Velocity field around an airfoil

AI Thread Summary
The discussion centers on the need for velocity measurement data in front of an airfoil to validate a program calculating the velocity field. Participants clarify that the airfoil affects the airflow upstream, particularly through phenomena like upwash. They suggest using potential flow theory for accurate calculations outside the boundary layer and mention the Joukowski airfoil as a reliable analytic solution for validation. Additionally, "Theory of Wing Sections" by Abbott and Doenhoff is recommended as a valuable resource for airfoil data. Overall, the conversation emphasizes the importance of theoretical and experimental data in understanding airflow dynamics around airfoils.
RandomGuy88
Messages
404
Reaction score
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.
 
Physics news on Phys.org
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!
 
"In front of?" You mean like free stream, before the airfoil has any effect on the air?
 
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.
 
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:
 
Does anyone know of any experimental data on the magnitude of this upwash? Or a way to calculate it?
 
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" 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" are available which allows one to make all necessary computations with respect to velocity, wing geometry, resulting lift and drag.
 
Last edited by a moderator:
and the pressure increases underneath such that more than half of the airflow is pushed up over the top.
& wht does ths mean??
 
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).
 
Back
Top