Numerical method to compute acoustic scattering effect of a moving source.

Area of Science:

• Aerospace Engineering
• Acoustics
• Computational Fluid Dynamics

Background:

• Tail rotors are crucial for helicopter stability but generate significant aerodynamic noise.
• Understanding and mitigating this noise is essential for helicopter operational efficiency and crew/passenger comfort.

Purpose of the Study:

• To numerically investigate the aerodynamic characteristics and acoustic performance of a ducted tail rotor in hover.
• To analyze the impact of duct geometry on sound pressure levels and sound directivity.

Main Methods:

• Computational Fluid Dynamics (CFD) was employed for numerical simulation.
• An analytical time-domain formulation based on the Ffowcs Williams-Hawkings (FW-H) equation was used for acoustic field prediction.
• A hybrid method combining computational aeroacoustics and an acoustic thin-body boundary element method was developed.

Main Results:

• The presence of a duct significantly alters the sound pressure levels (SPLs) and sound directivity of the tail rotor.
• Compared to an isolated tail rotor, the ducted configuration exhibits lower SPLs at specific azimuth angles.
• Simulation results were validated against known methods, confirming the accuracy of the proposed approach.

Conclusions:

• Ducting the tail rotor is an effective strategy for aerodynamic noise reduction.
• The study provides valuable insights into the aeroacoustic behavior of ducted rotors for future helicopter designs.