Hong Li, Junping Liu, Yue Jiang
Research Center of Fluid Machinery Engineering and Technology, Jiangsu University, China
Lowering the pressure of the sprinkler irrigation system is an effective way to save energy and water. However, when the sprinkler runs at a lower pressure, out of the operating pressure range, it will result in a uniform water distribution, with too much water concentrating at the end of the range distance. The research on the water jet breakup characteristics and spraying droplets movement of sprinklers will help to know the spraying mechanism under different pressures, which will help to improve the distribution under lower pressures.
The dispersion equation of cylindrical jet was established based on the surface wave linear instability theory. The rules of jet maximum perturbation growth rate and unstable wave number changing with the nozzle radius, jet speeds and nozzle angles were also studied. The theoretical values of jet breakup length were calculated based on the theoretical analyses and experiment data. Experiments using a particle image velocimetry (PIV) technique and a high-speed photography (HSP) technique were carried out to investigate the influences of nozzle geometric parameters and injection pressure on jet breakup characteristics. The flow fields, concentration fields of jet flow and the lengths of the initial section and breakup section of jet flow were obtained and analyzed. And then numerical simulations were carried out using finite volume method and Level set-VOF method to obtain velocity flow and phase distribution outside the nozzle, describing the unstable development of gas–fluid interface, the breaking process at the initial section and breakup section. The lengths of the initial section and breakup section of jet flow were measured and compared with the experimental results.
The characteristics of spraying droplets were researched by the droplets distribution experiment with a Thies Clima laser precipitation monitor (TCLPM). The mathematical models of spraying droplet sizes, frequencies, speeds and kinetic energy distributions were established based on the test. The motion trajectories of spraying droplets were simulating calculated based on the establishment of droplet moving model and random distribution model. The good consistency of the calculation results and experimental results showed that the models could simulate the characteristics of spraying droplet distribution well.
