I am using the open source code susp3d. In this code density (in lattice unit of course) of fluid is set as 36. From my knowledge so far lattice system density is set up based on a reference density, i.e. density in physical unit= reference density * density in the lattice unit. Most of the time i observe that density in the lattice system is set as 1. Hence where could be this constant value (36) origin? By the way, it is the average value of density in the fluid as total density is expressed as the sum of average and fluctuating component，

My only assumption is that the velocity weights and populations are scaled differently in susp3d. A sum of 36 would result in velocity weights of 1;2;12 instead of 1/36;1/18;1/3 for a D3Q19 lattice. Don’t really see a reason for this, as it would make unit conversion even more tedious than it already is in LB

btw: I tried to find a copy of susp3d for download - would you mind sending me your copy?

Just saw your post , Thanks for swift response. I will send as soon as i go back to Lab. I am in vacation currently.

From your post, i can see that your argument for appearance of 36 is related to the weights. I had such observation , too. However, i couldn’t find any single reference which explain why there is a definition of Rho_Fl= 36 which is related to the average density.