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-   -   Coefficient Cp (http://www.cfd-online.com/Forums/flow-3d/116201-coefficient-cp.html)

pyxbird April 15, 2013 06:32

Coefficient Cp
 
Dear all,
Hi, after simulating the flow motion around a vertical cylinder under steady current, I should caluculate the coefficient Cp to validate my model. As is known to all, the Cp of the stagnation line at the front side of the cylinder of different depth is below 1.
But always the Cp I calculate is above 1.
Here the book mention that Cp=(p-p0)/(0.5*density*vo*vo), so how to pick datas of po and v0 in flow3d?
po----inlet boundary or developed pressure? vo--inlet velocity or developed velocity, constant or different in z direction? Or I should try another formular? p--the pressure of the grids near the surface of the cylinder?
I have tried many times, but the Cp is still not correct.
So anyone can tell me the best solution?
PS. the model runs well I don't think there is any fatal error.

pyxbird April 15, 2013 21:33

1 Attachment(s)
Why always above 1?
I choosed pressure at the inlet boundary as po(developed). In addition, mean velocity or z-direction-changed velocity is also used but still not solved.
In experiment, Cp is smaller than 1.

pyxbird April 15, 2013 21:39

1 Attachment(s)
Here is the experiment picture

mahdi1 April 23, 2013 17:58

Quote:

Originally Posted by pyxbird (Post 420791)
Here is the experiment picture

Hello
Cp=(pi-p)/(p0-p)
Pi= circumferential pressure
p0=stagnation pressure
p= free stream pressure

when tete=0 : pi=p0 :........... Cp=1

If your goal is estimation of drag coefficient, I suggest to you that you get darg force from software directly and then calculate drag coefficient.


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