getting negative static pressure on airfoil surface

rishad · July 15, 2014, 13:57

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.

Far · July 15, 2014, 14:37

it simply shows that velocity is increasing

rishad · July 15, 2014, 14:45

hello far
how can pressure be negative on airfoil surface ? shouldn't it be of some positive value ?

Far · July 15, 2014, 15:16

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

rishad · July 15, 2014, 15:27

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

July 15, 2014, 13:57	getting negative static pressure on airfoil surface	#1
rishad New Member rishad rizwan Join Date: Dec 2013 Location: Dhaka, Bangladesh Posts: 7 Rep Power: 12	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.

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July 15, 2014, 14:37		#2
Far Senior Member Sijal Join Date: Mar 2009 Location: Islamabad Posts: 4,558 Blog Entries: 6 Rep Power: 54	it simply shows that velocity is increasing

July 15, 2014, 14:45		#3
rishad New Member rishad rizwan Join Date: Dec 2013 Location: Dhaka, Bangladesh Posts: 7 Rep Power: 12	hello far how can pressure be negative on airfoil surface ? shouldn't it be of some positive value ?

July 15, 2014, 15:27		#5
rishad New Member rishad rizwan Join Date: Dec 2013 Location: Dhaka, Bangladesh Posts: 7 Rep Power: 12	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