Investigations On Primary Breakup Process Of Impact Sprinkler Round Jet With Numerical Simulation And Experimental Methods

Water-saving irrigation technology has been used widely in many parts of China, as one of the world’s most advanced water-saving irrigation methods, Sprinkler irrigation is widely used in agricultural irrigation, garden irrigation and so on.Impact sprinkler is one of the main equipments in irrigation system. It is necessary to do research about round jet primary fragmentation. In order to investigate the round jet fragmentation mechanism of impact sprinkler, based on VOF multiphase flow model provided by Fluent, used Geo-Reconstruct interface tracking method to simulate the primary breakup process of impact sprinkler round jet and obtained the primary breakup length and droplet size, then made a comparison with the high speed camera technology, analyzed relative errors about the primary breakup length and droplet size between numerical simulation and experiment. The results showed as followed:(1)The simulation of nozzle flow shows that, With nozzle cone angle increases, the gradient of flow velocity distribution increases, the average speed of nozzle outlet is reduced. The aspect ratio has little effect on the axial velocity distribution. In order to obtain a large jet kinetic energy, using ? =30~45° cone angle, the l1/d =1~2 is appropriate.(2)Nozzle size and inlet pressure were the main factors which affecting droplet size and breakup length. Through the method of numerical simulation, obtained the contours of primary breakup of round jet, measured primary breakup length and droplet size. Analysis shows that primary length and droplet diameter are linear distribution,with the inlet pressure and nozzle diameter increased.(3)Based on the simulation of round jet primary breakup process, liquid column formed after jet leaving the nozzle, the length of liquid column gradually increased, jet area started to increase and had an expansion trend, and finally formed the formation of mushroom, In the formation of the jet, it will produce large pieces of droplets from the mushroom-shaped area, droplet backward random motion and continues to be torn apart into smaller droplets.(4)Numerical Simulation of jet breakup length was greater than the measured value. The maximum relative error was 16.24%, a minimum was 3.50%, the average error between simulated and measured values was 10.78%. Numerical Simulation of droplet size was greater than the measured value. The maximum relative error was 29.03%, a minimum was 21.48%, the average error between simulated and measured values was 24.39%.(5)Under low pressure conditions(200 ~ 600kPa), as the increasing of Weber number, the breakup length increased. The fitted relationship between Weber number(We) and breakup length Ls(Ls/d=15.62lnWe‐11.22 R2=0.917) could predict the jet breakup length under low pressure conditions.(6) Primary droplet size and the nozzle diameter d(d>5mm)had a good correlation(Ds=1.634 d, R2=0.912), the relative error of droplet diameter between simulation and experiment was 23.92%. We can use this model to predict sprinkler droplet size of large-diameter nozzle under low pressure conditions.The results in this paper can be useful on simulation and experiment of impact sprinkle and have a good significance on the theory of round jet spray dispersion and improving the irrigation uniformity.