On the psychoacoustic impact of synchrophasing for distributed propellers and ducted fans

Abstract

This study examines whether synchrophasing and stator clocking can reduce tonal noise emissions in distributed propulsion systems under realistic flight conditions. Using measurement-informed auralization, we evaluate two configurations: an eight-propeller tilt-prop aircraft and a tilt-duct system with 26 fans. For the distributed propellers, results demonstrate that synchrophasing at specific phase angles (e.g. half propeller blade-to-blade angle) induces destructive interference at the blade-passing frequency and its harmonics, leading to sound pressure level reductions of approximately 10 dB and a reduction of tonality and fluctuation strength larger than one just-noticeable difference compared to in-phase operation. For the ducted fans, an evolutionary optimization routine determines optimal stator clocking positions to minimize tonal interaction noise. This approach achieves tonal noise reduction of approximately 10 dBA at centerline certification positions. Whereas the optimized stator distribution successfully lowers centerline noise levels by creating a narrow low-tonal noise corridor beneath the flight path, a significant lateral reduction (e.g. for surrounding communities) could not be achieved. The findings establish phase control and stator clocking as viable, yet sensitive, degrees of freedom for minimizing tonal noise in distributed propulsion systems.