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# How to generate viscous layers through multiple volumes/partitions?

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### How to generate viscous layers through multiple volumes/partitions?

Posted by bthomas at August 15. 2018
Hello,

How can I propagate the viscous layer between two volumes meshed with different 3D algorithms?

My use case is the following: I would like to create a mesh for a square channel flow with a cylinder in the middle. The diameter of the cylinder is much bigger than the required viscous layer. So to get around this, I have created two partitions where the narrow region is by partitioning with two 45deg cuts. On the common faces with the rest of the domain I defined a 2D quad mesh wirth 2D viscous layers and used this for the hexa i-j-k meshing in the narrow regions. Now I would like to  mesh the rest of the domain with (preferably netgen 3D tetras) with a viscous layer conforming on the common faces and this is where I am stuck.

P.S.: I am more interested on a general approach how to continue a viscous layer from one volume/partition to another when meshed sequentially rather than how to hack this particular case, because I am having this type of problem appearing on much more complex geometries.

Kind Regards:
Tamás

### Re: How to generate viscous layers through multiple volumes/partitions?

Posted by Saint Michael at August 28. 2018

Hi Tamás

I don't understand the problem from your description. Can you provide an image or a study with your mesh?

St.Michael

### Re: How to generate viscous layers through multiple volumes/partitions?

Posted by bthomas at September 04. 2018

Hi Michael,

I prepared a simplified example, hopefully it's more clear this way.

I would like to mesh a channel flow (flowing left to right) for CFD with a choke much larger than the default boundary layer. I got to the point on the picture by partitioning into two volumes: left for unstructured, right for structured. Then I did quad meshing the cross-sectional faces with 2d viscous layers and hexa i-j-k meshing the right volume. Now I would like to mesh the right volume with tetra mesh + viscous layer matching with the faces.

The real left volume is more complicated therefore needs to be meshed unstructured.

Tamás

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### Re: How to generate viscous layers through multiple volumes/partitions?

Posted by Saint Michael at September 04. 2018

Hi Tamás,

Normally one uses Viscous Layers additional hypothesis of 3D algorithms to get what you need. If you want or have to define viscous layers your own way, then you need to additionally partition the left part into two sub-domains: 1) flow and 2) layers, and to use a tetrahedral algorithm for the flow sub-domain and a hexa or Extrusion 3D algorithm for the layers sub-domain.

St.Michael