Innovative coatings for reducing flow-induced cylinder noise by altering the sound diffraction

R. Zamponi*, D. Ragni, S. van der Zwaag, F. Avallone

*Corresponding author for this work

Research output: Contribution to journalArticleScientificpeer-review

2 Citations (Scopus)
47 Downloads (Pure)

Abstract

The aerodynamic noise radiated by the flow past a cylinder in the subcritical regime can be modeled by a quadrupolar sound source placed at the onset position of the vortex-shedding instability that is scattered by the surface with a dipolar directivity. When the cylinder is coated with a porous material, the intensity of the shed vortices is greatly reduced, determining a downstream shift of the instability-outbreak location. Consequently, sound diffraction is less efficient, and noise is mitigated. In this paper, an innovative design approach for a flow-permeable coating based on a further enhancement of such an effect is proposed. The results of phased-microphone-array measurements show that, once the leeward part of the cover is integrated with components that make the flow within the porous medium more streamlined, the quadrupolar source associated with the vortex-shedding onset is displaced more downstream, yielding additional noise attenuation of up to 10 dB with respect to a uniform coating. Furthermore, the same noise-control mechanism based on the weakening of the sound scattering can be exploited when these components are connected to the bare cylinder without the porous cover. In this case, the mitigation of overall sound pressure levels is comparable to that induced by the coated configurations due to the lack of noise increase produced by the inner flow interacting within the pores of the material. Remarkable sound reductions of up to 10 dB and a potential drag-force decrease are achieved with this approach, which paves the way for disruptive and more optimized noise-attenuation solutions.

Original languageEnglish
Article number127120
JournalPhysics of Fluids
Volume35
Issue number12
DOIs
Publication statusPublished - 2023

Funding

This work was part of the IPER-MAN Project (Innovative PERmeable Materials for Airfoil Noise Reduction), Project No. 15452, funded by the Netherlands Organization for Scientific Research (NWO). The authors would like to gratefully acknowledge Rob van der List for his assistance in 3D printing the innovative coatings.

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