Screens can exclude insects from greenhouses and reduce the need for pesticides. They can also be used to create a barrier against the outside environment, to facilitate biological control within the greenhouse. However the screens have a majordrawback in that they reduce the rate of ventilation because of their resistance to airflow. As air flows through the screen a static pressure drop occurs across it. This pressure loss is usually specified in the literature by a pressure-loss coefficient, K, which is a junction of the porosity of the screen and of the Reynolds number Numerical simulations show that the pressure loss coefficient of a woven screen may also be dependent on the texture of the weave when the spacing between two adjacent threads of the screen is small in comparison with the thread diameter. The simulations show that the velocity field immediately downstream from the screen is strongly dependent on the weave texture. Under certain conditions, a backflow could develop immediatelydownstream from the screen, which might hinder insect penetration.
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