# Gambit Problem Size Function

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 April 11, 2011, 11:56 Gambit Problem Size Function #1 New Member   Basti Join Date: Apr 2011 Posts: 7 Rep Power: 13 Hello I´m working on a numerical analisys of a turbine blade (2D). I have already done some simulations in fluent with my gambit-made 20.000 cells grid. In Fluent I adapted this grid with the dynamic refine function, so I had a almost perfectly refined grid apart from the trailing edge, where you could see 20 edges put together forming the trailing edge instead of the semicircle as expected. Therefor I tried to change my grid in Gambit meshing the turbine blade with an interval size of 0.001 and creating a size funcion (meshed type / 1.1 growth factor / 3 max.). Instead of showing me cells starting with the interval size of 0.001, Gambit shows me a grid in the trailing edge that doesn't fulfil this criterion. (Only in a really unimportant part of the profile this criterion is fulfilled) It would be very nice if somebody can help me with my problem. Thank you in advance. El Wastl

 April 12, 2011, 03:43 #2 Super Moderator     Maxime Perelli Join Date: Mar 2009 Location: Switzerland Posts: 3,293 Rep Power: 39 if you attached a picture I cannot see anything __________________ In memory of my friend Hervé: CFD engineer & freerider

April 12, 2011, 05:39
#3
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Basti
Join Date: Apr 2011
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Of course... here it is
In the image you can see the meshed trailing edge, but the grid, generated with the meshed-type size function, doesn't fulfil the given distances of the first row of cells....
Attached Images
 trailing edge_prob_size function_50.JPG (72.7 KB, 92 views)

 April 12, 2011, 08:44 #4 Super Moderator     Maxime Perelli Join Date: Mar 2009 Location: Switzerland Posts: 3,293 Rep Power: 39 delete your mesh, also your size function. Create a new size function (type fixed) Select your edge as source, give 0.001 as start size, 1.1 as growth, and 3 as max size. __________________ In memory of my friend Hervé: CFD engineer & freerider

April 13, 2011, 11:16
#5
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Basti
Join Date: Apr 2011
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Now I have two size function:

sf1:
source all edges of the profil
attachment: face (flow field)

sf2:
source: trailing edge semi circle
attachment: face (flow field)

With these functions I would like to have a grid with small cells next two the edges of my profil. But why Gambit makes me a non symetric grid like you can see it in the image. Info: The edges of the profil are NURBS! Are there problems with meshing NuRBS?

But there's n other problem:
Attached Images
 trailing edge_sfedge_klein.JPG (55.7 KB, 63 views)

 April 14, 2011, 08:23 #6 Super Moderator     Maxime Perelli Join Date: Mar 2009 Location: Switzerland Posts: 3,293 Rep Power: 39 do you have only one face? If you want a full symetric mesh around your trailing edge you can enforce gambit to link surface mesh together. But you will need to split your surface into smaller surfaces __________________ In memory of my friend Hervé: CFD engineer & freerider

 April 14, 2011, 10:13 #7 New Member   Basti Join Date: Apr 2011 Posts: 7 Rep Power: 13 Thank you very much, at last I can really improve my grid!!! I tried it with an extra face around my trailing edge and it works Can you recommend me adding a certain number of faces (and their form!!) all round my profile? The face linking function, you mentioned, is it called "LInk face meshes" in Gambit? Why does Gambit want to know sth about vertices?

 April 14, 2011, 10:41 #8 Super Moderator     Maxime Perelli Join Date: Mar 2009 Location: Switzerland Posts: 3,293 Rep Power: 39 you are free to decompose your surface as you want.(for unstructured mesh) But it has to be symmetric. For linking the surface mesh, you need to give one vertice for the first surface, and another one for the linked surface. In your case you will give the same vertice. http://my.fit.edu/itresources/manual...mg0303.htm#689 ScreenShot.jpg __________________ In memory of my friend Hervé: CFD engineer & freerider

 April 14, 2011, 10:59 #9 New Member   Basti Join Date: Apr 2011 Posts: 7 Rep Power: 13 perfect...thank you for your helful explaination

April 15, 2011, 06:51
#10
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Basti
Join Date: Apr 2011
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Hello Max
Thank you for your tips. Already I have obtained some results with my old "bad" grid (only one face) in FLuent, but now I want to improve my grid. In my case I cannot create symetric subfaces because of the "flow channel"??!! You can see my geometry in the attachement
Basti
Attached Images
 channel+profile.JPG (31.5 KB, 31 views)

 April 15, 2011, 06:55 #11 Super Moderator     Maxime Perelli Join Date: Mar 2009 Location: Switzerland Posts: 3,293 Rep Power: 39 what is your question? __________________ In memory of my friend Hervé: CFD engineer & freerider

April 15, 2011, 07:18
#12
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Basti
Join Date: Apr 2011
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Quote:
 Originally Posted by -mAx- you are free to decompose your surface as you want.(for unstructured mesh) But it has to be symmetric. Attachment 7265
In my case I can't create symmetric subfaces because of the channel geometry (periodic boundaries). But nevertheless I would like to have a fine and symmetric grid all round the trailing edge! Do you have a recommendation? Thanks

 April 15, 2011, 08:17 #13 Super Moderator     Maxime Perelli Join Date: Mar 2009 Location: Switzerland Posts: 3,293 Rep Power: 39 Then create a subdomain in the wake of trailing edge which will be symmetric in respect of your yellow edges-chain. In my example, I meshed the subdomains very quick with pave, but you can more decompose those sufaces for having a nice quad mesh I also attached a BL at the trailing edge, showing you that you can also include one. Sans titre.jpg __________________ In memory of my friend Hervé: CFD engineer & freerider