| Rapeseed and wheat are the main grain and oil crops for winter sowing in the middle and lower reaches of the Yangtze River in China.Their mechanical sowing processes are similar,and their sowing seasons are adjacent.The development of centralized metering device for rapeseed and wheat has significant implications for reducing mechanization costs and improving sowing machine utilization.Based on the analysis of the current research status of domestic and foreign air-assisted centralized pneumatic planter and the existing problems of existing air-assisted centralized metering device,this paper designs a air-assisted centralized metering device for rapeseed and wheat based on a slotted seed supply device.The sowing volume adjustment device composed of a vertical groove wheel and a variable volume regulator is used to achieve the compatibility of rapeseed and wheat seeds.The structural design and parameter analysis of the key components of the centralized metering device are carried out,and the parameters of the centralized metering device are optimized and improved through discrete element method(DEM)simulation and computational fluid dynamics(DEM-CFD)gas-solid coupling simulation experiments.The performance of the seed drill is verified through bench tests and field experiments.The main research contents and conclusions are as follows:(1)Two overall design schemes for air-assisted centralized metering device for rapeseed and wheat are proposed,and pneumatic seed supply systems based on a spiraltype and a slotted-type seed supply device are designed respectively.Feasibility comparative analysis of the two schemes is completed,and the overall structural scheme based on the slotted-type seed supply device is determined.The structural parameters and working performance parameters of the air-assisted centralized metering device,such as Venturi tube,booster tube,and distributor,are clarified.(2)The structural design and parameter analysis of the slotted-type seed supply device are carried out,and the relationship between the seed and the seed supply device during the seed supply process is analyzed,including:(1)A slotted-type seed supply device that can achieve variable volume sowing volume adjustment is designed.The stirring process is reduced during the seed supply process,and the flowability of the population is enhanced by the movement of the vertical groove wheel blades.The main structural parameters of the vertical groove wheel and the variable volume regulator are determined through theoretical calculations.The analysis shows that the outer radius of the variable volume regulator is 62 mm,the cylindrical sleeve radius of the vertical groove wheel is 32 mm,the range of the extension of the vertical groove wheel blades relative to the variable volume regulator is 0-21 mm,the number of vertical groove wheel blades is 9,and the actual height of the blades is30 mm.(2)The dynamics models of the filling,carrying,and seeding stages are constructed separately for the different stages of the seed supply process,and the working principle of the clearing stage is analyzed.The calculation and analysis show that the included angle between the main axis of the vertical groove wheel blade and the horizontal direction is 45°,and the acceleration of the seed at the moment of entering the seeding stage will undergo a sudden change.(3)DEM discrete element simulation experiments and DEM-CFD gas-solid coupling simulation experiments were conducted on the seed supply device and Venturi tube of the air-assisted centralized metering device for rapeseed and wheat,respectively.The population disturbance ability of the seed supply device was clarified and the structural parameters of the Venturi tube were optimized.Specifically:(1)The population disturbance ability of the rapeseed and the impact of the deep groove structure of the variable volume regulator on the seeding rate of rapeseed were analyzed based on DEM discrete element simulation.The simulation results showed that the grooved seed supply device can create a highly dynamic disturbance area through forced driving,and under the condition of no agitator installation,the flowability of wheat and rapeseed seeds was good.The seeding rate of rapeseed seeds was related to the depth of the deep groove on the variable volume regulator,and the depth of the deep groove was determined to be 4mm in combination with the seeding amount requirement per unit area of rapeseed seeds.(2)The single-factor simulation experiment was conducted based on Ansys Fluent to investigate the influence of the length of the mixing section,the length of the acceleration section,and the angle coefficient on the airflow field.The experimental results showed that the different lengths of the mixing section,the acceleration section,and the angle coefficient had little effect on the airflow velocity and pressure at the outlet.A mixing section length of 35 mm and an acceleration section length of 40 mm were found to be more conducive to the acceleration of seeds from the acceleration section to the extension section,and a coefficient of 1.5 was determined to be the optimal value.By comparing the airflow velocity and pressure data of six groups of height combinations under the optimal coefficient,it was found that the acceleration effect of the Venturi tube on the airflow was more significant in the range of mixing section length of 20-30 mm,and the acceleration effect weakened when the mixing section length exceeded 30 mm.(3)DEM-CFD coupling simulation experiments were conducted to further explore the impact of height combinations on the distribution of airflow fields and the trajectory of seed transport.The experiments found that the three height combinations had a small difference in the average speed of rapeseed populations,but a large difference in the average speed of wheat populations.When the mixing section length was 20 mm,the acceleration effect of wheat seeds was the most obvious,but the collision phenomenon was more severe than that of other groups.When the mixing section length was 24 mm,the acceleration effect of rapeseed seeds was the most obvious.Taking all factors into consideration,a mixing section length of 24 mm and an acceleration section length of16 mm were determined to be the optimal height combination.(4)Performance tests were conducted separately for slot-type seeding device and the air-assisted centralized metering device for rapeseed and wheat,including:(1)For the slot-type seeding device,a two-factor experiment was conducted to investigate the effects of the extension amount of the vertical slot wheel blades relative to the variable volume regulator(blade relative height)and seeding speed on seeding stability.The results showed that seeding speed and blade relative height had no significant effect on the total coefficient of variation(TCV)of seeding device discharge stability,with TCV all below 1%,and seed damage rate below 0.15% for both rapeseedand wheat.(2)To determine the optimal combination of airflow pressure and seeding speed for the centralized metering device,a two-factor experiment was conducted.Bench test results showed that for canola seeding,with a seeding speed of 5-15 r/min and an airflow pressure range of 800-1600 Pa,the coefficient of variation of discharge consistency(RCV)for each row was below 4%,and TCV was below 1%.For wheat seeding,with a seeding speed of 10-25 r/min and an airflow pressure range of 1200-1600 Pa,RCV was below 3% and TCV was below 1%,with seed damage rate below 0.15% for both crops.(3)Field seeding tests were conducted with the centralized metering device,and the average plant spacing was 56.96 mm for canola and 23.34 mm for wheat,with coefficient of variation of plant distribution at 16.92% and 18.02% respectively,meeting the requirements of agronomic planting. |
PDF Full Text Request