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-   -   Valildation of OF for external aerodinamics (http://www.cfd-online.com/Forums/openfoam-verification-validation/109845-valildation-external-aerodinamics.html)

andrea.ciarella November 28, 2012 04:25

Valildation of OF for external aerodinamics
 
3 Attachment(s)
Hi,

I have one problem with OF. I am trying to validate SimpleFOAM for external aerodynamics.

The problem is

Airfoil: s822
Mach: 0.1
Reynolds: 500000

I am generating the polar from the angle of attack -10 to 14 with steps of 1 degree.

I compared the results with Experimental data and another code.


I used Spalart-Allmaras turbulence model with y+ = 1 and tested several numerical schemes. I only attached the best results


Attachment 17291

Attachment 17292

Attachment 17293

my questions are:

The drag is wrong after the linear range, the cause is a wrong stagnation pressure. Is here any way to improve it?

If I want to use a wall fuction which one do you think I have to use?

Do you think will be better with other solvers or turbulences? I test K-Omega sst but the results are similar.

Does a validation of OpenFOAM for external aerodynamics exist?

Thank you in advance
Andrea

sail November 28, 2012 13:52

Hi there.

could if be possible to see your mesh? my suspect is that you don't have enough spatial resolution in the chord direction and not enough layers in the boundary layer. I got excellent results with 100-150 points for in the chord and at lest 20 cells across the BL

also, it the error can be due to the turbulence model. SA is mostly effective for high Mach numbers, say 0.6+

at your Re lot of drag is due to friction more than pressure, so i would reccomand a model that can show laminar-turbulent transition like the k-o SST gamma-re-theta.

there is an excelent implementation for openfoam in the forum. try to google it.

calim_cfd November 29, 2012 14:09

hi!

just to emphasize.. a pic of your mesh would be helpfull.

try plotting the y+(y*) values for each aoa too along the wing span.

also, make sure ur boundary conditions match the experimental one.

other than that i dont c where the problem could be

gl

andrea.ciarella November 30, 2012 03:51

Mesh
 
1 Attachment(s)
Thank you for your replay.

The mesh is a semistructured mesh

Attachment 17350

I used different mesh with y+ between 0.1 an 3 to see if it is an effect of the mesh, but I didn't get much difference

I will try the transition model next week and I will post the results.

From my point of view the biggest problem is the wrong stagnation pressure that is the cause of he wrong drag.

I already tested other farfield boundary conditions, but doesn't change the solution.

Did somebody have/know some proper validation of the solver for external aero?

Thank you


Regards
Andrea Ciarella

calim_cfd November 30, 2012 12:28

hi again!

im not an expert in lift/drag calculations but are you updating the reference area with the aoa? do ppl usually do that when plotting those charts?:confused: ;)


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