Effects of superhydrophobic surfaces on turbulent boundary layer induced vibration and drag - Report Year 2

The general objective of the project was to perform experimental tests on superhydrophobic (SH) materials, focused on resistance and vibration measurements, to assess their ability to modify the hydrodynamic drag and the vibrational response of structures excited by turbulent boundary layers. In the experimental test, fundamental parameters were varied to collect accurate information on the effects of (i) material (substrate) roughness or surface geometry, (ii) flow velocity and, (iii) for specific SH material (SLIPS), lubricant oil viscosity, on the material performances. The approach included also an analysis of the material's properties in terms of time durability. Specific feedback actions on coatings and materials design, in order to improve the SH behavior and the related performances were major project's objectives as well. During the present reporting period, major attention was devoted to the design and fabrication of new water-repellent surfaces based on the deposition of nanostructured hybrid coatings coupled with the infusion of lubricant oils, as per the so-called SLIPS approach. More specifically, two aspects of the coating fabrication process were investigated: the presence of microchannels on the substrate prior to coating deposition and the viscosity of the infused liquid. The SH properties of the coating before oil infusion i.e. with the traditional solid-air interface were also analized.