Gmsh to Create elbow.msh and Use it in OpenFOAM Tutorial

Friday 05 December 2025

It is interesting to think about and create the elbow geometry in Gmsh for the 2D elbow mesh. Figure 1 shows the drawing [1]. 

Fig. 1. The drawing of the elbow [1]

// elbow_new.geo

Point(1) = {0, 4.54, 0, 1.0}; Point(2) = {32, 4.54, 0, 1.0};

Point(3) = {52.54, 20.54, 0, 1.0}; Point(4) = {52.54, 0, 0, 1.0};

Point(5) = {56.54, 0, 0, 1.0}; Point(6) = {56.54, 20.54, 0, 1.0};

Point(7) = {64, 36.54, 0, 1.0}; Point(8) = {64, 68.54, 0, 1.0};

Point(9) = {48, 68.54, 0, 1.0}; Point(10) = {48, 36.54, 0, 1.0};

Point(11) = {32, 20.54, 0, 1.0}; Point(12) = {0, 20.54, 0, 1.0};

Line(1) = {1, 2}; // Line(2) = {3, 4}; Line(3) = {5, 6};

Line(4) = {7, 8}; Line(5) = {8, 9}; Line(6) = {9, 10};

Line(7) = {11, 12}; Line(8) = {1, 12}; Line(9) = {4, 5};

//

Point(13) = {32, 36.54, 0, 1.0};

Circle(10) = {11, 13, 10}; Circle(11) = {2, 13, 7};

//

Line(2) = {3, 4}; Line(3) = {5, 6};

Coherence;

//

Delete {

  Point{13}; Curve{11}; Curve{14}; Point{14}; Point{17}; Curve{16}; 

}

//

Curve Loop(1) = {15, 12, 9, 13, 17, 4, 5, 6, -10, 7, -8, 1};

Plane Surface(1) = {1};

//

Extrude {0, 0, 1} {

  Surface{1}; 

}

//

Physical Surface("velocity-inlet-5", 42) = {12};

Physical Surface("velocity-inlet-6", 43) = {4};

Physical Surface("pressure-outlet-7", 44) = {8};

Physical Surface("wall-4", 45) = {9, 10, 3, 5, 2, 11, 13};

Physical Surface("wall-8", 46) = {6, 7};

Physical Surface("frontAndBackPlanes", 47) = {14, 1};

Physical Volume("elbow-new", 49) = {1};

// uniform triangular 

mesh_size = 2.0;

Mesh.RecombineAll = 0; // 0 for triangles, 1 for quads

Mesh.Algorithm = 6; // 6 for triangles, 8 for quads

Mesh.CharacteristicLengthMin = mesh_size;

Mesh.CharacteristicLengthMax = mesh_size;

Mesh.CharacteristicLengthExtendFromBoundary = 0;

//

Mesh 3;

Fig. 2. The 2D elbow mesh created in Gmsh

Exported from Gmsh as elbow_new.msh, See Fig. 3, with option 'Save parameteric coordinates.'

Fig. 3. Mesh exported from Gmsh to use in OpenFoam

Files copied from the elbow tutorial to a new folder elbow_new created for this purpose. 

Fig. 4. Tree structure of the elbow_new folder

Execute the commands gmshToFoam elbow_new.msh and checkMesh. Ensure the Mesh OK and a new folder polyMesh in the constant folder.

Fig. 5. Converting mesh from Gmsh format to OpenFOAM

Execute the commands icoFoam and then foamToVTK. To visualize the simulation execute the command paraview foam.foam &. To create the foam.foam use the command touch foam.foam.

Fig. 6. Visualize the simulation

[1] https://www.tfd.chalmers.se/~hani/kurser/TMEX02_2007/Gambit/tg02.htm

Learning Point

• For p and U in folder 0, use type slip; for frontAndBackPlanes