Flow physics

Seeing the invisible

 Aircraft model in a wind tunnel
zum Bild Aircraft model in a wind tunnel
Why can an airplane fly? How does the air behave that flows around automobiles, trains, buildings or aircraft, and what influence does it have? To be able to answer such questions, scientists first of all had to develop various methods for making flows in water or in air visible.

At the beginning of the 20th century, Ludwig Prandtl carried out experiments with a small channel of water in an attempt to make flow visible. At DLR_School_Lab Göttingen we'll experiment using what's now called a Prandtl water channel. With the help of this simple device the behaviour of water as it flows over and around various profiles can be investigated and we can record images of the flow with a digital camera.

Flow images

Many bodies subjected to the flow of air or water, like chimneys, flagpoles, swimmers, aircraft, trains or motor vehicles, are investigated in flow research. In all experiments investigating flow processes, scientists first try to obtain an overview of the flow behaviour before making any detailed measurements. How does the flow behave? Where do eddies form which could compromise flight safety, for example? Since most flow processes are invisible, we have to devise a way to see them. How can we make processes visible that cannot be directly observed? Like flowing air, for example? At the Institute of Aerodynamics and Flow Technology scientists have developed innovative, contact-free measurement methods for the purpose. In a visit to a wind tunnel you can look over the shoulders of scientists at work.

The Prandtl circulating water channel

At the Prandtl channel students can make eddies visible

On profiles of aircraft wings and other models you can investigate the behaviour of water flow in a Prandtl channel. By putting aluminium flakes on the water surface you can make the flow images (eddies) visible. You'll find out what effect the shape of the model has on flow behaviour. With a digital camera you can record the flow images and discuss them in a team.

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A frisbee in a Prandtl channel (http://www.dlr.de/schoollab/en/Portaldata/24/Resources/videos/go/prandtl_frisb.mpg)
The Prandtl channel (http://www.dlr.de/schoollab/en/Portaldata/24/Resources/videos/go/prandtl-kanal.mpg)
Experiment description Flow physics (German only) (http://www.dlr.de/schoollab/en/Portaldata/24/Resources/dokumente/go/prandtl.pdf)