[Gmsh] Trouble meshing 3d shape in "wind tunnel"

Bob Basham bob at whitecloudaviation.com
Wed Nov 3 21:40:42 CET 2010

Well, I finally got a mesh of the air inside my wind tunnel!  I was 
trying to use the GUI to accomplish everything, but maybe I am not doing 
something correctly.  Anyways, I found the gmsh example of the bus 
inside a wind tunnel and after studying the GEO file I determined what 
kind of format I needed and then manually edited my GEO file 
accordingly, success!  It ended up being a very large file and was very 
slow and difficult to work with once I turned on the volume mesh 
visibilities, then I used clipping to see inside, and it looked good!  
Now time to put it in ELMER...


César A. Vecchio Toloy wrote:
> Bob, I think you're making a common mistake among CFD newcomers: you're modelling the bodies but not the air. I mean, the solid of your STEP must be the air and not the bodies surrounding it or the bodies in it. I give you the following example:
> Let's suppose you want to model the flow around a sphere. First we make a solid box which delimits the space we will model (even if you are modeling something in free space, you must limit it in the model). Now, to represent the sphere you must "take it out" from the solid box, for example by boolean substracting a solid sphere from the solid box, so you will end up with a solid box having an spherical cavity. That is the correct way of modeling in CFD with these kind of general purpose meshers.
> If you already knew this, I apologize. Check the message console in Gmsh (under "tools" menu) to see if there was some error. Perhaps you could be having extra surfaces or lines, that happened to me with some Rhino versions. If the STEP file is not very big, you can try attaching it.
> César
> On Mon, 01 Nov 2010 15:13:55 -0600
> Bob Basham <bob at whitecloudaviation.com> wrote:
>> Hi All,
>>      I am pretty new to CFD in general.  Just starting to figure out 
>> gmsh in order to run some simulations using ELMER.  I need to put a 3d 
>> shape inside of  a wind tunnel.  I have created the shape in Rhino 3d 
>> and finally have success with importing to gmsh as a STEP file (IGES 
>> gave all sorts of little holes in surface).  I have tried and tried to 
>> get a 3d mesh of the volume inside the "tunnel" and outside the shape, 
>> no luck.  I am sure that I am missing something basic.  Can someone 
>> point me in the right direction.  I have lastly tried merging a STP of 
>> the "tunnel" with a STP of the surface, but can't get a 3d mesh of the 
>> inside.  I get a self intersecting error.  I have successfully used a 
>> half model (like symmetry), the surface and tunnel are joined at the 
>> middle.  I would like to have my surface suspended in the tunnel 
>> though.  Thank you very much!
>> -- 
>> Bob Basham
>> _______________________________________________
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>> gmsh at geuz.org
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Bob Basham
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