Estimation of the aerodynamic tortuosity of woven/wire screens

Abstract

The use of wire/woven screens (WSs) is frequent in applications such as particle or insect-proof screen in home/greenhouse/farm with natural ventilation. Although this passive element has been studied for decades, most previous works have focused on relating the airflow performance only to porosity. However, most recent investigations have demonstrated that other pore-related parameters such as constriction factor and tortuosity are necessary for the characterisation of screens. Tortuosity of WSs is a parameter that has been broadly estimated in the literature, whose calculations to date are not physics-based and yield a constant value without dependence on airflow velocity. The present investigation proposes a novel method to calculate tortuosity of WS. The new approach uses the flow potential flow theory to estimate realistic curvatures of the streamlines around the inclined threads of the WS. The calculated tortuosity has been made also velocity-dependent, because its value changes for Reynolds numbers below 200, generally. The accurate estimation of tortuosity is a very important contribution to the field, because it is a missing link to develop a universal model to estimate pressure drop for any WS performance. This calculation has been added to AeroScreen software, which allows to obtain porosity, constriction and tortuosity from geometry data.