This thesis presents research on Boundary Layer Ingestion (BLI). BLI is an unconventional aircraft-engine integration technique which aims at integrating the aircraft and the propulsion system such that the overall aircraft fuel consumption can be reduced. This research begins with a literature survey on propulsion integration. The literature is not only limited to recent work on novel aircraft concepts utilizing BLI but also covers the previous studies on ship propellers and pusher propellers used for aircraft. Various studies in the literature show that BLI and/or similar configurations can effectively reduce the total power consumption of the propulsion system. However, discrepancies can be identified amongst various research with respect to the improvements that BLI could provide in terms of reduction in the power consumption. Different research methods have been used to investigate and study this phenomenon in the literature. In particular, the various research methods give an indication that the physics involved in BLI might not be well understood. As a result, the current research aims to enhance the fundamental understanding of BLI. The main research questions are identified below: - What are the mechanisms of BLI for the provided benefit? - How large is the benefit of BLI?@en

The current experimental study aims at quantifying the power conversion processes involved in a propulsor ingesting body wake. Stereoscopic particle image velocimetry is employed for the first time to visualize the flowfield at the location of interaction between a propeller and an incoming body wake, as well as to provide experimental data to be used for the power balance method. Besides experimentally quantifying the power conversion method, the results show that one of the main mechanisms responsible for the claimed efficiency enhancement in the experimental setup is due to the utilization of body-wake energy by the wake-ingesting propeller.

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This paper presents conceptual studies to evaluate the performance of the propulsor and its associated vehicle in the configurations of wake ingestion and boundary-layer ingestion. A power conversion analysis uses the power balance method to elaborate the power-saving mechanism of wake ingestion, showing that the Froude’s propulsive efficiency as a figure of merit should be separated from the power conversion efficiency in these configurations. The body/ propulsor interaction occurring in the boundary-layer ingestion configuration is qualitatively analyzed to clarify its influence on the performance of the integrated vehicle. The results suggest that the minimization of power consumption should be used as a design criterion for aircraft using boundary-layer ingestion. @en