Optimal Design And Ventilative Test Of Mutual Insert Multi-span Greenhouse

Commercial greenhouses widespread rate is very low in China. Some high-grade and secondary commercial greenhouses are used by some department groups, army, farm and scientific research departments. Simple tunnels are often adopted by peasantry and their occupancy is over 60 percent of greenhouse gross in our country. This kind of tunnels' ventilation are bad due to using plastic film as slipcover and can but open cultivation in summer and its periodical using efficiency is reduced. So scientific and technical researcher need to do some deeper optimizing about tunnel's structure. With the implements of industrialization and super efficient agricultural model project, multi-greenhouse has been developed rapidly and used extensively. But the multi-greenhouse's one-off investment, building and operating costs is so huge that farms and common corporations can not afford. It is wonderful to design a new kind of greenhouse which possesses tunnel's low building costs and multi-greenhouse's high efficiency, which holds many merits such as low building cost, well ventilation and used broadly in windy coastal regions. This new kind of greenhouse can serve better for agriculture and farms and bring notable social benefit and huge economic efficiency.The mutual inserted multi-greenhouse belongs to East -China type simple multi-span plastic greenhouses and belongs to a kind of economical and applied greenhouse. Using arch pipes instead of stand-up pillars is the character of mutual inserted multi-greenhouse. The weight of steels and building costs of mutual insert multi-span greenhouse are under of the same structure parameter pillar type multi-span greenhouse. But if popularizing the new greenhouse needs farther optimal design on its structure and thoroughly simulation and test research about its windproof character and ventilation effect.The paper takes mutual inserted multi-greenhouse as research object, optimizing its structure from segment to integer, investigating its windproof character through wind tunnel test, simulating its flow field using FLUENT and doing PIV test. The primary contents and conclusions are as follows.①Investigating major components such as cullis and steel pipe of mutual inserted multi-greenhouse bases on the test and optimized its whole structure by finite element method. The object of optimal design is, on the one hand for enhancing the windproof and snowproof capability of mutual inserted multi-greenhouse, on the other hand for reducing the building costs. The test result indicates that the groove cullis's capacity of resisting bent was better than the same parameter non-groove cullis under the same loads. The bigger of inserting anger the steadier of pole under the same loads but the conclusion was contrary on the same pull power. For improving the capability of resisting pull and press of greenhouse, we may install syphon on the bottom of steel pipe in windy region. Synthesizing the capacity of resisting pull and press of greenhouse, the syphon should be set 100mm on the bottom of the pipe. The paper analyzed the stability of vault when bringing even static water preload load to bear on vault. The result of optimal design using ANSYS indicates the weight of steels and building costs of mutual insert multi-span greenhouse are under of the same structure parameter pillar type multi-span greenhouse.②For ascertaining the place of ventilators in the mutual inserted multi-greenhouse, the author simulates the airflow around the greenhouse using ANSYS CFD bases on a single greenhouse. The result of simulation shows aeration effect is better using roof ventilators and side ventilators when the greenhouse ventilate by natural wind load. Article simulates the natural aeration effect of mutual inserted multi-greenhouse bases on the analysis method of a single greenhouse. The research indicates that ventilation effect of roof and side ventilators is better than shoulder and side ventilators when wind direction is perpendicular to the side ventilators. In fact, people usually make use of shoulder and side ventilators from the view of structure design and convenient operation in building a greenhouse. ANSYS can be used to optimize the greenhouse structure and research the flow field and temperature distribution and offer foundation for building a greenhouse reasonably. Comprehend ventilation effect of all kinds of ventilation method, and provide theory foundation for building greenhouse. ANSYS simulation will reduce the process of multiform comparative design and indoor environmental control test design. As far as multi-project design of greenhouse structure and inner environmental control design of a greenhouse concerned, Its design time and process can be shorten distinctly using simulation of ANSYS.③The advanced flow field display technique-PIV is applied to research the indoor and outdoor flow field of mutual inserted multi-greenhouse bases on research of the common flow field visualization technique. The result of test shows there is most wind speed on roof and the smallest wind speed on cullis of mutual inserted multi-greenhouse in time-averaged flow when the greenhouse ventilates using shoulder and side ventilators. The wind speed of inner air flow field is small and the smallest wind speed on roof in mutual inserted multi-greenhouse. So the ventilation effect is not good and the heat congregates at housetop in the greenhouse. The instantaneous process of vortex is analyzed and the movement of circumfluence vortex is obtained in instantaneous flow field. The drag coefficient C_D, is 0.565 according to the vortex distribution of outer greenhouse. According to the vortex movement pictures of inner mutual inserted multi-greenhouse, we can find that the change of vortex in arch 1 is slower than in arch 2 and 3. So air ventilation effect is bad in arch 1. Fans can be emplaced in arch 1, it can increase air circulation and the cost is cheap. In steady flow, the ventilation effect of shoulder and side ventilators is worse than roof and side ventilators through comparing these two ways of ventilation, but the greenhouse which applied roof and side ventilators need bear more wind load than the greenhouse which applied shoulder and side ventilators. In fact, people usually make use of shoulder and side ventilators from the view of structure design and convenient operation in building a mutual inserted multi-greenhouse.④The distribution of wind pressure of a mutual inserted multi-greenhouse is researched comprehensively on the different wind angles and canopy or non-canopy on the basis of wind tunnel test. The result of test shows the trend of wind pressure distribution is general homology under different Re when Re is over3~106, so the impact of Re to wind pressure distribution is not notable. The wind pressure of roof is negative pressure mainly on the mutual inserted multi-greenhouse and the biggest negative pressure appears on vault. The main action is lift when wind load acts on a mutual inserted multi-greenhouse. Wind pressure coefficient of open ventilators is distinctly bigger than the coefficient of closed ventilators and the changing scope of wind pressure coefficient is wide. As a result, the wind pressure coefficient of closed ventilators should be chosen when computing the wind pressure of greenhouse surface. The wind pressure of roof is negative pressure mainly on a mutual inserted multi-greenhouse when the ventilators were opened and wind angle changed from 15°to 90°(△(?)＝15°) and the drastic changing region appears windward side. The greenhouse structure should be strengthened or ameliorated aiming at the wind pressure which bringing by the most disadvantageous wind angles. The intensity and direction of airstream is changed when the airstream flows through the greenhouse roof. Wind pressure distribution of greenhouse which has canopy is more complicated than non canopy .The positive and negative wind pressure appears alternately when roof of greenhouse is overlaid by canopy. For assuring the safety of greenhouse design, we should choose the bigger wind pressure shape coefficient of two states when the wind pressure is computed. The wind pressure shape coefficient of arch which computes by wind tunnel test is more precise than the wind pressure shape coefficient which provides by criterion. We should combine the wind pressure shape coefficient of the two states of canopy and non-canopy when computing the mutual inserted multi-greenhouse's wind pressure, namely, we should select the bigger one as the warrant of greenhouse structural design.⑤Mathematical model and boundary condition about airflow around a mutual insert multi-greenhouse is established which based on CFD theory. Wind pressure distribution is simulated and analyzed using FLUENT software. The simulant result indicates that the wind force has a primary effect on the greenhouse's upward force. The numerical simulation result of wind pressure distribution along the greenhouse span is consistent with the wind tunnel test result. The wind pressure coefficient of windward and leeward is quadric distribution along the greenhouse's height, and correlative coefficient is 0.975 and 0.990 respectively. The simulative wind pressure coefficient was transformed to wind load shape coefficient, the coefficient provides reference for optimizing the structure of greenhouse.