# Lattice units to physical units - permeability tutorial

Hi,

I have gone through the other threads about lattice unit conversion and the document lbunits.pdf still cant figure this out, any help would be appreciated .

For the permeability tutorial case with nx = 48 ny = 64 nz = 64

The output in lattice units

Average velocity (meanU, darcy velocity) = 0.000177152
Lattice viscosity nu = 0.166667
Permeability = 27.7539
Reynolds Number meanU*(nx-1)/ nu = 0.049957

Can’t yet figure out how to get the physical velocity. pressure, viscoity…

Dear ananjund,

for what I have understood on this topic, I suggest you to define as many physical units as the number of basic units you use:
1 which contains the length (e.g. the length of the rector)
1 which contains the time (e.g. the velocity or the viscosity)
1 which contains the mass (e.g. the density)

after that you can evaluate the dt, dx and drho.
Reynolds number is the same in both cases whereas for the permeability I don’t know what to tell you.

Cheers

Antonio

Permeability should be the same whether working in lattice units or physical units, just like Reynolds number.

No, permeability should not be same in lattice units and physical units. In the first place, permeability has units of length squared, so you’d have to do some unit conversion from the lattice unit for length to the physical units

If the permeability has unit m[sup]2[/sup], then k[sub]p[/sub] = k[sub]l[/sub] * dx[sup]2[/sup] where l and p denote lattice and physical units and dx is the length of the LBM lattice unit.

Timm,

I am wondering if you have done any simulations related to the Beta factor (Forchheimer constant) calculation using the LBM?

No, I have not. I am sorry.

I instantly regret writing that with so much certainty, thanks for pointing that out.