Real-time flow simulation of indoor environments using lattice Boltzmann method

A novel lattice Boltzmann method (LBM) based 3D computational fluid dynamics (CFD) technique has been implemented on the graphics processing unit (GPU) for the purpose of simulating the indoor environment in real-time. We study the time evolution of the turbulent airflow and temperature inside a test chamber and in a simple model of a four-bed hospital room. The predicted results from LBM are compared with traditional CFD based large eddy simulations (LES). Reasonable agreement between LBM results and LES method is observed with significantly faster computational times

Lattice Boltzmann simulations of soft matter systems

This article concerns numerical simulations of the dynamics of particles immersed in a continuum solvent. As prototypical systems, we consider colloidal dispersions of spherical particles and solutions of uncharged polymers. After a brief explanation of the concept of hydrodynamic interactions, we give a general overview over the various simulation methods that have been developed to cope with the resulting computational problems. We then focus on the approach we have developed, which couples a system of particles to a lattice Boltzmann model representing the solvent degrees of freedom. The standard D3Q19 lattice Boltzmann model is derived and explained in depth, followed by a detailed discussion of complementary methods for the coupling of solvent and solute. Colloidal dispersions are best described in terms of extended particles with appropriate boundary conditions at the surfaces, while particles with internal degrees of freedom are easier to simulate as an arrangement of mass points with frictional coupling to the solvent. In both cases, particular care has been taken to simulate thermal fluctuations in a consistent way. The usefulness of this methodology is illustrated by studies from our own research, where the dynamics of colloidal and polymeric systems has been investigated in both equilibrium and nonequilibrium situations.Comment: Review article, submitted to Advances in Polymer Science. 16 figures, 76 page

Effect of tube diameter and capillary number on platelet margination and near-wall dynamics

The effect of tube diameter $D$ and capillary number $Ca$ on platelet margination in blood flow at $\approx 37\%$ tube haematocrit is investigated. The system is modelled as three-dimensional suspension of deformable red blood cells and nearly rigid platelets using a combination of the lattice-Boltzmann, immersed boundary and finite element methods. Results show that margination is facilitated by a non-diffusive radial platelet transport. This effect is important near the edge of the cell-free layer, but it is only observed for $Ca > 0.2$, when red blood cells are tank-treading rather than tumbling. It is also shown that platelet trapping in the cell-free layer is reversible for $Ca \leq 0.2$. Only for the smallest investigated tube ($D = 10 \mu\text{m}$) margination is essentially independent of $Ca$. Once platelets have reached the cell-free layer, they tend to slide rather than tumble. The tumbling rate is essentially independent of $Ca$ but increases with $D$. Tumbling is suppressed by the strong confinement due to the relatively small cell-free layer thickness at $\approx 37\%$ tube haematocrit.Comment: 16 pages, 10 figure

Condensate flow inside paper dryer cylinders

The rimming flow of condensate in horizontal rotating dryer cylinders has been studied computationally by solving the full Navier-Stokes equations coupled with a volume of fluid method for tracking the free surface. It was shown that significant variations in both condensate velocity and thickness exist at moderate dryer speeds, whereas at higher speeds the variations are of less significance. Regardless of dryer speed or condensate film thickness, the film can be divided into two distinct regions: a viscous sub-layer adjacent to the cylinder wall and an inviscid, oscillating layer close to the free surface. The thickness of the viscous layer decreases as the dryer speed increases, whereas, for a certain speed, it is independent of the total film thickness. The computational results are compared with measurements of both the film thickness and the pressure normal to the cylinder wall. In both cases the agreement is excellent. Some implications for heat transfer through the condensate film are briefly discussed