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-   -   High skin friction coefficient, (http://www.cfd-online.com/Forums/fluent/100263-high-skin-friction-coefficient.html)

amir7 April 22, 2012 13:23

High skin friction coefficient,
 
1 Attachment(s)
Hello all,
I tried to do the tutorial of the cornell website for the turbulent flow, with the pipe dimenstion 8mX0.1m. and the inlet velocity of 1 m/s.
choosing k-epsilon turbulence flow.
but choosing material as water ( density-1000 kg/m3, and viscosity 0.0007 pa.s). I tried to make the mesh fine, to have low yplus ( I obtained yplus about 0.3 for fully developerd flow). but i wonder why the skin friction coefficient is 3.5 while in the moody diagram the maximum value is 0.1? why my result doesn't match with moody diagram. i attached the skin friction plot here.
thanks
Attachment 12677

LuckyTran April 22, 2012 14:46

Quote:

Originally Posted by amir7 (Post 356233)
Hello all,
but i wonder why the skin friction coefficient is 3.5 while in the moody diagram the maximum value is 0.1? why my result doesn't match with moody diagram. i attached the skin friction plot here.
thanks

Did you remember to set your reference values? A reference velocity is used to calculate the skin friction coefficient. Not sure what the default in Fluent is. You should set it your bulk velocity (average cross sectional velocity) I believe. Also check to make sure the reference density is correct.

amir7 April 22, 2012 18:13

Aaaahh!! you are right!!! thank you sooo much for the response, I put many times and trying different meshes!! now i tried to put reference values and it seems it's ok. thanks again :)


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