如何确定绝对渗透率的物理单位？

[eromanga233]

老师您好。 K = q * u (viscosity)/(fy) 是计算绝对渗透率的公式。取参数niu=0.1 ，fy = 1.0e-6，那么代入到公式中得到的K的结果的物理单位是什么？ 如果需要根据分辨率进行调整，假设分辨率是3μm/voxel，在原始K计算值的基础上乘以9，就能得到单位是μm2的结果了吗？

[yjhp1016]

用量纲分析就能做渗透率的格子单位和物理单位之间的转换，不是特别复杂，好像是格子单位的渗透率乘分辨率的平方就是物理单位的渗透率。你需要查下文章，很多里面都有

eromanga233 @.***> 于 2024年4月11日周四 下午6:08写道：

老师您好。 K = q * u (viscosity)/(fy) 是计算绝对渗透率的公式。取参数niu=0.1 ，fy = 1.0e-6，那么代入到公式中得到的K的结果的物理单位是什么？ 如果需要根据分辨率进行调整，假设分辨率是3μm/voxel，在原始K计算值的基础上乘以9，就能得到单位是μm2的结果了吗？

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[Clifford-Wang]

Hello, I'm a beginner in LBM. I recently started working on a project involving Taichi LBM3D. I want to reproduce the example of Taichi_LBM3D single-phase flow. I set the fluid viscosity to 0.1, resolution to 7.5, and imposed periodic boundary conditions on all sides. The flow is solely driven by body force fx = 1e-5 .However, I'm experiencing an issue where the calculated permeability converges to around 500, which is lower than the reported 789 in the literature. However, the flow field visualization appears to be normal. I'm wondering if there's a mistake in my parameter settings.

[yjhp1016]

The permeability calculation is heavily rely on the selection of geometry and the size of the geometry. I think the example geometry in repo is just part of the REV(representative element volume), so the perm is different than the value I reported. I used a much bigger geometry to calculate the perm. But it's not appropriate to put a big geometry file in repo, so I cut it into a smaller piece.

Clifford @.***> 于 2024年4月21日周日 下午3:27写道：

Hello, I'm a beginner in LBM. I recently started working on a project involving Taichi LBM3D. I want to reproduce the example of Taichi_LBM3D single-phase flow. I set the fluid viscosity to 0.1, resolution to 7.5, and imposed periodic boundary conditions on all sides. The flow is solely driven by body force fx = 1e-5 .However, I'm experiencing an issue where the calculated permeability converges to around 500, which is lower than the reported 789 in the literature. However, the flow field visualization appears to be normal. I'm wondering if there's a mistake in my parameter settings.

image.png (view on web) https://github.com/yjhp1016/taichi_LBM3D/assets/167417015/901c5c0e-4dba-47cc-883a-529aae891b77

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[Clifford-Wang]

Thank you for your kind words. So, if I understand correctly, the "img_ftb131.txt" file in your repository is not the file you actually used for calculation in the article "Taichi-LBM3D: A Single-Phase and Multiphase Lattice Boltzmann Solver on Cross-Platform Multicore CPU/GPUs," even though they have the same size of 131131131. Therefore, it means that the permeability of this file is not 789md, is that correct?

[yjhp1016]

Yes, that's correct

Clifford @.***> 于 2024年4月21日周日 下午4:01写道：

Thank you for your kind words. So, if I understand correctly, the "img_ftb131.txt" file in your repository is not the file you actually used for calculation in the article "Taichi-LBM3D: A Single-Phase and Multiphase Lattice Boltzmann Solver on Cross-Platform Multicore CPU/GPUs," even though they have the same size of 131131131. Therefore, it means that the permeability of this file is not 789md, is that correct?

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[yjhp1016]

By the way what boundary condition did you use to calculate permeability. The best way is mirror the geometry, and apply periodic boundary condition

Clifford @.***> 于 2024年4月21日周日 下午4:01写道：

Thank you for your kind words. So, if I understand correctly, the "img_ftb131.txt" file in your repository is not the file you actually used for calculation in the article "Taichi-LBM3D: A Single-Phase and Multiphase Lattice Boltzmann Solver on Cross-Platform Multicore CPU/GPUs," even though they have the same size of 131131131. Therefore, it means that the permeability of this file is not 789md, is that correct?

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[Clifford-Wang]

I'm sorry, I'm new to LBM and don't know how to mirror geometry. I simply set all six faces of the geometry as periodic boundaries, which means I set all boundary conditions to 0. For fx (external force), I set it to 1e-5, and I didn't set anything else

[yjhp1016]

probably that's why your result is much lower tha 798...... as you actually block some pore/throats...

periodic means the flow going out from outlet will re-enter inlet, so you need to mirror the geometry to make sure outlet has same geometry ad inlet.

I use some small python code to mirrow geometry.

Clifford @.***> 于 2024年4月21日周日 下午4:14写道：

I'm sorry, I'm new to LBM and don't know how to mirror geometry. I simply set all six faces of the geometry as periodic boundaries, which means I set all boundary conditions to 0. For fx (external force), I set it to 1e-5, and I didn't set anything else

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[Clifford-Wang]

Oh, I see. Thank you very much for your help. I didn't pay attention to this issue in my previous research. I will continue to explore how to apply the geometric mirroring method you mentioned. I'm wondering if it's possible to simply mirror the image geometry in ImageJ, as coding is not my strong suit. If possible, I may consult you for some questions in my future research, but I won't take up too much of your time. I hope to receive your assistance.