how can they see the wind in a wind tunnel?

Question

at my new job, they told me that the airplanes take off in the direction of the wind. so they take off against the wind. they said that the wings create a vacuum that pushes and lifts the plane up in the air. is there a website that fully explains this. how do they see the air in the wind tunnel and know how to shape the winds accordingly?

Answer 1

The smoke they add to it.

Answer 2

We do not usually bother to look at the wind in the wind tunnel, those flow visualisation techniques are seldom used, as smoke would accumulate and pretty soon, the whole wind tunnel would be filled with the stuff. Besides, "flow vis", as we call it, is done at realtively low speed, while good results call for much higher Reynolds number, implying speeds that are incompatible with smoke. Smoke is seemingly used more often in TV advertisements than in real experimental aerodynamics.
If a problem is suspected, it can be modelled with tufts, or pressure sensitive oil. We also sometimes have pressure taps drilled in components; but by the time you are in wind tunnel, the shape of the airfoil and other components is prety much unchangeable; those were established by computational fluid dynamics.
When in wind tunnel, we are more interested in forces and moments, and the balance in the wind tunnel gives that.

At very high speed, above mach 1, techniques called Schlieren and shadowgraph, will show shock waves.

As for how a wing develops lift, you are somewhat on the right track. The shape of the wing, the upper surface curvature, reduces the pressure, creating a succion. This never gets all the way to vacuum, however. There is just so much pressure reduction one can achieve before the flow stalls and the wing start losing lifting capability.

In order to reduce the take off distance, and since the airspeed is what makes lift, airplane will take off with the wind blowing "in their face", gaining the speed of the wind as free velocity that does not have to come from rolling down and accelerating on the runway. Airplane can take off with a tailwind, but that takes more runway length.

As for websites that would explain all of this, whoa... I am not sure you can find a complete aerodynamicist course on line. There could be, I never really looked, since I already did it at university years ago.

Answer 3

They do use smoke released in the tunnel to aid in visulization of the airflow. Small pieces of string can also be attached to airfoils (wings). The strings are placed all over the airfoil, parallel with the flow. This technique now gives a clear view of the flow and lets laminar (smooth) and turbulent (rough) flow over the airfoil be identified.

Another technique to "see" the flow is to measure it's pressure through many tiny ports in the airfoil. The velocity of the airflow is already known, and by knowing the pressure, lift equations can be used to calculate other aerodynamic data.

Also, if you want a website, www.howstuffworks.com does a good job. If you really want in depth knowledge, the book "Aerodynamics for Naval Aviators" does a great job.

Answer 4

To see the air moving they use smoke, or sometimes talco with a particular illumination, or to see air movements around objects they use red light wires.
At university we visited and few time used windtunnel but we never saw or used smoke, etc. we used balance and a profile with a lot of holes, with a manometer for every hole,we don't needed to see the wind.

Answer 5

In the supersonic tunnels we could see the shockwaves, other than that we just used instrumentation to measure pressure and loads as others have said.

Answer 6

they add smoke sometimes steam to the air flow to make it visible .

Answer 7

one word: computer tehnology