Abstract
In October 2009 the European Commission decided that fuel consumption by aviation and shipping has to be reduced by 10% and 20% respectively by 2020. A significant contribution to this challenging goal could be a coating that reduces drag. For about 20 years it has been known that special microstructures ("riblets") can lower drag by up to 10%. A new process for the production of such microstructured coatings on large surfaces is presented in this article. This process allows coating application, embossing, and partial curing in a single step. The coating material consists of VOC-free nanocomposites that give the coating the necessary abrasion resistance and weathering stability. Drag measurements have been carried out in a ship model basin and in a wind-tunnel respectively. In these experiments, smooth coatings were compared to riblet-structured coatings. These structures were adapted to the flow-parameters of the fluid. A surface-drag reduction of 5.2% for a torpedo-shaped specimen was measured in a large hydrodynamic and cavitation tunnel. In a wind-tunnel experiment a reduction of the total drag of a wing-profile by 6.2% was measured. Both experiments indicate the high potential for fuel savings in the transportation sector.