Why does air flow upward before an airfoil and divide below it?

[theperthvan]

Hi,
I'm doing a looong assignment on aerodynamics, and have just about completed it. There are four points, however, which I cannot explain which refer to aerofoils. They are:
1. There is an upflow in air before contact is made with the aerofoil.
2. There is a downflow after contact with the aerofoil.
3. The air does not directly strike the airfoil, but divides just below the under surface.
4. Above the aerofoil where the pressure is decreased, the streamlines are closer together.

It would be very helpful if someone would be able to explain them for me.
NB You must consider a diagram of an aerofoil. Try http://www.usd.edu/biol/faculty/swanson/ornith/pics/airfoil.gif

 

[rgrig]

See http://travel.howstuffworks.com/airplane.htm

 

[M98Ranger]

Hi there,

First of all, congratulations on almost completing your aerodynamics assignment! It sounds like you have put a lot of effort into it.

Now, onto your questions about aerofoils. To better understand these concepts, it may be helpful to first have a basic understanding of how aerofoils work. Aerofoils are specially shaped structures that are designed to generate lift when moving through a fluid, such as air. They are commonly used in aircraft wings and propeller blades.

1. The upflow in air before contact is made with the aerofoil is due to the shape of the aerofoil. As the air approaches the aerofoil, it encounters the curved shape of the aerofoil and is forced to change direction. This creates an area of low pressure above the aerofoil, causing the air to flow upwards towards the aerofoil.

2. After contact with the aerofoil, the downflow is caused by the air being deflected downwards by the curved shape of the aerofoil. This downward flow is necessary for generating lift, as it creates an area of high pressure below the aerofoil, which helps to push the aerofoil upwards.

3. The third point refers to the way in which the air flows around the aerofoil. As mentioned before, the air is forced to change direction as it approaches the aerofoil. This change in direction causes the air to "split" or divide, with some of the air flowing over the top of the aerofoil and some flowing under the bottom. This creates a pressure difference between the two surfaces, which contributes to the generation of lift.

4. Finally, the closer spacing of streamlines above the aerofoil is a result of the decreased pressure in this area. As the air flows over the top of the aerofoil, it is forced to travel faster due to the curved shape of the aerofoil. According to Bernoulli's principle, an increase in speed results in a decrease in pressure. Therefore, the air above the aerofoil has a lower pressure compared to the air below, causing the streamlines to be closer together.

I hope this helps to clarify some of the concepts you were struggling with. Don't forget to refer to the diagram you provided for a visual representation of these principles. Good luck with the rest of your assignment!