Acoustic characteristics of phase-synchronized adjacent propellers

Area of Science:

• Acoustics
• Aerodynamics
• Propulsion Systems

Background:

• Distributed electric propulsion (DEP) systems utilize multiple synchronized propellers.
• Noise generation from propellers is a significant concern for aircraft and other applications.
• Controlling propeller noise is crucial for environmental and operational reasons.

Purpose of the Study:

• To investigate the impact of blade phase angle on noise attenuation in adjacent, electronically synchronized propellers.
• To quantify noise reduction at various advance ratios and phase angles.
• To determine the optimal phase angle for noise control in DEP systems.

Main Methods:

• Acoustic measurements were conducted in an aeroacoustic wind tunnel.
• Two adjacent, 2-bladed propellers were electronically synchronized.
• Relative phase angles (Δψ) from 0° to 90° were tested at various advance ratios (J = 0–0.73) and a fixed rotation speed (5000 rpm).

Main Results:

• A relative phase angle of Δψ = 90° yielded maximum noise reduction.
• At J = 0, an 8 dB decrease at the first blade pass frequency (BPF) and a 2 dB overall sound pressure level (SPL) reduction were observed.
• Under in-flow conditions (J > 0), Δψ = 90° resulted in approximately 24 dB reduction at the first BPF and 6 dB overall SPL reduction compared to Δψ = 0°.
• Significant reductions in noise directivity and tonal noise at the BPF were observed.

Conclusions:

• The blade phase angle is an effective method for controlling propeller noise in DEP systems.
• A 90° relative phase angle is optimal for noise attenuation.
• Findings provide critical insights for designing quieter electric propulsion systems.