Dear Lammps members,
I am trying to create a argon flow with uniform velocity in a channel.
The purpose is to , then, introduce a carbon nanotube (cnt) inside the channel and study the drag on the cnt.
In the description below, there is no cnt yet.
I have also enclosed the lammps code as attachment.
I am working with a small system of 800 argon atoms in a channel size 54 X 27 X 27 ( angstroms ).
This is compressed liquid argon at 1342 kg/m^3 density, and at temperature 125K.
Using periodic domain, and “atom” style for argon.
I do the computation in two parts:
-
run a NVT simulation to equilibrium at 125K.
-
then run NVE simulation for uniform flow.
For the NVE simulation:
- I partition the channel into 3 sections: entrance, center and exit sections.
The entrance and exit are 20% of the channel length each.
-
At the entrance and exit, at each time step I reset the thermal velocity at 125K and add
desired flow velocity. This maintains the temperature and velocity at those two sections. -
I expect that will establish a similar state at the center section also.
The average velocity at the center section reaches the desired value, but the temperature
is way too high around 3500K ( depending on the speed ).
If the velocity bias is not removed at the entrance/exit sections, then the temperature is about
1000K; with bias removed the temperature is 125K as desired.
So the high temp. of 3500K at center is way above the velocity bias.
Could anyone suggest the cause for this high temperature ?
- Is it because the speed is not properly removed in computing the temperature ?
I am using “temp/com” lammps command that is supposed to remove the velocity bias.
This command seem to work because, if I just use “temp” command the temperature
at the entrance/exit section is about 1000K and not 125K as desired.
-
Perhaps the initial NVT run is not long enough, and so the initial energy is too high in
subsequent NVE run ? -
Is the concept correct , to start with ?
concept == maintaining entrance/exit sections at a certain state and expecting the same state at the center section.
I would appreciate any help.
regards,
shankar
uniform_flow_argon.lmp (28.9 KB)