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• # Final Mini Project – CFD foundation course

Posted by on January 5, 2024 at 2:15 pm

Hi !

I have designed AHMED model using Design-modeler & Space-claim.

Meshing and setup done by fluent.

When I run calculation for lift & drag after initialization,result is not converged even after 1000 iterations.

I couldn’t my mistake.
Please guide to get converged solution.

Thank You!

replied 2 months, 3 weeks ago 3 Members · 7 Replies
• 7 Replies
• ### Sujith FTL

Member
January 5, 2024 at 3:22 pm

Hi Mathanraj,

Please check you reference values youâ€™ve given as the drag and lift values seems to be very large from the data youâ€™ve shown. Give averaging for every 200 iterations as the fluctuations seem to be periodic for every 200 iterations and check the values.

Regards,

Sujith

• ### Mathanraj

Member
January 7, 2024 at 7:06 am

Hi sujith !

I have a doubt.

What is the reference value which you are mentioned here?

• ### Sujith FTL

Member
January 8, 2024 at 7:30 am

Hi, you can find the reference values section after the boundary conditions section in the setup tree.

• ### Mathanraj

Member
January 17, 2024 at 4:19 pm

Thank u Sujith..
I have calculated area of inlet using report option in results.

Updated the calculated area as ‘reference value’ & changed ‘pseudo time explicit relaxation factors’ like pressure & momentum as 0.25 from 0.50.

Now my solution is converged after 348 iterations.

Solution: drag co-efficient = 30.15 & lift co-efficient = 79.61

Is my solution correct?

• ### Orhan

Member
January 17, 2024 at 5:17 pm

Hello Matranhaj,

I see in the previous message that you said that you calculated the projected area of the inlet. In my project, my drag_coefficient value in the project I made for Ahmed body geometry (slant angle 30Â°) was: 0.297. This was consistent with the wind tunnel test values. If you take the projected area from ahmad_body, your drag values will be calculated more accurately.

• ### Mathanraj

Member
January 18, 2024 at 5:38 pm

Thank you Orhan !

I have changed the projected area & velocity reference values.

Now i got Cd value as 0.33 for 35 degree ahmed model with flap on sides.

• ### Orhan

Member
January 20, 2024 at 6:37 pm

You are welcome Mathanraj, good luck