# Problem: calculating drag coefficient

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February 7, 2011, 05:55
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.
Attached Images
 Mesh.jpg (97.1 KB, 11 views) Reference_values.jpg (31.9 KB, 9 views) Results.jpg (50.4 KB, 9 views)

 February 7, 2011, 10:02 #2 Senior Member   Join Date: Nov 2009 Posts: 411 Rep Power: 12 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

 February 8, 2011, 05:23 #3 New Member   Join Date: Feb 2011 Posts: 2 Rep Power: 0 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

 February 8, 2011, 09:36 #4 Senior Member   Join Date: Nov 2009 Posts: 411 Rep Power: 12 Yes, you have understand correctly, see this thread for a similar discussions: http://www.cfd-online.com/Forums/flu...same-time.html

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