On the Wind Reduction Effect of Windbreak Nets in Front of the Simple Greenhouse for Planting Fruits and Vegetables
Keywords:windbreak net, porosity, tilt angle, wind tunnel test
The island of Taiwan experiences frequent strong winds coming with typhoons in the summer and with northeast monsoons in the winter. The strong winds are hazardous to the structure of a simple greenhouse that is widely used for vegetable and fruit plantation. The damage may reduce agricultural yields. Windbreak netting is a practical procedure for protecting a greenhouse from strong winds. The purpose of this study is to carry on the wind tunnel simulation test of windbreak nets in front of the simple greenhouse. Windbreak nets of densities 50%, 40%, 30% and 20% had a uniform dimension of 10 cm (per unit 1 h) in height and 29.2 cm in width. A windbreak net was tested at tilt angles of 0o, 5o, 10o and 15o. The wind tunnel simulation test is carried on at 10 m/s of reference wind velocity. The wind velocities at different horizontal distances and vertical distances front and behind the windbreak net are measured. The relative wind velocity is calculated. The wind reduction effect at different horizontal distances behind the windbreak net is analyzed and discussed. From the test results, it is known that when the tilt angle of windbreak net is 0o and the height of windbreak net is 1h, the corresponding wind reduction effect of windbreak nets with 20%, 30%, 40% and 50% porosity is 62%, 61%, 59% and 52% respectively at 2h horizontal distance. The corresponding wind reduction effect of windbreak nets with 20%, 30%, 40% and 50% porosity is 46%, 45%, 40% and 32% respectively at 10h horizontal distance. However, the increase of tilt angle of windbreak net does not have much influence on the wind reduction effect.
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