The efficiency of modern transportation is severely compromised by the prevalence of turbulent drag and icing. The high level of turbulent skin-friction occurring, e.g., on the surface of an aircraft, is responsible for excess fuel consumption and increased carbon emissions. The environmental, political, and economic pressure to improve fuel efficiency and reduce carbon emissions associated with transportation means that reducing turbulent skin-friction drag is a pressing engineering problem.

SANAD project is dealing with these issues by developing superhydrophobic nanostructured top coatings, which do not only exhibit improved aerodynamic efficiency but at the same time they prevent icing on the aircraft. The nanostructured coatings will be based on metal oxides or nanostructured carbon (carbon nanotubes or graphene oxide).

The scientific targets include the synthesis and chemical modification of nanoparticles to be used as fillers. These nanomaterials were employed for the synthesis of novel composite coatings, based on suitable resins (mainly polyurethane). The developed coatings were characterized to obtain information on the structure and topology of the coatings. Specifically, the contact angle values were determined for the selected coating formulations in order to account for their hydrophobic nature.  In several cases samples, the contact angle was improved by 18-47% - depending on the incorporated nanomaterials - over the paints that did not contain nanoparticles. The wettability of the surfaces, using common de-icing fluid, was also investigated and was not found to be significantly affected by their enhanced hydrophobic nature. Furthermore, RMS surface roughness calculations were performed with Atomic Force Microscopy (AFM) and revealed that there is a clear reduction of the RMS roughness due to improved surface coating. This result will be further investigated, along with the testing of additional formulations that contain nanoparticles with new functionalities and the optimization of the application techniques of the best performing coatings to date.

Furthermore, most promising formulations were evaluated as to their effect in wind tunnel tests and by simulation with computational fluid dynamics (CFD). For the CFD simulation studies, commercial software was tested. Extensive wind tunnel testing was also carried out at Kingston University. The key results obtained indicate that the boundary layer thickness is visibly thinner and the stagnation points are moved towards the upper surface. Further wind tunnel tests will be performed on both the existing and the newly developed coatings in order to confirm and optimise the improvements, which may be achieved (e.g. delay in flow transition). Moreover, wind tunnel tests, in combination with fluid dynamics modelling, were conducted to optimise the application methods and the effect of different substrates, icing fluids, contaminants etc., thus correlating the aerodynamic and de-icing behaviour to the morphology of the material. The performance of the developed coatings was compared with that of existing coatings already produced by a partner of the consortium. The material with the most promising characterization data was produced in large-scale and provided to the partner “British Airways” for applying it as top coating on Airbus A320aircraft for testing it in flight conditions.

https://cordis.europa.eu/project/id/324443