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Old   February 7, 2011, 04:55
Default Problem: calculating drag coefficient
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Hi,

i've got a problem i want to calculate the Drag coefficient of a Plate. I tried it in 3D but it didn'nt work, now i try it in 2D but without success. I use Fluent 6.2.16 and Gambit.
The Fluent settings that i used, ke Modell, 3m/s inlet velocity, reference value see in picture. Dimensions of the plate are 0,25m x 0,15m x 0,005m.

In literature the plate has a cd of nearly 1,1 but in fluent nearly 3 how is this possible and what do i do wrong? Have anybody got a tutorial or an example of an drag coefficient calculation for me? The Fluent tutorial 3 doesn't really help.
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File Type: jpg Mesh.jpg (97.1 KB, 9 views)
File Type: jpg Reference_values.jpg (31.9 KB, 8 views)
File Type: jpg Results.jpg (50.4 KB, 8 views)
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Old   February 7, 2011, 09:02
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I suppose the k-epsilon turbulence mode you have used was activate on the entire flow domain, if this is the case ... let's the source of your error. See this article for the effect of using a turbulence model in the entire flow domain for low speed flows:

http://larcase.etsmtl.ca/PDF/Note-Paul-f.pdf

in Fig. 8 you will see a simulation similar with your own, using a turbulence model active on the entire flow can basically give you more than 50% error on Cd.

It is not too clear from your picture but your flat plate is vertical ?

Do
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Old   February 8, 2011, 04:23
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Hi Do,

first thank you for the fast answer and yes the plate is vertical in the flow.
Did I understand it right, is it neccessary to use more than one modell on the Mesh. How is it possible in Fluent?

RFH
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Old   February 8, 2011, 08:36
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Yes, you have understand correctly, see this thread for a similar discussions:

using turbulence and laminar model in the same time
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