| Frost is a typical agro meteorological disaster,which brings great harm to the growth of tea and other horticultural crops.As a kind of mechanical frost protection equipment,the frost protection wind machine has better effect of frost protection,large coverage area,time-saving and labor-saving than other technical measures,and it is also convenient for automatic control,so it has been applied in a certain scale in China.Compared with some large-scale frost protection wind machines in the United States and other countries and small-scale frost protection fans in Japan,a kind of frost protection wind machine with frost area between them is needed in hilly areas and other places in China.However,at present,there are some problems in domestic frost protection wind machines,such as small frost area and high cost.In this study,the aim is to optimize the design of a kind of frost protection wind machine with circular-arc blade which has stronger air supply capacity and better effect of frost protection.Based on the analysis of the meteorological characteristics of frost protection using wind machine,the design of wind machine's system is carried out and the feasibility of 360° rotary frost protection wind machine is verified.Then the parameters of circular-arc blade type of wind machine are optimized.Finally,the influence of installation parameters on frost protection wind machines is explored to further increase the cover of frost protection.The main research contents and results are as follows:(1)Experimental study on frost meteorological characteristics of tea gardenFrost is often accompanied by radiation inversion.Under the typical frost conditions,the temperature changes in the height range of 11 m near the ground of the tea garden were tested and analyzed.The results show that: 17:00 ~ 8:00 of the next day is the period of inversion,and the temperature gradually increases with the increase of height.21:00 ~ 6:00 of the next day is the most significant inversion,and the inversion intensity is relatively stable.The temperature at 11 m is 4.09 ? higher than that at 1 m.There is a significant quadratic polynomial relationship between the intensity and height of the inversion.Therefore,8~10 m is selected as the installation height of the frost protection wind machine.The frost data in tea garden was analyzed.The results show that with the increase of frost grade,the temperature,wind speed and soil heat flux decrease,the humidity slightly increases,and the time when the temperature drops to 4? obviously advances.(2)Design and feasibility study of 360° rotating frost protection wind machineOn the basis of the overall design of the frost protection wind machine,based on the similar design theory of the wind machine,it is determined that the rotating speed of the required circular-arc blade is 960 rpm and the rotating diameter is 1160 mm.The difference between the calculation of similar design and the CFD numerical simulation is 0.87% and 2.98% respectively.A gear mechanism capable of 360° rotation is designed to increase the cover of prost protection,and the feasibility of 360° rotation frost is studied.The results show that the duration of wind speed at each measuring point increases with the increase of the maximum wind speed,and the wind speed presents the trend of rising,fluctuating,and decaying.10~40 m is the effective area of air flow disturbance.The temperature rise at 10 m and 20 m is large however the temperature rising is relatively small at 30 m and 40 m.There is a phenomenon of "low temperature and high temperature on top" in the canopy temperature of tea trees at night.The air flow disturbed by wind machine aggravates the temperature difference between the top and the bottom of the tea canopy.0~8 m is the blind area of frost protection.8~25 m has better effect of frost protection and 25~40 m has general effect of frost protection.Therefore,the validity and reliability of 360° rotating frost protection wind machine are verified.(3)Optimization of circular-arc blade parameters of frost protection wind machineOn the basis of the structure model of the circular-arc blade,the installation angle,swept angle and circular radius of section of the circular arc blade are selected as the factors and the air volume,wind pressure and power of the fan are taken as the evaluation indexes.The orthogonal test and CFD numerical simulation are used to calculate and analyze.It is found that the installation angle is the most significant factor affecting each index,followed by the circular radius of section,while swept angle has little influence on each index.Under the condition that the power is less than 5.5 kW,the optimal structural parameters of the blade are obtained: the installation angle is 25°,the swept angle is 87°,and the circular radius of section is 1200 mm.After optimization,the air volume and air pressure increase by 3.72% and 8.07% respectively.(4)Influence of installation parameters of frost protection areaThe air flow model of frost protection wind machine is established.The pre-processing,grid division and setting calculation are completed through the Workbench platform under ANSYS.The data processing is carried out through Tecplot to simulate the air flow disturbance range under different working conditions.The results show that the frost protection area can be increased by moderately reducing the installation height and the installation pitch angle.However,with the decrease of the installation angle,the area of the blind area increases;with the decrease of the installation height,the value of the right end of the frost protection range does not change much.After optimization and design of the circular-arc blade,the frost protective area is greatly improved.Finally,a scheme to make up the blind area of frost protection is proposed.The coverage of the blind area of the main frost protection wind machine can reach 100% through the reasonable selection and arrangement of the auxiliary frost protection wind machine. |
PDF Full Text Request