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2D-empty vs pseudo 2D upd. results

Posted April 18, 2013 at 02:53 by skeptik (CFD notes)
Updated April 18, 2013 at 03:15 by skeptik

Pseudo 2D results is here on the graph
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Cx is predicted very well, so let's make a comparation with 2D results

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The difference is really big on supercritical angles, the PISO's results on 2D tetra meshes were also bad and quite similar to the 2D hexa's results.

So, it's better to use PISO with symmPlane or slip BC on domain's sides

#OpenFoam #2Dairfoil
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Old

2D-empty vs pseudo 2D - symmPlane

Posted April 15, 2013 at 04:35 by skeptik (CFD notes)

It seems there is big difference in case with 1-cell thick domain where we set empty BC compare to case with 5-cells or 3 - cells thick where we set symmPlane

for SST and NACA23012 we have (17 and 15 grad angle of attack)

Click image for larger version

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So when we use PISO, it would be better to use 5 or 3 -cells thick domain.
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blockMesh,snappyMesh and experimental results for 2D airfoil

Posted April 1, 2013 at 04:17 by skeptik (CFD notes)

A certain Mahdi wrote me via e-mail, that my tetra-mesh and hybrid mesh was not good for simulations.

So here i show results which were obtained with C-mesh generated by blockMesh utility OF, and snappyHexMesh.

blockMesh domain

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mesh near wall

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snappyHexMesh domain

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boundary layer discretization

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File Type: jpg hexasSimple.jpg (44.1 KB, 1188 views)
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Old

about polyDualMesh "Try something smaller than 90"

Posted March 28, 2013 at 02:06 by skeptik (CFD notes)

Quote:
Originally Posted by lillberg View Post
Try something smaller than 90 deg feature angle since it represents the maximum angle between two neighboring surface normals on a surface without corners. That is, the mesh will consider your surface shape a corner if the angel is larger than this value. I typically use something between 45 and 80 depending on the tet mesh resolution on highly curved surfaces. This might be the root of your problem. Looking at my picture the curved surface in the middle would (wrongly) be treated as a corner if
...
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Old

note about convergence

Posted March 26, 2013 at 05:39 by skeptik (CFD notes)

Quote:
Originally Posted by chegdan View Post
Nick,

There are some strategies that I would try to get these residuals down to something you would like.
  1. Lower your pressure relTol by an order of magnitude compared to U i.e. relTol = 0.001 for P and relTol = 0.01 for U.
  2. Without knowing the mesh you are using you may need to increase the nonorthogonal corrector by 1 or 2. if you are using a tet mesh...then there are many things you can do.
  3. Use first order schemes to start with (you will move to higher order ones
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