error problems between experimental and numerical study

d118i · June 12, 2010, 11:24

Hello,

i am a spanish man that are doing an aerodynamic study of a motorsport spoiler. I had done a numerical simulation with star ccm+ and now i am taking some information with this spoilers in a wind tunnel. My project tutor/teacher said me that the cfd can be until 20% of error (more or less) between the cfd mesurements and the mesures of wind tunnel. I don't understand because my mesurements in wind tunnel are ok with Drag component but not with Lift component (Downforce).

For example: with 0 degrees inclination the cfd study shows 38,33 N of Downforce and 8,84 N of Drag and the wind tunnel measures are 22,5 N of Downforce and 7,1 N of Drag. If I applicate the teacher's theorem, the drag are in the 20% of error. 7,1 + (20% of 8,84 = 1,77) = 8,87 N but if I do the same with the Downforce the result is not valid with this theory.

Someone know if is true that's the maximum error between cfd and experimental study are 20% or can be more?? What can I do?

Thanks,

david.

Maddin · June 15, 2010, 05:23

Mesh problem, maybe wrong solver.

trex930 · June 18, 2010, 01:39

Can you post a picture of your mesh. As well as tell us your physic models? Then we can try and help!

Are you positive all the boundaries are set right??

CFD_4 · June 18, 2010, 07:34

Use fine mesh with quality.

Maddin · June 18, 2010, 12:45

Quote:

Originally Posted by CFD_4

Use fine mesh with quality.

Very helpful... maybe he can't

June 12, 2010, 11:24	error problems between experimental and numerical study	#1
d118i New Member ok Join Date: Jun 2010 Posts: 2 Rep Power: 0	Hello, i am a spanish man that are doing an aerodynamic study of a motorsport spoiler. I had done a numerical simulation with star ccm+ and now i am taking some information with this spoilers in a wind tunnel. My project tutor/teacher said me that the cfd can be until 20% of error (more or less) between the cfd mesurements and the mesures of wind tunnel. I don't understand because my mesurements in wind tunnel are ok with Drag component but not with Lift component (Downforce). For example: with 0 degrees inclination the cfd study shows 38,33 N of Downforce and 8,84 N of Drag and the wind tunnel measures are 22,5 N of Downforce and 7,1 N of Drag. If I applicate the teacher's theorem, the drag are in the 20% of error. 7,1 + (20% of 8,84 = 1,77) = 8,87 N but if I do the same with the Downforce the result is not valid with this theory. Someone know if is true that's the maximum error between cfd and experimental study are 20% or can be more?? What can I do? Thanks, david.

June 18, 2010, 07:34		#4
CFD_4 New Member wayusen Join Date: Oct 2009 Location: Pune Posts: 6 Rep Power: 16	Use fine mesh with quality. __________________

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June 15, 2010, 05:23		#2
Maddin Senior Member Join Date: Mar 2009 Posts: 260 Rep Power: 18	Mesh problem, maybe wrong solver.

June 18, 2010, 01:39		#3
trex930 Member Join Date: Jun 2010 Posts: 33 Rep Power: 15	Can you post a picture of your mesh. As well as tell us your physic models? Then we can try and help! Are you positive all the boundaries are set right??