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March 6, 2013, 06:49 |
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#61 |
Senior Member
Francisco
Join Date: Mar 2012
Location: Spain
Posts: 273
Rep Power: 15 |
I've been moving vertices and changing nodes number, negative volumes change in number and distribution (see pics) but they are always there.
I've been checking http://www.youtube.com/watch?v=tYrbScUH9RE for some blocking ideas but every blocking strategy I try to imitate gives negatives volumes for me. Is there any base problem? Isn't it a common mistake in Icem practice? Cause I'm facing it too often! Any suggestion? Thanks! |
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March 6, 2013, 07:06 |
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#63 |
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Francisco
Join Date: Mar 2012
Location: Spain
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Rep Power: 15 |
Here you are
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March 6, 2013, 08:46 |
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#65 |
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Francisco
Join Date: Mar 2012
Location: Spain
Posts: 273
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I've converted one of the meshes to unstructured and then exported it to fluent and it doesn't detect any negative volumes! I had tried that before with no success but now it works...
How does the pre-mesh to unstructured step work? Apparently Negative Volume indicator doesn't mean too much... Which quality parameters should I pay attention to? Quality, angle, volume change? Thanks! |
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March 7, 2013, 06:01 |
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#67 |
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Francisco
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March 7, 2013, 06:08 |
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#69 | |
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AB
Join Date: Sep 2009
Location: France
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Quote:
About the values of quality, Far is right, but quality, > 0.2 is good too. |
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March 7, 2013, 06:37 |
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#70 | |
Senior Member
Francisco
Join Date: Mar 2012
Location: Spain
Posts: 273
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Quote:
Then in fluent it doesn't show any negative volumes. However, for this mesh, my fluent case diverges from the beginning. I'm using 33.87 m/s, k-ep standard with TI=1% and TLS=1e-4m at the inlet. Adaptive time-step starting at 1e-8. I've tried reducing under-relax factors one order of magnitude but it doesn't avoid divergence. |
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March 7, 2013, 06:42 |
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#71 |
Senior Member
AB
Join Date: Sep 2009
Location: France
Posts: 323
Rep Power: 22 |
No negative volume in this project, the pre-mesh quality > 0.8.
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March 7, 2013, 06:51 |
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#72 |
Senior Member
Francisco
Join Date: Mar 2012
Location: Spain
Posts: 273
Rep Power: 15 |
But if I select Volume in the quality menu, select histogram form -1 to 0 you can see there are negative volumes. In the image there's the histogram from 1e-15 to 0 showing many elements, even if quality histogram is >0.6...
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March 7, 2013, 06:55 |
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#74 |
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Francisco
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Location: Spain
Posts: 273
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March 7, 2013, 07:30 |
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#75 |
Senior Member
Francisco
Join Date: Mar 2012
Location: Spain
Posts: 273
Rep Power: 15 |
I've discovered that just changing the min distance of the edge near the wall from 1e-5 to 5e-5 it improves quality a lot, from having near zero quality elements to a minimum quality of 0.6. It's pretty sensitive to node distribution!
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March 7, 2013, 10:11 |
naca wing volume change
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#76 | |
Senior Member
Francisco
Join Date: Mar 2012
Location: Spain
Posts: 273
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Okay, so negative volumes is solved so far. Now I want to make some test with the mesh but it diverges no matter what I do.
Quote:
Could it be the problem for not reaching convergence? Could I reach convergence with a coarser mesh? Thanks! |
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March 7, 2013, 11:16 |
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#77 |
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Francisco
Join Date: Mar 2012
Location: Spain
Posts: 273
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I thought an appropiarte volume change was 20% so I understood that higher than 1.2 was not good. But as I've read in the user guide, less than 20 means 20 times the maximum neighbour volume. So my volume change dsitribution is pretty good! So I don't know what can be wrong
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March 7, 2013, 11:20 |
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#78 | |
Senior Member
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Quote:
Just few thoughts: 1. Open up mesh in far field. In other words do not carry forward mesh sizing and growth ratio in farfield. Instead make spacing uniform and use match edges. 2. check domain extents |
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March 7, 2013, 14:13 |
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#79 | |
Senior Member
Francisco
Join Date: Mar 2012
Location: Spain
Posts: 273
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Quote:
And use uniform spacing instead of hyperbolic or geometric or whichever? Which edges should I matche to which ones? Thanks! |
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March 8, 2013, 05:26 |
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#80 |
Senior Member
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Download file from first post in following thread and look at the meshing in farfield.
http://www.cfd-online.com/Forums/ans...take-mesh.html |
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Tags |
blade tip, hexa mesh, sharp edge, wind turbine |
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