Porous media simulation

I am trying to simulate unidirectional flow in a CT image using the cavity3d example as template. My initial condition is zero velocity everywhere. The flow is driven by a pressure difference (density difference) between the inlet and outlet. The LBunits converter needs to have the Reynolds number to compute omega and the others. However, I do not know the Reynolds number at the beginning of the iteration as that is what I am interested in obtaining for a given pressure difference.
I would appreciate if somebody helps me with information on how to go about this.


I would suggest that you search for the keyword “unit conversion” on the lattice Boltzmann forum, as this topic has been extensively discussed.

Thanks Jonat,

My problem is not lattice conversion as I am pretty comfortable with it, It is just what would be the Reynolds number argument in the lBUnits converter since my fluid is intially at rest and the LBUnits converter needs a Reynolds number value to calculate omega.



The Reynolds number is defined with respect to a characteristic velocity. If you impose a pressure gradient, you should use your physical understanding of the problem (such as, an analytical solution for a simpler yet similar problem) to relate the pressure gradient to a characteristic velocity. If you can’t do this, your best bet is probably an a-posteriori estimate of the Reynolds number, by measuring the velocity at the end of the simulation.

But I insist: this type of arguments have already been discussed in the forum, and I’m sure it’ll be helpful for you to run a search.

Thanks Jonas for your explanation. I have read the comments in the previous threads and they were really helpful.

The first method you suggested is going to be kind of difficult because this is a 3D problem in cubic geometry.
I do want to start my simulation from zero initial velocity everywhere. What I ended up doing is to still use the LBUnits converter, but I manually calculated my omega while the Reynolds number argument in the converter is going to be zero (if it does not work, I will leave it blank in the converter). The velocity at the end of the simulation would then be used to calculate the Reynolds number (though the important parameter I need is the velocity for a particular pressure difference)