Simulation of fully resolved finite-size particles in a turbulent flow

In this study we are interested on the statistics of finite sized particles. A sustained homogeneous isotropic turbulence with particles is numerically simulated in order to obtain those statistics

Simulation numérique des écoulements de suspension à l'aide d'une méthode de pénalisation des équations de Navier-Stokes

Une méthode de simulation des écoulements particulaires avec des particules de taille finie est proposée. Il s'agit d'une méthode à un fluide pour laquelle la partie solide est représentée par une viscosité très élevée. Le calcul se réalise sur maillage cartésien décalé. Les particules sont repérées de façon lagrangienne. Cette méthode de domaines fictifs à comme particularité que le déplacement de particules se fait implicitement par la résolution de Navier-Stokes. Malgré le rapport de viscosités, la méthode du lagrangien augmenté converge tout en gardant la contrainte d'incompressibilité

Particle resolved direct numerical simulation of a liquid–solid fluidized bed: Comparison with experimental data

Particle-resolved direct numerical simulations of a 3-D liquid–solid fluidized bed experimentally investigated by Aguilar-Corona (2008) have been performed at different fluidization velocities (corresponding to a range of bed solid volume fraction between 0.1 and 0.4), using Implicit Tensorial Penalty Method. Particle Reynolds number and Stokes number are O(100) and O(10), respectively. In this paper, we compare the statistical quantities computed from numerical results with the experimental data obtained with 3-D trajectography and High Frequency PIV. Fluidization law predicted by the numerical simulations is in very good agreement with the experimental curve and the main features of trajectories and Lagrangian velocity signal of the particles are well reproduced by the simulations. The evolution of particle and flow velocity variances as a function of bed solid volume fraction is also well captured by the simulations. In particular, the numerical simulations predict the right level of anisotropy of the dispersed phase fluctuations and its independence of bed solid volume fraction. They also confirm the high value of the ratio between the fluid and the particle phase fluctuating kinetic energy. A quick analysis suggests that the fluid velocity fluctuations are mainly driven by fluid–particle wake interactions (pseudo-turbulence) whereas the particle velocity fluctuations derive essentially from the large scale flow motion (recirculation). Lagrangian autocorrelation function of particle fluctuating velocity exhibits large-scale oscillations, which are not observed in the corresponding experimental curves, a difference probably due to a statistical averaging effect. Evolution as a function of the bed solid volume fraction and the collision frequency based upon transverse component of particle kinetic energy correctly matches the experimental trend and is well fitted by a theoretical expression derived from Kinetic Theory of Granular Flows

Prise en compte des effets de lubrification lors de la simulation de la collision de deux particules dans un fluide

Dans la simulation des écoulements particulaires denses, il est nécessaire d'avoir des modèles de collision performants. Afin de garder un pas de temps et un maillage raisonnables il est nécessaire d'inclure dans ces modèles la collision à sec et la lubrification. On expose un modèle d'interaction particule-particule particule-paroi basé sur l'approche de W.P. Breugem. Ce modèle a été validé pour des particules de taille finie avec une approche de pénalisation sur domaines fictifs. Il vérifie les coefficients de restitution expérimentaux pour une large gamme de nombre de Stokes

DNS and LES of primary atomization of turbulent liquid jet injection into a gaseous crossflow environment

International audienceIn this paper, we study the primary atomization characteristics of liquid jet injected into a gaseous crossow through direct numerical simulations (DNS) and large eddy simulations (LES). The DNS use a coupled level set volume of uid (CLSVOF) sharp interface capturing method resolving all relevant scales to predict the drop size distribution (DSD) for drops larger than the grid spacing. The LES use a volume of uid (VOF) diused interface method modelling the sub grid droplets. The purpose of this paper is to provide a comparison of the results of drop data between DNS and LES. The simulations are performed for a liquid jet injection with liquid-gas momentum ux ratio of 6.6, liquid jet Reynolds number of 14,000 injected into a crossowing air with Reynolds number 570,000 and Weber number of 330 at a liquid-togas density ratio of 10. Two distinct and simultaneous atomization/breakup mechanisms have been observed in the simulations: column/bag breakup and ligament/surface breakup. It was found that the DSDs obtained from the DNS and LES each follow a log-normal distribution based on their respective droplet diameter data. An overlap region exists between the individual DSDs from the DNS and LES when combined. The width of this overlap region decreases along the downstream direction. A log-normal distribution is found to be a good t to the combined DSD incorporating both resolved and sub-grid droplets. This information is relevant for the secondary atomization simulations and modeling