| Unmanned aerial vehicle(UAV)and self-propelled sprayer have become the main methods of plant protection in China.As a key part of plant protection equipment,the performance of nozzle,especially its atomization characteristics,seriously affects the overall performance and operation effect of plant protection machinery.Compared with other nozzles,fan-shaped nozzles have the characteristics of wide flow range,large fog Angle and good atomization performance at low pressure,etc.,and are gradually being widely used in the field of plant protection and irrigation.In this paper,the atomization characteristics of the fan nozzle are studied by combining numerical simulation with experimental research,which provides theoretical reference for the further popularization and application of the fan nozzle.The research contents of this paper include the following aspects:1.Aiming at the influence of internal flow field of fan nozzle with variable parameters,a water model of fan nozzle was established.The influence of nozzle inlet diameter,relative cutting depth,cutting Angle,inlet cylinder length and inlet pressure on velocity and pressure of flow field in nozzle was calculated by ANSYS FLUENT.Studies show that the flow field inside the nozzle axis near cutting Angle speed increase according to the aperture size,relative speed of cutting depth,cutting groove Angle from small to large distribution from big to small,and the size of the inlet pressure for faster growth,by contrast,the influence of different sizes of inlet length of cylindrical section near the cutting Angle of nozzle axis same speed increase.The velocity at the end of the axis is also distributed from small to large according to the order of aperture,relative cutting depth,cutting Angle and inlet pressure.The velocity at the end of the axis is not affected by the length of the inlet cylinder.The pressure drop on the axis near the slot Angle of the fan nozzle is distributed from large to small according to the order of aperture,relative cutting depth and slot Angle from small to large.The effect of inlet pressure on pressure drop is the opposite.The pressure drop rate near the groove Angle is not affected by the length of inlet cylinder.2.According to the atomization characteristics of the fan nozzle,the coupling algorithm of Eulerian-Lagrangian continuous phase and discrete phase was adopted in ANSYS Fluent based on the Taylor Analogy(TAB)breakage model.The unsteady numerical simulation of droplet breakage,atomization formation and gas-liquid two-phase flow field in a fan nozzle was realized.The effects of spray pressure and spray height on droplet velocity,droplet diameter,DPM mass concentration,droplet flux(N)and other atomization characteristics of the fan nozzle were studied.The results show that with the increase of injection pressure,the droplet velocity increases and the droplet average residence time in the calculation domain becomes shorter.The less droplets stay in the calculation domain;The mean diameter(SMD),median volume diameter(VMD)and median number diameter(NMD)of droplet decrease with the increase of injection pressure,and the decreasing trend of droplet diameter becomes larger when the SMD pressure is0.3MPa.The mass concentration of droplet DPM on different collection surfaces is not affected by the injection pressure.The higher the injection pressure,the lower the SMD of droplet and the larger the number flux of droplet.The higher the spray height is,the smaller the proportion of droplet with high velocity is,that is,the smaller the axial velocity of droplet is,and the average axial velocity of droplet decreases with the increase of the spray height and tends to decrease slowly.Under different spray heights,the particle size distribution and cumulative distribution are similar.When the spray pressure is 0.1MPa～0.3MPa,the particle size presents a normal distribution and the distribution trend is roughly symmetric relative to 120μm.Under the condition of no wind,the spray height has little effect on the particle size.The mass concentration of droplet DPM decreases with the increase of spray height.With the increase of spray height,the number flux of droplet decreases due to the increase of spray coverage area,which is different from the influence principle of spray pressure on the number flux of droplet.3.The laser particle size analyzer test bed and PAQXOS-RODOS software were used to complete the experimental verification of droplet size distribution and SMD under different spray pressures and different spray heights.The results show that the variation trend of SMD obtained by experiment and simulation under different spray pressure and different spray height is consistent,and the error of the whole process is not more than 10%.When the injection pressure is 0.13 Pa,the test SMD value is larger than the simulated SMD value,and the subsequent test SMD is smaller than the simulated SMD value.Both the test and the simulation calculation show that the spray height has no effect on the droplet SMD value. |
