Aerothermal assessment of an integrated fan-heat exchanger propulsor at system- and component-level

In the context of hydrogen-electric aircraft propulsion, low-temperature proton exchange membrane fuel-cell (LT-PEMFC) represents a promising and sufficiently mature technology to achieve in-flight zero carbon emissions. Despite its high efficiency, LT-PEMFC comes with the major problem of waste heat dissipation. Integrating a ducted heat exchanger (HEX) within the flowpath of an e-fan can leverage the "Meredith effect" by exchanging the heat at higher pressure, thus reducing and potentially overcoming the drag penalties associated with the use of a radiator for heat dissipation. This study investigates the feasibility of using an integrated fan-heat exchanger propulsor to propel a mid-range aircraft. In the first part of this work, a cycle-level assessment is conducted implementing a 1D engine conceptual design tool. Acknowledging the different airflow Mach work ranges of the fan and the heat exchanger placed behind it, different options of flow diffusion are explored between the intake and the heat exchanger by varying the corresponding Mach numbers. Two promising designs are obtained using inclined heat exchanger configurations and guide vanes to facilitate the flow turning toward the radiator inlet. The design presenting a fan pressure ratio of 1.32 and a HEX inlet Mach of 0.14 is selected for a subsequent fan stage analysis, despite a 5% decrease in installed overall efficiency compared to the optimal cycle-performance design. This choice is made as this design is considered more feasible for under-wing installation on a mid-range aircraft. The second part of the thesis zooms in on the preliminary fan stage design. Component-level performance is investigated using a 2D throughflow solver, while system-level performance is assessed using the aforementioned 1D tool. Initially, a sensitivity analysis is conducted to investigate different fan-face Mach numbers, proving that the optimum in fan stage performance does not correspond to the optimum in system-level performance for this concept. Furthermore, increased diffusion within the fan stage is demonstrated to be an efficient way to reduce stagnation pressure losses of the system, thus enhancing its overall installed efficiency. Finally, a full performance map of the optimum design is built to evaluate the operability of the fan during off-design conditions, showing encouraging results.