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[Other] Structured quadrangular 3D mesh rounded cube

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Old   July 5, 2018, 09:24
Default Structured quadrangular 3D mesh rounded cube
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Cristina Hernandez
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Hi,

I want to use OpenFOAM to simulate the flow around a cube with rounded edges and calculate de drag coefficient. An example of the geometry is attached as a .stl file.

I am trying to create a quadrangular structured mesh for the whole domain, with a finer mesh around the cube to accurately model the pressure (ideally, the size of the cells around the cube should be 1/20 the characteristic length and get bigger as we move away from it).

Do you have any suggestions on which meshing utility could be easily used for this? Any help would be welcome.

Cristina
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Old   July 5, 2018, 09:38
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Cristina Hernandez
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Quote:
Originally Posted by crizpi21 View Post
Hi,

I want to use OpenFOAM to simulate the flow around a cube with rounded edges and calculate de drag coefficient. An example of the geometry is attached as a .stl file.

I am trying to create a quadrangular structured mesh for the whole domain, with a finer mesh around the cube to accurately model the pressure (ideally, the size of the cells around the cube should be 1/20 the characteristic length and get bigger as we move away from it).

Do you have any suggestions on which meshing utility could be easily used for this? Any help would be welcome.

Cristina
This is an example of how I would like the mesh to look like
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Old   July 5, 2018, 10:38
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Cristina Hernandez
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So far, I have explored the following:

First I tried gmsh, but I could only obtain a triangular unstructured mesh (Transfinite Volume didn't work).

Then, I changed to cfmesh OpenFOAM utility. I imported my geometry generated from gmesh, extracted the surface as a .stl file and generated the mesh with cfmesh command "cartesianMesh". To obtain the mesh I want, I have tried different strategies (I am posting my meshDict):

1) anisotropicSources: defining a box that contains my cube

maxCellSize 1;
x_cube 1.5; y_cube 1.5; z_cube 1.5;

anisotropicSources
{
box
{
type box;
centre (20.75 17.5 7.5); //centre of cube

lengthX 5*$x_cube; //5 times characteristic length
lengthY 5*$y_cube; //5 times characteristic length
lengthZ 5*$z_cube; //5 times characteristic length

//scaling factors in each direction
scaleX 0.05*$x_cube;
scaleY 0.05*$y_cube;
scaleZ 0.05*$z_cube;
}
}

But I do not know how to change the size of the cells within the box, so that there is a gradient and cells become bigger as I move away from the cube.

2. boundaryLayer: treat the cube wall as a boundary layer and use local refinement to set the number of cells in the first layer

maxCellSize 1;
x_cube 1.5; y_cube 1.5; z_cube 1.5;

localRefinement
{
cube
{
cellSize 0.05*$x_cube; //characteristic length/20
}
boundaryLayers
{
//global number of boundaryLayers, set to 0 so that the rest of the boundaries (walls of the domain) are not meshed
nLayers 0;
//local settings for individual patches (cube)
patchBoundaryLayers
{
boundaryCellSize 0.1;
"cube"
{
nLayers 5;
thicknessRatio 1;
maxFirstLayerThickness 1; //characteristic length of cube/20
allowDiscontinuity 0;
}
}
}


What I would like to obtain is a refined mesh around a region at a distance equal to 5 times the characteristic length from the cube.

Could anyone help me obtain this adjusting my setting in meshDict for cfmesh? I am also open to other alternatives.
I can provide you any file you need.

Thanks in advance,

Cristina
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Old   July 17, 2018, 14:12
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Luis Eduardo
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Hi Cristina,

Have you tried blockMesh and/or snappyHexMesh?

The round edges will be a little difficult to treat, but it is possible to do it (I didn't open your geometry file to check it).
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