[cfdoruk]

Hi everybody,

I'm trying to have boundary layer for a very simple geometry by using Gmsh. I can construct the layers; however, I want to exclude one of the faces from the boundary layer list. Although I tried ExcludedFaceList, it still produces layer there.

My surface and curve tags are shown in "Tags.png".
What I want to have is shown in "Desired.png".
What I get in Gmsh is shown in "Result.png".

The script is as follows:

// Gmsh project created on Fri May 15 18:00:20 2020
SetFactory("OpenCASCADE");
//+
Point(1) = {0.5, 0.5, 0, 1.0};
//+
Point(2) = {0, 1, 0, 1.0};
//+
Point(3) = {0.5, 1, 0, 1.0};
//+
Point(4) = {0, 0.5, 0, 1.0};
//+
Line(1) = {2, 3};
//+
Line(2) = {3, 1};
//+
Line(3) = {1, 4};
//+
Line(4) = {4, 2};
//+
Curve Loop(1) = {1, 2, 3, 4};
//+
Plane Surface(1) = {1};
//+
Extrude {0, 0, 0.1} {
Surface{1}; Layers{5}; Recombine;
}

Field[1] = BoundaryLayer;
//+
Field[1].AnisoMax = 1000;
//+
Field[1].EdgesList = {1, 2, 3, 4};
//+
Field[1].ExcludedFaceList = {4};
//+
Field[1].IntersectMetrics = 0;
//+
Field[1].Quads = 1;
//+
Field[1].hfar = 0.75;
//+
Field[1].hwall_n = 0.001;
//+
Field[1].ratio = 1.300000;
//+
Field[1].thickness = 0.025;

BoundaryLayer Field = 1;

Thank you.

[Flowkersma]

Hi Doruk,

The boundary layers in GMSH are not working very well in 3D. So I would first create a 2D mesh with the boundary layer and then extrude that. Here is an example:

SetFactory("OpenCASCADE");
Rectangle(1) = {0, 0, 0, 1, 1, 0}; 

Field[1] = BoundaryLayer;
Field[1].EdgesList = {2, 3, 4}; 
Field[1].NodesList = {1, 2, 3, 4}; 
Field[1].hwall_n = 0.01;
Field[1].thickness = 0.1;
Field[1].ratio = 1.2;
Field[1].Quads = 1;
BoundaryLayer Field = 1;
Extrude {0, 0, 0.1} { Surface{1}; Layers{10}; Recombine; }

Best, Mikko

[cfdoruk]

Hi Mikko,

This works, thank you.

Regards
Doruk

[ari003]

Originally Posted by Flowkersma

Hi Doruk,

The boundary layers in GMSH are not working very well in 3D. So I would first create a 2D mesh with the boundary layer and then extrude that. Here is an example:

SetFactory("OpenCASCADE");
Rectangle(1) = {0, 0, 0, 1, 1, 0}; 

Field[1] = BoundaryLayer;
Field[1].EdgesList = {2, 3, 4}; 
Field[1].NodesList = {1, 2, 3, 4}; 
Field[1].hwall_n = 0.01;
Field[1].thickness = 0.1;
Field[1].ratio = 1.2;
Field[1].Quads = 1;
BoundaryLayer Field = 1;
Extrude {0, 0, 0.1} { Surface{1}; Layers{10}; Recombine; }

Best, Mikko

I have a small question and that is why you didnt include hfar or farfield size? Does it become redundant?

[Flowkersma]

Indeed it becomes redundant. You can calculate the number of cells and largest cell size from geometric series.

[ari003]

Originally Posted by Flowkersma

Indeed it becomes redundant. You can calculate the number of cells and largest cell size from geometric series.

Thanks for your response. Maybe it is a very lame question to ask atm but is it that hfar is the last boundary cell or the very adjacent region outside the boundary layer?