# Coefficient Cp

 Register Blogs Members List Search Today's Posts Mark Forums Read

 April 15, 2013, 06:32 Coefficient Cp #1 Member   bird Join Date: Sep 2012 Posts: 42 Rep Power: 7 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.

April 15, 2013, 21:33
#2
Member

bird
Join Date: Sep 2012
Posts: 42
Rep Power: 7
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.
Attached Images
 cp.jpg (15.3 KB, 18 views)

April 15, 2013, 21:39
#3
Member

bird
Join Date: Sep 2012
Posts: 42
Rep Power: 7
Here is the experiment picture
Attached Images
 exp.jpg (25.0 KB, 19 views)

April 23, 2013, 17:58
#4
Member

mahdi
Join Date: Jan 2013
Posts: 43
Rep Power: 7
Quote:
 Originally Posted by pyxbird 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.

 Thread Tools Display Modes Linear Mode

 Posting Rules You may not post new threads You may not post replies You may not post attachments You may not edit your posts BB code is On Smilies are On [IMG] code is On HTML code is OffTrackbacks are On Pingbacks are On Refbacks are On Forum Rules

 Similar Threads Thread Thread Starter Forum Replies Last Post Suzzn CFX 21 January 29, 2018 01:58 cuteapathy CFX 14 March 20, 2012 07:45 Sas CFX 15 July 13, 2010 08:56 vinz OpenFOAM Running, Solving & CFD 98 October 27, 2008 09:43 Miguel Baritto CFX 4 August 31, 2006 12:02

All times are GMT -4. The time now is 07:02.