## Fluids

#### Computing Integral of static pressure over a wing surface

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• Vanesa
Subscriber

Hello,

I have done a 3D simulation of a Boeing 737 wing (half-model) at a particular flow condition. I did report definitions of Lift and CL which were obtained as 835.26 N and 0.638 respectively.

Now I want to verify the lift obtained using pressure distribution. However when I am computing the value of 'Integral of static pressure over wing surface' it is giving a value of -1703.45 N.

Why is the lift value different? Or where am I going wrong? Also, how do I know along which axis is the integral of static pressure over wing (which is a force with a negative sign) directed?

• Rob
Ansys Employee
Lift, drag, force, drag coefficient etc are defined in the documentation. If you integrate the static pressure you'll get the sign and value relative to the operating pressure so it may or may not be negative. If the wing is working the upper surface may be more negative than the lower surface.
• Vanesa
Subscriber
Definition of lift (2D): Total lift is the integral of the pressure, in the direction perpendicular to the farfield flow, over the airfoil surface.

For a given flow conditions of density, velocity, operating pressure, shouldn't the outcome of lift (given as report definition) and the outcome of computed value of 'integral of static pressure over wing surface' be equal?

The computed value of integral of pressure over the wing is always around 2 times the lift which is computed. Why is it so? I am not able to understand why this mismatch is happening. Please clarify.
• Vanesa
Subscriber
My case is inviscid flow over 3d wing where drag comes around 64 N, lift of 1468 N, and the resultant of them is 1469 N.

So shouldn't this resultant force come equal to the integral of pressure over the wing? The integral of pressure comes about -3023 N.

• DrAmine
Ansys Employee
You need to build the areaInt in X, Y and Z Directions. You can use Sum reduction function and multiply the Static Pressure with the Facet Area in the appropriate direction. You get a vector and you can get its magnitude or scalar product with the direction to get the right magnitude in the requested direction. Integral of pressure is WRONG.
• Vanesa
Subscriber
Okay. Thank you very much for showing the path. Thank you.
• DrAmine
Ansys Employee
Welcome!

• DrAmine
Ansys Employee
:)