[lammps-users] Poisseuille flow

Dear Users,

1. In the example of Poisseuille flow, the flow is created by addforce command applied to every atoms. This means that the flow has body force driven and is not pressure driven. Is this correct? How do I create a pressure driven flow?

2. How do I add force to atoms present in a particular geometric region at any given time rather than to atom belonging to a particular group? Basically, I want to add force to atoms only at the entrance of the simulation box on one side and then let them move across the box.


Bhavin N. Vadgama


You're right that it is body force driven rather than truly pressure driven. To do truly pressure driven, you'd need to include a density gradient with something like a gravitational field or a piston. In practice, this is not done in order to make the problem tractable within a reasonable amount of CPU time.

As far as your second question goes, take a look at the "region" and "group" commands.


You can define a static group, but you can't define a dynamic group (members change with time). You could write your own fix to do what you're asking.