How Does the Shape of a Fan's Wing Affect Air Flow?

In summary, the different pressure in each side of a blade creates a sucking or blowing effect on the wing.
  • #1
zaroori
6
0
hi can anybody explain for me why some fans blow the air and some suck the air?.I know it depends on the form of its wing, but how?
 
Physics news on Phys.org
  • #2
Short/easy answer: One side of the wing/blade has high pressure, the other side has low pressure. Air gets pulled in on the low pressure side and expelled on the high side.
 
  • #3
To elaborate slightly regarding Fred's post:
All fans do both. Whether you perceive one as sucking or blowing is entirely dependent upon your position in relation to it.
 
  • #4
I understood that blowing and suction depends on which side is low pressure and which is high pressure and thus we have blowing and suction is that right?
but there is another question and that is how blades have designed that can product(please tell me a better word)different pressure in each side
 
  • #5
All moving surfaces displace air. If that surface is angled, the displaced air tends to go in a particular direction. That is essentially all that a fan is and does. You can make a simple one just by taping some cardboard together.
If you're asking about specific blade design, that is an extremely complex subject. Russ might be able to give you some guidance, since he seems to field most airflow related questions, but it will of necessity be limited in scope.
 
  • #6
zaroori said:
how blades are designed to produce different pressure in each side
Its simply a matter of angle of attack and forward speed that ends up deflecting the air. You can take a flat board, angle it a bit upwards relative to it's velocity, and it will deflect the air downwards. The bottom surface of the board simply deflects the air downwards. As the upper surface of the board moves through the air, its downwards movment relative to the air causes the air to follow what would otherwise become a void (vacuum). Wiki's wording on this:

In that case a low pressure region is generated on the upper surface of the wing which draws the air above the wing downwards towards what would otherwise be a void after the wing had passed.

http://en.wikipedia.org/wiki/Wing

So the forwards moving flat board ends up with low pressure above and high pressure below, coexisting with the downwards acceleration of air, drawing it downwards from above, pushing it downwards from below. The air senses this pressure differential at the speed of sound, so just before the board arrives through a volume of air, that air is initially accelerates upwards towards that low pressure area above the flat board, then is accelerated downwards as the board passes by, with a net downwards acceleration, corresponding to lift (and some forwards acceleration, corresponding to drag).

To reduce the drag, the leading edge of that flat board can be curved downwards to somewhat follow the expected flow that is initially upwards, and then downwards as it flows across the board. Next it's noticed that the downwards acceleration of air is in effect colliding with the trailing half of the board, so it's also curved downwards a bit, again to somewhat follow the expected flow of air. The result is a curved board that produces the same amount of lift but with less drag than the flat board. This is a crude description of the design of thin airfoils.

To further reduce drag, the aero guys know that tear drop like shapes have low drag, so efficient wings will end up looking like elongated tear drops that are curved downwards, and it turns out that these somewhat thicker tear drop based airfoils will produce the same lift with even less drag than thin airfoils.
 
  • #7
thank you
 

Related to How Does the Shape of a Fan's Wing Affect Air Flow?

1. How does the shape of a fan's wing affect air flow?

The shape of a fan's wing, also known as the blade or propeller, plays a crucial role in determining the direction and strength of the air flow it generates. The shape of the wing affects the amount of air that can be moved, the pressure difference between the front and back of the fan, and the direction of the air flow.

2. What are the different shapes of fan wings and how do they affect air flow?

There are two main types of fan wings: axial and centrifugal. Axial fan wings have long, narrow blades that rotate around a central hub, while centrifugal fan wings have curved blades that rotate around a central axis. Axial fan wings are better for producing high volumes of air flow, while centrifugal fan wings are better for generating high pressure and directing air flow in a specific direction.

3. How does the angle of a fan's wing affect air flow?

The angle, or pitch, of a fan's wing also plays a significant role in determining the air flow it produces. A steeper angle will produce higher pressure and slower air flow, while a shallower angle will produce lower pressure and faster air flow. This is because a steeper angle creates a larger difference in air pressure between the front and back of the fan, while a shallower angle allows air to pass through more easily.

4. Can the shape of a fan's wing be changed to alter air flow?

Yes, the shape of a fan's wing can be modified to alter the air flow it produces. For example, changing the angle of the wing or adding winglets can increase or decrease pressure and air flow. However, this should only be done by trained professionals as altering the wing shape can also affect the balance and efficiency of the fan.

5. How does the size of a fan's wing affect air flow?

The size of a fan's wing is directly related to the amount of air that can be moved. A larger wing will move more air, while a smaller wing will move less air. However, other factors such as the shape, angle, and speed of the fan's wing also play a role in determining the air flow. In general, larger fan wings are better for moving air over a larger area, while smaller fan wings are better for focused air flow in a specific direction.

Similar threads

  • Classical Physics
Replies
12
Views
1K
Replies
2
Views
673
  • Classical Physics
Replies
7
Views
957
Replies
8
Views
1K
  • Classical Physics
Replies
13
Views
2K
  • Classical Physics
Replies
3
Views
903
Replies
5
Views
331
  • Classical Physics
Replies
30
Views
3K
  • Classical Physics
Replies
3
Views
2K
Replies
4
Views
2K
Back
Top