Numerical Analysis And Experimental Study On Spray Droplet Distribution Of Single Rotor UAV

As a new type of agricultural plant protection machinery,the single-rotor plant protection UAV has the advantages of high efficiency and good performance.In recent years,it has been developing rapidly in a blowout way in China.In this paper,the numerical analysis and experimental verification method are used to study the rotor wind field and spray deposition distribution of single-rotor plant protection UAV.Numeric modeling and analysis methods of the rotor wind field and spray flow field are discussed based on Computational Fluid Dynamics(CFD).The numerical modeling can be used to describe the wind flow,spray deposition distribution,and effective spray width of the rotor of the UAV.The relationship model between flight speed,droplet size,flying height and droplet deposition distribution is analyzed,and the regression equation of variation coefficients of droplet deposition in the effective spray width is obtained.The main research contents are as follows:(1)Research on rotor wind field of single-rotor UAV at low altitude.The numerical model of the rotor field of the single-rotor plant protection UAV is established.The wind field law of the single-rotor UAV operating at a low-altitude is analyzed,and the test rig of the rotor wind field of the UAV is built to finish a wind field test when the UAV works at a low altitude.In case of the high-speed rotation of the main rotor,the air shrinks rapidly,and the wind speed and flow direction of the rotor wind field change.The rotor wind field has an obvious rotational component along the rotation direction of the main rotor.The airflow of the rotor wind field is mainly concentrated directly below the main rotor.The wind speed is clearly mitigated below the fuselage,and from the center of the main rotor to the boundary of the wind field,the vertical wind speed of the wind field first gradually increases and then decreases sharply.The test results of the rotor wind field test are basically consistent with the trend of the numerical analysis results.The wind field data measured by the field test is slightly smaller than the simulated wind field data.The wind field test not only provides a basis for the numerical analysis of the single-rotor UAV rotor wind field,but establishes basis for the numerical analysis of the single-rotor UAV spray flow field.(2)Numerical analysis of the spray flow field of a single-rotor UAV.The numerical analysis of the spray deposition distribution law and effective spray width of single-rotor UAV in cases of different flight speeds,droplet sizes and flight height conditions were carried out.The orthogonal scheme is used to analyze the influence of working conditions on droplet deposition distribution and effective spray amplitude.From the range of the orthogonal table,the influence of working conditions on the uniformity of droplet deposition is concluded as follows in a descending order: flight speed,flight altitude,flight speed,droplet size,droplet size,the product of the droplet size and the flying height.The results also show that under the condition of the constant flight height and the particle size of the droplets,the angle between the droplet drop trajectory and the horizontal line gradually decreases with the increase of the flight speed,and the influence range of the rotor wind field on the droplets is also slowing shrieking.When the flight speeds are 3m/s,4m/s and 5m/s,the angles corresponding to the falling path of the droplets and the horizontal lines are 25°,21° and 17°,respectively.The smaller the angle,the smaller the downward movement of the droplet,and the longer it takes to fall onto the target,which means that a smaller lowering effect of the rotor wind field on the droplet.As the flight speed increases,the phenomenon of droplet entrainment becomes more apparent under the action of the tail fin,and the possibility of drift of the droplets increases.(3)Experimental study on the distribution of droplet deposition and the effective spray width during single-rotor UAV operation.The experimental study on droplet deposition of single-rotor plant protection UAVs under three different working conditions was carried out.By means of comparative analysis of the regression equation fitting data,numerical analysis data,and experimental data,the result shows that the fitting value of the above-mentioned droplet deposition distribution variation coefficient regression equation is consistent with the trend of the test results.For the effective spray amplitude,the numerical analysis results and the test results are basically at about 4.0m,and the trends are basically the same.The results show that the numerical analysis method can be used to accurately analyze the variation coefficient and effective spray width of the droplet deposition distribution of the single-rotor plant protection UAV during aviation spray,which provides reference for the subsequent research.