This paper presents results for the behavior of particle-laden gases in a small Reynolds number vertical channel down flow. Results will be presented for the effects of particle feedback on the gas-phase turbulence and for the concentration profile of the particles. The effects of density ratio, mass loading, and particle inertia will be discussed. The results were obtained from a numerical simulation that included the effects of particle feedback on the gas phase and particle-particle collisions. The resolution of the simulation was comparable to the smallest scales in the particle-free flow, but the grid spacings were larger than the particle size. Particle mass loadings up to 2 and both elastic and inelastic collisions were considered. Particle feedback causes the turbulent intensities to become more anisotropic as the particle loading is increased. For small mass loadings, the particles cause an increase in the gas flow rate. It will be shown that the particles tend to increase the characteristic length scales of the fluctuations in the streamwise component of velocity and that this reduces the transfer of turbulent energy between the streamwise component of velocity and the components transverse to the flow. Particle-particle collisions greatly reduce the tendency of particles to accumulate at the wall for the range of mass loadings considered. This was true even when the collisions were inelastic.

a b s t r a c tIn this paper the results of an international collaborative test case relative to the production of a direct numerical simulation and Lagrangian particle tracking database for turbulent particle dispersion in channel flow at low Reynolds number are presented. The objective of this test case is to establish a homogeneous source of data relevant to the general problem of particle dispersion in wall-bounded turbulence. Different numerical approaches and computational codes have been used to simulate the particle-laden flow and calculations have been carried on long enough to achieve a statistically steady condition for particle distribution. In such stationary regime, a comprehensive database including both post-processed statistics and raw data for the fluid and for the particles has been obtained. The complete datasets can be downloaded from the web at HTTP://CFD.CINECA.IT/CFD/REPOSITORY/. In this paper the most relevant velocity statistics (for both phases) and particle distribution statistics are discussed and benchmarked by direct comparison between the different numerical predictions.

No abstract

Fully resolved simulations of particles suspended in a sustained turbulent flow field are presented. To solve the Navier-Stokes equations a lattice-Boltzmann scheme was used. A spectral forcing scheme is applied to maintain turbulent conditions at a Taylor microscale Reynolds number of 61. The simulations contained between 2 and 10 vol % particles with a solid to fluid density ratio between 1.15 and 1.73. A lubrication force is used to account for subgrid hydrodynamic interaction between approaching particles. Results are presented on the influence of the particle phase on the turbulence spectrum and on particle collisions. Energy spectra of the simulations show that the particles generate fluid motion at length scales of the order of the particle size. This results in a strong increase in the rate of energy dissipation at these length scales and a decrease of kinetic energy at larger length scales. Collisions due to uncorrelated particle motion are observed (primary collisions), and collision frequencies are in agreement with theory on inertial particle collisions. In addition to this, a large number of collisions at high frequencies is encountered. These secondary collisions are due to the correlated motion of particles resulting from shortrange hydrodynamic interactions and spatial correlation of the turbulent velocity field at short distances. This view is supported by the distribution of relative particle velocities, the particle velocity correlation functions and the particle radial distribution function. IntroductionIn industrial processes where solid materials are produced or handled, often dense slurries are processed under highly turbulent conditions. Turbulence is required to maintain the slurry suspended and well mixed. While operating under such conditions, phenomena such as breakage, agglomeration and segregation of particles can occur; these phenomena can be either desired or potential problems in the operation of these processes (Zwietering 1958;Wibowo & Ng 2001).One specific example is industrial crystallization, which deals with the production of solid crystals from a supersaturated liquid. The crystal suspension typically contains between 5 and 20 vol % solids with an average particle size in the range of 100 to 1000 µm, and with a solid to liquid density ratio in the range of 1 to 2.5. The Kolmogorov length scale typically is one order of magnitude smaller than the mean crystal size (Ten Cate et al. 2001). Under the action of the turbulent flow field, agglomeration (Hollander et al. 2001), abrasion, and fracture (Gahn & Mersmann 234 A. Ten Cate, J. J. Derksen, L. M. Portela and H. E. A. Van den Akker 1999) take place. These phenomena have a strong influence on the performance of the crystallization process and hence on the resulting product, and make scale-up a non-trivial exercise.In this paper we study turbulent solid-liquid suspensions under conditions that are comparable to those encountered in industrial crystallization processes (i.e. d p > η, where d p is the particle diameter and η th...