Research On Corn Straw Chopping And Spreading Machine Design And Dynamic Characteristic Of Straw

Crop straw chopping and returning to field which could significantly increase soil fertility,improve environment by reducing residue burning and fertilizer application,contributes considerable economic,environment and social benefits.Straw is usually chopped and spread via straw chopper.Nevertheless,contemporary straw choppers have a number of operational issues,including undesirable chopped straw lengths(too long),uneven lengths and nonuniform distribution of chopped straw.This study aimed to improve chopped straw spreading uniformity.To achieve this goal,a straw chopper cum spreader with adjustable spreading device was developed.Based on this machine,straw chopping and spreading process,flow field characteristic in the chopping chamber,motion of straw particle swarm was studied.The main innovation achievements and conclusions were obtained as follows.(1)A straw chopper cum spreader was developed to deal with the problems of unadjustable chopped straw spreading uniformity and width.The machine which is mainly composed of a curved shell,transmission system,a guide vane regulating device,a running gear,a hood and a straw chopping device can realize the function of crop straw chopping and chopped straw spreading.Field experiments showed that:with the forward speed at 1.8 m/s,straw moisture at 78.4%,and PTO rotation speed at 540 rpm on the unharvested cornfield,the machine could achieve a qualification rate of straw chopping of 90.01%,spreading width of 2223.3 mm,average stubble height of 62.0 mm,and spreading unevenness of 22.95%.(2)According to shape and spatial position of straw,the working process of the straw chopper cum spreader was divided into four phases:straw cutting process,cut straw follow-up process,cut straw chopping process and chopped straw spreading process.Then,kinetic models of straw moving were built after some assumptions being given.The experimental results showed that the calculate value and the experimental value had the same changing trend under different design parameters,although there were some variances in magnitude.The method of overlapping straw in adjacent spreading widths was put forward to improve straw spreading uniformity.Two straw overlap methods(back-and-forth pass overlapping and single direction pass overlapping)were provided according to the spreading curve.Calculation values indicated that single direction pass overlapping method and back-and-forth pass overlapping method increased straw spreading uniformity by 4.9%and 8.1%,respectively.(3)A CFD(Computational Fluid Dynamics)numerical model of chopping chamber of the straw chopper cum spreader was built to analyse flow field characteristic in the chopping chamber and the influence of machine design parameters on flow field characteristic and machine working performance.The results of numerical calculation showed that the rotor generated negative pressure at the inlet and increased fluid flow velocity.However,in the chamber,velocity increased and it generated numerous vortices.The increase in rotor speed improved straw flow-ability in the chamber.However,increased fan blade number would decrease straw flow-ability.An increase in flail tip clearance appeared to improve straw feeding performance and straw flow-ability,but degrade the straw spreading performance.Mounting guide vanes at the chopping chamber outlet could improve straw flow-ability and spreading performance,whereas increase forward speed would degrade straw feeding performance and decrease straw flow-ability.(4)A CFD-DEM(Computational Fluid Dynamics-Discrete Element Method)coupling model of straw particle swarm motion was developed to analyse the variation of force,trajectory,orientation angle,etc.Besides,the influence of rotor speed on spreading uniformity was also studied.The results of numerical calculation showed that most of straw in the chopping chamber discharge from top of the shell after several collisions with wall.The straw magnitude in the chopping chamber rapidly increased at first,then changed to stabilize.Force between straw and straw was much larger than that between straw and air.Rotor speed had little effect on straw pitch angle,but great influence on straw yaw angle.The effect of rotor speed on straw spreading uniformty slowly reduced and became stable as the rotor speed increased.