| Xinjiang,the country’s largest cotton production base,will produce 5.129 million tonnes of cotton in2021.With a machine picking rate of nearly 100% within the northern border and up to 80% across the whole of the country,mechanised operations are an important factor in obtaining high yields.Compared to traditional manual picking,mechanisation brings higher harvesting efficiency,but it also brings many problems,for example,there are many impurities mixed into the seed cotton in various ways during the work of the cotton picker,among which are boll shells,branches and leaves,as well as fragments of residual film floating on the surface.Studies have shown that the high speed upward airflow in the tube makes the bottom of the picking head negative pressure,the residual film fragments on the surface at the location of the slag hole are sucked into the picking head by this negative pressure and mixed in with the seed cotton,as these tiny residual film fragments are difficult to be cleaned out in the early cleaning process,and these residual film fragments seriously affect the quality of cotton at a later stage,and the more costly the cleaning process is at a later stage,with the machine picking cotton As machine picked cotton yields increase,more film debris is drawn in and economic losses increase.In order to reduce the inhalation rate of residual film at the front end of the cotton industry chain,save the cost of cleaning and improve the quality of cotton,this thesis improves and optimises the design of the components of the existing air curtain type residual film barrier device to improve its internal and jet outlet airflow unevenness,internal eddy current loss and other problems,so that the device can produce a uniform and stable jet air curtain at the jet outlet to better block the negative pressure at the bottom of the picking head on the surface of the broken film.Based on this,the following research has been carried out.1.Computational Fluid Dynamics(CFD)theory combined with the simulation techniques used in the research process are summarised.2.Simulation analysis of the existing air inlet components of the film barrier device and structural optimisation using orthogonal experimental design,to obtain the optimal structural parameters for the air inlet components of He=50 mm,D=60 mm and Hc=45 mm.Firstly,the structure of the bottom plate of the picking head of the cotton picker is analysed,the cavity structure of the residual film barrier device and its improved structure are designed,and the locking parts of the original device are improved,and the flow field of the different structures of the cavity is compared through simulation.The effect of the deflector structure and the different angle α of the blunt body on the flow field was found to increase the average velocity by3.95% when α = 115° compared to the untreated velocity,and the winding and vortex conditions of the original device were reduced,which improved the uniformity of the flow field inside the cavity and the jet exit velocity.3.According to the optimization design results of the cavity and the position of the bottom slag discharge hole,the structural design of two air curtain forming nozzles was carried out.The structural optimization of the air curtain forming nozzle 1 was carried out,and the contraction type and trapezoidal structure were proposed.The simulation analysis under different structural parameters was carried out,and it was concluded that the trapezoidal structure was better than the contraction type.When the inlet size of the trapezoidal nozzle was determined,the structure was the best when D=25 mm.The velocity nonuniformity coefficients corresponding to the jet outlet 1 and 2 were 4.82 % and 5.25 %,respectively,and the velocity deviation between the two was 0.19.Compared with the original model,the uniformity and stability of the jet air curtain were significantly improved.Finally,the experimental results show that the average relative errors between the simulated and measured velocities of jet exit 1 and 2 on both sides of the nozzle are 1.54 % and 2.32 %,respectively,and the correlation coefficients are 96.0 % and 95.4 %,respectively,indicating that the simulation results are reliable.4.The optimized residual film barrier device was made and tested on CP690 cotton picker.The average residual film barrier rate of the three groups of comparative tests was 74.41 %,which could form a certain barrier effect on the surface residual film and would not cause the blockage of the cotton conveying system of the cotton picker.Finally,the field wind speed test was carried out to verify the simulation results,which showed that the optimization results were good. |
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