# the skin friction coefficient error from Fluent

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 November 13, 2012, 07:02 the skin friction coefficient error from Fluent #1 New Member   sutthinan Join Date: Feb 2011 Posts: 9 Rep Power: 14 Hi Everyone I have solved the fluid flow problem by using the CFD model. For all results are look good, just only the skin friction coefficient that is quite strange. I have tried to calculate the friction coefficient by using the Ansys Fluent software, but I still got the result that is impossible (it higher than 1 ). As the skin friction coefficient is calculated by using equation (1). I rechecked the reference values that I used, especially the density and the velocity. I am wondering what can cause the skin friction coefficient error. Could you please suggest me on this problem? skin friction coefficient =Wall shear stress/(0.5*Density*Bulk velocity ) I have printed out the wall shear stress as it is a function of velocity gradient and I found that some area the Fluent cannot calculate the velocity gradient as my mesh are too small (around 1*10-6 m). So I 'm wondering that how to get more accuracy of velocity in fluent. As the mesh is very small, then the velocity between the centre of mesh are not different. If any have same problem or have a solution for this problem, please let me know. I would appreciate your help in this matter. Cheers, Sutthinan

 November 13, 2012, 13:56 #2 Senior Member   Join Date: Jul 2009 Posts: 335 Rep Power: 17 Shouldn't the wall shear stress be non-dimensionalized by the square of the bulk velocity?

November 28, 2012, 14:03
#3
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sutthinan
Join Date: Feb 2011
Posts: 9
Rep Power: 14
Quote:
 Originally Posted by agd Shouldn't the wall shear stress be non-dimensionalized by the square of the bulk velocity?
Yes, you are right. The bulk velocity should be square in the formula above.

Many thanks