Overview
The objective of the ICECOAT project was to minimise the run-back icing over the natural laminar flow (NLF) wing surface by optimising the anti-icing coatings and electro-thermal de-icing system. This will help implement the laminar flow control technology currently investigated by Clean Sky Joint Undertaking.
This objective was tackled by a combination of four technical work packages:
- Wettability and ice adhesion study (WP1)
- Development of smart anti-icing coatings (WP2)
- De-icing by electro-thermal system (WP3)
- Validation of mixed strategies (WP4)
together with Administrative work (WP0) and Dissemination/exploitation (WP5).
The proposed work was carried out by advancing our understanding of the heat transfer processes that determine runback icing accretion by fully considering the influence of both trapped air pockets and water within the developing ice matrix. We also selected and/or developed new types of coating matrices, new nanoparticles for nanocomposites, and a new method for coating surface modification to produce anti-icing coating with higher hardness and erosion resistance. These new anti-icing coatings were tested in conjunction with an electro-thermal de-icing system, which was optimised for its location over the wing. Pulsing operation of the de-icing system was also tested to minimise the occurrence of run-back icing. Finally, the effect of laminar-to-turbulent transition of the boundary layer over the wing surface on the behaviour of run-back icing will be investigated in an icing wind tunnel.
Funding
Results
Executive Summary:
Icing on aircraft wings can occur in clouds at mid-range heights where the conditions are conducive to formation of super-cooled microscopic water droplets in clouds. The current control over adverse effects of ice formation on the wing is usually heating of the leading edge, which can release the ice from point of formation, but which has a following risk of run-back icing, where the melted ice in a film runs back over the upper surface of the wing and refreezes. This project addressed the development and application of ice-phobic surface treatments to prevent run-back ice accumulation.
Dynamic wettability of surfaces was tested in a wind tunnel which could produce temperatures down to -10ºC, with increased temperature with increasing air flow rate due to fan work. Atomised spray can be delivered in tests up to 88 g/m3 covering the main zone of interest at 0.3 g/m3. A slot flow delivery to simulate runback wetting of the aerofoil provides the opportunity to control rate of flow over the test surface. Centrifuge tests demonstrate the ability of the treated surface to remove glaze ice once formed, and the 10 tested coatings demonstrated varying positive outcomes over the parameters tested for effect on the material piece, but showing a clear candidate from cyclic testing for a repeatably high adhesion reduction factor.
Run back icing tests demonstrated the effect of the high latent heat of fusion of water on time to form ice on the surface in freezing conditions. At landing approach conditions, the time to freeze a water film 0.05mm thick is in the order of 0.3s, and given the speed of approach, icing on untreated surface will occur about half way down the aerofoil upper surface. The coatings demonstrated that the freezing time could be more than doubled, which would lead to no icing on the wing surface at all. The rivulet flow demonstrated in the wind tunnel tests indicates that although faster flow may lead to a thinner film, the thickening of that film into rivulet flow will mean that the risk of faster freezing is avoided.