so far, in the LBM scheme only the body force
is implemented and no velocity/pressure boundary condition.
So I was thinking on a way of mimicking a “velocity
boundary” condition without changing the source code. I am
aware that one should, as a proper approach, using Zou/He
boundary conditions and adjusting the distribution functions
according to the boundary conditions.
For that I have constructed a channel with
rectangular cross section and put the fluid inside.
Furthermore, two rhomboids where put inside, one at the
inlet of the channel, one at the outlet. The cross section
of the two rhomboids is equal to the cross section of the
channel, furthermore they have a constant velocity v0.
My idea was, that, since the no-slip boundary
condition is implemented, I force the fluid nodes adjacent
to the rhomboids to have a constant velocity, thus achieving
constant velocity inlet/outlet condition.
As a result I achieve a poiseuille profile in
the middle of the channel (fully developed flow after
inlet/outlet effects). The qualitative pressure gradient
looks proper, too.
Nevertheless, the maximum velocity is not the
same as I expected (factor 3 to the expected one).