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-   -   Grid types and change of angle of attack (http://www.cfd-online.com/Forums/main/93232-grid-types-change-angle-attack.html)

cpinz October 9, 2011 07:10

Grid types and change of angle of attack
 
Hi all,

I wonder if C-grid or O grids are the only solution for analyzing airfoils under change of angle of attack without rotate the airfoil itself ( that is without rotate the geometry and re-meshing again).

Is the same task possible with standard rectangular domains ( where I have velocity inlet, pressure outlet and symmetry up and bottom as boundary conditions ) ?

Thank you

Far October 9, 2011 09:31

yes you can

cpinz October 9, 2011 12:07

Hi Far ,

thank you for your reply.
Do you mean that it is sufficient to input the components (u,v) of inlet velocity , keeping other boundary conditions unchanged ? Or have I to change the type of some boundary condition ?

For high angles of attack , the fact that v component of velocity has a steep angle respect to the (vertical) inlet of a rectangular domain, doesn't affect the analysis ?

Thanks

truffaldino October 9, 2011 14:51

I would rather use velocity inlet bc on top and bottom too. You can change inlet velocity rather than mesh, no problems. Just make sure that near-field wake does not go to low-resolution mesh region under high aoa.

cpinz October 9, 2011 17:51

Quote:

Originally Posted by truffaldino (Post 327220)
I would rather use velocity inlet bc on top and bottom too. You can change inlet velocity rather than mesh, no problems. Just make sure that near-field wake does not go to low-resolution mesh region under high aoa.

Are you saying that the boundary condition would be (supposing flow coming from left):
left side, bottom,top= velocity inlet
right side = pressure outlet ?

truffaldino October 10, 2011 09:57

Quote:

Originally Posted by cpinz (Post 327232)
Are you saying that the boundary condition would be (supposing flow coming from left):
left side, bottom,top= velocity inlet
right side = pressure outlet ?

Yes, exactly. If your top and bottom are far enough from the airfoil it does not really matter if they are velocity inlet or periodic. I usually take about 12 chord distances from airfoil to the top/bottom with velocity inlet on 3 sides and pressure outlet at the right side and it works just fine.

If your angle of attack is really huge, i.e. a such that wake goes to the top side, rather than into the outlet, you could change role of the sides and put outlet on the top and velocity inlet on the right, but I think the latter is not your case.

Hope it helps
Truffaldino

cpinz October 10, 2011 11:56

Quote:

Originally Posted by truffaldino (Post 327327)
Yes, exactly. If your top and bottom are far enough from the airfoil it does not really matter if they are velocity inlet or periodic. I usually take about 12 chord distances from airfoil to the top/bottom with velocity inlet on 3 sides and pressure outlet at the right side and it works just fine.

If your angle of attack is really huge, i.e. a such that wake goes to the top side, rather than into the outlet, you could change role of the sides and put outlet on the top and velocity inlet on the right, but I think the latter is not your case.

Hope it helps
Truffaldino


Thank you very much for your helpful posts


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