Near-wall Energy Processes with Efficient Materials – WALL-EE

4.3 billion passengers used air transportation in 2018, and forecasts announce an annual 4.5% increase over the next 20 years. These figures raise environmental concerns because the aviation activity contributes to the overall carbon footprint (2-4% of total greenhouse gas emissions). European and International organizations have therefore released radical environmental regulations. For instance, ACARE flightpath goals include a 75% reduction in carbon dioxide emissions by 2050 (compared to 2000). Aero-engine manufacturers are encouraged to identify most-effective pathways favoring the emergence of alternative low-carbon propulsion systems. Among others, electric hybridization appears to be a long-term promising technological breakthrough which could mitigate carbon dioxide emissions up to 50%. The feasibility of this technological breakthrough demands to revolutionize the design of aircrafts in order to integrate electrical generators and energy coupling / storage systems. However, this will definitely increase the engine weight and reduce the propulsive efficiency. Then, downsizing the entire propulsion system architecture combined with lighter materials is mandatory. Specifically, this calls for the creation of ultra-compact aero-engine combustors although this ambitious target raises a major technological challenge regarding wall thermal management. Indeed, hot section component materials must sustain long periods (> 10 000 hours) exposed to high-temperature (~2000 K) and severe oxidizing/corrosive environments. Even though considerable efforts were devoted to increase allowable temperature of advanced metal casting, the current solution consists in adding various thermal protective methods. Unfortunately, these methods also incur a thermal yield penalty. Development of higher-temperature materials such as ceramic matrix composites (CMCs) is thereby crucial to enable significant efficiency gains.

WALL-EE is soundly positioned at the frontier between reactive fluid mechanics, optical diagnostics and material science to lead a groundbreaking and multi-physical experimental research in order to address critical unanswered questions of heat transfer and cooling performances with promising materials. With the intent to establish a systemic methodology to advance the state-of-the-art, WALL-EE will take advantage of a novel experimental facility offering various optical accesses, thus allowing to obtain simultaneous detailed data by means of advanced laser-based diagnostics. A simplified cooling system producing a parietal air-film will enable to investigate thermal loading mechanisms as well as cooling performances of superalloys and high-temperature ceramic matrix composites. Wall-bounded aerodynamics/mixing properties will be evaluated with Particle image velocimetry (PIV) and planar laser-induced fluorescence (PLIF) on acetone. Hydroxyl (OH) PLIF and PIV will be implemented to elucidate the interactions between the reaction zone and near-wall flow dynamics. Finally, planar laser-induced phosphorescence (PLIP), two-line atomic fluorescence (TLAF) will provide coupled insights between local wall heat transfer, the material nature and the cooling performances of the envelope.

Technical and scientific progresses achieved in this project will establish a world-leading research theme on near-wall energy transfer processes, including the development and implementation of advanced laser-based optical diagnostic tools. Over the long term, WALL-EE knowledge will stand as a springboard to future academic and industrial collaborations. Supporting effectively cleaner propulsion technologies, it will also help overcome technical barriers in many other fields (chemical processes, biomedical).