Aerodynamic and Aeroacoustic Analysis of Distributed Electric Propulsion (DEP) Systems

A comprehensive study of the aerodynamic and aeroacoustic performance of Distributed Electric Propulsion (DEP) configurations was conducted through experiments at the University of Bristol's state-of-the-art wind tunnel facilities. The investigation focuses on the aerodynamic performance of DEP configurations across various design and operational parameters. Key factors analysed include the effects of angle of attack, changes in inflow speed, and the impact of different propeller configurations. In the 12-12-12 configuration (three 12-inch propellers), propeller performance shows less sensitivity to variations in the angle of attack, whereas the 15-15-15 configuration (three 15-inch propellers) shows a noticeable thrust increase for the inboard propeller. Regarding wing performance, the 15-15-15 configuration offers slight improvements in the CL/CD ratio at low angles of attack, while the 12-12-12 configuration performs better at higher angles of attack. In addition to the aerodynamic analysis, the aeroacoustic performance of DEP configurations is thoroughly examined. The study explores the effect of propeller phase synchronization as a noise reduction strategy, particularly under forward flight conditions. Results show significant reductions in both noise directivity and tonal noise at the blade-passing frequency (BPF), with a relative phase angle of ∆ψ = 90° achieving the greatest noise reduction—a 24 dB decrease at the first BPF. The acoustic signature of the DEP configuration is further analysed to assess the impact of separation distance during forward flight. Notably, the Overall Sound Pressure Level (OASPL) and the first BPF display distinct behaviours when the separation distance is reduced to less than 5% of the propeller diameter, highlighting the substantial effect of close proximity on acoustic performance. These findings offer valuable insights for optimizing DEP systems, supporting quieter and more efficient propulsion technologies that align with net-zero aviation goals by reducing noise and enhancing sustainability in urban air mobility.