[Other] Best method for layer generation

chriss85 · April 24, 2015, 07:02

What's you favorite method for generating layers when you already have a base mesh?

BlockMesh is often sufficient for my geometries but I need to have finer cell resolution close to the walls.

I often find snappyHexMesh to be bothersome in a way that it either distorts my mesh so it doesn't fit the outer boundaries anymore, collapses layers which shouldn't be collapsed etc. Most of these things are fixable by tuning the parameters but it's not exactly easy to tell where a problem lies for me.

Sometimes I have used a manual refinement using (auto)refineMesh, this creates very nice meshes for me but requires lots of work to get all the refinements oriented properly.

Any other suggestions?

On another topic, how do you deal with strongly varying CFL numbers when you have different cell sizes due to layers? I'm using an adaptive time step method based on the max. CFL number so the time step size can be affected by the layer cells once the flow goes in a direction orthogonal to the wall.

KateEisenhower · May 13, 2015, 07:11

Hello there,

regarding snappyHexMesh, I have experienced the same as you have. Currently I am working with enGrid, but this tool generates the boundary layer first and creates the volume mesh afterwards. So I think it is not what you are looking for. Frankly, I am still struggling with it and I do not know if it is able to create proper prismatic layers for my use case. Also I am trying to get a grip on gmsh, but I am still at the very beginning.
Recently I discovered a very interesting thread regarding this topic:
http://www.cfd-online.com/Forums/ope...pyhexmesh.html

Kate

April 24, 2015, 07:02	Best method for layer generation	#1
chriss85 Senior Member Join Date: Oct 2013 Posts: 397 Rep Power: 18	What's you favorite method for generating layers when you already have a base mesh? BlockMesh is often sufficient for my geometries but I need to have finer cell resolution close to the walls. I often find snappyHexMesh to be bothersome in a way that it either distorts my mesh so it doesn't fit the outer boundaries anymore, collapses layers which shouldn't be collapsed etc. Most of these things are fixable by tuning the parameters but it's not exactly easy to tell where a problem lies for me. Sometimes I have used a manual refinement using (auto)refineMesh, this creates very nice meshes for me but requires lots of work to get all the refinements oriented properly. Any other suggestions? On another topic, how do you deal with strongly varying CFL numbers when you have different cell sizes due to layers? I'm using an adaptive time step method based on the max. CFL number so the time step size can be affected by the layer cells once the flow goes in a direction orthogonal to the wall.

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May 13, 2015, 07:11		#2
KateEisenhower Senior Member Join Date: Mar 2015 Posts: 250 Rep Power: 12	Hello there, regarding snappyHexMesh, I have experienced the same as you have. Currently I am working with enGrid, but this tool generates the boundary layer first and creates the volume mesh afterwards. So I think it is not what you are looking for. Frankly, I am still struggling with it and I do not know if it is able to create proper prismatic layers for my use case. Also I am trying to get a grip on gmsh, but I am still at the very beginning. Recently I discovered a very interesting thread regarding this topic: http://www.cfd-online.com/Forums/ope...pyhexmesh.html Kate