ICE GENESIS is an EU-funded project in the Horizon 2020 framework (project number 824310) which started in January 2019 and ended in December 2023, with the main objective to create the next generation of 3D simulation means for icing. A need for this project arose since, with the forthcoming disruptive architectures for air vehicles and propulsive systems, it will no longer be possible to rely on the existing design methodologies mainly based on experience and comparative analysis. These difficulties would moreover be increased with the recent changes in certification regulations, in particular regarding Supercooled Large Drops (SLD). Snow was also identified as a specific challenge to be addressed for the certification of turbine engines and APUs, with little development and certification compliance means available apart from flight testing. There was therefore a strong need for more mature tools to support the development and certification of aircraft, rotorcraft and engines in supercooled liquid water and snow conditions. To cover this need, the top-level objective of ICE GENESIS was to provide the European aeronautical industry with a validated new generation of 3D icing engineering tools (numerical simulation tools and upgraded test capabilities), addressing Appendix C, Appendix O and snow conditions, for safe, efficient, right first time, and cost-effective design and certification of future regional, business and large aircraft, rotorcraft and engines.
ICE GENESIS faced several challenges during its execution phase. Two of them had sufficiently notable impacts to be mentioned in this report: the COVID-19 crisis, which led to an extension of the project duration, and the termination, for geopolitical reasons, of an international partnership around which some major activities of the project were articulated. Some mitigation means were found to continue the project, but with some impacts on its overall scope and outcomes.
Supercooled Liquid Icing in ICE GENESIS
During ICE GENESIS, efforts on supercooled liquid icing have been concentrated on the upgrade and validation of test facilities for Supercooled Large Drops (SLD) conditions and on the improvement of numerical tools to perform 3D icing simulations and model SLD conditions.
First of all, the requirements targeting at the reproduction of SLD conditions in ground wind tunnel facilities were defined. The most appropriate instrumentation for SLD wind tunnel calibration was then selected. Further to the selection of the appropriate instrumentation, a calibration methodology for SLD test facilities was derived from the SAE ARP 5905. In particular, relevant parameters and acceptance criteria for SLD cloud calibration were updated. With that respect, ICE GENESIS enabled to achieve upgraded icing wind tunnel test capabilities in freezing drizzle conditions, both at CIRA (Italy) and RTA (Austria). A preliminary capability for freezing rain was even demonstrated at RTA. In terms of maturity assessment for freezing drizzle conditions, RTA achieved the TRL5 maturity targeted at the end of the project, while CIRA achieved a TRL4. The lack of calibration of the CIRA icing wind tunnel in its complete broad envelope covering altitude and high speed is the main reason why CIRA could not achieve TRL5. This calibration work is to be continued through other projects. On top of the upgrading of the test facilities, some trials were performed to characterize the droplet temperature in the wind tunnel, as it is a parameter that is believed to play a role in the accretion process. This was a first time for a European project and it provided encouraging results. It was also the first time that extensive 3D scanning of ice shapes was performed. The scanned ice shapes have been stored in the ICE GENESIS common database and can later be used for tool validation. Although the freezing drizzle capabilities of CIRA and RTA icing wind tunnels were significantly increased over the course of ICE GENESIS, some gaps remain to achieve a full freezing drizzle capability. Indeed, there are still some issues with the cloud uniformity and the Liquid Water Content (LWC) achieved is often too high compared to the certification requirements. Moreover, the effect of droplet temperature on the ice accretions needs to be further characterized. Some standardization efforts on the instrumentation for particle size distribution and LWC measurement are also required to ensure more consistency on the calibration of different test facilities. Furthermore, in order to use the test capabilities for industrial applications, the efficiency of the SLD set-up will have to be improved and it will be necessary to find a way to switch easily between Appendices C and O. At the end of ICE GENESIS, the upgraded icing wind tunnel capabilities for Appendix O conditions provide more possibilities of testing but they are not yet at a level that would enable their use as a comprehensive means of compliance for aircraft certification.
As for the test facilities, a set of target requirements for the 3D icing numerical tools were defined at the beginning of the project, including requirements for the SLD capability. At the end of ICE GENESIS, some numerical capabilities were demonstrated in freezing drizzle based on the initial target requirements. In particular, some models were developed to simulate drop impact and mass deposition after splashing, as well as droplet re-emission. Moreover, a 3D capability was demonstrated with new methodologies for remeshing or multi-step processes. In consideration of this progress, the numerical tools for supercooled liquid icing, and in particular for SLD icing, achieved a TRL4. A TRL5 assessment was also performed but was not conclusive due to the remaining model limitations and the lack of industrialization of the tools. It was recommended to continue the research to improve SLD models, in particular addressing altitude and high-speed effects, which were identified in the course of the project. A significant gap was as well highlighted on roughness modelling. Recommendations also insisted on the need to further work on automation, user-friendliness, robustness and accuracy of 3D algorithms for predictor/corrector and/or multi-stepping method to allow their use to non-expert users. Finally, there is a lack of reliable experimental data to properly assess the models. For instance, experimental data enabling to properly differentiate the contributions of each individual phenomena is missing, as well as test data on more complex configurations. Overall major progress on numerical tools for liquid icing has been done during ICE GENESIS. However, the maturity of the tools upgraded with SLD models is not yet sufficient for them to be used as certification means of compliance. Some efforts are still needed to provide a better level of acceptance of these tools as certification means of compliance, as it is the case today for Appendix C. Considering the complexity and dimension of the topic, collaborative research efforts will be mandatory.
Snow in ICE GENESIS
During ICE GENESIS, efforts on snow have been concentrated on the characterization of falling snow conditions, on the upgrade and validation of test facilities and on the improvement of numerical tools.
One of the first achievements of ICE GENESIS regarding snow was the characterization of falling snow conditions through field campaigns, during which valuable data was gathered thanks to developed synergies between the flight test aircraft, ground in-situ measurements and ground remote sensing (winter 2020/21). Considerable efforts were made on the data processing to retrieve the snow microphysical properties. The results were later used in the project as a support for the development of snow test and numerical capabilities.
The target requirements for snow test facilities were defined at the beginning of ICE GENESIS. These requirements were aiming at the reproduction of natural-like falling and blowing snow conditions in ground wind tunnel facilities. The most appropriate instrumentation for snow wind tunnel calibration was then selected. Further to the selection of the appropriate instrumentation, a calibration methodology for snow test facilities was derived from the SAE ARP 5905. In particular, relevant parameters and acceptance criteria for snow cloud calibration were updated. ICE GENESIS enabled the development of snow generation systems in RTA and NRC, with the capability to change the particle melt. The wind tunnel test facilities upgraded with these capabilities were then calibrated following the methodology previously defined. Though the snow generation systems used by the two facilities are based on different principles, they both enabled to achieve comparable results which provided a good confidence on the calibration of both facilities. Even though the maturity of the snow generation system in RTA was significantly increased during the project, it still needs to be upscaled in order to achieve the regulatory Total Water Content (TWC > 1g/m3) as defined in AC29 or AMC25.1093(b). Moreover, the efficiency and operability of the snow generation systems will have to be improved for industrial use. Finally, it will be necessary to use the upgraded test facilities to generate a validation database on representative industrial configurations (turbo propeller or helicopter engine air inlet) to be used to assess the numerical capabilities.
Some target requirements for the snow numerical tools were defined at the beginning of the project, complementing those defined for supercooled liquid water since the same tools were expected to integrate both the snow and supercooled liquid water capability. Several physical phenomena related to snow were modelled during ICE GENESIS, starting from ice crystals models developed in the framework of the HAIC and MUSIC-HAIC projects. The physical phenomena addressed were drag, melting, erosion and sticking efficiency. The modelling of the particle trajectories (drag and melting) was assessed as sufficiently mature to achieve a TRL4 based on the good correlation with the experimental database. On the opposite, the erosion and sticking models obtained are only preliminary, equivalent to a TRL3 maturity. The snow models were then implemented into industrial 2D/3D icing tools, which were assessed by comparison with experimental results from the CSTB, NRC and RTA databases. The TRL5 assessment for snow numerical tools was not conclusive due to several remaining gaps which are listed hereafter. The snow accretion modelling is less mature than the snowflake trajectory modelling. In particular, models of snowflake impact and accretion will need more development. The case of snow accretion on heated surfaces will also have to be considered. Moreover, ice shedding and snow saltation should be further modelled. Finally, the numerical capabilities could not be properly assessed due to the lack of experimental data on complex 3D cases. This will have to be done in the future. Nevertheless, the panel recommended to proceed, since the progress made was significant and seemed to tend in the right direction. Achievements within ICE GENESIS provide already major improvement compared to the state of the art especially with regards to the transport model and efforts are to be continued.
ICE GENESIS common experimental database
One of the main outcomes of ICE GENESIS is the generation of a common experimental database, that gathers data from previous projects worldwide (example: NASA SLD Database) as well as ICE GENESIS data. The database contains Appendix C and Appendix O icing test cases, which represent in total 390 individual icing runs on 17 different test objects.
Conclusion
ICE GENESIS enabled significant progress on wind tunnel test facilities for the simulation of SLD and Snow conditions. The project also led to an improved understanding and modelling of SLD and Snow physics, though some progress remains necessary on the new models in order to use them as certification means of compliance. All along the project, the international cooperation has been beneficial and is to be continued.
Further efforts are necessary to achieve workable means of compliance for the future generation of disruptive products. They could take the shape of collaborative research activities feeding two separate roadmaps focusing respectively on supercooled large drops and snow & ice crystals. Launching the necessary activities to achieve the targets of these roadmaps will be critical to enable the development and certification of low-CO2 aircraft and engines. Some coordination efforts are currently ongoing at international level to define in more details the scope of the required future activities and to identify the best funding opportunities in the coming years.
