Research Of Narrow Droplets Spectral Atomization Property Of Centrifugal Nozzle In Low Volume Aviation Spray

Aviation spray by use UAV is rapidly developed in China, however, due to the spraying parts’ backward technology, resulting in uneven distribution of droplet deposition and high drift risk. Nozzle’s atomization property, especially droplet size and droplet spectral width, have a directly impact on the pesticide spray quality. Centrifugal nozzle has a broad prospect in the aviation application field because of it is reliable, and has a narrow droplet spectrum width and a wide spraying swath. In order to obtain narrow spectrum of droplets centrifugal nozzle which can satisfy aviation high altitude, high speed and big flow rate of aviation application spraying conditions, Research of centrifugal nozzle atomization mechanism will provide theoretical support and experimental basis to improve the nozzle structure and optimize rotor parameters.In this paper, combined with theoretical analysis, numerical simulation and experimental research method, the centrifugal nozzle atomization process and droplet trajectory was analyzed, the centrifugal nozzle internal and external flow distribution was simulated, and the nozzle operating parameters and optimize the rotor structure parameters was determined. The main contents are as follows:(1) By comparing the atomization principle between centrifugal nozzle and hydraulic nozzle, choose centrifugal nozzle as the research object, which is more suitable for aviation spray. Nozzle’s atomization property has a directly effect on spray quality, the research methods and implementation scheme of the centrifugal nozzle atomization mechanism were designed.(2) In order to obtain narrow droplet spectrum centrifugal nozzle, the droplet volume medium diameter and the droplet spectrum width were proposed as evaluation indicators of centrifugal atomizing atomization property. The working conditions and test location of sampling sites were determined, provided a basis for optimizing the rotary cup structure. The results of variance analysis and mean comparison showed that, the best rotary cup groove shape was square, diameter and teeth number had a significant effect on droplet volume medium diameter and droplet spectrum width. The narrow droplet spectrum centrifugal nozzle can be obtained by the right combination of diameter and teeth number. Droplet volume medium diameter and droplet spectrum width regression model were built by the software SAS response surface analysis. The coefficient of determination R2 were 0.803 and 0.834 respectively, which indicated that the regression models fit well. To meet the low volume spray requirement, optimized rotary cup structure with a diameter of 65 mm and teeth number of 168, and the simulation value of droplet volume medium diameter and droplet spectrum width were 165.6μm and 102.1μm.(3) On the basis of a clear comprehend of centrifugal nozzle structure and working principle, based on MATLAB platform the standard fourth order Runge-Kutta algorithm was used to obtain the droplet motion trajectory in the air,and the variation rules of the horizontal velocity and vertical velocity. Numerical solution solved the difficult to obtain analytical solution of complex differential equations.(4) The rotary cup internal and external flow field distribution were numerical modeled by using RNG k-ε model algorithm based on CFD simulation platform. Rotary cup internal liquid flow field distribution and the edge radius of droplet deposition amount range first increased and then decreased.(5) To increase the reliability of test results, a centrifugal atomization test equipment was designed and built by use inverter to adjust the motor speed and back-water valve to stable liquid flow rate and pressure. Nozzle spray shape, droplet deposition distribution were researched by experimental means. Since the deflection of inlet, from the inlet point, spray radius, droplet size and droplet deposition amount were gradually increased with the rotation direction of the rotary cup, and then gradually decreased until it reached a certain position. The relative error of droplet theoretical value of horizontal displacement and deposition distribution boundary simulated value between effective placement values were less than 5.31% and 14.49% respectively, indicated that the droplet equations of motion analysis, simulated deposition profile boundary were correct.