Study On Optimization And Experiment Of The Cleaning Unit Of Small Rice And Wheat Combine Harvester

The cleaning unit is an important part of the rice and wheat combine harvester,and its performance directly affects the quality of the harvester.At present,the large and medium-sized rice and wheat combine harvesters are well developed,while the cleaning unit of small rice and wheat combine harvester generally has the problems in high impurity rate and high loss rate.So,it has important theoretical significance and demand background for improving the quality of small combine harvesters to develop a high-performance cleaning unit.In this thesis,the problem of excessive impurity rate and loss rate of a new type of small combine harvester developed by a company is optimized by numerical simulation and experimental research to reduce its impurity content and Loss rate,improve cleaning performance.The main research work of the thesis is:1.The simulation model of the cleaning unit was established.On the simulation model of the cleaning unit was established,which was by ignoring the influence of the grass guiding rod,the cross conveyor auger and the inverted separation cone bracket on the flow field,simplifying the coupling calculation domain based on analyzing the structure of the cleaning unit and its working process.2.Research on numerical simulation accuracy of granular material throwing process.A rice variety was selected as the test object.The rice grain model was established,and the model contact parameters were calibrated.The numerical simulation of the throwing process was carried out.The simulation results showed that the characteristic size error of the particle formation morphology formed by the throwing is less than 5.7%,which indicates that the numerical simulation can better describe the motion process of the particles thrown.3.Gas-solid coupling simulation and experimental study of the multi-stage cleaning process.Based on the CFD-DEM coupling calculation framework,the cleaning process of multi-stage cleaning equipment was simulated.Considering the difference between rice grain and straw in shape,different drag models were applied to rice grain and short straw particles to ensure different types of particles forced more accurately by air-flow.The model,parameters and the analysis methods were verified by field rice harvest experiment.The results indicate that the impurity and loss rate obtained by numerical simulation is2.37% and 2.41%,respectively,while the impurity and loss rate obtained by field experiment is 2.64% and 2.21%,respectively,and the relative errors are 10.22% and9.55%,respectively.This indicates that the model,parameters and analysis methods used in this thesis are effective,and the analysis results are credible.4.Performance optimization of a multi-stage cleaning unit.Through the single factor analysis,the influence factors of impurity and loss rate were determined.Through orthogonal test analysis,the influence degree of each factor on the impurity and loss rate was further determined.What's more,the regression model between the impurity and loss rate and each influencing parameter.The genetic algorithm was used to optimize the parameters of the cleaning unit,and the optimal parameters were found for the cleaning unit.