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Recirculation bubble and wall shear stress

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Old   July 9, 2010, 10:23
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Daniele
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I try to use with my case the mesh of pitzDaily tutorials, I only change mesh, and in this case a I haven't overshooting on step. Why on my mesh is there this overshooting?
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Old   July 12, 2010, 07:18
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I can see two jumps in the size of the cells in the x directions, of a factor 2 or 3, which is not a good meshing practice. You should use very smooth variations in the cell sizes, in all directions. Variations of 10 % between two consecutive cells, especially in critical areas such as the boundary layer, is sometimes cited, which is not stupid in the experience I had.

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Old   July 12, 2010, 07:24
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I eliminate the overshooting I change mesh add a cell where the shape change slope
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Old   July 12, 2010, 07:28
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That seems to be better, did you keep the same cell height at the wall because of the y+ criteria ? Any improvement in the results ?
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Old   July 12, 2010, 07:36
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No because the three cell near the slope has different areas the solution is bad
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Old   July 12, 2010, 07:41
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I am sorry but I don't understand.
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Old   July 12, 2010, 07:46
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My English is very bad!
In my previous mesh near the slope i have only two cell. In my new cell three. Three cell with at least a vertex shared with the vertex where th obstacle changes its slope.
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Old   July 12, 2010, 08:11
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I don't understand why the mesh configuration could change the geometry. This is more a problem of how you do the mesh.
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Old   July 12, 2010, 08:15
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Uhmm I don't understand your question. Sorry
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Old   July 12, 2010, 08:19
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I think I did not understand what you said before.

-In my previous mesh near the slope i have only two cell. In my new cell three.
Here you say that you didn't use the same number of cells in the slope, is it that ?


- Three cell with at least a vertex shared with the vertex where th obstacle changes its slope.

And here that this change in the mesh configuration changes the slope of the obstacle.

This is not normal. The geometry should be fixed and then you do the mesh on it. If the way you do the mesh changes the geometry it is because you don't do the mesh in an appropriate manner.
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Old   July 12, 2010, 08:27
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No. I didn't change the shape of th obstacle, I divide my domain i four hex in my blockMeshDict, so near the vertex where start the step I have more cell. The cell number, two or three, aren't the number of cell on slope, but the cell number that surrounding the vertex where start the step
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Old   September 20, 2010, 12:54
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hi
I return on this problem. I must try to solve it with a monoblock grid instead of a multiblock grid. The problem isn't the separation a use obstacle with high aspect ratio, and I haven't overshooting. I think that the problem is the point with differet value of derivate (left and right). Is possible resolve it?
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