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-   -   Velocity changes through an airfoil (http://www.cfd-online.com/Forums/main/84037-velocity-changes-through-airfoil.html)

roger_pn January 18, 2011 16:50

Velocity changes through an airfoil
 
See if anyone can help me. I'm trying to iterate in fluent an airfoil with an extern domain. I've done all the meshing in gambit, checked it for highly skewed elements and for inverted elements and all is Ok. I import it into fluent, made the grid check, changed materials to ideal gas and tried to iterate. HEre comes the problem. As I iterate, i don't know why, the velocity increases at the far end of the outer domain, but only on a very little region. ALl the other parts feel as they should.

If anyone can give me some advice or give his/her email adress so i can show the problem clearly (i don't know how to post imatges here XD).

Thank u.

mettler January 19, 2011 09:17

one thing you can try is making a smaller mesh and seeing if the solution is the same. I know from experience that if your mesh isn't good enough your solution might be wacky. But, that is what I would try. I would make a tiny mesh and get an answer, and then do a really coarse mesh and get an answer and see how much different they are..basically, a grid check. And, when you are done, you will know the optimum sized grid you need for your problem.

roger_pn January 19, 2011 10:04

I've done the adapt-> gradient process and checked the skewness of the cells with the grid-check and case->check and showed no errors.

The strange thing is that the increase of velocity is only in a small part of the volume. It's quite difficult to explain it without nay pictures. My email is rogerpn@hotmail.com, if someone may help me.

mettler January 19, 2011 10:26

you need to completely re-grid with a fine grid. Your grid can be correct in all manners, but the solution can still be wrong.


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