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This study aims to analyse the corresponding business models of the aviation industry regarding airline and air navigation service provider strategic alliances during the COVD-19 pandemic. An extensive literature review is carried out on airline cooperative arrangements and each specific alliance with a special focus on their performance during and after the pandemic. Therefore, the chosen methodology in order to conduct the analysis is the EcoCanvas business model, which is based on the traditional business model canvas with additional aspects on sustainability and circular economy. The analysis has shown that the pandemic was an unprecedented challenge for the aviation industry with great losses on revenue due to border restrictions. The global airline alliances have proved to be a very stable business model that helped their members to deal with these challenges, promoting safety measures, investing and implementing IT, health and safety technologies. On the other hand, air navigation service providers had to readjust their financial structure and find alternative funding sources in order to operate and to continue or at least not abandon their technological development and modernisation. Additionally, the corresponding methodology allows us to describe the social and environmental impact and foresight, which have been analysed and assessed. Also, it has been shown that the aviation sector is committed towards their sustainable development with various measures ranging from sustainable aviation fuel procurement and refurbishment promoted by airline alliances on the one hand, and on the other hand, the air navigation service providers contribution with the use of renewable sources of energy in their infrastructures and technology improvements aimed to increase the airspace safety, capacity, cost efficiency and reduce aviation noise and emissions.

A bellmouth intake to adapt the airflow into a micro turbojet (EvoJet170neo) during on ground rig testing has been designed and optimised through numerical simulation with OpenFOAM. The design that has been chosen for the bellmouth is based on a parametrized elliptical shape that has been generated using CAD tools. Also, 2D axis-symmetrical simulations have been run by taking advantage of the geometry symmetries that are common in a real bellmouth around its axis. The airflow is considered to be incompressible, turbulent and at sea level conditions according to ISA. It has been simulated employing the k-omega SST turbulence model, which implies a careful mesh design. Hence, the mesh has been designed so that in the boundary layers near the walls and inside the intake a structured mesh with quadrilateral cells is maintained, while an unstructured mesh with triangular cells is used in the quiescent atmosphere. Also, a mesh refinement study has been carried out and it has shown that 39 quad cells in wall-normal direction and a thickness below of 0.0265717 m for the first layer of cells away from the walls are needed in order to guarantee that y+ is lower than 2 as required by the turbulence model. The resulting design has guaranteed a good conditioning of the airflow fed into the engine so that the boundary layers remain attached on all walls and that the airflow is homogeneous with deviations way less than 1.8% of the airflow¿s mean velocity. Finally, a rigorous study has been performed to choose the ideal locations for placing total and static pressure probes that give a good estimation of the delivered air mass flow to the engine with numerical background and also an analysis of the correlation with the air mass flow over the full operational range of the engine and how positioning errors of the probes would affect the measurements when installed. In general, it has been demonstrated that we have a good correlation with the air mass flow at these probe positions and