The present paper focuses on the assessment of the aerodynamic and aeroacoustic interaction of propellers suitable for innovative hybrid-electric aircraft. Attention is paid to the effect on the overall efficiency, the total thrust provided and the acoustic emissions as a function of the relative position for co- and counter-rotating configurations. The scope of this study is led by the demanding abatement targets imposed by authorities, in terms of noise and chemical pollution, in view of the air traffic growth foreseen in the near future. The use of distributed hybrid-electric propulsion and suitable innovative configurations allows for on-top engines installation. This is nowadays one of the most promising solutions to comply with the strict environmental targets foreseen, and it is therefore of high interest for the aeronautical community. Simulation based data could clarify many aspects regarding the acoustic impact due to the installation effects of the distributed propulsion. Here, the analysis is limited to a couple of rotors in free space in order to capture the fundamental interaction effects. The results have been obtained using a boundary integral formulation for unsteady, incompressible, potential flows which accounts for interaction between free wakes and propellers. Aeroacoustic analyses have been performed trough the Farassat 1A boundary integral formulation for the solution of the Ffowcs-Williams and Hawkings equation. Several distributed propulsion layouts are presented at the end of the analysis as tentative configurations potentially suitable for installation on a hybrid--electric regional aircraft with and without boundary layer ingestion.
