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The drag, lift and moment coefficient of differently shaped single particles with respect to the angle of incidence and to the particle Reynolds number under different conditions were determined. For this purpose simulations of the flow around these particles were performed using the three-dimensional Lattice Boltzmann method. The first case studied was a fixed particle in a plug flow, the second case a rotating particle in a plug flow to determine the Magnus lift force and the third case a fixed particle in a linear shear flow to determine the Saffman lift force. In the first case six particle shapes were considered, which are two spheroids, two cuboids and two cylinders with an axis ratio of 1 and 1.5, respectively. In the second and third case, only the sphere was considered. The particle Reynolds number was varied between 0.3 and 480.

Although much research has been performed on the motion of contact lines on solid surfaces, many questions remain. This paper presents results obtained with molecular dynamics (“MD”) simulations that address some of these questions. Of specific interest is the nature of the frictional resistance to contact line motion.

In the paper a Direct Numerical Simulation (DNS) scheme, named Fluctuating Immersed MATerial (FIMAT) dynamics, for the Brownian motion of particles is presented. In this approach the thermal fluctuations are included in the fluid equations via random stress terms. Solving the fluctuating hydrodynamic equations coupled with the particle equations of motion results in the Brownian motion of the particles. There is no need to add a random force term in the particle equations. The particles acquire random motion through the hydrodynamic force acting on its surface from the surrounding fluctuating fluid. The random stresses in the fluid equations are easy to calculate unlike the random terms in the conventional Brownian Dynamics (BD) type approaches.

In this paper, we present a new definition of liquid—vapor interface at the molecular level which can capture the local and instantaneous structure of the interface. The new definition is not a thermodynamic definition of the interface, such as the equimolar surface, but is based on the instantaneous particle density distribution of molecules. Applying the new definition of the interface to the MD result of the liquid—vapor interface, we found that our definition of the interface was able to capture the microscopic fluctuation caused by molecular motion. Furthermore, we confirmed that on the longtime average our definition of the interface shows good agreement with the equimolar surface.

To investigate the two-way interaction between solid particles and fluid turbulence, a homogeneous flow field including more than 2000 spherical particles was directly simulated. Since flow around each particle is approximately resolved, no models were used for particle motion or fluid turbulence. A particle settles under gravity with the Reynolds number ranging from 50 to 300, based on diameter and slip velocity. When particle clusters are formed due to the wake attraction, the average settling velocity increases. Thus particular attention was focused on the distribution of particles. The influence of Reynolds number and loading ratio are assessed. It is found that the rotation of particle dominates the cluster dynamics.

is a new code that utilizes elements of the Immersed Boundary (IB) and Lattice Boltzmann Method (LBM) as well as a Direct Forcing (DF) scheme. As a computational method, it is very flexible and it appears to be ideal in solving fluid-particle interaction problems including problems with deformable boundaries. Proteus uses a regular Eulerian grid for the flow domain and a regular Lagrangian grid to follow particles that are contained in the flow field. The rigid body conditions for the fluid and the particles are enforced by applying the external force acting on the boundary of particles. A penalty method is used, which assumes that the particle boundary is deformable with a high stiffness constant. The velocity fields for the fluid and particles are solved by incorporating a force density term into the lattice Boltzmann equation. This force term is determined by using a technique that is based on the direct forcing scheme. preserves all the advantages of LBM in tracking a group of particles and, at the same time, provides an alternative and better approach to treating the solid-fluid boundary conditions. Because of this it provides for a smooth boundary interface, with only a few nodes assigned for the size of particles. This new method also solves the problems of fluctuation of the forces and velocities on the particles when the “bounceback” boundary conditions are applied. The method has the capability to simulate deformable particles and fluid-structure deformation. The results of the Proteus code have been validated by comparison with results from other computational methods as well as experimental data. Some of the validation results will be given in the presentation of this paper.

We present an explicit finite-difference scheme for direct simulation of the motion of solid particles in a fluid. The method is based on a second-order MacCormack finitedifference solver for the flow, and Newton’s equations for the particles. The fluid is modeled with fully compressible mass and momentum balances; the technique is intended to be used at moderate particle Reynolds number. Several examples are shown, including a single stationary circular particle in a uniform flow between two moving walls, a particle dropped in a stationary fluid at particle Reynolds number of 20, the drafting, kissing, and tumbling of two particles, and 100 particles falling in a closed box.

Although much research has been performed on the motion of contact lines on solid surfaces, many questions remain. This paper presents results obtained with molecular dynamics (“MD”) simulations that address some of these questions. Of specific interest is the nature of the frictional resistance to contact line motion.

In the paper a Direct Numerical Simulation (DNS) scheme, named Fluctuating Immersed MATerial (FIMAT) dynamics, for the Brownian motion of particles is presented. In this approach the thermal fluctuations are included in the fluid equations via random stress terms. Solving the fluctuating hydrodynamic equations coupled with the particle equations of motion results in the Brownian motion of the particles. There is no need to add a random force term in the particle equations. The particles acquire random motion through the hydrodynamic force acting on its surface from the surrounding fluctuating fluid. The random stresses in the fluid equations are easy to calculate unlike the random terms in the conventional Brownian Dynamics (BD) type approaches.

The results of a fully-resolved simulation of 1,024 particles settling under gravity in a periodic domain are described and analyzed. The particle volume fraction is about 13% and the single-particle terminal Reynolds number is about 10. Collisions are modelled as completely elastic. The results show that the formation of nearly-horizontal particle pairs is an important phenomenon which affects the mean settling velocity as well as the velocity fluctuations.