The amount of error which is acceptable for a simulation

Goli · October 19, 2019, 23:46

Hello everyone,

I am simulating an airfoil with angle of attack of zero using simpleFoam. The value I derived for lift coefficient (Cl) is -3.67271e-08, but it should be zero.

Is it acceptable to consider this value as zero or not?

Generally speaking, what is the order of errors for difference between OpenFoam simulation's results and experimental values?

Thanks

Carlo_P · October 21, 2019, 05:06

Hey Goli,
there are no common rule to say if one results is correct enough.
It depends of your intend. If you are design the F-25, you have to reach an error of 0.0001%.
If you are designing a commercial airplane an error of 1-2% con be enought.
Normally speaking, is considered a good simulation when residuals are less than 1e-4, continuity less then 0.5%.
Furthemore simmetrical forces two order of magnitude less then other forces.
Other forces have to change less then 0.1% each iteration.
This can be a good simulation.

In you case, you have to compare drag and lift.
Id drag/lift is 100 or more, the simulation can be correct.

October 19, 2019, 23:46	The amount of error which is acceptable for a simulation	#1
Goli New Member Goli Join Date: Jul 2019 Posts: 7 Rep Power: 6	Hello everyone, I am simulating an airfoil with angle of attack of zero using simpleFoam. The value I derived for lift coefficient (Cl) is -3.67271e-08, but it should be zero. Is it acceptable to consider this value as zero or not? Generally speaking, what is the order of errors for difference between OpenFoam simulation's results and experimental values? Thanks

October 21, 2019, 05:06		#2
Carlo_P Senior Member Carlo_P Join Date: May 2019 Location: Italy Posts: 176 Rep Power: 7	Hey Goli, there are no common rule to say if one results is correct enough. It depends of your intend. If you are design the F-25, you have to reach an error of 0.0001%. If you are designing a commercial airplane an error of 1-2% con be enought. Normally speaking, is considered a good simulation when residuals are less than 1e-4, continuity less then 0.5%. Furthemore simmetrical forces two order of magnitude less then other forces. Other forces have to change less then 0.1% each iteration. This can be a good simulation. In you case, you have to compare drag and lift. Id drag/lift is 100 or more, the simulation can be correct. Goli likes this.

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