Droplets Distribution Characteristic Study On Complete Fluidic Sprinkler

Research on the outlet droplets distribution for complete fluidic sprinkler is one of the main contents of the China National High-tech Program “Precision Sprinkling Irrigation Technology and Product”(No.2011AA100506), the National Science Foundation of China “Study on the Jet Flow Fragmentation Mechanism and Model of Gas-liquid Phases Fluidic Sprinkler”(No.51309117) and “Inner Flow Characteristics and Rules of Jet Attachment for the Complete Fluidic Sprinkler”(No.51109098).The complete fluidic sprinkler was a new type irrigation equipment with simple structure and excellent hydraulic performance. The outlet droplets distribution was closely related to the sprinkler structure and hydraulic performance. Therefore, its systematical studying had academic value and practice significance, which could optimize the sprinkler structure,improve hydraulic performance and design irrigation system. Combined with theoretical analysis, experiment tests and numerical simulation, the outlet droplets distribution law was systematically investigated. The outlet droplets properties mainly contained the droplets motion, the droplets diameter, the droplets velocity and kinetic energy distribution.The main contents of the research were presented as follows:(1) Through comprehensive analysis of the sprinkler structure and working principle, a preliminary study of the jet form, aerated process, spraying water tongue crushing mechanism and droplets secondary crushing theory was carried out. The results show that an asymmetric surface wave was formed around the surface of the spraying water tongue. As the amplitude of the vibration increased with an increasing distance, droplets formed in a wide range of sizes. Based on the theory of droplets secondary crushing, the maximum stable size value could be computed.(2) Under the factor of working pressure, sprinkler installation height, nozzle diameter and nozzle elevation, the complete fluidic sprinkler wetted radius were tested using single factor methods. By analyzing the wetted radius data, the multivariate empirical formula for complete fluidic sprinkler was built. On the basis of complete fluidic sprinkler, the wetted radius calculated model for other types of sprinklers was deduced by theoretical analysis. The error between calculated range and experimental values was lower than 5% for complete fluidic sprinkler and lower than 10% for other types of sprinklers. The results show these models could be used effectively in the engineering.(3) The droplets diameter and velocity of 3 sprinklers were measured by the Laser Precipitation Monitor(LPM) in the experiments for nozzle diameter of 4, 5 and 6mm, respectively. To improve the reliability of the test data, the “3? principle” was utilized to identify and eliminate the abnormal data. This paper did a systematic analysis for droplets distribution of the droplets diameter, the droplets frequency, the droplets speed and droplets kinetic energy. Besides, the droplets distribution models were established. The correlation coefficients of these models were all up to 0.9 in different pressures and nozzle diameter. Under different pressures, uniformity coefficients of specific power about the rectangle combination spacing of complete fluidic sprinkler were simulated by MATLAB. The rectangle combination spacing was 1.0R, 1.1R, 1.2R, 1.3R, 1.4R. The simulated results show that under the operating pressure of 0.15, 0.20, 0.25,0.30 and 0.35 MPa, the optimum combination spacing were 1.2R, 1.0R, 1.1R, 1.0R and 1.1R, and the uniformity coefficients of specific power were 56.6%, 71.1%, 76.2%, 77.2% and 72.9%, respectively. The results promote certain academic value to study the sprinkler external spraying characteristics, to optimize sprinkler structure and irrigation system.(4) Through further analysis of the forces for moving droplets in the air and exploring the relationship between air drag coefficient and droplet trajectory, the droplets motion model was established. On the basis of random simulation theory, the droplets trajectories were simulated by MATLAB software. The simulated results show that compared with the tested value, the simulated error for average droplet diameter reduced from 53% to 2% as an increasing distance. The simulated value for droplets cumulative frequency and droplets speed were almost as same as tested value in a small error. Both water distribution and kinetic energy, the relative error were lower than 20%. Therefore, the stochastic simulation method could simulate the sprinkler spraying droplets distribution characteristics, which provide as a good method to research the sprinkler hydraulic performance.