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Velocity field around an airfoil

by RandomGuy88
Tags: airfoil, field, velocity
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RandomGuy88
#1
Sep13-10, 07:46 PM
P: 363
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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boneh3ad
#2
Sep13-10, 08:56 PM
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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!
mugaliens
#3
Sep14-10, 04:49 AM
P: 595
"In front of?" You mean like free stream, before the airfoil has any effect on the air?

RandomGuy88
#4
Sep14-10, 09:32 AM
P: 363
Velocity field around an airfoil

Quote Quote by mugaliens View Post
"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.
Cyrus
#5
Sep14-10, 09:42 AM
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Quote Quote by RandomGuy88 View Post
No. The airfoil effects the air upstream of the actual airfoil, for example the upwash right in front of the leading edge.
RandomGuy88
#6
Sep14-10, 01:59 PM
P: 363
Does anyone know of any experimental data on the magnitude of this upwash? Or a way to calculate it?
mugaliens
#7
Sep14-10, 08:48 PM
P: 595
Quote Quote by RandomGuy88 View Post
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 compressible flow. That's a start, but the section on gas dynamics 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 airfoils are available which allows one to make all necessary computations with respect to velocity, wing geometry, resulting lift and drag.
sorter
#8
Nov5-10, 10:07 AM
P: 45
and the pressure increases underneath such that more than half of the airflow is pushed up over the top.
& wht does ths mean??
boneh3ad
#9
Nov5-10, 02:42 PM
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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.
minger
#10
Nov5-10, 06:08 PM
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Quote Quote by boneh3ad View Post
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).


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