Analysis of drag-reducing air-water interfaces

Identifying technical surfaces which are able to hold persistent air layers according to immersed biological objects

Air-water interfaces around an immersed object can lead to considerable drag reduction. Persistent air layers are also interesting with respect to anti-fouling (overgrowth of marine technical objects with marine organisms) and various clothing products.

The stability and persistence of air layers around technical objects is, however, low to date. In numerous animal and plant species of different systematic groups, air-water interfaces which appear to be much more stable are created by special surface structures (hairs, feathers, leaves). In this project, the dependence of (mechanical) stability and (temporal) persistence of an air layer around a (biological) object from various surface parameters of the object (surface geometry, biochemical properties) will be explored thoroughly. For this purpose, detailed theoretical analyses of the surface-interface relationship will be carried out (mathematical-analytical, numerical) with special attention to biological surfaces which are able to hold stable and persistent air layers. Presently, Salvinia molesta represents the main biological object. The project is carried out in cooperation with the Nees-Institute where extensive studies of biological surfaces which are able to hold air layers are performed. The results will be interpreted in order to generate a concept for an "ideal" technical surface which is able to hold a persistent air layer.

Details of the hairs of the leaf surface of Salvinia sp. Scale bar: 0.5 mm.

Surface of a leaf of Salvinia sp. The water droplet on the surface is suspended by the hairs. Scale bar: 1 mm.

Cooperation partner:

Nees-Institut Bonn

Recent Publications:

Wilfried Konrad, Christian Apeltauer, Jörg Frauendiener, Wilhelm Barthlott, Anita Roth-Nebelsick (2009): Applying methods from differential geometry to devise stable and persistent air layers attached to objects immersed in water. Journal of Bionic Engineering 6 , 350-356, doi: 10.1016/S1672-6529(08)60133-X