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-   -   stl geometries are never good enough - why? (http://www.cfd-online.com/Forums/engrid/115724-stl-geometries-never-good-enough-why.html)

klausb April 5, 2013 10:00

stl geometries are never good enough - why?
 
Hello,

after completing the damper tutorial, I am trying to create an alternative mesh for an OpenFoam tutorial using enGrid.

When I try to import a stl geometry, I get the error message:

p, li { white-space: pre-wrap; } "The STL geometry could not be cleaned"


The same happened with an airfoil.stl I created.


What are the required settings?


Klaus

ogloth April 5, 2013 12:33

STL is an awful format and most CAD programs fail to export water-tight STL files. Open-Cascade based software generally does a good job of this. Alternatively you can fix the geometry using Blender.

Feel free to post a geometry which fails and I'll have a look at night -- not before Monday, unfortunately.

Engrid badly needs an import function for CAD files without the detour via STL or any other mesh based format.

Regards,
Oliver

klausb April 5, 2013 13:12

S809 airfoil.stl needed
 
1 Attachment(s)
Hello,

the stl file is too large to post.

What I need is a stl file of the S809 airfoil with a span twice the chord. Find the coordinate file for the S809 airfoil attached.

Airfoil coordinate files describe the geometry for a chord of 1 which will be interpreted for my simulation as 1m so the span should be 2 (2m).

If the program can't handle coordinates ranging from 0 to 1, they can be multiplied by e.g. 100 or 1000. A correction factor can easily be set in OpenFoam.

How can such an stl be created?

Do you have plans to enable step or iges imports?

Klaus

ogloth April 8, 2013 09:20

Hi Klaus,

I just had a look at your airfoil and it imports after changing the format slightly to match the Selig airfoil format. It can then be exported to Blender and within Blender a proper volume can be created with little effort.

Do you want your wing between two walls (symmetry planes), or do you want a proper wing tip?

I'll send you a file which you can import into enGrid later today or tomorrow, because there is loads of other work to do ...

Cheers,
Oliver

klausb April 8, 2013 17:39

The S809 test case
 
Hello,

my intention is to use enGrid to create the mesh for the S809 3D test case described in the ris-r-1581.pdf paper.

Paper download: http://http://www.findthatpdf.com/se...r-1581.pdf.htm

Klaus

ogloth April 9, 2013 03:12

1 Attachment(s)
Hello,

here is the promised file. It is in the enGrid <-> Blender exchange format which can be directly imported into enGrid. Boundary codes have already been defined. Please note that the wing is split into an upper and lower part; this is important to keep the sharp trailing edge intact.

Cheers,
Oliver

robyTKD November 28, 2013 19:37

Hallo Oliver,

I am very much interested in building a mesh using Blender + enGrid.

I have downloaded the file you attached in previous post (it is great!!:D). I would like to know how did you build the .becg file (from the definition of the airfoil curve to the definition of boundaries).
Is it possible to have any advice? or do you know where I can find a little guide?

Thank you very much for the attention!

Cheers,
Roberto

wyldckat November 29, 2013 17:40

Greetings to all!

@Roberto: I'm not certain how Oliver did it, but the following tutorials come to mind:
And enGrid's wiki is open to public contributions, so please do contribute if you can: https://github.com/enGits/engrid/wik...nGrid%27s-wiki

Last but not least, do keep in mind that Oliver can provide faster support if you use the very accessible and helpful support line at http://engits.eu/en/support ! ;)

Best regards,
Bruno

robyTKD December 1, 2013 16:10

Thank you for the quick reply Bruno.

I followed the tutorials that you proposed above, unfortunately I am not able to obtain something like the file made by Oliver. In particular I met difficulties in extruding the airfoil profile (producing a good .stl) and creating symmetry planes with holes in correspondence of the airfoil in Blender.

However I'll ask for help on the enGits forum as you proposed!! :D

I would be pleased to contribute to the enGrid's wiki!

Cheers,
Roberto


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