## 5 Conclusions  
As environmental sustainability is a key problem for the air transport, electric propulsion is giving promising answers to improve the aircraft efficiency. The opportunity of distributing the electric engines power on the aircraft leads to explore unconventional aircraft configurations as those involving engines partially embedded in the fuselage (BLI). Even though engine Boundary Layer Ingestion is a promising solution to reduce the aerodynamic drag, it causes a nonuniformity in the axial fan inflow, with aeroacoustic drawbacks. Using a mid-fidelity comprehensive Computational Aeroacoustics approach, the tonal Rotor-Stator Interaction noise problem was investigated with and without boundary layer ingestion. An engine noise source model was fed with a CFD solution of the fan stage and the in-duct acoustic field was computed. The fan stage was properly designed through the CFD approach to account for the inflow distortion, leading to a RSI under BLI with a lower 2 nd BPF and greater higher BPFs. As the 2 nd BPF dominates the overall sound power, RSI under BLI was less noisy than the clean one. The acoustic solution at the engine inlet and outlet was used as boundary condition of an Integral Boundary Element approach. The far-field propagation was computed on a microphones hemisphere surrounding the aircraft configuration including the acoustic masking effects due to the engine-fuselage installation. The generated hemispheres, representing the acoustic map of RSI with and without BLI and the fuselage masking effects, were exploited for a final assessment at ground level in terms of Sound Exposure Level. The environmental acoustic analyses confirmed the BLI overall noise levels are lower than the Clean one thanks to the proper design of the fan stage. However the effect of the engine-fuselage installation degraded the BLI benefit due to the reflection effects that play a major role at higher frequencies at which BLI is noisier than clean one. This result confirms the importance of properly designing the engine-fuselage integration taking into account also the masking effects in the early aircraft design stage for an effective noise reduction at ground level.  
Conceptualization, M.B.; Formal analysis, F.P. and M.S.; Investigation, F.P. and M.S.; Methodology, M.B. and M.S.; Project administration, M.B.; Software, M.B. and M.S.; Supervision, M.B.; Visualization, F.P. and M.B.; Writing original draft, F.P. and M.S.; Writing review and editing, F.P. All authors have read and agreed to the published version of the manuscript.  
This project has received funding from the Clean Sky 2 Joint Undertaking (JU) under grant agreement No 945583. The JU receives support from the European Union's Horizon 2020 research and innovation programme and the Clean Sky 2 JU members other than the Union.  
Not applicable.  
The data presented in this study are available on request from the corresponding author. The data are not publicly available due to Clean Sky 2 Joint Undertaking copyright regulation.  
The authors acknowledge the support given by the CIRA colleagues [PERSON] and [PERSON] for the definition of the geometries, and [PERSON] for the project management support. The authors also acknowledge the support given by DLR colleagues [PERSON] and [PERSON] for the propulsor design.  
The authors declare no conflict of interest. The results, opinions, conclusions, etc. presented in this work are those of the author(s) only and do not necessarily represent the position of the JU; the JU is not responsible for any use made of the information contained herein.