NICE - Reduction of ice formation by nanostructuring of surfaces with an ultrashort pulse laser

funded by: Climate and Energy Fund, opens an external URL in a new window from the Energy Research Program 2018 (together with FFG, opens an external URL in a new window)

project number: 871733

project end: March 2023

Worldwide, many locations with icing conditions offer excellent wind conditions and thus great potential for the installation of wind turbines. According to the current report of Task 19 of the IEA Wind TCP, more than 130 GW of wind energy have already been installed internationally at locations with icing conditions and an annual increase of 12 GW is expected. In Austria, practically all wind turbines installed so far are at least affected by moderate icing conditions.

However, these icing conditions are a considerable challenge both in the planning and operation of wind turbines. The three main aspects are:

1. The risk to life and limb caused by an icy wind turbine with regard to persons staying in the vicinity of the wind turbine.
2. The geometrical change of the rotor blade profile leads to a drastic degradation of the aerodynamic properties of the rotor and thus to a reduction of the energy output.
3. Uneven ice formation on the different rotor blades (or uneven fall of the ice) can lead to a strong asymmetrical force (imbalance) which can cause extreme stress on the wind turbines.

Icing plays a major role in the operation of wind turbines, from the three points mentioned above: risk for persons, reduction of energy output and turbine stress, plays a major role.

As soon as icing is detected on a wind turbine or the atmospheric conditions indicate a risk of icing, the ice can be removed or the formation of ice can be prevented by heating the rotor with hot air or with electrical resistance heating on the rotor blade surface. Depending on the power of the heater, this strategy is only possible for a limited temperature range. Other methods rely, for example, on mechanical impulses by means of vibrators, eddy currents, electrical heating elements, microwaves and chemical de-icing. However, these methods face various problems and are often difficult to use on wind turbines.

Within the scope of this project we are working on the modification of surfaces to reduce the adhesion of snow and ice by means of ultrashort laser pulses.

For this purpose, nanostructures in the sub-µm range are generated on technical surfaces using an ultrashort pulse laser (UKPL) in order to avoid or hinder the adhesion of ice or to reduce the lifetime of ice layers.

Preliminary investigations have shown that laser nanostructuring of the surface of samples can make icing more difficult or reduce the duration of icing. In this project, samples of different materials will be nanostructured with a UKPL and the formation, periodicity and composition of the generated sub-µm structures on the samples will be investigated. The effects of different structuring on the wetting behaviour of different sample materials by water droplets will be analysed with a contact angle measuring device. In addition, the simulation model of the wetting behaviour of surfaces available at the institute will be extended into the sub-µm range. This should enable the identification of optimal structures, reduce the number of experiments and improve the general understanding of the processes. The growth of ice on nanostructured samples is observed in a climatic wind tunnel. In this climatic wind tunnel defined conditions (temperature, wind speed, droplet size, etc.) are set. These investigations should lead to a better understanding of the relationships between the surface structure of the samples, their hydrophobic behaviour and the growth of ice.

Individual samples will be used in field tests on a smallscale wind turbine and exposed together with reference samples. The laser processed samples will be continuously monitored together with unprocessed reference samples and the ice formation on the sample surface will be quantitatively measured. This should allow statements about the degree of ice formation and the duration of icing. The samples are disassembled after the exposure, examined and compared with the results before the exposure. A comparison of surface profiles and the hydrophobic behaviour before and after exposure allows statements about changes and the lifetime of the nanostructures. The results of the planned investigations will reveal the relationships between the structure, the (super)hydrophobic behaviour and the growth of ice. The tests under real conditions will also provide information on the durability of laser-generated nanostructures.