# getting negative static pressure on airfoil surface

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 July 15, 2014, 12:57 getting negative static pressure on airfoil surface #1 New Member   rishad rizwan Join Date: Dec 2013 Location: Dhaka, Bangladesh Posts: 7 Rep Power: 4 hello all! i am doing a simulation in ansys fluent on flow over an airfoil at transonic speed. i got very good Cl , Cd and Cp distribution. but i'm getting negative static pressure when i'm monitoring surface points on the foil. also my static pressure contour shows negative area... i've set the operating pressure = 101325 Pa in B.C, gauge pressure = 0 Pa i cannot detect the fault....as i went through some tutorials and followed them..... would you please say me how to encounter this problem of negative static pressure ? thanks and regards.

 July 15, 2014, 13:37 #2 Super Moderator   Sijal Join Date: Mar 2009 Location: Islamabad Posts: 4,010 Blog Entries: 6 Rep Power: 40 it simply shows that velocity is increasing

 July 15, 2014, 13:45 #3 New Member   rishad rizwan Join Date: Dec 2013 Location: Dhaka, Bangladesh Posts: 7 Rep Power: 4 hello far how can pressure be negative on airfoil surface ? shouldn't it be of some positive value ?

July 15, 2014, 14:16
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Sijal
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Quote:
 Originally Posted by rishad hello far how can pressure be negative on airfoil surface ? shouldn't it be of some positive value ?
You are correct.

Absolute pressure = atmospheric pressure + gauge pressure

Results you are getting are in terms of gauge pressure, just add atmospheric pressure to get some positive value

 July 15, 2014, 14:27 #5 New Member   rishad rizwan Join Date: Dec 2013 Location: Dhaka, Bangladesh Posts: 7 Rep Power: 4 thank you sir... but can you clarify me one more thing please ? in ansys tutorial : fluent_13.0_workshop02-airfoil.pdf , they set # the operating pressure = 0 Pa # Pressure (gauge) at Boundary condition, P = 71150.4 which they obtained from Po/P relation. and in my simulation i set # operating pressure = 101325 Pa and boundary condition # gauge P = 0 Pa when i tried that of ansys tutorial i got positive pressure but my set up produces negative one... would u explain this please ? i need to know which one is correct ? thank you for your time. regards

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