| Stalk feed utilization is an important way to solve the shortage of animal husbandry feed and promote the comprehensive utilization of stalk resources.A stalk feed harvesting machinery is the key equipment for utilizing and transforming stalk feed.In the working process of the stalk feed harvesting machinery,the stalk scattered on the surface is usually picked up by reducing the clearance of the flail knife from the ground.Still,it is easy to occur the phenomenon of flail knife into the soil,increasing impurity rate,loss rate,and power consumption of stalk feed,which seriously affects the quality of stalk feed and the performance of the machine.Researchers have noticed that the airflow field generated by the high-speed rotation of the flail knife is the key to picking up the surface stalk,but the mechanism of the airflow field adsorption picking the surface stalk is unclear.With the help of relevant theories and research methods,it is of great significance to explore the formation conditions of the airflow field and the mechanism of adsorption picking and to clarify the influence of the characteristics of the adsorption picking flow field on the movement law of stalk,which is of great significance to promote the development of stalk feed harvester.Based on the study of the physical characteristics of maize stalk,the distribution characteristics of the stalk in the field after harvest,and the aerodynamic characteristics of the stalk,this thesis puts forward the method of stalk adsorption picking and the technology of high ground clearance adsorption picking of the flail knife and designs the stalk adsorption picking test bench.Through the combination of theoretical analysis,bench test,wind pressure test,high-speed camera,and numerical simulation of the gas-solid flow field,the motion law of stalk and the distribution characteristics of the gas-solid flow field in the high ground clearance adsorption picking of flail knife were explored.The influence of the adsorption picking device on flow field characteristics was analyzed,and the key parameters of the adsorption picking device were optimized.The influence of the key parameters of the adsorption picking device on the performance of stalk adsorption picking under the characteristics of the gas-solid coupling flow field was further analyzed,and the mechanism of stalk adsorption picking was revealed.The optimized adsorption picking device was used to carry out the stalk adsorption picking bench test,the working parameter combination with high quality and low consumption was selected,and the field test was carried out.The specific research contents and results are as follows:(1)The physical properties of maize stalk were studied,and maize stalk’s size,density,and moisture content were measured.After the maize harvest,the field distribution characteristics of the stalk were analyzed,and the air-dried stalk’s field coverage and stubble height were measured to obtain the distribution the law of stalk scattered in the field.The aerodynamic characteristics of the stalk were studied,and the variation law of stalk suspension velocity with stem length and diameter was obtained.Then,the stalk adsorption picking method was put forward,and the conditions of maize stalk adsorption picking were discussed.The linear velocity of the end of the flail knife should be between40 ～ 70 m / s,and the clearance between the flail knife and the ground should be between60 ～ 150 mm.It provides a basis for the rational design of the adsorption picking device of the stalk feed harvester,the establishment of the discrete element model of maize stalk,and the setting of numerical simulation parameters for the adsorption picking process..(2)Based on the method of straw adsorption and pickup,a high ground clearance adsorption and pickup process with a swing knife was proposed.The mechanical and kinematic models of straw cutting and adsorption and pickup were established,and an adsorption and pickup test rig and testing system were designed.Through the straw adsorption and pickup test conducted on a test bench,the movement rules of different characteristics of straw were analyzed,and combined with the high-speed camera test results,it was concluded that when straw with longer length,larger diameter,and no bracts was fed laterally,it was difficult for the adsorption and pickup device to pick it up.Through the wind pressure testing system,it was found that the air pressure difference between the tip of the blade and the nearest end of the ground was the largest.(3)The CFD numerical calculation model of the adsorption picking device was established.The distribution characteristics of the velocity and pressure fields in the adsorption picking device under different structures and working parameters were analyzed.The results showed that the hammer-claw flail knife could form a more favorable flow field in the adsorption picking device than the Y-type and Y-straight flail knife.The influence of the staggered balanced arrangement of the flail knives on the flow field in the adsorption picking device is more significant than that of the spiral and symmetrical arrangements.The distribution of the adsorption picking flow field formed by the rotation of the flail knives under the staggered balanced arrangement is more uniform,which is conducive to the stable movement of the stalk.The smaller the clearance between the flail knife and the ground,the stronger the adsorption picking ability of the flow field,and the larger the clearance between the flail knife and the ground,the better the throwing ability of the flow field.Based on the above research results,the tool axis mechanism of the adsorption picking device was optimized,and the wind pressure test was carried out.By comparing the numerical simulation and the actual test,the distribution of the adsorption picking flow field was the same,indicating that the CFD numerical simulation results were reliable.(4)Based on the CFD-DEM gas-solid coupling method,the influence of the adsorption picking device on the motion law of stalk particles was analyzed.The motion trajectory of stalk particles,the motion state of stalk particles under different feeding methods,and the motion velocity and energy variation of stalk particles with different lengths were clarified.The motion characteristics of stalk particles under different operating parameters of the adsorption picking device were analyzed.The adsorption picking and throwing ability of stalk particles increased with the increase of the rotation speed of the cutter shaft,but the higher the rotation speed of the cutter shaft,the greater the energy consumption.The adsorption picking ability of stalk particles increased with the decrease of the clearance between the flail knife and the ground,and the throwing ability of stalk particles increased with the increase of the clearance between the flail knife and the ground.The change in the forward speed of the adsorption picking device has no significant effect on the adsorption picking and throwing ability of stalk particles.Based on the above research results,the mechanism of stalk adsorption picking was revealed.(5)The optimized adsorption picking device was used for the bench test.The three-factor and five-level quadratic regression orthogonal combination test design method was used to establish a regression model with the knife shaft speed,the forward speed of the machine and the clearance of the flail knife from the ground as the test factors,and the stalk harvest loss rate,the stalk cutting length qualification rate and the specific power consumption as the response index.The influence of various factors and their interactions on the performance of the adsorption picking device was analyzed,and the significant influence parameters were determined.To find the high quality and low consumption operation parameters of the adsorption picking device,the multi-objective optimization method was used to screen out the combination of high quality and low consumption operation parameters: the rotation speed of the cutter shaft was 2150 r/min,the forward speed was 3 km/h,and the clearance between the flail knife and the ground was 100 mm.On this basis,the field test of the stalk feed harvester was carried out.The results showed that the stalk harvest loss rate was 5.22%,the qualified rate of stalk cutting length was92.54%,the impurity rate of the stalk was 2.34%,and the height of stalk cutting was 131.7mm.All indexes met the requirements of national standards for the operation performance of stalk recycling machines,indicating that the high ground clearance adsorption picking technology of yellow-storage maize stalk could meet the requirements of stalk feed harvesting.This study provides ideas and methods for studying the adsorption picking performance of crop stalk harvesting machinery,which is of great significance in promoting the development of stalk recycling machinery and the comprehensive utilization of stalk resources. |
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