Ice Adhesion Performance of Superhydrophobic Coatings in Aerospace Icing Conditions 2015-01-2120
Researchers have recently focused on superhydrophobic coatings as an ice-mitigation tool. These surfaces have a high degree of water-repellency and were shown in previous low-speed droplet studies to reduce surface ice adhesion strength. However, there is little research regarding testing in aerospace icing conditions, i.e. high-speed super-cooled droplet impact (> 50 m/s) on a freezing substrate and air temperature. A detailed set of experiments were conducted in an icing wind tunnel to measure the ice adhesion strength of various superhydrophobic coatings by subjecting the surfaces to a super-cooled icing cloud consisting of 20 μm droplets and at a constant LWC of 0.4 g/m3. Test conditions include air speeds of 50 m/s and 70 m/s and in glaze (−5°C) and rime ice regimes (−15°C). The accreted ice was then removed by pressurized nitrogen in a mode 1 (tensile) adhesion test. The pressure required for ice removal and the fraction of ice remaining were combined into an overall adhesion parameter. Results showed that the present superhydrophobic coatings generally resulted in increased ice adhesion parameters relative to the baseline titanium surface. The strongest indicator of ice adhesion performance for these coatings was found to be the surface roughness lateral auto-correlation length. Only superhydrophobic coatings with length-scales less than 40 μm reduce the ice adhesion parameter. When compared to previous results, it can be noted that increased droplet impact speeds unfortunately tend to increase the ice adhesion strength on the superhydrophobic coatings.