[lammps-users] can't get linear velocity profile in couette flows


I am using LAMMPS to simulate a 3D couette flow, however, I could not
get the classic linear velocity profile. I created my script mostly
from the 2D couette flow example.

I created 2 slabs of wall atoms of type 1 and 3, flow atoms are of
type 2. For the wall atoms I use setforce 0 0 0 and gave the upper
wall atoms a constant velocity ux=1.0. Then I used fix ave/spatial to
get the averaged atoms number density and velocity profile. I tried
nvt,temp/rescale, langevin, but the results are same.

The results are very strange for both the number density and ux which
are attached with the script.

Your advice is greatly appreciated. The version i used is lammps-7Mar07.

Attached files:
In.flow.couette: the input script.
Ux.jpg: the velocity profile for ux.


in.flow.couette (1.42 KB)


The 2 May 07 patch probably fixes any problem with fix ave/spatial
you are seeing.