Outflow boundary conditions and mass conservation

Hello everybody!

I am simulating a Poiseuille flow. On walls I use bounce back,
while for inflow and outflow I respectively use Zou-He scheme
for a fixed velocity and a null velocity gradient implemented
as suggested in

http://www.lbmethod.org/_media/howtos:neumann.pdf

by Malaspinas. What I found is that the total mass is no
longer conserved when I apply this outflow BC, but
it constantly grows up. That
happened also if I copied the x-velocity of the Nx-1
section into the Nx (outflow) section as input for a diriclet
BC (Zou scheme again). Is that normal or am I doing
something wrong?

Thanks in advance to all who`ll answer :slight_smile:

Ern

Hello,

you are doing nothing wrong. In this paper we have investigated the effect of mass increase. Just read the corresponding sections and you will see that it is quite a natural effect of velocity boundary conditions.

Timm

1 Like

Maybe you can refer to the following paper in which mass modification method is applied to guaratee the mass conservation in the open flow problems.

Mass modified outlet boundary for a fully developed flow in the lattice Boltzmann equation, International Journal of Modern Physics C, 2007, 18(7): 1209-1221.

Dear Timm and Don,

thank you all for the suggested referencies, I`ll study them and
compare with the results of my code :slight_smile:

Oh, I was not aware of the other paper when I submitted mine.

Don Wrote:

Maybe you can refer to the following paper in
which mass modification method is applied to
guaratee the mass conservation in the open flow
problems.

Mass modified outlet boundary for a fully
developed flow in the lattice Boltzmann equation,
International Journal of Modern Physics C, 2007,
18(7): 1209-1221.

Hi Don
Is it possible for you to send me this paper?
my email: mrahmani79@yahoo.com
with best regards

Hi All,

Please suggest a solution for this problem. Can somebody send me the paper

Mass modified outlet boundary for a fully developed flow in the lattice Boltzmann equation, International Journal of Modern Physics C, 2007, 18(7): 1209-1221.

My email Id is narender.koosukuntla@gmail.com

Thanks,
Narender