Aeroacoustic Characteristics of a Twin-Propeller Distributed Electric Propulsion System with Phase Synchronisation at Various Wing Angles of Attack

The noise emission of future distributed electric propulsion (DEP) concepts has been a primary concern throughout the design process. This work focuses on experimentally and numerically examining the noise produced by a leading-edge-mounted twin-propeller DEP system with phase-controlled two-bladed 9-inch propellers, at various wing angles of attack (AoAs). The experiments were conducted in the University of Bristol Wind Tunnel, complemented by mid-fidelity numerical simulations. The results show that the sensitivity of the first blade passing frequency tonal noise directivity to wing AoA change decreases with decreasing advance ratio 𝐽 for zero-degree relative phase angles (𝚫𝝍 = 0°). The implementation of propeller relative phase control is shown to effectively reduce tonal noise across all wing AoAs at different propeller advance ratios, although the level of attenuation depends strongly on observer positions and operating conditions. The minimum noise levels are typically achieved at 𝚫𝝍 = 60° for observer positions representative of the passenger side (top microphone arc), and at 𝚫𝝍 = 90° for measurement locations aligned with the propeller separation plane (horizontal microphone arc). This behaviour is consistent across the studied range of wing AoA. The numerical predictions using the vortex particle method (VPM) successfully captured the overall directivity trends and relative phase effects, although a consistent underprediction of sound pressure level (SPL) was observed on the top microphone arc. These results demonstrate that propeller phase control can effectively mitigate tonal noise in DEP systems at non-zero AoA, while further model refinement is needed to improve predictive accuracy under complex inflow conditions.