MilesBuzz! - The small airfoil like surfaces on airplane wings

Is this MilesBuzz worthy? I don't know. It's midnight and I was curious so I did some research and thought I would share it.

Have you ever noticed the small, vertical, airfoil like fins on the surface of many commercial jets? I noticed them on my last ride in a 737, I wondered what they were for, and here is the answer.

They are vortex generators. Vortex generators are small airfoil like surfaces on the wing which project vertically into the airstream. Vortices are formed at the tip of these generators just as they are on ordinary wingtips. These vortices add energy to the boundary layer (the layer of air next to the surface of the wing) to prevent airflow separation. This reduces stall speeds and can increase take off and landing performance. Many animals, including bats, owls, beetles, flies, moths, and even dolphins have mechanisms for controlling lift and drag through control of the boundary layer. For example, blood vessels in the wings of a worker bee stabilize the membranes and increase the energy of the turbulant boundary layer flow.

So now you know. http://www.flyertalk.com/forum/smile.gif

[edited for 2 typos]

[This message has been edited by eastwest (edited 02-14-2002).]

Thanks, this is very interesting. I'd love to hear more. Everything about flight interests me.

Does the little fin on the inboard side of the engine of a 737 qualify as one of these devices?

That little fin mounted on the engine is called a Nacelle Strake. It is a vortex generator. It's purpose is to create a single controlled vortex instead of many small uncontrolled, unstable vortices of air around the engine when the aircraft is operated at high angles of attack.

[This message has been edited by WHY2K (edited 02-14-2002).]

In high humidity areas, its really neat to see them work! The vorticies are of higher pressure, which generates condensation which make them visible. Its really cool stuff.

<font face="Verdana, Arial, Helvetica, sans-serif" size="2">Originally posted by Indurain:
The vorticies are of higher pressure, which generates condensation which make them visible.</font>The pressure in the vortex is always less than the local (static) atmospheric pressure. The rotating air in the vortex creates a centrifugal force which pushes the air outwards. A pressure gradient then arises to create a force that exactly opposes the outwards rotational force. The pressure in a vortex is thus always lower than the local pressure, and is lowest at the center of rotation of the vortex.

It is the low pressure of the air in the core (center) of the vortex that lowers the partial pressure of the water vapor. If the partial pressure of the water vapor is low enough, condensation occurs.

That is why, in addition to wingtip and vortex-generator vortices, one also often observes condensation over the upper, low-pressure, surface of the wing. The effect is usually quite pronounced near the leading-edge, when the wing is in a high-lift configuration (e.g. takeoff and landing).

Cool! Great thread! I always wondered about seeing that condensation stream upon final approach -- now it makes more sense.

UAL Traveler is correct. I often mix high speed with high pressure, when its in fact the other way around...

I actually laughed when a friend explained that condensation is generated when the pressure is high enough to "squeeze" the moisture out of the air... and then I do this... (blush)

Oh, one other thing. I believe the vortex generators are sometimes installed on the wing or the tail to remove vibrations or buffeting at specific areas within the flight envelope.

Indurain, no need to blush. This stuff is tricky business. Many moons ago, Phil Saffman, a Caltech professor of applied math who worked extensively with rotational flows, said 'anyone who thinks they understand vorticity is either Lord Kelvin, or a fool.' Well, I can categorically state that I am no Lord Kelvin (one of the early giants in fluid mechanics and vorticity). So, I guess I have to say that either I don't understand vorticity, or I am a ...