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The deposition of aluminium oxide 12 and 23 μm particles onto a horizontal flat plate within the laminar boundary layer in the free-stream moderate turbulent flow was studied. The present numerical model considered the deposition onto the surface to be a probabilistic process determined both by hydrodynamics and the adhesive behaviour of particles and surface. Numerical simulation was realised for the flat-plate laminar boundary layer. The two-fluid approach was used for writing the Euler equations for a carrier gas and particulate phase. The effects of gravity and lift forces on the particles velocities and mass concentration, occurring within the boundary layer, and deposition were studied separately for various particle sizes. It was revealed that gravity and lift forces have decisive influence on the behaviour of solid particles taken place within the laminar boundary layer and on their deposition that is expressed via the distributions of the particles transverse velocity and mass concentration. These effects become more pronounced for the larger 23 μm particles. This fact, coupled with the higher probability of entrainment by the surface, results in their larger deposition velocity. The given study is the attempt to combine the hydrodynamic and adhesive aspects of the particles deposition for its more accurate estimate that is suitable for various practical devices. [ABSTRACT FROM AUTHOR]

A three-dimensional (3D) Reynolds stress turbulence model based on 3D Reynolds-averaged Navier-Stokes equations has been elaborated for grid-generated turbulence in particulate downward flow arranged in the channel domain of the square cross section. The model presented considers both the enhancement and attenuation of turbulence by means of the additional terms of the transport equations of the normal Reynolds stress components. It allows us to carry out calculations covering the long distance of the channel length without using algebraic assumptions for various components of the Reynolds stress. The results obtained show the effects of particles and mesh size of the turbulence generating grids on turbulence modification. In particular, the presence of solid particles at the initial period of turbulence decay results in the pronounced enhancement of turbulence that diminishes appreciably downwards in the area of typical channel turbulent flow. As the results show, the character of modification of all three normal components of the Reynolds stress taking place at the initial period of turbulence decay are uniform almost all over the channel cross sections. The increase in the grid mesh size slows down the rate of the turbulence enhancement which is caused by particles. [ABSTRACT FROM AUTHOR]

The method based on 2D Reynolds-averaged Navier-Stokes equations has been employed for the simulation of upward turbulent particulate cylindrical pipe flows of different diameters for a constant flow Reynolds number. This approach was supplied with appropriate closure equations which took into account all pertinent forces and effects that exerted influence on gas and particles: the particle-particle, particle-wall, and particle-turbulence interactions; gravitation, viscous drag, and lift forces; and turbulence modulation. The finite volume technique was applied to the numerical solution of the governing equations. The results show the effect of the mass loading on the radial distributions of the longitudinal velocity lag, the turbulence modulation, and particle concentration. In particular, the two-way coupling of turbulence with the given particles raises simultaneously the velocity lag between gas and particles, originating from direct impact of turbulence on particle motion, and turbulence attenuation by the particles. The radial distributions of longitudinal particle velocity and mass concentration become flatter for higher flow mass loading. [ABSTRACT FROM AUTHOR]

A model of a viscous vortex pair, based on a solution of the Stokes equation, is applied for studying particle dynamics and mixing in vortex-pair-like structures. The perturbed flow field and dynamics of small spherical particles, contained in this flow, are studied on the basis of this solution. The particle-path equations and well-established techniques, such as computing of Poincaré maps, is used. It is shown that the flow inside the vortex pair can behave chaotically when a relatively thick pair (core size of the pair comparable with its radius) is under the influence of a periodic perturbation. This is expected to lead to better mixing of the fluid. However, an increase of the perturbation frequency causes the appearance of regions where a bounded quasi-periodic motion occurs. These regions behave like barriers in the phase space, reducing mixing and transport processes in the fluid. Introduction of the perturbation causes changes in the trajectories of the spherical aerosol-type particles. For a certain range of Stokes numbers (St < 10), long-term accumulation inside the vortex pair is observed for these particles, while the same particles in the unperturbed flow are forced out of the pair into the ambient flow. [ABSTRACT FROM AUTHOR]

Experimental data on the effects of the velocity slip and mass loading on a grid-generated turbulence in gas-solid particles flow are presented. Glass beads (700 µm) were used as the dispersed phase. Velocities of both phases were measured with a Laser Doppler Anemometer. Turbulence decay curves, obtained for different grids, show that particles enhance turbulence for small grids and attenuate it for the large ones. Turbulence enhancement and attenuation are intensified with the increase of the flow mass loading. The particles effect on turbulence changes from turbulence attenuation for a small velocity slip to its enhancement for a large velocity slip. A criterion for the evaluation of turbulence modification in gas-solid particles flow is proposed. [ABSTRACT FROM AUTHOR]