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https://github.com/yjhp1016/taichi_LBM3D

A 3D sparse LBM solver implemented using Taichi
https://github.com/yjhp1016/taichi_LBM3D

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A 3D sparse LBM solver implemented using Taichi

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README 

        
# taichi_LBM3D

## Documentation 

[https://yjhp1016.github.io/taichi_LBM3D/](https://yjhp1016.github.io/taichi_LBM3D/)

## Background

Taichi_LBM3D is a 3D lattice Boltzmann solver with Multi-Relaxation-Time collision scheme and sparse storage structure implemented using [Taichi programming language](https://github.com/taichi-dev/taichi), which is designed for porous medium flow simulation. Taking advantage of Taichi's computing structure, Taichi_LBM3D can be employed on shared-memory multi-core CPUs or massively parallel GPUs (OpenGL and CUDA). **The code achieved 900 MLUPS in a 3D lid-driven test case using a A100 NVIDIA GPU**. The code is only around 400 lines, highly extensible and very intuitive to understand.



## Installation

This solver is developed using Taichi programming language (a python embedded programming language), install [Taichi](https://github.com/taichi-dev/taichi) is required, by `python3 -m pip install taichi`.  



Pyevtk is required for export simualtion result for visualization in Paraview, install [Pyevtk](https://pypi.org/project/pyevtk/) by `pip install pyevtk`



## Usage

There are several place for users to modify to fit their problems:

###### set computing backend

First the computing backend should be specified by `ti.init(arch=ti.cpu)` *using parallel CPU backend*, or by `ti.init(arch=ti.gpu)` *to use OpenGL or CUDA(is available) as computing backend*

###### set input geometry

LBM uses uniform mesh, the geometry is import as a ASCII file with 0 and 1, where 0 represent fluid point and 1 represent solid point. They are stored in format:

```

for k in range(nz)

  for j in range(ny)

    for i in range(nx)

      geometry[i,j,k]

```

You can specify the input file at:

`solid_np = init_geo('./img_ftb131.txt')`



For two phase solver, a two phase distribution input file is also requred. This file is composed of -1 and 1 representing phase 1 and 2 respectively



###### set geometry size

Set geometry input file size here: `nx,ny,nz = 131,131,131`



###### set external force

Set expernal force applied on the fluid here: `fx,fy,fz = 0.0e-6,0.0,0.0`



###### set boundary conditions

There are three boundary conditions used in this code: Periodic boundary condition, fix pressure boundary condition, and fix velocity boundary condition

We use the left side of X direction as an example: `bc_x_left, rho_bcxl, vx_bcxl, vy_bcxl, vz_bcxl = 1, 1.0, 0.0e-5, 0.0, 0.0`

set boundary condition type in `bc_x_left`; 0=periodic boundary condition, 1 = fix pressure boundary condition, 2 = fix velocity boundary condition

if `bc_x_left == 1` is select, then the desired pressure on the left side of X direction need to be given in `rho_bcxl`

if `bc_x_left == 2` is select, then the desired velocity on the left side of X direction need to be given in `vx_bcxl, vy_bcxl, vz_bcxl`



The same rules applied to the other five sides



###### set viscosity

Viscosity is set in `niu = 0.1` for single phase solver

```

niu_l = 0.05

niu_g = 0.2

```

for two phase solver, niu_l for liquid phase, niu_g for phase 2



###### Additional parameters for two phase solver

- Contact angle of the solid surface can be specified in `psi_solid = 0.7` this value is the cosine of the desired contact angle, so the value is between -1 and 1

- Interfical tension of two phases is set in `CapA = 0.005`

- Boundary condition for the phase setting: `bc_psi_x_left, psi_x_left = 1, -1.0 ` bc_psi_x_left = 0 for periodic boundary for the phase field, 1 = constant phase field value boundary. If bc_psi_x_left is set as 1, then the next parameter is desired constant phase for this boundary: psi_x_left should be set as -1.0 or 1.0 for phase 1 or phase 2 respectively. 



**All the quantities are in lattice units**



## Examples (Direct Numerical Simulation)



###### Flow over a vehicle: inertia dominated

![image](https://github.com/yjhp1016/taichi_LBM3D/blob/main/img/car1.png)

![image](https://github.com/yjhp1016/taichi_LBM3D/blob/main/img/car2.png)



###### Single phase flow in a sandstone (Sandstone geometry is build from Micro-CT images at 7.5 microns): viscous dominated

![image](https://github.com/yjhp1016/taichi_LBM3D/blob/main/img/ftb1.png)



###### Urban air flow: inertia dominated

![image](https://github.com/yjhp1016/taichi_LBM3D/blob/main/img/city1.png)



###### Two Phase flow: oil (non-wetting phase) into a ketton carbonate rock saturated with water (wetting phase): capillary dominated

![Alt text](https://github.com/yjhp1016/taichi_LBM3D/blob/main/img/ket_drain.gif)



## Authors

Jianhui Yang @yjhp1016

Liang Yang @ly16302



## License 

MIT



## Citations

If you use Taichi-LBM3D in your research, please cite the corresponding paper:



    @Article{fluids7080270,

     AUTHOR = {Yang, Jianhui and Xu, Yi and Yang, Liang},

     TITLE = {Taichi-LBM3D: A Single-Phase and Multiphase Lattice Boltzmann Solver on Cross-Platform Multicore CPU/GPUs},

     JOURNAL = {Fluids},

     VOLUME = {7},

     YEAR = {2022},

     NUMBER = {8},

     ARTICLE-NUMBER = {270},

     URL = {https://www.mdpi.com/2311-5521/7/8/270},

     ISSN = {2311-5521},

     DOI = {10.3390/fluids7080270}

    }

    

## Acknowledgement

We acknowledge the support from ARCHER2 eCSE Programme.

### To do list:

- wrap functions into class to faciliate direct use from users

- Modify single phase gray scale and two phase data structure to improve computing efficiency (single phase code is done)

- Packing through pip

- Installation on ARCHER2