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thui930
Posts: 2
Registered: ‎07-16-2013

Pressure Distribution over Airfoil

127 Views, 2 Replies
07-16-2013 04:09 PM

Hi there,

 

My simulation involves looking at the stresses that a simple NACA airfoil withstands during flight.

 

I have generated an equation for the Coefficient of pressure. When I enter this into the variable pressure function area, it generates a plot thats very close to my Cp vs. x.

 

The only issue I am having now is that the simulation gives me extremely high readings. My question is, does anyone have any idea how the variable pressure works?

 

eg. If i have an x^2 varaible pressure along the flat plate, does each cross sectional piece see an pressure distribution of x^2 and then do all the pressures compound? or does it spread the pressure across the entire span of the plate?

 

Thanks

-T

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Valued Mentor
AstroJohnPE
Posts: 500
Registered: ‎08-30-2012

Re: Pressure Distribution over Airfoil

07-17-2013 10:11 AM in reply to: thui930

Hi T-

 

Are the reactions correct, as in equaling the expected lift and drag? ("Results Contours > Other Results > Reactions > Reaction Force (Negative)")

  • If not, then the pressure is not applied properly.
  • If the reactions are correct, then something else is wrong in the setup of the model.

To answer your question, the pressure is applied to each element face on the surface(s) that you select. As a confirmation, the title bar of the dialog indicates how many surfaces are selected. The calculation is something like this:

  1. Based on the equation you enter, the pressure at each element on the selected surface(s) is calculated: Pi=(x coordinate of the element i)^2
  2. The pressure and the area of the element is used to calculate the equivalent force. Fi = Pi * Ai
  3. The equivalent force is distributed among all of the nodes on the element. f=Fi/n (?)

The math may be more complex that this simple example.

John Holtz, PE
Mechanical Engineer
Pittsburgh, PA

16 years experience with Simulation Mechanical
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New Member
thui930
Posts: 2
Registered: ‎07-16-2013

Re: Pressure Distribution over Airfoil

07-17-2013 02:23 PM in reply to: AstroJohnPE

Right, thats what I thought.

I think I've debugged the issue. Currently, the Top surface is working fine and producing reasonable reaction forces on the airfoil. The issue I am having now is the lower surface. Its producing a force of 3.7kN.

 

Are there issues with using negative pressures?

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