| The greenhouse is the equipment for planting by the methods of controlling the surrounding environmental factors, and at the aim of optimum growth conditions and extended production period to improve crop yield and quality. As the largest cultivation country China is, the government focuses on the agriculture problem for ten years from the Central First Document, which emphasizes the "shopping basket program "that means strengthening agricultural material and technical equipment. This program will accelerate the development of greenhouse in agriculture.The greenhouse is a type of unique lower construction that possess perfect performances in security, stability and durability. With the same time the greenhouse also should meet the need of integrity and efficiency. A favorable type of structure can make sure the productivity and energy efficiency of greenhouse. Currently most scholars all over the world focused on the internal environment of the greenhouse, and little research about the safety and reliability of the greenhouse have been done.From the complicated topography in China, the safety of greenhouse is doubted. This situation will limit the development of greenhouse. Wind load has key effect on the greenhouse structure, and the changeful wind is exist everywhere. The greenhouse is located in the atmospheric boundary layer, where has a complex wind field. Therefore, grasp the role of law of wind stress distribution in greenhouse is vital in design.In the first place, this paper introduce the present situation in abroad and at home, and summarized the progress of research in greenhouse structure especially for wind load. Then described the CFD theory and numerical computation method in a concise way. For the research of the impact of different window’s layout for Venlo’s type multi-span greenhouse’s wind-pressure coefficient, this paper use the turbulence model of Realizable k-ε with the help of ANSYS. Then the factors that impact the wind pressure distribution such as open situation (closed, semi-open and full open) and angle of wind direction (0°,45°and90°) were analyzed and summarized for the greenhouse structure design. The results showed that:(1) When the wind reach to the greenhouse, there will attach a series of gas flow phenomena including, separation, reflux and whirlpool. The numerical simulation have a perfect perform in reflect the situation of pressure distribution and the flow field around the greenhouse. The apply of CFD will increasingly widely with the upgrade of computer hardware that simulate the real conditions exactly with low cost.(2) From the research of the wind load characteristics for three types of Venlo type multi-span greenhouse including, roof-long window, roofing crisscross window and full open window. The numerical simulation results show that:the coefficient of wind pressure changes with the layout of top window; the maximum of coefficient of wind pressure and Wind pressure gradient always present to the roof, exterior walls and other upper margin and corner region of the greenhouse.(3) The Venlo type multi-span greenhouse with different windows layout have different characteristics in ventilation. When selecting the layout of roof windows, the wind load shape coefficient should take into account. Therefore, the greenhouse will achieve the optimum in safety and economy. |
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