scholarly journals Phase-field-based lattice Boltzmann modeling of large-density-ratio two-phase flows

2018 ◽  
Vol 97 (3) ◽  
Author(s):  
Hong Liang ◽  
Jiangrong Xu ◽  
Jiangxing Chen ◽  
Huili Wang ◽  
Zhenhua Chai ◽  
...  
Keyword(s):  
Phase Field ◽  
Lattice Boltzmann ◽  
Density Ratio ◽  
Two Phase Flows ◽  
Two Phase ◽  
Large Density ◽  
Large Density Ratio ◽  
Lattice Boltzmann Modeling

scholarly journals A diffuse domain method for two-phase flows with large density ratio in complex geometries

2020 ◽  
Vol 907 ◽  
Author(s):  
Zhenlin Guo ◽  
Fei Yu ◽  
Ping Lin ◽  
Steven Wise ◽  
John Lowengrub
Keyword(s):  
Density Ratio ◽  
Complex Geometries ◽  
Two Phase Flows ◽  
Two Phase ◽  
Large Density ◽  
Domain Method ◽  
Large Density Ratio

Abstract

A Novel Numerical Scheme for Outlet Boundary Conditions in Large Density Ratio Lattice Boltzmann Model

2016 ◽  
Author(s):  
Long Li ◽  
Yongwen Liu
Keyword(s):  
Boundary Condition ◽  
Lattice Boltzmann ◽  
Numerical Scheme ◽  
Density Ratio ◽  
Two Phase ◽  
Droplet Shape ◽  
Large Density ◽  
Large Velocity ◽  
Large Density Ratio ◽  
Outlet Boundary Condition

In the past decades, the Lattice Boltzmann method has gained much success in variety fields especially in multiphase flow, porous media flow, and other complex flow, and become a promising method for computational fluid dynamic (CFD). The outlet boundary condition (OBC) and its numerical scheme are critical issues in CFD, which may influence the accuracy and stability of the calculation. The common OBCs i.e. Neumann boundary condition (NBC), extrapolation boundary condition (EBC), and convection boundary condition (CBC), which have been widely investigated in single-phase LB model, have rarely been investigated in multiphase LB model. The previous research on the OBCs for two-phase LB model only aims at small density ratio. While in most industrial applications, the density ratio often ranges from a hundred to a thousand, and a large density ratio would bring some problems such as parasitic current and bad stability in LB method. Lee and Fischer have proposed an improved LB model which is suitable for large density ratio two-phase flow. In order to assess the OBCs for large density ratio LB model, the OBCs are investigated. And it is found that the existing OBC numerical scheme cannot be directly applied to the large density ratio LB model. In present study, a novel numerical scheme for the OBCs is proposed assuming that the outlet velocity is gained by the outlet boundary condition instead of the momentum equation which is an improvement of previous scheme, and it can be used in large density ratio LB model. The performance of the proposed OBC scheme is examined for different density ratios. The results show that the proposed OBC scheme could converge in a stable manner. Comparing with the reference flow condition, the CBC scheme shows a better performance than the NBC scheme and the EBC scheme. The NBC scheme would lead a large droplet deformation, large velocity peaks at the outlet, and large errors for both small and large density ratio. And the EBC scheme keeps a good droplet shape, but it would lead large velocity peaks at the outlet and large error when large density ratio is considered. The CBC scheme always shows superior performance including a good droplet shape, smooth outlet velocity profile, and small errors no matter whether the density ratio is small or large. Hence the CBC scheme could be applied in large density ratio LB model for the outlet boundary condition, which has a good accuracy and stability in the calculation.

Modified Outlet Boundary Condition Schemes for Large Density Ratio Lattice Boltzmann Models

2017 ◽  
Vol 139 (5) ◽  
Author(s):  
Long Li ◽  
Xiaodong Jia ◽  
Yongwen Liu
Keyword(s):  
Boundary Condition ◽  
Distribution Function ◽  
Lattice Boltzmann ◽  
Density Ratio ◽  
Neumann Boundary ◽  
Momentum Balance ◽  
Two Phase ◽  
Large Density ◽  
Large Density Ratio ◽  
Density Ratios

Outlet boundary conditions (OBCs) and their numerical descriptions are critical to computational fluid dynamics (CFD) since they have significant influence on the numerical accuracy and stability. They present significant challenges to the two-phase lattice Boltzmann (LB) method, especially in the limit of large density ratio. In this study, three commonly used OBCs: convection boundary condition (CBC), Neumann boundary condition (NBC), and extrapolation boundary condition (EBC), are investigated and improved on basis of two LB models for large density ratios (single and double distribution function models). The existing numerical schemes for the OBCs are not directly applicable to the LB models because of the deviation of the momentum balance at the outlet boundary. The deviation becomes substantial at a large density ratio. Thus, in this work, modified OBC schemes are proposed to make the OBCs suitable for the two-phase LB models by adding an independent equation to obtain the outlet velocity. Numerical tests on droplet flowing in a channel are performed to evaluate the performance of the modified OBC schemes. Results indicate that the modified OBC schemes may be extended to tackle large density ratio situations. The modified NBC and EBC schemes are only suitable for the LB model with single distribution function. Three modified CBC schemes exhibit optimum performance for both single and double distribution function LB models which can be implemented for large density ratios.

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