Research And Development On Air Blowing Header Of Plot Combine Harvester For Grain

Plot experiment is the necessary procedure of field breeding,and plot harvest is the important procedure to obtain the correct results in field breeding experiment.In order to solve residual seeds and difficulties in cleaning machine for plot combine harvester of grain seeds,an air blowing header that was suitable for plot combine harvester was designed and developed in this study.Firstly,according to the principle of mechanics,air blowing system for header was designed.A blowing cereal model with uniform air velocity was established and relationship formula between the deflection and velocity of air flow was derived under considering the drag formula of aerodynamics and the deflection differential equation of the material mechanics.At the same time,the relationship between the deflection and the outlet velocity of air flow branch pipe was calculated and the dimension of air flow branch pipe was determined based on the gas jet dynamics.In order to obtain air flow branch pipe with uniform outlet velocity,tapered main pipe was design,and taper of air flow main pipe was calculated according to static regain design method of multiple-branch duct system.Theoretical calculation results manifest that the outlet velocity of air flow branch pipe is relatively uniform when the air flow main pipe taper is 1:14.29.The deflection of the wheat is 188.33 mm under the condition of air flow branch pipe diameter 30mm,air flow branch pipe interval distance 100mm,outlet velocity of air flow branch pipe 48.73m/s and distance between wheat and air flow branch pipe outlet 300mm.This deflection of the wheat fulfills the requirement of wheat smoothly entering into the harvester header without dropping.Secondly,in order to obtain uniform air flow at the outlets,structure of the air flow pipe optimized by using the CFD simulation.The air velocity distribution regulation inside and outside the pipe was analyzed.The optimum structure was validated by experiment.The results show that the uniform air flow is achieved when the taperaof the branch pipes is 11°.The outlet air velocity of branch pipes is 45.00～48.76m/s with a maximum deviation ratio of 3.70%and a coefficient of variation of 3.01%under this situation.The result of validated experiment show the maximum relative error between the simulating and measured velocity is 6.28%.Finally,Three key parameters,vertical and horizontal distance between cutting knife and air flow branch pipe outlet,the angle between air flow branch pipe and level,that affected header residual amount and total loss rate regarded as experimental factors for conducting single factor and multi-factors orthogonal experiments.The wheat single factor experiments show that the vertical and horizontal distances between cutting knife and outlet of air flow branch pipe within a scope of 15-27cm make the total loss rate of header firstly increasing and then decreasing.The residues on the header are little affected by horizontal distance between cutting knife and outlet of air flow branch pipe causes.But there is larger effect on the residues on the header for the vertical distance between cutting knife and outlet of air flow branch pipe.The higher the vertical distance,the more residues,and even wheat ear is left.The angle between air flow branch pipe and level make the residual and total loss rate of header slowly decreasing in 0-10°,but rapidly increasing in 10-20°.The wheat orthogonal experiments demonstrate that the effect of horizontal distance between cutting knife and outlet of air flow branch pipe on total loss rate of header is greatest,but the effect of the angle between air flow branch pipe and level on residual amount is greatest.The vertical distance between cutting knife and outlet of air flow branch pipe of 21 cm,the angle between air flow branch pipe and level of 10°,and horizontal distance between cutting knife and outlet of air flow branch pipe of 21 cm are the optimal orthogonal experiments combination.The total loss rate is 0.88%and the header residues is 1.21 g under the optimal orthogonal experiments combination.The single factor experiment results in rice field are consistent with that of wheat,and the rice loss rate is slightly larger than that of wheat.The vertical distance between cutting knife and outlet of-air flow branch pipe of 21 cm,the angle between air flow branch pipe and level of 10°,and horizontal distance between cutting knife and outlet of air flow branch pipe of 23 cm are the optimal orthogonal experiments combination.The total loss rate is 1.24%and the header residues is 1.19g under the optimal orthogonal experiments combination.The developed air blowing header with little header residual amount and low total loss rate achieves the technical requirements of the plot harvesting wheat seed.