Progress in Lattice Boltzmann Method

We review the recent progress and successful applications of lattice Boltzmann method (LBM) to computational fluid dynamics. To clarify the important issue in the LBM simulation, this report shows the recent progress in the LBM, and summarizes both the advantages and disadvantages of the LBM. We also discuss the immersed boundary-lattice Boltzmann method (IB-LBM) that has received much attention in recent years. Due to the common feature of using the Cartesian mesh, the IB-LBM successfully calculates the rigid particle motions in a viscous fluid. We present one of key issues in the IB-LBM, and examine the applicability of the Immersed Boundary Method to the lattice kinetic scheme (LKS) for particulate flow

On the Calculation of Gas Distribution Function by Utilizing TIME Dependent Temperature

The method for determining gas distribution function is reconstructed. In this study, theBoltzmann equation is bypassed by converse method. The temperature change is specified first inorder to determine the distribution function. The argument of this method is explained both byanalytically solving Bolztmann equation and pure probabilistic consideration in statisticalthermodynamics. Boltzmann equation is solved by modeling collision terms with severalassumptions and It is found that the results are similar. On the other hand, probabilistic methodgives no rigorous physical understanding so it offer several justifications about the resultingdistribution function. The calculation shows that the distribution function is totally Maxwellian inall cases. The temperature dependency only affects the peak value and the shape curve. It is foundthat more slender curve is resulted in higher temperature and quick sampling data is required toprobe the rapidly change temperature processes

Lattice Boltzmann simulation of water and gas flow in porous gas diffusion layers in fuel cells reconstructed from micro-tomography

The porous gas diffusion layers (GDLs) are key components in hydrogen fuel cells. During their operation the cells produce water at the cathode, and to avoid flooding, the water has to be removed out of the cells. How to manage the water is therefore an important issue in fuel cell design. In this paper we investigated water flow in the GDLs using a combination of the lattice Boltzmann method and X-ray computed tomography at the micron scale. Water flow in the GDL depends on water–air surface tension and hydrophobicity. To correctly represent the water–gas surface tension, the formations of water droplets in air were simulated, and the water–gas surface tension was obtained by fitting the simulated results to the Young–Laplace formula. The hydrophobicity is represented by the water–gasfabric contact angle. For a given water–gas surface tension the value of the contact angle was determined by simulating the formations of water droplets on a solid surface with different hydrophobicity. We then applied the model to simulate water intrusion into initially dry GDLs driven by a pressure gradient in attempts to understand the impact of hydrophobicity on water distribution in the GDLs. The structures of the GDL were acquired by X-ray micro-tomography at a resolution of 1.7 microns. The simulated results revealed that with an increase in hydrophobicity, water transport in GDLs changes from piston-flow to channelled flow

Lattice Boltzmann simulations of 3D crystal growth: Numerical schemes for a phase-field model with anti-trapping current

A lattice-Boltzmann (LB) scheme, based on the Bhatnagar-Gross-Krook (BGK) collision rules is developed for a phase-field model of alloy solidification in order to simulate the growth of dendrites. The solidification of a binary alloy is considered, taking into account diffusive transport of heat and solute, as well as the anisotropy of the solid-liquid interfacial free energy. The anisotropic terms in the phase-field evolution equation, the phenomenological anti-trapping current (introduced in the solute evolution equation to avoid spurious solute trapping), and the variation of the solute diffusion coefficient between phases, make it necessary to modify the equilibrium distribution functions of the LB scheme with respect to the one used in the standard method for the solution of advection-diffusion equations. The effects of grid anisotropy are removed by using the lattices D3Q15 and D3Q19 instead of D3Q7. The method is validated by direct comparison of the simulation results with a numerical code that uses the finite-difference method. Simulations are also carried out for two different anisotropy functions in order to demonstrate the capability of the method to generate various crystal shapes

NUMERICAL INVESTIGATION OF POOL NUCLEATE BOILING IN NANOFLUID WITH LATTICE BOLTZMANN METHOD

Due to significant improvement of thermal performance and other properties of nanofluids, this group of liquids is in high demand. According to the literature, the effect of nanoparticles on boiling heat transfer enhancement or degradation is not the same among different investigations. In the present article, the pseudo-potential multiphase lattice Boltzmann method is used to simulate nucleate pool boiling with two different fluids: a pure liquid and a nanofluid. The current results indicate that the contact angle is the same for both the fluid and nanofluid when the vapor bubble detachment occurs. Also, bubble departure diameter is greater in the base liquid while bubble release frequency is higher in the nanofluid. In brief, the present results demonstrate that using a nanofluid instead of its base fluid will increase the boiling heat transfer coefficient

Modeling ice crystal growth using the lattice Boltzmann method

Given the multitude of growth habits, pronounced sensitivity to ambient conditions and wide range of scales involved, snowflake crystals are one of the most challenging systems to model. The present work focuses on the development and validation of a coupled flow/species/phase solver based on the lattice Boltzmann method. It is first shown that the model is able to correctly capture species and phase growth coupling. Furthermore, through a study of crystal growth subject to ventilation effects, it is shown that the model correctly captures hydrodynamics-induced asymmetrical growth. The validated solver is then used to model snowflake growth under different ambient conditions with respect to humidity and temperature in the plate-growth regime section of the Nakaya diagram. The resulting crystal habits are compared to both numerical and experimental reference data available in the literature. The overall agreement with experimental data shows that the proposed algorithm correctly captures both the crystal shape and the onset of primary and secondary branching instabilities. As a final part of the study the effects of forced convection on snowflake growth are studied. It is shown, in agreement with observations in the literature, that under such condition the crystal exhibits non-symmetrical growth. The non-uniform humidity around the crystal due to forced convection can even result in the coexistence of different growth modes on different sides of the same crystal