Influence of propeller arrangement on aeroacoustic interactions in distributed-propulsion systems in forward flight

Distributed Electric Propulsion (DEP) systems offer strong potential for sustainable aviation, yet unconventional rotor installations introduce new aerodynamic and acoustic challenges. This study experimentally examines how rotor–rotor separation influences the aerodynamic and acoustic performance of twin-isolated and wing-mounted DEP configurations using 9 ′ ′ , five-bladed P / D = 1 propellers. The presence of the wing provides a small but repeatable installation benefit, resulting in an approximately 4 % improvement in propulsive efficiency for advance ratios J > 0.4 . For the twin-isolated configuration, separations up to 3 % of propeller diameter produce noise levels around 2 dB higher than those at larger spacings, while noise characteristics stabilise for 4 % of the propeller diameter. At the smallest spacing 1 % of the propeller diameter, enhanced wake interaction leads to elevated velocity fluctuations and increased noise. In contrast, the DEP configuration shows only minor sensitivity to separation, providing acoustic shielding that reduces noise above the propulsion system, while increasing side-field radiation. Under static thrust conditions ( M T ≈ 0.210 to 0.315 ) , the twin-isolated and DEP configurations show nearly identical noise levels, indicating that tip speed dominates the acoustic response. Under inflow, the twin-isolated configuration produces stronger broadband and tonal noise, with increases of up to 4 dB and 3 to 5 dB respectively, while the DEP configuration consistently remains quieter.