Numerical modeling of advanced technological solutions for sustainable aviation

The aviation sector is among the fastest-growing transportation industries in terms of greenhouse gas emissions. Regulatory agencies and international institutions have therefore established ambitious targets to mitigate the aviation climate impact. These regulations have caused a disruption in the aerospace industry, prompting a shift towards the development of new propulsion architectures and the integration of alternative jet fuels in conventional engine systems. In this thesis, a comprehensive exploration of next-generation propulsion system solutions is conducted. To date, the most promising concepts for green aviation are the integration of electric motors to hybridize powertrain architectures and the use of sustainable aviation fuels in existing aeroengines. The first technology, being at a low technological readiness level, is analyzed in the first part of the thesis employing a conceptual design approach. To this end, a Python object-oriented framework for hybrid/electric aircraft conceptual design, PhlyGreen, is first introduced. The code modularity allows for a simple implementation and communication between the different disciplines involved in the design process. Leveraging this tool, the feasibility of sustainable aviation fuels (SAF)-driven gas turbines, hybrid architectures, and fully electric motors is investigated through an analysis performed over a regional aircraft. Two studies on the optimization of the in-flight hybridization strategies are carried out, taking into account the well-to-wake (WTW) cycle of energy vectors. First, a multi-objective optimization across various WTW scenarios is performed to assess how different SAF production routes and electricity pathways influence the reduction of climate impact. Subsequently, an uncertain op- timization framework is employed to propagate the effects of uncertainties in SAF production and electricity grid mix onto the aircraft’s optimal configuration. In the second part of the thesis, the focus is shifted toward the chemical and combustion characterization of SAFs. To support the de-risking of widespread adoption of unconventional fuels, this thesis presents a set of numerical tools aimed at facilitating the SAF approval process. In the first place, a methodology for the generation of tailored kinetic mechanisms for multi-component mixtures is introduced. This approach enables the description of the oxidation of a multi-component physicochemical SAF surrogate, allowing the assessment of the fuel’s combustion properties. Then, a numerical analysis on an n-heptane turbulent spray flame is performed to pursue a two-fold scope: evaluate the impact of combustion and chemistry modeling on the flame topology and characteristics. Finally, a direct numerical simulation of a SAF droplet cloud autoignition is carried out to evaluate the effect of the non-standard physicochemical properties of unconventional fuels on the ignition of a spray flame.