| As a vital component of combine harvester,cleaning unit directly affect performance of the harvester.The cleaning lost ratio,dirt percentage are the key indicators for evaluating the quality of combine harvester.The air flow of screen surface affects the quality of cleaning in the cleaning unit of air and screen.It is very important to get the reasonable air flow field of screen surface to study fans.Firstly,experimental study has been processed for the velocity of air outlet of Ward-2 entire feeding combine harvester.In a 3-meter space,126 measuring points were set for measuring velocity of wind under 5 kinds of rotational speed.Meanwhile we extended air outlet for 30cm and 50cm to measure the velocity of wind.Through the experiment,the dynamic pressure and flow of air outlet,the axis-power of fan,the distribution of airflow in the 3-meter space,were obtained.Coordinate experiment was processed between the former fan and the 30cm extended fan.25 measuring points were set for measuring the velocity of wind.By analyzing the experimental results,it was concluded that the transverse distribution of airflow was more even and airflow attenuated slower than the former fan,when the air outlet was extended 30cm.Secondly,utilizing the device of DFPF-25 type made by ourselves,3 kinds of rice varieties were selected for measuring the suspended velocities of saturated grain,dry grain, big stem and small stem with grain,handle grain,stem and leaf.According to the experiment results,the airflow velocity of screen surface ranged from 2m/s to 6m/s.Through the experiment processed on the DFQX-3 test bench of material cleaning simulation and control, we gained the conclusion that the cleaning effect would be the best when the rational speed was 1050 r/min,which provided basis for next numerical simulation of airflow field.Last,4 kinds of fan models were set by the software of Gambit,which were model of 4-vane and angle of inclination,model of 4-vane and no angle of inclination,model of 6-vane and angle of inclination and model of 6-vane of no angle of inclination.We also simulated the inner airflow field by the software of FLUENT.In the process of simulation, unsteady calculation was carried in the Sliding Mesh.Much fluid information of the fan was captured by simulation.In addition,the effects of the number of vanes and angle of inclination on the performance of fan were discussed.Comparison with velocities of wind in the middle layer of air outlet and direction of Z under the 4-kind models,we attained the conclusion that the coefficient of variability of air speed was lowest,that was,the distribution of airflow was much more even when the number of vanes was 6 and no angle of inclination.Through the study of this subject,experimental data and methods were provided for the optimal design of centrifugal blower in the device of cleaning unit.And the unsteady calculation provided the reference for the simulation of inner airflow field of less-vane fan in the Sliding Mesh.
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