Simulation Research On Grain Air-and-Screen Cleaning Process And Optimization Of Key Parameters

Air-and-screen cleaning device is a key component of the full-feeding combine harvester,which functions to clean and separate grains and material other than grains(short straws,broken straws,dust,rice leaves,etc.)falling from the threshing apparatus,so as to realize the low loss and highly pure harvest of grains.Its performance directly affects the core indicators of the combine harvester:loss rate and impurity rate.Due to the operating environment of harvesting machinery is complex and changeable,and the particularity of long-term continuous heavy-duty work,domestic combined harvester often encounters serious problems such as high grain loss rate and high impurity content,which restricts the development and progress of the domestic full-feeding combine harvester.Based on the actual demands of cooperative enterprise in product development process,aiming at the difficult problems of cleaning separation with high loss rate and impurity content,this paper carried out simulation research on the cleaning device,and analyzed in detail the vibration screening laws of the separated mixture under the condition of no wind field,the distribution characteristics of air flow field inside the cross-flow grain air-and-screen cleaning device and the mechanism of gas-solid two-phase flow process in the cleaning device.On this basis,an optimization method for key parameters of cleaning device based on GA-SVR surrogate models and NSGA-II multi-objective optimization algorithm was proposed,which greatly reduced the loss rate and impurity content after optimization.The main contents of this paper are as follows:(1)Based on the Discrete Element Method(DEM),a discrete element model of vibrating screen for the mixture was established.Then,the vibrating screen characteristics of the mixture under the action of a vibrating screen composed of a wave plate,a louver sieve and a woven screen were quantified.At last,the effects of parameters such as amplitude,frequency,direction angle of vibration and sieve hole size on the screening process of grains and short straws were also carried out.(2)Based on Computational Fluid Dynamics theory and technology(CFD),the visualization of internal airflow field in cross-flow grain air-and-screen cleaning room was studied.Orthogonal optimization method was used to optimize the main structural parameters affecting the distribution of internal flow field in the cleaning device:the angle of upper air separator,the angle of lower air separator and the inclination angle of louver sieve.(3)Combining the respective advantages of CFD and DEM methods,a CFD-DEM coupled numerical model of gas-solid two-phase flow in the air-and-screen cleaning process was proposed,realizing the numerical simulation of the mixture separation process.Then the mechanism of the mixture air-screen cleaning process was revealed from the particle scale.(4)The surrogate models of loss rate and impurity rate were constructed respectively by using the method of support vector regression prediction method,whose parameters were optimized based on genetic algorithm(GA-SVR).Then the key parameters of grain screening were optimized by using NSGA-? multi-objective optimization algorithm on the basis of surrogate models.It has been verified that when the screen hole size was 17mm,the amplitude was 32mm,the vibration frequency was 6Hz,and the wind speed was 9.5m/s,the cleaning loss rate and the impurity index are relatively better.The research in this paper provides a theoretical basis and reference for the selection and design of combine harvester cleaning shoes.