A comprehensive experimental study was conducted to explore the noise generation mechanism of a structured porous-coated cylinder (SPCC) in cross-flow. Coherence analysis between the velocity field, near-field surface-pressure fluctuations, and far-field noise was performed to identify the relative contributions of dipole and quadrupole sources to far-field sound in the case of the SPCC. The velocity field was measured using planar particle image velocimetry (PIV) along the streamwise direction, while near-field surface pressure was measured using pressure taps via a remote-sensing method. The results demonstrated that turbulent wake velocity fluctuations, particularly the vertical component associated with quadrupole-type sources, exhibit significant coupling with the cylinder-surface pressure response and the radiated acoustic field. This correlation behavior suggests a possible pathway by which wake-associated unsteady fluctuations influence the near-wall surface-pressure response, which provides an equivalent dipole representation of the body-induced acoustic radiation. Both dipole- and quadrupole-related source mechanisms were suppressed by the SPCC. Dipole suppression was influenced by two mechanisms—delayed vortex shedding and reduced turbulence energy—whereas quadrupole attenuation primarily resulted from turbulence reduction. Consequently, although dipole sources remained important contributors, the relative dynamic coupling of quadrupole fluctuations with the far-field noise was stronger than in the baseline case. This led to a mixed acoustic contribution for the SPCC, in contrast to the baseline, where dipole sources dominated tonal noise.

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• Aeroacoustics
• Aerodynamic noise
• Flow control
• Vortex shedding