[ESPResSo-users] LBM, speed of sound, stability

[Ivan Cimrak]

Hi all,

In one of his emails Ulf Shiller explained that:
"you need to make sure that h*c_s^2/\nu is small to avoid nonlinear 
instabilities. h is the LB timestep, c_s is the speed of sound, and \nu 
is the kinematic viscosity. In the D3Q19 model, c_s^2=1/3*a^2/h^2, so 
a^2/(3*\nu*h) must be small. It may work with values O(1) but it is not
guaranteed."


Ulf, could you please give me the reason why this is necessary? And what 
does it mean "is small"? Are the values 0.1 - 0.99 ok?


Thanks,
Ivan


--
Ivan Cimrak
FRI Zilinska Univerzita v Ziline
personal web: http://www.kst.fri.uniza.sk/~icimrak/
cell-in-fluid group: http://cell-in-fluid.fri.uniza.sk