Composite Coatings with Drag Reduction and Self-Cleaning Properties

Abstract

Today, the efficiency of turbines is limited by different losses. Minimizing these losses is a main goal to reduce fuel consumption and produce more environmentally friendly machines. Observations on the scales of fast swimming sharks display a riblet structure. These riblets provide a significant reduction of drag losses, but are quite sensitive on pollution. Therefore, for a good performance, it is essential to combine these structures with self-cleaning properties. A lateral- and depth-selective distribution of particles with a negative thermal expansion coefficient (NTE) in a binder with positive thermal expansion coefficient can be used to deform the surfaces depending on the temperature. At high temperatures a riblet structure will be formed by local expansion or shrinkage and at cooling down the surface will be cleaned by the reversal of the deformation. Beside the production of a coating with a lateral- and depth-selective distribution of the NTE-ceramics within the binder the thermodynamical stability of the ceramics inside the binder is part of the investigations to provide a sufficient long-time stability of the coating.