I ran several tests on the current Lattice Boltzmann implementations (D3Q18 and D3Q19). From my results, I conclude that there is a bug in the implementation with regards to the lattice spacing (a). According to the theory, the single particle diffusion (D) should decrease with increasing lattice spacing (see paper by Ahlrichs et al 1999). Exactly the opposite is observed, but I didn't yet delve into the code, to find out where the error arises from. For a grid spacing of 1, the results agree with the prediction, therefore it is safe to assume, that for this specific grid spacing the code works fine.
I attached a plot illustrating my findings.
Kai
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Dipl. Phys. Kai Grass
Frankfurt Institute for Advanced Studies (FIAS)
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