to generate a detailed data base from direct numerical simulation (DNS) of two-phase interfacial flows in order to clearly understand interactions between small turbulent scales and the interface separating the two phases. This work is a first contribution in the study of the interface/turbulence interaction in the configuration where the interface is widely deformed and where both phases are resolved by DNS. To do this, the interaction between an initially plane interface and a freely decaying homogeneous isotropic turbulence (HIT) is studied. The densities and viscosities are the same for both phases in order to focus on the effect of the surface tension coefficient. Comparisons with existing theories built on wall-bounded or free-surface turbulence are carried out. To understand energy transfers between the interfacial energy and the turbulent one, PDFs of the droplet sizes distribution are calculated. An energy budget is carried out and turbulent statistics are performed including the distance to the interface as a parameter. A spectral analysis is achieved to highlight the energy transfer between turbulent scales of different sizes. The originality of this work is the study of the interface/turbulence interactions in the case of a widely deformed interface evolving in a turbulent flow

Numerical modelling of finite-size particle collisions in a viscous fluid

A general model is presented for short-range hydrodynamic interactions and head-on particle-particle/wall collisions. The model has been embedded in two distinct numerical methods for fully resolved simulation of finite-size particles in a viscous fluid. It accounts for the material properties of the particles and lubrication effects prior to collision that cannot be fully resolved on a fixed grid. We demonstrate that the model is able to reproduce experimental data for the coefficient of restitution of particle-wall collisions over a wide range of Stokes number based on the particle impact velocity. The set of model parameters we selected and more generally the modelling approach we propose can be efficiently used for fully resolved simulations of moderately dense solid-liquid suspensions.Process and EnergyMechanical, Maritime and Materials Engineerin