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Cylindrical bodies in uniform flows can be coated with a porous medium as a passive flow and noise control method in an effort to reduce the acoustic effects of vortex shedding. To date, the employed open-cell porous materials typically possess a randomized internal structure. This paper presents the design and validation of a novel 3-D printed structured porous coated cylinder that has significant flexibility, in that the porosity and pores per inch of the porous coating can be modified independently and relatively easily. The performance of the structured porous coating design is compared against porous polyurethane and metal foam with the same coating dimensions and similar pores per inch and porosity via an experimental acoustic investigation, revealing strong similarity in the passive noise control performance of each material type. A numerical comparison illustrates the similarities of the wake structure of the 3-D printed porous coated cylinder to an equivalent Darcy–Forchheimer model simulation that represents a randomized internal porous structure. The performance similarities of these different porous material types indicate that a structured porous geometry can be used to understand the internal flow behavior of the porous medium responsible for reducing the cylinder vortex shedding tone that is otherwise extremely difficult or impossible with typical randomized porous structures. Moreover, significant potential exists for the porous structure to be further optimized or smartly tailored by architectural design for different control purposes, coating geometries and dimensions, and working conditions.

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The vortex shedding tone of a cylinder in uniform flow can be reduced by applying a porous coating yet this mechanism is not fully understood. An experimental investigation of asymmetric structured porous coated cylinders (SPCCs) was conducted in a small anechoic wind tunnel using a hot-wire anemometry probe placed in the boundary layer, separated shear layer and wake, in conjunction with a microphone in the far-field. Tests were conducted at Reynolds numbers 105, 1.53×105, and 1.66×105. Each SPCC revealed a widened and deeper wake and reduced turbulent kinetic energy levels in the separated shear layer than the bare baseline cylinder. Furthermore, each SPCC revealed two tones that were a multiple of two apart in both the velocity and acoustic power spectral densities. It was shown that the higher frequency tone is generated by localized flow behaviors in the separated shear layer, independent of the vortex shedding tone and its magnitude is inversely related to the SPCC windward surface porosity. Applying a more densely spaced porous region on the cylinder windward side resulted in higher frequency broadband contributions that were shown to be independent of the velocity fluctuations in the wake region. Time-averaged velocity profiles in the wake revealed that the leeward side porosity strongly influences the drag coefficient. Linear stability analysis revealed that the SPCCs develop absolute instabilities in the near wake.