Numerical Simulation And Experiment Of Gas-solid Two-phase Flow In Multiple-ducts Cleaning Device

In order to study the airflow field distribution and motion law of threshed particles group in multiple-ducts cleaning device and their relationships with the cleaning performance,used the CFD software respectively to simulate the airflow field under the different working parameters conditions of multiple-ducts cleaning device.At the same time the measurement test of the internal airflow field was carried out under the corresponding conditions in multiple-ducts cleaning test-bed.The numerical simulation and experiment results were compared and analyzed,and the influence of each working parameter on the airflow field and operation quality of the cleaning device was obtained.Used the CFD-DEM software to simulate the threshed materials’ movement by orthogonal test method in multiple-ducts cleaning device under large amount of feed(whole feed quantity 9.0kg/s)working environment.The threshed particles group dispersion,centroid motion law and their relationships with cleaning performance were analyzed.The above researches provide theoretical and experimental bases for the optimal design of the combine harvester cleaning device and adjustment of working parameters in the field harvesting operation.The specific works done in this paper are as follows:(1)Construction of multiple-ducts cleaning test-bedReferred to the oblique tangential longitudinal flow combine harvester,designed the main structures and transmission line of multiple-ducts cleaning test-bed.And accorded to the working parameters and working performance of experiments,the specific structures and sizes of the multiple-ducts centrifugal fan,vibrating sieve and return board,grain and impurity augers,parameter adjusting mechanisms were determined.The multiple-ducts cleaning test-bed was constructed in accordance with the above design requirements.The test-bed could realize that the real-time adjustment of cleaning parameters(multiple-ducts centrifugal fan speed is 0 ~1500r/min,louver sieve opening is 18 mm ~ 30 mm,wind-board dip angle is 20 DEG~ 32 DEG,vibration frequency of vibrating screen is 0 ~ 7Hz)and change of threshedmaterials feed quantity(1.0kg/s ~ 4.0kg/s).(2)The establishment of whole flow-path model in threshing and cleaning device and CFD numerical simulationAccorded to the internal structures of oblique tangential longitudinal flow combine harvester,established the whole flow-path models in threshing and cleaning device under different working parameters conditions.The models’ shape,sizes,internal structures were consistent with the actual machines,also included multiple-ducts centrifugal fan,tangential/longitudinal flow threshing cylinder and other working parts.They made up for the shortcomings of previous studies,so that the numerical simulation results would be more reliable.The ICEM software was used to mesh the flow-path models.Then the FLUENT software was used to simulate the grids.And used the CFX software to deal with the results of numerical simulation.Obtained the preliminary analysis results of airflow velocity streamlines and contours.And the airflow velocity contours of internal sections were analyzed according to the measurement test of airflow field.(3)Measurement test of airflow field in multiple-ducts cleaning device and threshing device50 airflow velocity measuring points are arranged in the multiple-ducts cleaning test-bed.And used VS110 type hot-wire anemometers to measure the measuring points;The airflow velocity measuring points of threshing device were measured by using a hand-held anemometer in the oblique tangential longitudinal flow combine harvester.The experiment and numerical simulation results were compared and analyzed.They show that the airflow field distributions of the two are similar;With the centrifugal fan speed increasing 150r/min,the wind speeds of measuring points increase 0.2m/s ~ 1.3m/s above vibrating sieve,and the centrifugal fan’s suitable speed is in the 1350r/min ~ 1500r/min.With the wind-board dip angle increasing every 4 DEG,the maximum velocity region of airflow field above the vibrating sieve moves forward about 82 mm ~ 110 mm and the best adjustment range is 20 DEG ~ 28DEG;With the decrease of 4mm louver sieve opening,the airflow velocities above the vibrating sieve increase 0.3m/s ~ 0.7m/s and the opening should be adjusted in18 mm ~ 26mm;The speed of tangential(longitudinal)flow cylinder should be adjusted in 620(580)r/min ~ 720(674)r/min according to the work environment and feed quantity,in order to achieve the best threshing performance.(4)Numerical simulation of threshed mixture motion in multiple-ducts cleaning device based on CFD-DEMMultiple factors orthogonal numerical simulations were carried out by CFD-DEM gas-solid two-phase flow coupling method under the condition of large feed quantity based on the research factors such as multiple-ducts centrifugal fan speed,louver sieve opening,wind-board dip angle and vibration frequency of vibrating screen.The numerical simulation results were processed and analyzed.And it shows that the upper air duct airflow of multiple-ducts centrifugal fan could be used for pre-cleaning and reducing cleaning load;The best cleaning performance is 0.76%under the working condition 4,and the worst is 1.13% under the working condition 8of the multiple-ducts cleaning device;Under different working conditions,the dispersion of threshed particles group is first increasing and then decreasing without exception,and the dispersion reaches the maximum(22.8% ~ 28.3%)in the cleaning time of 0.6s ~ 1.0s;The effects of different working conditions on the grain particles group’s centroid in Y direction are smaller,and at the same cleaning time the magnitude of the change in speeds are between 0 and 57.9%;The maximum velocities of grain,light impurity and short stalk particles groups in X direction are greater than the maximum velocities in Y direction.(5)Experiment on cleaning performance of multiple-ducts cleaning device with large feed quantityBy controlling the opening of material outlet and the frequency of electromagnetic feeder,the working environment of the feeding quantity of 9.0kg/s was achieved.According to the orthogonal gas-solid two-phase flow numerical simulation,the performance verification test was carried out.The test-bed experiment and numerical simulation results were compared and analyzed.It shows that the cleaning loss of error rate is within 17.5% and the impurity rate error is within 14.3%of the two under the same operating condition;The optimum working parameters ofmultiple-ducts cleaning device are as follows: the multiple-ducts centrifugal fan speed is 1300r/min,the louver sieve opening is 18 mm,the wind-board dip angle is 24 DEG,the vibration frequency of vibrating screen is 6.5Hz.