Numerical modelling of three-dimensional screens, treated as porous media

Porous structures have a very wide spectrum of application fields. Among them, building engineering and architecture have recently shown the trend of adopting what are called permeable double screen façades as cladding. These are made up of two façades (or skins): the inner one is usually a sealed continuous glazed facade while the outer one is characterized by a porous metallic screen. When it comes to the assessment of the wind loading on such cladding, the aerodynamic behaviour of the outer skin plays a crucial role. This is one of the reasons why the wind's interaction with these porous panels is currently an open research field. The complex 3D shapes the porous skin may have and the intrinsic multi-scale nature of the wind's interaction lead to the need for a general reduced-order model that fully represents the aerodynamic behaviour of the permeable structures. This paper addresses the implementation of a tensorial numerical model that describes the aerodynamics of 3D porous screens, with no geometrical modelling of the porous layer in the computational domain. The proposed reduced-order model is able to address the substantial three-dimensionality and anisotropy of the modern porous structures by full-tensor implementation of the classical Darcy-Forchheimer porosity model. The tensorial formulation of the model together with easy numerical implementation and limited computational onerousness are the strengths of the model proposed here. It is presented together with a validation of the same in the form of a fully resolved CFD solution in which the porous screen is explicitly reproduced. The results reflect the new model's capability to catch the global effects due to the porous structures, in terms of both pressure and velocity fields.