Fabrication, Oxidation and Characterization of Shark Skin Inspired Riblet Structures as Aerodynamically Optimized High Temperature Coatings for Blades of Aeroengines

This paper deals with the study of different structuring methods for high temperature nickel alloys, which are used for compressor and turbine blades in aeroengines. The ideal structured surface combines high oxidation resistance with low drag in a hot gas flow. The effect of drag reduction due to riblet structured surfaces was originally inspired by the shark scales, which have a drag reducing riblet structure. Riblets were successfully produced on a NiCoCrAlY coating by picosecond laser treatment. This method is suitable for larger structures within the range of some tens of micrometers. Furthermore, experiments were performed by depositing different materials through polymer and metal masks via electrodeposition and physical vapor deposition. All fabricated structures were oxidized at 900–1100°C for up to 100 h to simulate the temperature conditions in an aeroengine. The resulting shape of the riblets was characterized using scanning electron microscopy. The most accurate structures were obtained by using photolithography with a subsequent electrodeposition of nickel. This method is suited for single digit micrometer structures. The reduction of the wall shear stress was measured in an oil channel. The riblet structures prior to oxidation showed a reduction of the wall shear stress of up to 4.9%.