Pascal Fede

Numerical study of the subgrid fluid turbulence effects on the statistics of heavy colliding particles

The main purpose of this article is to investigate the effects of the subgrid fluid turbulence on the motion of nonsettling colliding particles suspended in steady homogeneous isotropic turbulent flow. An additional goal is to characterize the statistical properties of the subgrid fluid turbulence “viewed” by inertial particles to support the development of large eddy simulation (LES) approach for particle-laden turbulent flows. Two types of numerical experiments have been carried out: first, the discrete particle trajectories were computed using the fluid velocity field given by direct numerical simulation (DNS) in order to characterize the small-scale fluid velocity fluctuations “seen” by the particles. In a second stage, the particle trajectory simulations were performed using several filtered velocity fields computed from the DNS data to evaluate the effect of the subgrid fluid turbulence on the particle statistics (turbulent dispersion, kinetic energy, accumulation efficiency, particle-particle relat...

Monte Carlo Simulation of Colliding Particles in Gas-Solid Turbulent Flows From a Joint Fluid-Particle PDF Equation

This paper is dedicated to Lagrangian approach for modelling particle-particle interactions in gas-solid turbulent flows. This approach is based on a joint fluid-particle pdf equation solved using Monte Carlo method which has been developed to take into account the correlation between colliding particles induced by the fluid. The modification of the turbulence by the particles is not included in the simulations. The Lagrangian results are presented in comparison with LES simulations (Lavieville et al., 1995) and continuum model.Copyright

DEVELOPMENT AND VALIDATION OF A BINARY COLLISION DETECTION ALGORITHM FOR A POLYDISPERSED PARTICLE MIXTURE

A time driven Lagrangian particle detection algorithm for a poly-dispersed mixture of particles is developed and validated. The advantage of this algorithm is the possibility to treat a distribution of particle diameters. We are especially interested in the collision treatment of poly-dispersed particle mixtures and coalescence. Particle pairs are found by applying the overlap criteria and additionally another second criterion, which allows a substantial increase of the time step without limiting the algorithm’s accuracy. The algorithm, which is developed here, is validated with test cases by comparison with predictions of the kinetic theory of rarefied gases. They are applied to dry granular flows. The algorithm accuracy is determined with respect to time step criteria, for both dilute and dense systems.Copyright

Application of a Perturbated Two-Maxwellian Approach for the Modelling of Kinetic Stress Transfer by Collision in Non-Equilibrium Binary Mixture of Inelastic Particles

This paper introduce a model for the kinetic stress transfer by collision in binary mixture of inelastic particles. The derived model is based on a perturbated two-Maxwellian approach allowing to described non-equilibrium particulate flows. The model is validated by comparison with numerical results carried out using a deterministic Discrete Particle Simulation (DPS).Copyright

Monte Carlo Simulation of Colliding Particles Suspended in Gas-Solid Homogeneous Turbulent Shear Flows

The purpose of this paper is the modelling of particle-particle collisions by Stochastic Lagrangian approach in gas-solid turbulent shear flows. A generalized Monte Carlo algorithm is introduced which takes into account the correlation between the colliding particles. Particle-particle and fluid-particle velocity correlations from Stochastic Lagrangian simulations are compared with results from Deterministic Particles Simulation coupled with Large Eddy Simulation of a gas turbulent shear flow (DPS/LES), and with predictions computed in the frame of the moment method using separate transport equation for the fluid and particle velocity correlations.Copyright

3D Numerical Prediction of Gas-Solid Flow Behavior in CFB Risers for Geldart A and B Particles

In this study, mono-disperse flows in squared risers conducted with A and B-type particles were simulated by Eulerian n-fluid 3D unsteady code. Two transport equations developed in the frame of kinetic theory of granular media supplemented by the interstitial fluid effect and the interaction with the turbulence (Balzer et al., 1996) are resolved to model the effect of velocity fluctuations and inter-particle collisions on the dispersed phase hydrodynamic. The studied flow geometries are three-dimensional vertical cold channels excluding cyclone, tampon and returning pipe of a typical circulating fluidized bed. For both type of particles, parametric studies were carried out to determine influences of boundary conditions, physical parameters and turbulence modeling. The grid dependency was analyzed with mesh refinement in horizontal and axial directions. For B-type particles, the results are in good qualitative agreement with the experiments and numerical predictions are slightly improved by the mesh refinement. On the contrary, the simulations with A-type particles show a less satisfactory agreement with available measurements and are highly sensitive to mesh refinement. Further studies are carried out to improve the A-type particles by modeling subgrid-scale effects in the frame of large-eddy simulation approach.

3D Numerical Simulation of Polydisperse Pressurized Gas-Solid Fluidized Bed

Three dimensional unsteady numerical simulations of dense pressurized polydisperse fluidized bed have been carried out. The geometry is a medium-scale industrial pilot for ethylene polymerization. The numerical simulation have been performed with a polydisperse collision model. The consistency of the polydisperse model predictions with the monodisperse ones is shown. The results show that the pressure distribution and the mean vertical gas velocity are not modified by polydispersion of the solid phase. In contrast, the solid particle species are not identically distributed in the fluidized bed indicating the presence of particle segregation.Copyright

Benchmark test on particle-laden channel flow with point-particle LES

Dispersion of particles in a turbulent wall-bounded flow is crucial in many practical applications. For numerical simulation of particle-laden turbulent flow various approaches are available. Among these, LES is perhaps the most promising because its computational cost is lower than that of DNS and its predictive capability is much higher than Reynolds-Averaged Navier-Stokes methods especially in case of particles-turbulence interaction in boundary layers. Various subgrid models are available which have proved their validity for several types of flow. However, the treatment of particles in LES is still a relatively new topic with open questions regarding e.g. Sub-Grid Scales (SGS) effects on particle behavior and the modeling of particle-particle, particle-fluid or particle-wall interactions. To address these issues, an international collaborative benchmark test has been proposed as part of the activity of the COST Action P20 LESAID. The objective is to gather a large database of results obtained with different numerical methods, SGS models and physical models in order to resolve questions about the validity of these models. In this paper the first statistics of the benchmark for a base Eulerian-Lagrangian simulation of particle-laden channel flow, are presented. The specific simulation parameters have been chosen also to allow estimate of the quality of the LES results upon comparison with available DNS results (Marchioli et al., 2008) for the same test case. The groups participating in the benchmark are: UUD-UPI (Marchioli, Soldati, Salvetti); TUE (Kuerten); IMFT-ASU (Konan, Fede, Simonin, Squires); TUM (Gobert, Manhart); TUK-TUD (Jaszczur, Portela). Results provided by each group refer to a statistically stationary situation in which the particle concentration has reached a steady state. The time taken to reach steady concentration is very long (up to 2⋅104 in wall units (Marchioli et al., 2008)) thus making the required computational effort quite high even for a LES-based calculation.

Effect of Particle-Particle Collisions on the Spatial Distribution of Inertial Particles Suspended in Homogeneous Isotropic Turbulent Flows

Preferential concentration of solid inertial colliding particles suspended in homogeneous isotropic turbulence is numerically investigated using Direct Numerical Simulation (DNS) coupled with Discrete Particle Simulation (DPS). The results show that the preferential concentration is decreasing when the collision frequency increases. This effect is found enhanced for non-elastic particle-particle collisions.

Numerical Simulation and Modelling of the Forces Acting on Single and Multiple Non-Spherical Particles

The paper deals with gas-solid turbulent flows carrying non-spherical particles. The main objective of the present paper is to compute the hydrodynamics forces on non-spherical particles as a function of the particle orientation, for different particle shapes and a large range of particle Reynolds number. Two Direct Numerical Simulations at the scale of the particle are used, i.e. a body-fitted approach and a viscous penalty approach, in the case of a uniform flow with a single ellipsoidal particle. Results are compared with several correlations from the literature and a new proposal for the drag coefficient is given. The study is then extended to the case of a lattice of non-spherical particles to measure the pressure drop and to connect it with the drag coefficient.