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-   -   surface orientation airfoil/domain always misaligned (https://www.cfd-online.com/Forums/engrid/150138-surface-orientation-airfoil-domain-always-misaligned.html)

klausb March 16, 2015 10:23

surface orientation airfoil/domain always misaligned
 
1 Attachment(s)
Hello,

I've created a flow domain including an airfoil to do a quasi 2D flow simulation (as I couldn't figure out whether there's a way to create a 2D mesh with boundary layer cells which is then extruded into 3D - just one layer thick).

My problem is, that the surface orientation is always wrong. Either the airfoil is correct OR the domain is correct but I am not able to change the surface orientation of just one of them to align them as needed for meshing.

I need a volume mesh between the outside of the airfoil and the inside of the domain of course. As you can see on the picture, the back (inside of the flow domain) has the wrong surface orientation.

How can I change the surface orientation of individual elements (airfoil or domain)?

Klaus

wyldckat April 4, 2015 08:46

Greetings Klaus,

According to this tutorial: https://github.com/enGits/engrid/wik...ing_Geometries - section "Importing Geometries":
Quote:

Individual flipped faces can be repaired by clicking Correct surface orientation. However, for elegance’s sake surface orientation should be checked from the very start in Blender.
Best regards,
Bruno

klausb April 4, 2015 16:08

not always...
 
thank you for your feedback, but I didn't use Blender and "Correct surface orientation" changes the surface orientation of all faces so I end up with the same problem the other way around.

Klaus

wyldckat April 4, 2015 17:30

Hi Klaus,

Mmm... if the surfaces are already roughly consistent in the orientation, you should be able to control which side the volume mesh should be generated, as explained near the end of the section "Setting Up the Boundary Conditions": https://github.com/enGits/engrid/wik...ary_Conditions

There is also a utility in OpenFOAM named surfaceOrient. You can check how it's used by running:
Code:

surfaceOrient -help
If this doesn't work either... I don't have an STL file handy to test this with :( If you could provide one, I or anyone else could have a look into this.

Best regards,
Bruno

taxalian April 6, 2015 08:18

Quote:

Originally Posted by klausb (Post 539955)
thank you for your feedback, but I didn't use Blender and "Correct surface orientation" changes the surface orientation of all faces so I end up with the same problem the other way around.

Klaus

Hi Klaus,

I agree with Bruno's suggestion and in addition you can also try this option from Jens Höpken's blog, which can be quite helpful:

http://www.sourceflux.de/blog/preparing-geometry/

Another way around could be to correct the surface orientation of your "airfoil.stl" file and then later on merge it with your bounding box defining the computational domain extent.

Good luck,
Taxalian

thomas. March 22, 2016 08:51

Hi,

one quick question: does it make a difference on which direction the normal vectors are pointing, whether it´s an external or an internal flow? Or does it only matter that the direction of all vectors is consistent (all out, all in)?

Thanks in advance!

wyldckat March 26, 2016 06:57

Quote:

Originally Posted by thomas. (Post 591066)
one quick question: does it make a difference on which direction the normal vectors are pointing, whether it´s an external or an internal flow? Or does it only matter that the direction of all vectors is consistent (all out, all in)?

Quick answer: Yes, it has to be consistent, at least along a particular surface. See Figure 10 on this wiki page for more details on how you can later assign the boundary conditions depending on the orientation: https://github.com/enGits/engrid/wik...and-enGrid-1.2

thomas. March 29, 2016 03:34

Hi,

thanks!


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