| Farm machinery and equipment manufacturing industry occupies a special important position under the construction of "agricultural modernization" in our country. The air-and-screen cleaning device is the core component of combine harvester, and the level of its cleaning performance greatly affects the performance of the machine. the different types of cleaning device have different distribution of the air-flow field, and the studies show that air distribution is closely related to the overall cleaning quality. Researching overall distribution of the air-flow field in air-and-screen cleaning device, which will be beneficial to enhance the overall quality and efficiency of cleaning. At present, a new type of longitudinal axial flow of combine harvester model has been developed in China, namely longitudinal axial drum-type threshing and separating structure (longitudinal axial flow). However, the mode of air-and-screen cleaning was mainly applied to the longitudinal axial flow combine harvester, in the condition of the large quantity in feeding and high-power field operations, there are some problems existing in material cleaning such as high loss rate and the high impurity rate, which is restricting the development of the longitudinal axial flow combine harvester nowadays. This topic was developed mainly on the optimization of flow field which affects the material cleaning performance of the longitudinal axial flow cleaning device and the improvement of physical structure of material cleaning device, thereby, which can improve the overall performance of material cleaning of the longitudinal axial flow, and it is of extremely important significance and practical value to the development of the longitudinal axial flow combine harvester.This topic studied the 4LZ-5.0Z type longitudinal axial flow full-feeding combine harvester produced by Huzhou Star Agricultural Mechinery Co., according to the feature of the cleaning device threshing way, this paper proposes a new style of centrifugal air-and-screen cleaning device with double air-outlets and six air-ducts, according to the feature of the cleaning device threshing way, this paper proposes a new style of centrifugal air-and-screen cleaning device with double air-outlets and six air-ducts. The mixed flow field produced by the threshing roller and the centrifugal fan in the cleaning device was numerically simulated with CFD software UG Nastran, By comparing and analyzing the improved and original structures of cleaning device, the airflow distribution on the surface of the sieve and the rear of the air-outlet was analyzed, meanwhile the orthogonal experiment and the field test of the improved double air-outlets mixed flow field was carried out, which provides a basis for optimization of the overall flow field distribution, and it further can improve the cleaning performance of the cleaning device. Finally, the cleaning device based on the cross flow fan was designed, meanwhile the field tests of the cross flow fan and optimization of the numerical simulation are carried out, which meets the cleaning requirements of the longitudinal axial flow. This paper draws the following conclusions:1. Build speed test platform of a single outlet fan, according to GB1236-1985 "fan aerodynamic performance test method", field wind-speed test of the traditional single-outlet fan was carried out, the impeller speed of the traditional single-outlet fan is 1800r/min, and the left and right sides are air-inlets, compared both of the Outlet air-speeds of the single-outlet and three air-ducts centrifugal fan and six air-ducts, the comparative analysis shows that using the CFD software to carry out simulation of cleaning device airflow field is feasible.2. The conditions are as follows:the incident angle of the fan is 22°, the included angle of sieve is 50°, the speed of threshing roller is 600 r/min, the speed of fan is 1800 r/min, the mixed flow field produced by the fan and the threshing roller was numerically simulated with CFD software UG Nastran. the velocity vector diagram of different sections in the cleaning device (Z =0, Z=300 mm, Z=-300 mm) was analyzed, results shows that the the overall flow field distribution and the shortcomings.3. This paper proposes a new style of centrifugal air-and-screen cleaning device with double air-outlets and six air-ducts, according to the comparative analysis of the the improved and original simulations, the new style of device is beneficial to enhance the air-speeds on the front of sieve obviously, meanwhile improve the uniformity of the overall fluid region. Results shows that the airflow distribution is more rational and efficient, which overcomes the deficiencies of the traditional device and greatly enhances the cleaning performance of the cleaning device.4. The conditions are as follows:the speed of threshing roller is 600 r/min, the orthogonal experiment was tested on a new type of cleaning device on the Z sections with the three factors(the fan speed、the incident angle of the fan, the included angle of the sieve). The optimal combinations are as follows:the incident angle of the fan is 30°, the included angle of sieve is 40°, the speed of fan is 1900 r/min. In this condition, the outlet air-speed in the front and rear of sieve is relatively high, and the overall air-flow of cleaning device is uniform, which is more beneficial to high-load and efficient cleaning. Meanwhile, three factors of the fan speed, the incident angle of the fan and the included angle of the sieve have significant influence on cleaning flow-field, changing the incident angle of the fan has significant impact on air-speeds on the middle and the rear of sieve; changing the included angle of the sieve has great impact on air-speeds on the rear of outlet; changing the fan speed has impact on the proportion of the air distribution on the upper and lower outlets.5. A series of the tests in rice and wheat fields were developed with the original structure、 the improved structure and the orthogonal Optimized structure respectively. Field tests verified the accuracy of the improved structure and optimization program. the loss rate of the rice is 2.70% and the impurity rate is 2.19% before the structure is improved, meanwhile, the loss rate of the wheat is 1.78% and impurity rate is 1.95%. the loss rate of the rice is 0.91% and the impurity rate is 0.87% after the structure is orthogonal Optimized, meanwhile, the loss rate of the wheat is 0.82% and impurity rate is 0.76%. it greatly improved the cleaning performance of the longitudinal axial flow.6. Based on the structure, principle and characteristics of the cross flow fan, this paper designed the cross flow fan for the longitudinal axial flow cleaning device of the combine harvester. Tests of field air-speed and verification of numerical simulation for different types of the cross flow fan were carried out, and obtained air-flow field distribution of cross-flow cleaning device. Field tests of the cross-flow cleaning device was developed.The result shows that the loss rate of the rice is 1.28% and the impurity rate is 1.40%, and the broken rate is 0.41%. Meanwhile the loss rate of the wheat is 1.14%, and the impurity rate is 1.50%, and the broken rate is 0.17%, which meets the cleaning requirements of the longitudinal axial flow and can be used for actual production. |
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