Hydraulic Performance And Droplet Fragmentation Characteristics Of Dynamic Fluidic Sprinkler

This research was supported by the National Key Research and Development Program of China(No.2016YFC0400202).The performance of Sprinkler can be evaluated by using a number of performance indicators.These indicators are measurable variables or coefficients that describe the condition and operation of the sprinkler system.Nozzle is the key equipment that affects the quality of sprinkler irrigation.Both developed and developing countries in the world have been committed to research and develop multifunctional,energy-saving and low-pressure nozzles.The goal of this research work was to improve the rotary nozzle under medium and low pressure working conditions,the major challenge with the existing rotary nozzle is inability to obtain signal water from the complete fluidic sprinkler.In this research,two-dimensional grid numerical interpolation,photographic method and particle tracking velocity measurement technology were used to study the hydraulic performance and water droplet breaking characteristics of the dynamic fluidic sprinkler.The main research contents include the following aspects:In the first study,Selection of four factors of the position difference,the length of the action zone,the angle of the water hole,and the diameter of the water hole.Each factor takes 3 levels.9 nozzles were designed for orthogonal test,and 9 sets of designed schemes were obtained under stable condition.The stepping frequency and stepping angle were taken as the test index by the step frequency and step angle of the nozzle.The influence law of the selected parameters on the test index was analyzed by the range analysis method,and the structural scheme with best nozzle was selected.The main structure of sprinkler head has the following parameters: angle of water dividing hole,diameter of water dividing hole and length of action zone.In the second study,the external characteristic test of the nozzle was carried out,and the influence of pressure and installation height on the flow coefficient,range and radial water distribution of the nozzle was studied.The rotation speed of the nozzle in 10 ray directions was measured,and the radial water volume and circumferential rotation speed of the nozzle were converted into grid type data in the irrigation area by spline interpolation,and the threedimensional water distribution under single nozzle and combined sprinkler irrigation was simulated.The uniformity coefficient and distribution uniformity coefficient of the nozzle under different combinations of spacing,different working pressures and pressure fluctuations were calculated.The simulated results showed that the watering peak of the nozzle decreased with an increase in pressure and eventually stabilized.The 1.4m installation height of the nozzle and the triangular combination of 1.4R spacing should be adopted under the pressure of 0.25 MPa.When the nozzle spacing was 1R,the water volume of the square combination under different pressures gradually decreased from the center to the periphery.There were three water concentration areas in the triangular combination sprinkler irrigation,and the water volume increased gradually from the edge as the pressure increased;The square combined sprinkler irrigation under the pressure of 0.2~0.3MPa had no significant effect on the uniformity of sprinkler irrigation and the peak of irrigation.The third study focused on,building a high-speed photography test bench,taking pictures of the water droplet movement of the nozzle,and extract the morphological characteristic parameters of the water droplet after pre-processing steps such as filtering,denoising,binarization,image filling and elimination of non-target water droplets.The parameters such as the arithmetic mean diameter,median diameter and standard deviation of the water droplets at the pressure of 0.2~0.3 MPa and the nozzles from 6 to 8 m were calculated.The three factors of working pressure,installation height and distance from the nozzle were discussed.The study showed that the cumulative frequency of water droplet diameter at 6~8m agreed with the Boltzmann distribution law.The order of influence on the degree of water droplet breaking is working pressure,distance from nozzle and installation height.In the fourth study,Using PTV technology to process a series of frame water droplet images,extracting the horizontal speed,vertical speed and combined speed of the water droplets moving from 0.2 to 0.3 MPa and 6 to 8 m from the nozzle,and establishing the water droplets at this point.The distribution model of velocity and frequency counts the numerical characteristics such as the maximum,minimum and variability of water droplet velocity.Finally,the trajectory of water droplets at 9m was simulated.The results showed that the established mathematical model can accurately reflect the movement law of the nozzle water droplets.The determination coefficient of the model fitting was above 0.9.The speed of a few water droplets in the water droplet group was much larger than the average speed of the water droplet group.The drop angle of the nozzle at 9m has a good log-normal distribution trend,and the impact angle increases as the pressure was increased.