Porous trailing edges attenuate hydrodynamic pressure fluctuations that scatter as trailing-edge noise, with their effectiveness governed by their material parameters. Conventional measurements of permeability rely on steady-flow rigs, which cannot capture the dynamic response of this parameter, which is relevant for predicting balancing pressure fluctuations under grazing-flow conditions. In this study, we introduce a method for directly determining the dynamic permeability of porous trailing edges from time-resolved particle image velocimetry (PIV) data. The approach employs a lumped-system circuit analogy that links unsteady pressure gradients to through-material velocities, enabling in situ characterisation without specialised porous rigs, thereby further extending its applicability to thin trailing-edge geometries. Two materials with similar porosity but distinct internal architectures are compared against a solid baseline: a structured porous trailing edge (SPTE) and a random foam trailing edge (RFTE). The extracted permeability curves show close agreement with the analytical model of Johnson et al. (J. Fluid Mech., 1987, vol. 176, pp. 379–402), validating the method for both structured and randomised porous materials. The procedure also allows for the estimation of the equivalent viscous characteristic length and tortuosity. A detailed comparison reveals that the SPTE exhibits a lower viscous length scale and tortuosity than the RFTE, with a relatively higher dynamic permeability response at high frequencies.

Vortex shedding in the wake of a cylinder in uniform flow can be suppressed via the application of a porous coating; however, the suppression mechanism is not fully understood. The internal flow field of a porous coated cylinder (PCC) can provide a deeper understanding of how the flow within the porous medium affects the wake development. A structured PCC (SPCC) was three-dimensionally printed using a transparent material and tested in water tunnel facilities using flow visualisation and tomographic particle image velocimetry at outer-diameter Reynolds numbers of and, respectively. The internal and near-wall flow fields are analysed at the windward and mid-circumference regions. Flow stagnation is observed in the porous layer on the windward side and its boundary is shown to fluctuate with time in the outermost porous layer. This stagnation region generates a quasi-aerodynamic body that influences boundary layer development on the SPCC inner diameter, that separates into a shear layer within the porous medium. For the first time via experiment, spectral content within the separated shear layer reveals vortex shedding processes emanating through single pores at the outer diameter, providing strong evidence that SPCC vortex shedding originates from the inner diameter. Velocity fluctuations linked to this vortex shedding propagate through the porous layers into the external flow field at a velocity less than that of the free stream. The Strouhal number linked to this velocity accurately predicts the SPCC vortex shedding frequency.