Understanding the non-dimensionalisation of LBM

Hi there,

I’ve been messing around with the tutorial (permeability) to see if I can implement a number of different things to try and get Palabos to calculate alternate setups:

  • Changed the geometry to flow past few spheres.
  • Added periodic boundary conditions to the side faces.
  • Changed the DeltaP condition to a velocity at input + density at input condition

All of these changes worked fine and I’m getting some reasonable simulation results that converge.

I then started to change the dimensions of the code and this is where I started having convergence issues. From what I can gather, the only things I’m able to change are (or things that were adjustable in the tutorial):

  • The inlet velocity
  • The inlet density
  • Omega

I’ve tried reading a number of textbooks on the issue, but I’m still having problems. The things I’ve got results for and am trying to recreate are : Re=7.9, u_in = 0.32, rho=0.44, Lx = 0.0023, Ly = Lz = 0.002, mu = 3.5e10-05. N are 720x600x600 (this what after I’ve refined them from 400x400x480 but the solver because unstable at the same iteration step). Omega also doesn’t seem to affect convergence in this instance, just input velocity (not sure about density).

I’m not looking for someone to do it for me, I’m just looking for where I can learn this stuff or the logical approach to this so in the future I can use the tool more intuitively.