Wind tunnel modelling of porous elements

Porous elements are commonly used as accessory devices in many technological sectors of civil engineering. In some cases it is necessary to test their behaviour with respect to the air flow, through appropriate wind tunnel experiments. The scale modelling of porous structures is very complex because their small openings are difficult to be represented at the common scales of the wind tunnels. In this work, the reference porous elements were perforated plates with various levels of porosity, as well as different geometries and thicknesses of the holes. Using a particular wind tunnel experimental set-up, it was possible to remark that the loss coefficient and the drag coefficient were almost coincident and interchangeable to characterize the aerodynamic behaviour of these porous media. In addition, the analysis of the wind tunnel data allowed to propose a scaling criterion for porous elements, represented by perforated plates. The criterion found can be used for the porous core of the element, adopting the simple geometric scaling similitude for the overall structure. The correct scaling from the model to the prototype can be achieved by maintaining the same porosity level, obtained with any shape and arrangement of the holes, the same thickness to hydraulic diameter ratio and ensuring that the Reynolds number effects are not present.