[Gmsh] checkMesh 'unused points' error after gmshToFoam

N1ckb45 · February 13, 2020, 11:52

Hi,

I am attempting to model an aerofoil using a hybrid mesh I have created in Gmsh, looking to extend it in 3D later. When I run gmshToFoam and then checkMesh, I am met with the following error:

***Unused points found in the mesh, number unused by faces: 398 number unused by cells: 398 <<Writing 398 unused points to set unusedPoints

I have looked into it and saw a post saying I need to edit my boundary file, deleting the default patch section and reducing the number of boundaries, but this hasn't made any difference. I also tried specifying the gmsh version, but that didn't work either. I have attached my .geo file, any help would be appreciated.

Thanks,
Nick

mzzmrt · February 14, 2020, 01:37

I think your problem has caused by the conforming error between tri and quad sections of the mesh so playing with the 2D/3D mesh algorithms may (or may not) help.

On the other hand I can advise using two other approaches:

1. Use the built-in boundary layer function which is powerful and gives far easier and better quality boundary layer mesh

2. Or make full quad based mesh instead of a hybrid one. You can make it by using a circle or ellipse for the far field instead of square same way as you meshed your boundary layer...

I hope this helps...

N1ckb45 · February 18, 2020, 04:28

I have considered using a full squad mesh, however this is just a stepping stone to solving flows with ground effects, so I will need a flat plate below the aerofoil. I have also heard the built-in boundary layer function doesn't work for 3D boundary layers anymore?

mzzmrt · February 19, 2020, 09:57

For a ground effect case, it depends on the wing model.

Will it be a simple (3D) section of a wing or will there be a wing tip with an end plate which is a must for a real wig craft?

For the first option, it is easy to extrude a built-in boundary layer mesh in 3rd dimension.

For the second option, gmsh is not easy to use because it is not a multi-block mesher (yet) as far as I know and the most tricky part will be the boundary layer meshing on the wing tip. If this is the case, it will be optimal to use a cartesian mesher such as snappy or cfmesh.

Artur.Ant · November 19, 2021, 08:49

I had a similar problem in a 3D case because I didn't define one of the internal volumes and so I got holes within the domain.
If you have similar problem check your physical volumes defined in Gmsh.

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February 14, 2020, 01:37		#2
mzzmrt Senior Member Join Date: Mar 2014 Posts: 112 Rep Power: 12	I think your problem has caused by the conforming error between tri and quad sections of the mesh so playing with the 2D/3D mesh algorithms may (or may not) help. On the other hand I can advise using two other approaches: 1. Use the built-in boundary layer function which is powerful and gives far easier and better quality boundary layer mesh 2. Or make full quad based mesh instead of a hybrid one. You can make it by using a circle or ellipse for the far field instead of square same way as you meshed your boundary layer... I hope this helps...

February 18, 2020, 04:28		#3
N1ckb45 New Member Nick Join Date: Feb 2020 Posts: 4 Rep Power: 6	I have considered using a full squad mesh, however this is just a stepping stone to solving flows with ground effects, so I will need a flat plate below the aerofoil. I have also heard the built-in boundary layer function doesn't work for 3D boundary layers anymore?

February 19, 2020, 09:57		#4
mzzmrt Senior Member Join Date: Mar 2014 Posts: 112 Rep Power: 12	For a ground effect case, it depends on the wing model. Will it be a simple (3D) section of a wing or will there be a wing tip with an end plate which is a must for a real wig craft? For the first option, it is easy to extrude a built-in boundary layer mesh in 3rd dimension. For the second option, gmsh is not easy to use because it is not a multi-block mesher (yet) as far as I know and the most tricky part will be the boundary layer meshing on the wing tip. If this is the case, it will be optimal to use a cartesian mesher such as snappy or cfmesh.

November 19, 2021, 08:49		#5
Artur.Ant Member Arthur Join Date: Aug 2014 Location: Italy Posts: 47 Rep Power: 11	I had a similar problem in a 3D case because I didn't define one of the internal volumes and so I got holes within the domain. If you have similar problem check your physical volumes defined in Gmsh.