From vortex shedding to Vortex-Induced Vibrations: The role of porous façades

• Porous façades alter the vortex shedding of rectangular cylinders, introducing additional separation points and shifting the dominant Strouhal number. • Homogenized CFD models based on the Darcy-Forchheimer approach accurately reproduce the aerodynamic effects of porosity on rigid configurations. • The ability of porous coverings to suppress VIV in 3D structures is strongly state-dependent, as initial motion promotes spatial force correlation. • At a given Scruton number, porosity raises the threshold for instability: oscillations are inhibited under quiescent conditions but can fully develop when the system is externally perturbed. This work examines the aerodynamic and aeroelastic effects of a porous envelope applied to a rectangular prism with aspect ratio B / D = 3.33 , representative of a high-rise building. Wind tunnel tests on rigid and aeroelastic models were combined with Large-Eddy Simulations (LES) using a Darcy-Forchheimer homogenized representation of porosity. On the rigid model, the porous shroud alters vortex shedding by introducing new separation points, widening the wake, and shifting the dominant Strouhal number to lower values. The numerical model reproduces these effects with good accuracy, confirming the suitability of the homogenized approach for capturing porosity-induced modifications. Aeroelastic tests reveal that the porous façade can suppress VIV initiation by disrupting force coherence during the first oscillation cycles, while external perturbations restore synchronization and lead to full VIV development. The results demonstrate that the mitigation effect of porosity is conditional and state-dependent, providing new insight into its potential as a VIV control strategy for civil structures.