   2d Lattice Boltzmann fluid simulation problems
  Hi,I've been reading up on LBM, and did a two dimensional (d2q9) test program. It basically works fine, but there are a few things that I'm not sure about.Sometimes the distribution functions of a node get negative values. Usually this leads to the simulation exploding. It usually happens with high-viscosity gases/fluids, especially if the whole lattice is initialized as a (physical) void, and a flow source is added.The second isn't really a problem, but a question that I haven't been able to find an answer to. How do you include gravity? Currently my "simulation" has a source, and it only spills out a gassy-cloudy-like field. It doesn't really look like water at all.If someone knows of a good simple example or article about LBM, I'd be grateful. A few days of googling mostly gave me articles about improving the basic LBM, and closed-source demo applications.   
  I don't know whether you've come across this one, but maybe it can help...http://www.cs.sunysb.edu/~vislab/projects/amorphous/WXMWebsite/smoke.pdf  edit:This one also seems to discuss some common errors with this method.http://www.phys.jyu.fi/theses/urpo_aaltosalmi.pdf I hope these are relevant to what you want[Edited by - someusername on December 11, 2005 9:13:47 AM]