Re: [ESPResSo-users] Lattice Boltzmann External Force

[Wolfgang Riefler]

Hello everyone.

First of all thanks for all your quick answers.

I probably should have said before that the offset I was getting was in the range of many times the maximum velocity (a maximum velocity of 0.04 had an offset of 0.5), so I don't think its because of the discrete boundaries. Just to be sure I checked the simulation again for a very small viscosity and I still get the offset.

At the moment I am working with the version 3.0.2.

Coming back to the original problem, it was actually the PhD thesis of Ulf "Thermal fluctuations and boundary conditions in the lattice Boltzmann method" that caught my eye and made me change the source code, since it says in equation (4.65):

                              j = j' + 0.5 * g * tau

where j is the hydrodynamic momentum density, g is the volumetric force and tau the lattice boltzmann time step.

Implementing this line, I get a much better result, with only a little offset, which is probably due to the discrete boundary.

Thanks again for your help,

Wolfgang