# Fluent diverges when using inflation layers

 Register Blogs Members List Search Today's Posts Mark Forums Read

 August 9, 2013, 09:51 Fluent diverges when using inflation layers #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` The first inflation layer thickness is set such that y+ is around 30. Setting it such that y+ is 1 did not solve the divergence. 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:

 August 9, 2013, 10:10 #2 Super Moderator     Alex Join Date: Jun 2012 Location: Germany Posts: 3,400 Rep Power: 47 Have a look at the cells at the sharp trailing edges of your geometry. I guess they have very small angles.

 August 9, 2013, 10:23 #3 Member   Bart A. Join Date: Feb 2012 Posts: 45 Rep Power: 0 The trailing edge looks like this: How do I prevent too sharp angles in the mesh?

 August 9, 2013, 10:28 #4 Super Moderator     Alex Join Date: Jun 2012 Location: Germany Posts: 3,400 Rep Power: 47 An easy way could be to refine the mesh in this region (which you should do anyway because the mesh is rather coarse here).

 August 9, 2013, 12:11 #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.

 Tags divergence, fluent 14, inflation layer