Measurement of an aeroacoustic dipole using a linear microphone array

Area of Science:

• Acoustics
• Signal Processing
• Fluid Dynamics

Background:

• Standard beamforming techniques often assume monopole propagation, which is inaccurate for dipole sources.
• This assumption leads to errors in source localization and energy measurement for dipole sources.

Purpose of the Study:

• To identify the inadequacy of standard beamforming for dipole sources.
• To develop and validate a corrected signal processing algorithm for accurate aeroacoustic dipole measurements.
• To demonstrate the enhanced filtering capabilities of the corrected beamformer.

Main Methods:

• Numerical simulations were employed to illustrate the limitations of standard beamforming.
• A modified signal processing algorithm was developed to incorporate dipole propagation characteristics.
• The corrected algorithm was applied to array measurements of an aeroacoustic dipole generated by a cylinder in cross-flow.

Main Results:

• The corrected beamformer accurately mapped the aeroacoustic dipole source.
• The beamformed spectrum provided a true representation of the source energy and frequency content.
• The corrected array demonstrated insensitivity to other source types, acting as a spatial and source filter.

Conclusions:

• The standard beamformer technique is inadequate for characterizing dipole sources.
• A corrected algorithm accounting for dipole propagation significantly improves source localization and measurement accuracy.
• The enhanced beamformer offers superior spatial and source filtering capabilities, preventing misinterpretation of array measurements.