Calculation Of Spray Flow Field In Air-Assist Boom Spraying And Spray Parameter Optimization

As a kind of advanced and efficient spraying technology,air-assist boom spraying effectively improve the uniformity of droplet deposition distribution,increase the deposition and penetrating ability of droplets,and drip the droplets to crop canopy to reduce the droplet drift.At present,there are few researches on the simulation of gasliquid two phase flow field characteristics in air-assist boom spraying.In this paper,based on the domestic and foreign study of relevant literature,simulation and experimental study on flow characteristics of air-assist boom spraying were carried out.The rules of airflow distribution and droplet drift in the spray flow field are analyzed and discussed.The main research contents are as follows:(1)The effect of air curtain velocity,lateral wind velocity and spray pressure on droplet drift was analyzed theoretically by analyzing the single droplet particles formed in three-dimensional coordinate system.Based on the Miller P H droplet velocity model and local approximation method,the calculation method of air-assist boom spraying drift distance was obtained.(2)The velocity distribution of the flow field outside the assist air was analyzed by using the simulation calculation model of air-assist boom spraying,and the air velocity was measured by KA31 type anemometer.The results show that air curtain airflow average speed of 6.3,12.3 m/s,the corresponding the axial fan speed at 1118,2320 r/min.The calculation results of the gas flow field are consistent with the experimental results.It can be concluded that the simulation model established in this paper can simulate the spray process of the air curtain.The air velocity in the middle of the air curtain is faster than the two ends of the Y-axis.Under the action of the air curtain airflow,the crosswind changes the original movement direction and moves along the air curtain airflow direction.The air curtain airflow can effectively restrain the movement of the crosswind to a certain extent.With the gradual increase of the wind speed,the effect of the air curtain on the side wind is gradually enhanced.(3)The gas-liquid two phase flow was simulated by software Fluent.The distribution of droplet size in the flow field was measured by laser particle size analyzer.From the results of droplet size,the droplet size of spray height of 700 mm was selected as the calculation parameters and test parameters of the droplet drift distance.The effect of lateral wind velocity,air curtain velocity and the spray pressure on the droplet drift distance were analyzed.The results show that spray pressure is the main factor affecting the change of droplet size.The particle size of the droplet decreases with the increase of the spray pressure,and increases with the increase of the airflow velocity and the spray height.The simulated values of the average volume diameter of the droplets are smaller than the experimental values.However,in general,the simulated values of the average volume diameter of the droplets coincide with the change trend of the test values,which indicates that the CFD calculation model is correct and feasible.The drift distance of the droplet increases with the increase of the wind speed and the spray pressure,and decreases with the increase of the airflow velocity of the air curtain.The calculation of the drift distance of the droplet drift is in good agreement with the change trend of the test value,which indicates that the method of calculating the drift distance of the sprayer spray is feasible.Droplet diffusion during the fogging process without air curtain and lateral wind cause drift.The air curtain can effectively suppress the droplet drift phenomenon,in the 4 wind(including 4 wind),air-assist boom spraying can also work properly.(4)The effect of the three factors on the anti-drift performance and the quantitative relationship between the factors and the droplet deposition were analyzed by orthogonal test and regression analysis respectively.And as a basis for air-assist boom spraying to optimize the operating parameters.The results show that the airflow velocity of air curtain is the strongest factor for anti-drift performance of air-assist boom spraying,followed by the lateral wind velocity.The spray pressure is the weakest factor among the three factors.Optimal operating parameters for anti-drift performance appeared to be the airflow velocity of air curtain of 12.3m/s,the lateral wind velocity of 0m/s and the spray pressure of 3bar.