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Development of SmarT Eco-friendly anticontamination technologies for LAminaR wings

Periodic Reporting for period 1 - STELLAR (Development of SmarT Eco-friendly anticontamination technologies for LAminaR wings)

Reporting period: 2019-10-01 to 2021-03-31

The aircraft industry is facing issues with the increase of drag directly impacting the fuel consumption of the fleet. Achieving natural laminar flow requires high surface quality. Tiny air flow disturbances at the surface can indeed cause an early transition from laminar to turbulent flow. The accumulation of insect debris on the leading edge of laminar wings has been recognized as one of the most significant operational concerns associated with laminar flow.

The main objective of STELLAR is to develop efficient and durable anticontamination coating and cleaning solutions designed following a deep understanding of the insect residues properties. Hence, STELLAR project seeks to gain insight on the understanding of the biochemical transformation of hemolymph during flight phases and the consequent physico-chemical modification of the surface.

In order to meet these goals, the project consortium gathers cutting edge multidisciplinary knowledge and the needed facilities to provide a deep understanding of the contamination issues. This approach has the potential to significantly enhance the current understanding of the key issues and highlight which surface characteristics have the greatest influence on insect residue adhesion. From this approach, new coating and cleaning solutions will be developed.

The knowledge acquired and the solutions developed will be evaluated through large scale tests : tests in wind tunnel which allow simulating extreme conditions occurring during flights, on a test aircraft (short flight tests) equipped with a cameras and sensors (T°, RH, pressure) to monitor all the parameters responsible of real condition contamination and on a commercial aircraft (long flight tests) flighing at higher altitudes and allowing a full validation of the newly developed solutions.

As a summary, the project STELLAR aims at producing sustainable solutions to reduce drag on aircrafts and enable laminar flow over time with direct impact on fuel consumption and thus contributes to aviation’s ecological footprint reduction, targeting a 50% reduction of wing friction and up to five percent lower CO2 emission.
During the first period of the project, the most important part of the work has been dedicated to the study of biochemical modification of hemolymph under atmospheric conditions, the physico-chemical properties modification during hemolymph coagulation and its impact on adhesion on model surfaces. In parallel the development of anticontamination coating and cleaning solutions has been started, whose design is based on the comprehensive study of hemolymph properties. Work has also been initiated to prepare the validation step, especially that related to the preparation of data base and sensor systems and equipment design.

1. Establishing the link between hemolymph modification (under atmospheric conditions) and interaction with the surface
After a review of literature on critical parameters conditioning contamination and mitigation solution a deep comprehenseive study was started by ESPCI and UMONS (with support of VKI) : a study of biochemical modification of hemolymph during coagulation which allowed to determine the main proteins undergoing chemical transformation and the study of physico-chemical properties of hemolymph under coagulation (microrheology, wetting, adhesion). Model coated surfaces were used to evaluate their influence on the interaction with hemolymph and potential effect on coagulation kinetics. The influence of atmospheric conditions has been mainly focused on the effect of temperature rapid modification during take-off and landing operations. At least two scientific publications are foreseen in the next period.
2. Formulation of smart eco-friendly anticontamination coatings
CIDETEC and MANO started the development of coatings from a predefined palettes of technologies refined on the basis of the literature review and designed on the basis of the knowledge acquired on hemolymph modification and interactions with surfaces. The coatings are based on several chemistries and include slippery effect and self-healing properties; The formulations will be further optimized in the next months and characterized to evaluate their durability (aeronautic requirements). Several communications (conferences, workshops, articles) were carried out to communicate on anticontamination coatings.
3. Development of eco-friendly cleaning solution
During this period, SOPURA started the development of different formulas : solvent-based formulas and enzyme-based formulas. Different compositions were tested and some provide very good detergency effect. The application process will be further optimized.
- Formulation of coatings which have direct impact on insect coagulation kinetics which is an unexpected results which was never reported in the literature; Cidetec is considering to patent the coating formulation.
- Formulation of self-healing polyurethane coating : replacement of a fraction of the binder by self-repairable (under RH trigger) was done with success and provide coatings with promising properties (further explored in the second period of the project).
- Formulation of innovative cleaning solutions showing synergistic effect with anticontamination coating leading to 100% removal of highly sticky insect debris.
By the end of the project, new coating and cleaning formulations will be available that fully or partially meet aviation requirements and provide an anti-contamination effect for leading edge applications. This type of coating may have a wider scope of application (including trains, automotive, etc.) and the knowledge acquired will be useful in understanding and minimizing contamination in general. Creation of new jobs can be expected at the end of the project in order to reinforce commercial, technical assistance and the industrialization of the new solution
Test aircraft used for validation of anticontamination coating (SONAIR)
Microrheology measurement on hemolymph (ESPCI)
Sliding angle measurement on coating (MANO)
Hemolymph extraction from insect (UMONS)