Flows around objects



Light brings clarity

 DLR's Falcon research aircraft
zum Bild DLR's Falcon research aircraft
Everything that flies makes use of flow. That's why someone who constructs aircraft has to completely understand flow to assure that a plane will fly safely and efficiently. Since flow generally cannot be seen, it has to be made visible. Scientists use various methods to do this; one of them involves a layer of soap film.

Now what does a soap bubble have to do with flow theory? Can it be used to explain flight? The beauty of soap bubbles fascinates all of us, not only because of their form, but especially because of their iridescent colours.

Iridescent colours

Wing profile in a soap film channel

Clever researchers who investigated the problem of how to make flow visible came up with the "soap film method." By causing a soap solution to flow around wing profiles and using white light, the structure of flow and the distribution of pressure can be made visible and thus analyzed. Making visible the flow around wing profiles and other objects is useful for a preliminary analysis of flow behaviour. In flow around a wing profile, for example, there are local variations in velocity which cause a change in the thickness of the film. This is revealed in a fascinating play of colours. In the right light, these changes in film thickness can be measured using optical interference. These interference stripes, called fringes, are just like the lines of elevation on a map. The now visible alterations in film thickness can be interpreted as air pressure changes.

The soap film channel

Students working at the soap film channel

Using a soap film channel you'll investigate the flow behaviour around aircraft wings and other objects. You can change the angle of pitch and the flow velocity, thereby simulating the air flow behaviour around a plane when it is taking off and landing. You'll soon understand how a plane flies. This experimental setup can easily be installed in your classroom. In your experiments you don't have to use only aircraft wings, you can build and investigate other models, like buildings, ship screws, cars, or chimneys, for example. The model construction center at DLR Göttingen makes wind tunnel models for researchers. You'll have a chance to get acquained with the work being done by the builders and mechanics right in their workshop.


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Cylinder in a soap film channel (http://www.dlr.de/schoollab/en/Portaldata/24/Resources/videos/go/sfi_zyl.mpg)
Wing profile in a soap film channel (http://www.dlr.de/schoollab/en/Portaldata/24/Resources/videos/go/sfi_flae.mpg)
Experiment description Flows around objects (German only) (http://www.dlr.de/schoollab/en/Portaldata/24/Resources/dokumente/go/seifenfilm.pdf)