Influence of Propeller Arrangement on Aeroacoustic Interactions in Distributed-Propulsion Systems in Forward Flight

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Abstract
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 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 efficiencyfor advance ratios J > 0.4. For the isolated configuration, separations up to 3% of propellerdiameter produce noise levels around 2 dB higher than those at larger spacings, while noisecharacteristics stabilise for 4% of propeller diameter. At the smallest spacing 1% of propellerdiameter, enhanced wake interaction leads to elevated velocity fluctuations and increasednoise. 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 (MT ≈ 0.21 to 0.315), the isolated andDEP configurations show nearly identical noise levels, indicating that tip speed dominatesthe acoustic response. Under inflow, the isolated configuration produces stronger broadbandand tonal noise, with increases of up to 4 dB and 3 to 5 dB, respectively, while the DEPconfiguration consistently remains quieter.

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