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August 9, 2013, 09:51 |
Fluent diverges when using inflation layers
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#1 |
Member
Bart A.
Join Date: Feb 2012
Posts: 45
Rep Power: 0 |
I'm simulating a 2D wedge in a flow with the transient standard k-epsilon model. The Reynolds number is around 400000.
The geometry is shown below. The mesh without inflation layers gives a solution with a CD of around 1.2. This is close to literature values of a 2D wedge in a flow. However, when I add the inflation layers (and change nothing else in the mesh), the solution diverges after one timestep and I get a warning that the turbulent viscosity is limited to a viscosity ratio of 1e5 in several thousand cells. In the end Fluent stops iterating with the message: Code:
Divergence detected in AMG solver:y-momentum I've read up on the viscosity ratio warning in different posts here and in other internet resources, but the remedies (refining the mesh, under-relaxing the k and e) did not work for me. I'm surprised that adding an inflation layer has such a big (negative) effect on my solution. Can someone explain what is happening here? Should I just leave the inflation layers out all together (sounds like a bad idea)? 1. Geometry overview, flow comes from the left, normal to the boundary: 2. Geometry close-up: The mesh without inflation layers looks as follows: 3. Mesh overview: 4. Mesh refined area: 5. Mesh around wedge: And with inflation layers: 6. Mesh around wedge with inflation layers: 7. Mesh around wedge nose with inflation layers: |
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August 9, 2013, 10:10 |
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#2 |
Super Moderator
Alex
Join Date: Jun 2012
Location: Germany
Posts: 3,426
Rep Power: 49 |
Have a look at the cells at the sharp trailing edges of your geometry.
I guess they have very small angles. |
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August 9, 2013, 10:23 |
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#3 |
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Bart A.
Join Date: Feb 2012
Posts: 45
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The trailing edge looks like this:
How do I prevent too sharp angles in the mesh? |
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August 9, 2013, 10:28 |
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#4 |
Super Moderator
Alex
Join Date: Jun 2012
Location: Germany
Posts: 3,426
Rep Power: 49 |
An easy way could be to refine the mesh in this region (which you should do anyway because the mesh is rather coarse here).
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August 9, 2013, 12:11 |
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#5 |
Member
Bart A.
Join Date: Feb 2012
Posts: 45
Rep Power: 0 |
I've refined the mesh at the trailing edge by adding an edge sizing restriction on the edges of the wedge. It now looks like this:
Fluent does converge now. Thank you for your help. |
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Tags |
divergence, fluent 14, inflation layer |
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