| Greenhouse has developed as most important agricultural production facility in modern horticultural facilities. Currently, there is blindness in application and production of modern greenhouse in our country, the research of key techniques, general design scheme and solution were still undeveloped. These problems seriously affected the benefit of protected horticulture. For the development of greenhouse in our country, the greenhouse system should be optimized to adapt to local climate based on former research.Mechanical Ventilation Multi-span Plastic Greenhouse was studied in this project. CFD method was used to 3D CFD model construction of greenhouse on the fundament of experiments. The distribution of temperature field and flow field on different external situation (include different combination of weather, fans and sunshade curtain service conditions) has been simulated by CFD model. Simulation and experiment results were further compared.Comparison result indicated that the internal greenhouse environment simulation through CFD method was reasonable. Furthermore, the validation of former established CDF model was testified. This model can reflect the distribution of greenhouse internal temperature and flow field correctly. In addition, the temperature and flow field problems of this testing greenhouse were found. The main problems were that the second span greenhouse inside temperature was relatively high, flow dispersed sparsely and velocity was very slow; the first and third flow velocity in direction of inlet was too high. It produced different size eddy current may damage vegetation caudexes; the flow field disperse extremely sparse even none in the four corners of greenhouseFor solve these problems, four optimization schemes were proposed (mainly by adjust the span, length of greenhouse and door open degree), the flow field of every scheme has been simulated by CFD method, the distribution of flow field was predicted. The conclusions were drawn as follow:1. The summer temperature in Wuhan was usually high. The temperature and flow field in mechanical ventilation multi-span greenhouse cannot be effectively changed only by sole ventilation method. It may produce some problems like the temperature of part areas were too high, air flow velocity was too slow and air flow dispersed sparsely in the corner.2. In sunshine high temperature status, the fans and inside sunshade curtain combination ventilated method can effectively improve the internal environment. This kind of method was able to accelerate the air exchange and take the high temperature air away. Therefore, the indoor temperature and flow field well distributed. Meanwhile, it avoids the phenomenon of large upper and lower temperature gradient in greenhouse and low air velocity in the corner.3. Compare mechanical ventilated method and natural ventilated method When lower outdoor temperature and high air velocity on cloudy. Mechanical method was a little better inn internal air velocity. However, there was no obvious improvement in cooling effect. Hence, cooling by fan should be reduced on cloudy to avoid energy waste.4. The 3D CFD model was established in this project. The mechanical ventilated plastic greenhouse inside temperature and flow field distribution has been predicted by model simulation and calculation. The simulation and testing comparing result indicated that the CFD simulation result of mechanical ventilated greenhouse by standard k-εturbulent model coincide with testing result. It demonstrated the validation of CFD simulation in mechanical ventilated greenhouse5. Four greenhouse structure optimization schemes were proposed to solve the current temperature and flow field distribution problems in this study. The inside temperature and flow field distribution of every scheme has been simulated by CFD. Simulation result shows that the third scheme (every span width was 8m, length was 24m, door open degree was 2m×2.3m) was the best structure. |
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