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Oscillating Force - External Aerodynamics

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Old   October 25, 2023, 02:18
Default Oscillating Force - External Aerodynamics
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Hello all,

I have an oscillating drag force in a steady state simulation in OpenFoam (external aerodynamics), see picture. The oscillation is always the same, starting with the first iteration. I therefore believe that it has no physical cause. The simulation also converges normally, and the force curve looks normal except for this fluctuation.

Does anyone have experience where this oscillation comes from or how to investigate it further?

Thanks a lot!
Martin
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Old   October 25, 2023, 04:12
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Hey


According to the scale, the oscillations are less than 0.001 which is already quite small in my opinion. I am not sure you can get even more stable results with a steadystate simulation. Depending on your conditions, the flow can be unsteady and it will be reflected on the values you monitor and the residuals. I believe these oscillations are mainly due to the limitations of a steady state approach and possibly numerical errors, because it looks otherwise decent.
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Old   October 26, 2023, 04:14
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Quote:
Originally Posted by Alczem View Post
Hey


According to the scale, the oscillations are less than 0.001 which is already quite small in my opinion. I am not sure you can get even more stable results with a steadystate simulation. Depending on your conditions, the flow can be unsteady and it will be reflected on the values you monitor and the residuals. I believe these oscillations are mainly due to the limitations of a steady state approach and possibly numerical errors, because it looks otherwise decent.
Thanks for your reply. But do you really think thatís a physical phenomena like flow separation etc.? I would expect a sinus like wave if itís a physical phenomena not a sawtooth profileÖ
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Old   October 26, 2023, 08:17
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It's not a flow feature - ignore it.

If you really want to go down the rabbit hole, increase the precision of the written data (writePrecision in controlDict), and you will probably find that the variation is even smaller than you reckon. As the earlier poster said - it's just noise, as demonstrated by the "saw tooth" profile.
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Old   October 26, 2023, 08:57
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Quote:
Originally Posted by Tobermory View Post
It's not a flow feature - ignore it.

If you really want to go down the rabbit hole, increase the precision of the written data (writePrecision in controlDict), and you will probably find that the variation is even smaller than you reckon. As the earlier poster said - it's just noise, as demonstrated by the "saw tooth" profile.

Ok, thanks your help guys!
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