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-   -   Help needed with Cornell's Gambit airfoil tutorial (http://www.cfd-online.com/Forums/fluent/46127-help-needed-cornells-gambit-airfoil-tutorial.html)

AW September 24, 2007 17:59

Help needed with Cornell's Gambit airfoil tutorial
 
Hi, I'm a biologist messing with Fluent/Gambit for my dissertation. I was wondering if someone could help me out with the airfoil tutorial at http://courses.cit.cornell.edu/fluent/airfoil/step1.htm

(the creator of the tutorial isn't answering his email which probably isn't current by now)

I can do everything great by skipping the do-it-yourself mesh generation step and running the provided mesh file in Fluent. When I create my own mesh from the tutorial's dat file, things get messed up. First of all, I've noticed that not all of the vertices are connected at the nose, so the nose is not very smooth at the small scale. Second, when I subtract the airfoil face from the circ1 face, Gambit deletes the edges when it leaves the hole. So the part where you mesh HI and HJ (front of airfoil), etc. can't be done unless you rename their edges. That's fine, but it seems some of the vertices go missing, so I lose points and can't retrieve them. I managed to recreate the airfoil edges before meshing it with circ1 and all went great, but my recreation probably wasn't very accurate (I used NURBs). It worked in Fluent ok, except my pressure coefficient plot showed high pressure under the airfoil going infinitely. Zooming on the nose showed it wasn't very smooth at all and I think this is where it's messing up the pressure plot. I have some jpg files documenting this if anyone is curious as to what the hell I mean.

So my question is that since I'm inputting the same values the tutorial gives for their mesh and my mesh, do you think the problem lies in the fact that the nose vertices aren't connected from the get-go, or is it where I have to recreate the edges after I subtract the airfoil face from circ1? I tried again to connect all the vertices using the straight-edge option, but it created as many edges as there were points and I couldn't figure out how to make it into one big edge (or in the tutorial's case, 2-4).

Thanks a lot, I really appreciate everyone's help and time. Hopefully I presented my problem clearly!

VV September 24, 2007 18:50

Re: Help needed with Cornell's Gambit airfoil tuto
 
Just checked the tutorial file and everything seems to be fine the way it is now. If you can upload or send me the journal file that gambit creates, I can help you out.

e-mail (vimalvinayan@yahoo.com)

AW September 24, 2007 19:16

Re: Help needed with Cornell's Gambit airfoil tuto
 
Thanks, VV, jou file is on the way!

AW October 3, 2007 14:42

Re: Help needed with Cornell's Gambit airfoil tuto
 
Ok here's the resolution thanks to Vimal-- before subtracting the faces, split the airfoil according to the tutorial. Then split the circular edges (make U=0.5). Draw a line from the vertex corresponding to the split on the circular edge to the vertex corresponding to the split on the airfoil. This completely skips the face subtracting part. Move on to the mesh. Put same # of elements on the edges that parallel AG/EG. Follow tutorial's instructions for meshing airfoil. For circular faces instead of using 0.02c as the first length, use successive ratio 1 with corresponding interval counts (35 or 40). Mesh. The mesh won't be identical to the tutorial's but it works well enough. When running this in Fluent, need to decrease the URFs since the resolution at the airfoil face is greater. Change it to pressure=0.1 and momentum=0.9; it'll take ~1200 iterations instead of ~540 but you get the same results as the tutorial.

Prakash.R October 6, 2007 01:30

Re: Help needed with Cornell's Gambit airfoil tuto
 
i am practising gambit and also fluent tutorials .so i need aerofoil equations to generate the model in gambit. so plz kindly send me that details.

V V October 6, 2007 01:49

Re: Help needed with Cornell's Gambit airfoil tuto
 
http://www.aerospaceweb.org/question...ls/q0041.shtml

http://www.ae.uiuc.edu/m-selig/ads/coord_database.html


balkrishna February 26, 2010 23:42

GAMBIT Error
 
In the tutorial while creating the face for GAFEG+airfoil (notation as per given in tutorial ) i get the following error :

ACIS Error 19002 : Edges for wire are not connected

Does anyone know the reason for this ?? and how to solve it ?


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