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Strange behavior of a diffusion model coupled with moving mesh
Posted Jan 15, 2012, 10:38 a.m. EST Version 4.2a 6 Replies
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I'm working on a simple 2D model of a chamber (rectangle) where I have Laminar Flow, Transport of Diluted Species and Moving Mesh physics.
This is my simple geometry:
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I'm expanding the chamber by moving up the top boundary; at the same time a Laminar Inflow is entering by the left boundary.
In the Laminar Flow I have set Inflow (Pressure=1atm), Initial Values (p=1atm) and Moving Wall;
In the Transport of Diluted Species I have set an Inlet (C=1.8mol/m^3), Initial Values (C=1.8mol/m^3), No Flux in every other boundary.
The study is Time Dependent.
The problem I have is that the concentration in the chamber increases near the boundary where I set the Moving Wall.
There is no physic explanation of that, and I don't know how to solve. I tried changing the Coordinate System, but I don't know if the problem is there, and it didn't work.
In the attachment there is an image of my result.
Can anyone help me?
Daniele
Attachments:
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could it be that you have 2 conditions, mass transfort (flow) and concentration diffusion, and a moving wall, moving perpendcular to the flow, should still have a "no-slip" condition along the flow (from my understanding), so I suspect that you have a rapid flow close to the moving wall.
have you checked carefully the other results, flow velocity, etc, also from your initial conditions
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Good luck
Ivar
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thank you for your answer.
The velocity seems to be correct, it's 0 m/s near the moving wall, as you can see in the attachment (I forgot to say that there is a symmetry on the bottom boundary, but I have the same problem without the symmetry condition).
In the second attachment there is a graph of the average concentration in the chamber. I'm expecting the average concentration to be constant in time, but it's increasing, and I don't know why.
Daniele
Attachments:
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today I discovered something that might be useful.
If in Transport Of Diluted Species model inputs I change the velocity field something changes:
-with Velocity Field = Velocity Field (spf/fp1), that is my standard, I have the problem
-with Velocity Field = User Defined, and x=u, y=v (that is the same of setting spf/fp1, right?), I have the problem
-with Velocity Field = User Defined, and x=u BUT y=0 the problem disappears!
So it seems to be a problem of the velocity field in transport of diluted species. Could it be caused by frames or coordinate system? Could it be a problem of the coupling of the two physics?
I double checked the Velocity (spf.U, u, v, etc) in Results and it seems to be correct.
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I can't find any solution, could anybody help me?
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daniele, did you find out more?
simon
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same problem here.
daniele, did you find out more?
simon
Hi,
yes I solved it. I rewrote the diffusion equation via the "PDE - coefficient form PDE" interface, and it works.
I think that there is a bug in "transport of diluted species" interface.