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Cylinder drag at Re5000 and mesh dependance

Question asked by Benoit Vincent on Sep 2, 2014
Latest reply on Sep 10, 2014 by Jared Conway

Good afternoon everybody,

 

I m trying to assess the effect of mesh siwe on the calculated drag of a circular cylinder in a 2D flow.

If I use :

20 mesh per cylinder diamater, I get Cd=0.90

40 mesh per cylinder diamter, I get Cd=1.2

80 mesh per cylinder diamter, I get Cd=1.4  

(more or less).

 

Correct Cd value is very close to 1.0, as found in literature.

 

Meshing considered here is not refined but just gently stretch far from the cylinder.

Domain is size around the cylinder : 10D upstream, 20D downstream (in the wake), 10D across. It seems there is no big difference if I use 5D  upstream, 10D downstream , 5D across. So I guess the boundaries are far enough from the cylinder.

 

I tried different diameters (0.005 and 1m) with same Re, even water and air, I always get the same behaviour.

 

 

I am quite surprised about these results, considering the document I found here (page 14) where they use same kinds of meshing (but at bigger Re 3.7e5) with much better consistency.

http://www.hawkridgesys.com/file/solidworks-flow-simulation/enhanced-turbulence-modeling.pdf

 

Thanks a lot for helping !

Benoit.

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