Velocity field around an airfoil

In summary: The paper is OLD and from what I remember is freely available online. There are also exact solutions to plunging and pitching cases as well, although the math gets a little ridiculous for those cases (pages and pages of appendix calculus).
  • #1
RandomGuy88
406
6
Does anyone know of any available data on velocity measurements in front of an airfoil. I have written a program to calculate the velocity field in front of an airfoil and I need to validate my results but I am having trouble finding any useful data or theory.
 
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  • #2
The book "Theory of Wing Sections" by Abbott and Doenhoff has pretty much anything you could need about most common airfoils.

It only costs something like $20 to boot!
 
  • #3
"In front of?" You mean like free stream, before the airfoil has any effect on the air?
 
  • #4
mugaliens said:
"In front of?" You mean like free stream, before the airfoil has any effect on the air?

No. The airfoil effects the air upstream of the actual airfoil, for example the upwash right in front of the leading edge.
 
  • #5
RandomGuy88 said:
No. The airfoil effects the air upstream of the actual airfoil, for example the upwash right in front of the leading edge.

:smile:
 
  • #6
Does anyone know of any experimental data on the magnitude of this upwash? Or a way to calculate it?
 
  • #7
RandomGuy88 said:
Does anyone know of any experimental data on the magnitude of this upwash? Or a way to calculate it?

Gotcha. A symettrical airfoil with no angle of attack will evenly spilit the airstream such that half of the air moves over the top, and half moves under the bottom. Give it a positive AOA, however, and the pressure increases underneath such that more than half of the airflow is pushed up over the top.

At velocities of less than Mach 0.3, the compressible effects are less than 5%, so it's considered subsonic flow. Between Mach 0.3 and 0.8, it's considered http://en.wikipedia.org/wiki/Compressible_flow" [Broken]contains links to many of the flows and issues associated with airfoils.

It's really necessary to calculate the volume of airflow going up over the wing, as parameters for http://en.wikipedia.org/wiki/Airfoil" [Broken]are available which allows one to make all necessary computations with respect to velocity, wing geometry, resulting lift and drag.
 
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  • #8
and the pressure increases underneath such that more than half of the airflow is pushed up over the top.
& wht does ths mean??
 
  • #9
It doesn't really mean anything, as that answer isn't really correct. You can't measure a volume of air over the top and bottom in an open system like that.

The flow upstream of the airfoil (and around it) can be fairly accurately calculated with potential flow theory. That can take care of everything outside the boundary layer.
 
  • #10
boneh3ad said:
The flow upstream of the airfoil (and around it) can be fairly accurately calculated with potential flow theory. That can take care of everything outside the boundary layer.

Aye. For a great analytic solution used often times, check out what's called an Joukowski airfoil. It's a shape derived from a complex transformation of a circle, so it has an exact solution. I've used it often for validation.

The paper is OLD and from what I remember is freely available online. There are also exact solutions to plunging and pitching cases as well, although the math gets a little ridiculous for those cases (pages and pages of appendix calculus).
 

1. What is the velocity field around an airfoil?

The velocity field around an airfoil refers to the distribution of velocities of the surrounding air particles as they flow over and around the airfoil's surface. It is affected by various factors such as the shape of the airfoil, its angle of attack, and the properties of the air.

2. How does the velocity field affect the lift and drag of an airfoil?

The velocity field plays a crucial role in determining the lift and drag forces on an airfoil. A higher velocity on the top surface of the airfoil creates a lower pressure area, resulting in lift. At the same time, a lower velocity on the bottom surface creates a higher pressure area, resulting in drag.

3. How does the angle of attack affect the velocity field around an airfoil?

The angle of attack, which is the angle between the airfoil and the oncoming air flow, influences the velocity field by changing the direction and magnitude of the airflow. A higher angle of attack results in a larger velocity difference between the top and bottom surfaces of the airfoil, leading to higher lift and drag forces.

4. What is the boundary layer and how does it relate to the velocity field around an airfoil?

The boundary layer is a thin layer of air that forms along the surface of an airfoil due to the friction between the air and the airfoil's surface. The velocity field in this layer is affected by the shape and smoothness of the airfoil, and it can impact the overall velocity field around the airfoil, affecting its lift and drag properties.

5. How is the velocity field around an airfoil calculated and studied?

The velocity field around an airfoil can be calculated and studied using various methods such as computational fluid dynamics (CFD) simulations, wind tunnel experiments, and mathematical models. These methods allow for the visualization and analysis of the velocity field to understand its behavior and optimize the design of airfoils for different applications.

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