Hi all Lammps users,
I want to setup velocity inlet boundary condition in Lammps, similar to the topics raised by Shankar Subramaniam about “uniform velocity” in this June and Auguest.
The question is simple, for example, I want to study the flow past a sphere. I can use the “fix addforce” command to drive the liquid flow along the channel. But two questions raise. First, if I use the periodic boundary condition in the flow direction, the liquid before the sphere will be affected by the “wake flow” of the sphere due to the periodic condition, even I enlarge the distance. Second, I want to set the macro velocity of liquid at inlet, but it can not be done using “fix addforce”.
This problem can be handled easily in my mind. For example, in periodic boundary condition, when an atom move out of the box (e.g. x_atom > x_max), the atom will reenter into the box at a_min. The velocity of the reenter atom can be set according to the inlet temperature and then an additional macro velocity can be added to vx.
But there is some questions to do this in Lammps. First, how to recognize the atoms enter into the box from x_min. Second, at what frequency should this process be repeated. Third, is it appropriate to setup a small region of box to stand for a reservoir and in this region, the velocity are reset every timestep.
Is there anyone who have done this or similar problems before? Looking forward to your reply. Thank you very much.