Numerical Simulation Study On The Wind Load Of The Single-span Plastic Greenhouses In East China

In recent years, especially in2007and2008, a large number of the greenhouses collapse under the impact of the typhoon in East China. Compared with the multi-span plastic greenhouses, many more single-greenhouses were used and more of them collapsed after the typhoon. In wind load research of the structure, the method of wind tunnel model test is mainly used. But the wind tunnel model test is confronted with many difficulties. For example, the test must use the scale model which is costly and time-consuming, and as a result of no contrast of multiple schemes, the results obtained may not necessarily be the optimal structural wind resistance performance. Computational fluid dynamics (CFD) is accomplished by computer numerical calculating and displaying images, and systematically analyzing such related physical phenomena as fluid flow and heat transfer. Using CFD method for numerical simulation of wind field and wind load can avoid those disadvantages, which has the advantages of being low-cost, fast and flexible and is convenient for comparing and optimizing multiple schemes and conditions before design. But using CFD to simulate stress situation in some problems also shows its limitations. Because many structures have blunt body shape, the flows around them are inevitably accompanied by such complicated flow phenomena as separation and vortex shedding, which is a very complicated problem with on mature technical solution so far. And it also relates to the reasonable selection of simulation factors such as the size of the objects, the surrounding environment, and atmospheric boundary layer. Sometimes it is also subject to double limitations of theory conditions and software and hardware conditions. So we must pay more attention and time to the further development of this research method.In this paper, with CFD and Standard k-ε model, I’ll use CFD software Fluent to form full size plastic greenhouse and make simulation analysis under different conditions. On the basis of existing study of the plastic greenhouse structure, I’ll make further study and improvement on some less-involved but common content. The research is mainly on the wind pressure under multiple schemes of plastic single building greenhouse monomer and group on southeast coastal region in the East China. I’ll put forward the appropriate CFD turbulence model and simulation conditions, and make evaluation on the simulation results and the existing standards, and finally put forward recommendation on the relevant body shape coefficient of which the existing specification hasn’t mentioned. Besides, on determining the greenhouse load of different arch form, this part of contents are incomplete in the existing greenhouse standard, and with great uncertainty, it’s not easy to handle in the design of applications. I plan to ascertain the law and the specific value, and make discussion on the wind pressure distribution of the surface.As research shows, in the fully closed condition, the surface wind pressure distribution characteristic value of single greenhouse monomer has certain relevance with specification, especially in the edge portion which has very good reference; In intensive greenhouse group, its adjacent greenhouse effects are larger. On the edge of greenhouse, wind load value can be appropriately reduced, thus to provide reference for reducing the weight of steel, cutting cost, promoting the popularization of greenhouse design. Under the condition of a45°angle wind, the circumfluence of wind will result in positive pressure on leeward side of adjacent greenhouse.Numerical simulation results show that the CFD method can qualitatively and quantitatively predict surface pressure distribution of the greenhouse, which can provide basis for the selection of a certain value in the standard range of wind pressure. The CFD method can reduce test cost, shorten research cycle and overcome various limitations in wind tunnel test. Although CFD method can’t completely replace the wind tunnel test, but as an auxiliary method, it can be widely used in test plan determination, the study of flow law, the preliminary design of structure and other series of work. The studies of this paper provide basis for further study of arched greenhouse concerning more complex conditions, analysis of multiple angle and design optimization.