| With the development of wind turbine technology, the application of fan in the field of tea garden has become more and more popular. Compared to the traditional smoking, cover, irrigation and other anti-frost methods, frost protection with fan has the advantage of mechanization and automation, high efficiency and good effect etc. However, researches on the frost protection with fan are almost based on experiment at home and abroad. Experimental research can be used to study effect of frost protection with fan from the macroscopic aspect, there is no essential to deeply study the fan anti-frost. So, with the help of the new research method, the study of the characteristics of the flow field and the temperature variations under the action of fan is of great significance. The main research content and innovation of this paper as follows:1. The working principle, application and development of anti-frost fan were introduced. Especially, the research status and the corresponding research trend of the airflow disturbance characteristics with the action of fan was forecasted. The tea garden in late spring coldness meteorological phenomenon and causes of forming inversion layer was also analyzed. The temperature variation distribution characteristic of inversion layer and numerical integration which will be used to the next numerical calculation and analysis was studied. Research on the effect of the forming factors of inversion layer in the numerical calculation. The starting time of the anti-frost fan and the distribution characteristics of temperature inversion in vertical space were studied in detail.2. Anti-frost fan types and anti-frost area were studied, combined with the research purpose to select fan type of circular plate blade to structure design. The design methods of different blade types were compared to the calculate radius and shape of the blade. And through the calculation of the design point coordinates to curve fitting by MATLAB.3. Acalculation model of fan was built,The mesh division, boundary condition setting, control equation, turbulence model and grid independence were studied and analyzed. The performance of fan was studied by numerical calculation method. It was found that the flow rate of the three fans was basically the same at the same speed, but the 3-blade fan has the highest efficiency and the stability was better.4. A fan anti-frost physical model was built, SST k–ω turbulence model suitable for the fully developed turbulent flow was selected. The research on characteristics of airflow and temperature variation on tea canopy was conducted. Found the speed of air flow in the canopy of the tea was proportional to the speed, however, the relationship between temperature variation and rotational speed was more complex. The average temperature of the whole canopy increased with the increase of rotational speed.5. The relationship between the characteristics of flow field and rotational speed was studied, It was found that the speed of fan was increased to a certain critical value,An approximate triangle spiral flow will be formed, the single side width of the spiral flow was about 1.5 m, and its radius was about 3~5 meters. But the center of vortex was on the left of fan. The angle between the connecting line of the center of the vortex center and the center of the wind turbine was about 15.83°,but the variation of the distance was not obvious with the increase of the speed. After calculation, the model of the fan angle is 50.9 degrees, the spiral flow effect area of the tree canopy reaches maximum.6. The temperature variation in space was studied. The relationship between temperature variation and the spiral flow was analyzed. The temperature on the spiral flow space was relatively uniform, Compared with the initial temperature was greatly improved, and the average temperature increases with the increase of rotational speed. |
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