Lift and Drag from Pressure Distribution over an Air Foil

In summary, it is possible to calculate Lift and Drag from the pressure distribution over an airfoil, but it is difficult to determine the pressure distribution over an airfoil without some form of instrumentation.
  • #1
Triggers12
4
0
Pretty simple question:

Is it possible to completely calculate Lift and Drag from the pressure distribution over an airfoil?

Atm, I have Lift worked out as well as the Induced drag ( correct me if I'm wrong. ) but am having trouble working out how it would be possible to get the skin friction / parasitic drag.

Thanks for your help!
Trigs
 
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  • #2
Triggers12 said:
Is it possible to completely calculate Lift and Drag from the pressure distribution over an airfoil?
How would you determine the pressure distribution over an airfoil? Perhaps some form of intrumentation, but that would have some effect on the flow. A simplified model could use static pressure distribuition and the normals (line perpendicular) to the sections of surface of a wing, but there are other factors. Static pressure isn't directional, but dynamic pressure and any related changes in momentum of the air are directional. Skin friction is nearly parallel to a wing surface. The shear boundary layer thickens over time, may detach and reattach as it transitions from laminar to turbulent, so that changes the effective air foil shape.

The best mathematical models for lift and drag are usually based on some simplified form of Navier Stokes equations:

http://en.wikipedia.org/wiki/Navier–Stokes_equations
 
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  • #3
rcgldr said:
How would you determine the pressure distributaion over an airfoil? Perhaps some form of intrumentation, but that would have some effect on the flow. A simplified model could use static pressure distribuition and the normals (line perpendicular) to the sections of surface of a wing, but there are other factors. Static pressure isn't directional, but dynamic pressure and any related changes in momentum of the air are directional. Skin friction is nearly parallel to a wing surface. The shear boundary layer thickens over time, may detach and reattach as it transitions from laminar to turbulent, so that changes the effective air foil shape.

The best mathematical models for lift and drag are usually based on some simplified form of Navier Stokes equations:

http://en.wikipedia.org/wiki/Navier–Stokes_equations

Hey thanks for the response,

Trigs
 
Last edited by a moderator:

1. What is an air foil?

An air foil is a shape or structure that is designed to produce lift when air flows over it. It is commonly used in the wings of airplanes to generate lift and allow for flight.

2. How does the pressure distribution over an air foil affect lift and drag?

The pressure distribution over an air foil is directly related to the lift and drag forces acting on the foil. When air flows over an air foil, the pressure on the upper surface is lower than the pressure on the lower surface. This creates a pressure difference, resulting in lift and drag forces.

3. What causes the pressure difference over an air foil?

The pressure difference over an air foil is caused by the shape and angle of the foil. The curved upper surface of the air foil causes the air to move faster, resulting in lower pressure, while the flat lower surface allows the air to move slower, creating higher pressure.

4. How does the angle of attack affect lift and drag?

The angle of attack, which is the angle at which the air foil meets the oncoming airflow, greatly affects the lift and drag forces. As the angle of attack increases, the lift force also increases, but at a certain point, the drag force begins to increase as well, reducing the overall efficiency of the air foil.

5. How can the pressure distribution over an air foil be measured?

There are various methods for measuring the pressure distribution over an air foil, including using pressure sensors, manometers, or pressure-sensitive paint. These tools can provide data on the pressure distribution at different points along the air foil, which can then be used to analyze and understand the lift and drag forces acting on the foil.

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