Aeroacoustic-Source Analysis of a Structured Porous Coated Cylinder

Among passive noise control strategies, the use of porous coatings around bluff bodies, such as circular cylinders, has been widely investigated in recent years. In the present work, a high-fidelity simulation based on the lattice-Boltzmann method has been employed to elucidate the noise generation mechanisms of a Structured Porous Coating. The results show that the acoustic field is dominated by high-frequency noise generated by the small-scale cylinders that constitutes the porous medium. In the low-frequency range, although the flow Mach number is low, the dominant noise contribution originates from wake sources. This finding enables an equivalent interpretation of cylinder noise as a diffraction problem. Indeed, the porous coating induces an increase of the vortex formation length, which displaces the quadrupolar source at the onset of vortex shedding further downstream and consequently diminishes the efficiency of the sound scattered by diffraction from the body surface. The relevance of wake sources is further confirmed through an alternative approach based on coherence analysis. These results are consistent with recent experimental evidence highlighting the significant role played by wake sources in porous cylinders, even at low Mach numbers.