# How to plot Cp Vs X/c

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 July 24, 2012, 09:56 How to plot Cp Vs X/c #1 New Member   Abhipray Jain Join Date: Mar 2012 Posts: 8 Rep Power: 7 Hi, I am trying to plot Cp Vs x/chord ... I tried to get the data from fluent but im not able to plot it .. I think i got the wrong data ... I went to XY plot and took headsail and headsail shadow and write the file and after opening it on excel i plot the graph which is wrong .. same i did for mainsail and mainsail shadow....plz help me its important .. moreover .. i saw in many other thesis .. their y axis says Cp and x axis says x/c but on x axis values are 0, 0.2, 0.4, 0.6, 0.8, 1.0. whereas if i plot same thing on fluent v6, it shows me somewhat right graph but with negative values of Cp on the y axis .. im very confused plz help me...

March 28, 2017, 02:58
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Aron Chand
Join Date: Mar 2017
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Quote:
 Originally Posted by abhiprayj Hi, I am trying to plot Cp Vs x/chord ... I tried to get the data from fluent but im not able to plot it .. I think i got the wrong data ... I went to XY plot and took headsail and headsail shadow and write the file and after opening it on excel i plot the graph which is wrong .. same i did for mainsail and mainsail shadow....plz help me its important .. moreover .. i saw in many other thesis .. their y axis says Cp and x axis says x/c but on x axis values are 0, 0.2, 0.4, 0.6, 0.8, 1.0. whereas if i plot same thing on fluent v6, it shows me somewhat right graph but with negative values of Cp on the y axis .. im very confused plz help me...
Cp is pressure coefficient and x/c also known as x/chord is; x=x coordinate distance of the specific point or tap from the leading edge, c=chord length. So if your point one is 2mm from the leading edge and your chord length is 100, therefore your x/c value is 2/100 i.e. 0.02. Note that the max value of x/c is 1 because at 1, x=c.

Different airfoils with different angle of attack will plot different graphs. Always know the Cp value can never exceed Positive 1 because when Cp=1, that is the stagnation point and at that point the velocity of the particles will be infinitesimally small or approx. zero. But it can never be practically zero on the dot because this is a dynamic system. There is a MS-Dos program made my MIT, its called XFOIL. LEarn its command, and it can tell you the exact graph for most of the airfoil at any angle of attack

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