Structural Optimization And Hydraulic Performance Characteristics Of Dynamic Fluidic Sprinkler For Saving Irrigation Water

This research was supported by the National Key Research and Development Program of China?No.2016YFC0400202?and the Key R&D Project of Jiangsu Province?Modern Agriculture??No.BE2018313?.The performance of sprinklers can be evaluated by using several performance indicators.These indicators are measurable variables or coefficients that describe the condition and operation of the sprinkler system.The sprinkler head is a key factor that affects the quality of sprinkler irrigation.Both developed and developing countries in the world have been committed to research and develop sprinklers which efficiently operate at low-pressure condition since low-pressure sprinkler irrigation is gaining momentum all over of the world.In this research,a newly designed dynamic fluidic sprinkler?DFS?was developed to improve hydraulic performance of the existing complete fluidic sprinkler?CFS?under low-pressure conditions.Extensive experiments were conducted under different types of nozzles at different operating pressures.The main contents and innovations of this dissertation were as follows,?1?The structure of the fluid component of CFS was optimized and the optimal combination of the newly designed sprinkle was studied.A newly designed DFS and nozzles size were designed and manufactured.The significant structural parameters of the new DFS used for this study were the length of the tube,working pressure,the diameter of the tube,nozzle diameter,and are represented by Factors A,B,C,and D,respectively.An orthogonal array with four factors and three levels was selected;the direct technique was employed to analyze the test data.The results confirmed the optimal values of the DFS structural parameters.The length of the tube is 25 mm,the working pressure is 150 kPa,the diameter of the tube is 3 mm,and the nozzle diameter is 5 mm.The influencing factors in decreasing order of importance were as follows:working pressure,length of the tube and nozzle diameter for CU and nozzle diameter,working pressure and diameter of the tube for range.The optimal combination of structural parameters was achieved with the factor combination of A3B1C3D1.?2?Numerical simulation of the inner flow characteristics was conducted and the simulation and experimental results were compared on the quadrant completion time of rotation using FLUENT software.The mathematical model for simulation of the inner flow distribution of the sprinkler was obtained by using computational fluid dynamics.A detailed study of the relationship between the velocity distribution,length of tube and nozzle sizes were studied.The results showed that maximum velocity occurred around the fluidic element.By comparison,the length of the tube and nozzle size had a significant influence on rotation speed,5 mm nozzle and 25 mm length of tube gave the optimum value of 50 and 55s,respectively.It was found that the rotation speed decreases approximately linearly as the length of the tube increases.There was a difference between calculated,simulated and experimental.The minimum average deviation between the calculated,simulation and experiment was 3.5%,whiles the maximum was 5.7%.The relative error was less than 4%for validated results indicating a perfect correlation between the values of numerical simulation,calculated and experiment results.According to the equation,the nozzle diameter,length of the tube and the operating pressure had a significant influence on the rotation speed of the test sprinkler.This study provides baseline information to improve water application efficiency in sprinkler irrigated fields?3?The hydraulic performance characteristics of DFS was evaluated.MATLAB R 2014a software was employed to establish the computational program for the computed uniformity.Droplet sizes were determined using a Two-dimensional video Distrometer technique.The results showed that the nozzle with a diameter of 5 mm gave the highest coefficient of uniformity value of 86%at a low pressure of 150 kPa.The comparison of water distribution profiles for the nozzle sizes?2,3,4,5,6 and 7 mm?at different operating pressures?100,150,200,250 and 300 kPa?showed that a 5 mm nozzle size produced a parabola-shaped profile at150 kPa.The mean droplet diameters for the nozzle sizes of 2,3,4,5,6 and 7 mm ranged from0 to 4.2,0 to 3.7,0 to 3.6,0 to 3.2,0 to 3.9 and 0 to 3.8 mm,respectively.The comparison of droplet size distributions showed that 5 mm had an optimum droplet diameter of 3.2 mm.The largest droplet sizes had a maximum value of 4.2 for a 2-mm nozzle size.For all the nozzles sizes,5 mm produced better results for hydraulic performance,which can significantly improve the performance and save water in sprinkler-irrigated fields.?4?A model was developed to simulate the effect of riser height on rotation uniformity and application rate of the newly designed DFS.It was found that the effect of riser height had a significant effect on application rate and uniformity.The comparison of standard deviation at different risers showed that differences in standard deviations were much lower for 1.9 m riser height.The differences in standard deviations were much lower for all the nozzle sizes under150 kPa.The deviation ranged from 0.14⁰.26,0.14⁰.42,0.18⁰.45,0.2⁰.66 mm h^-1considering the height of 1.9,1.7,1.5 and 1.3 m,respectively.For the nozzle sizes,5 mm gave better standard deviations and the deviations ranged from 0.14⁰.26,0.15⁰.45,0.2⁰.7,0.23⁰.74 mm h^-1 at radial heights of 1.9,1.7,1.5 and 1.3 m,respectively.The range of coefficient of uniformity values for overlapped quadrants for 5 mm nozzle was as follows:78%at a spacing of 10%to 72%at 80%spacing of overlapped.The highest occurred at 50%spacing and increased with an overlapped spacing of 10 to 50%,ranging from 78 to 87%with an average of 82.5%.?5?A comparative evaluation of the hydraulic performance was conducted of a newly designed DFS,CFS,and D 3000 rotating spray sprinklers.In this study,the droplet size and velocity distribution of three kinds of sprinklers were measured by a Thiess Clima laser precipitation monitor under indoor conditions and simulated CUs were calculated from application rate data.The results showed that the discharge coefficient of the DFS and D3000 was slightly larger than that of the CFS.The water distribution profiles of the DFS,D3000,and CFS were parabola-shaped,ellipse-shaped,and doughnut-shaped,respectively.It was observed that CFS had the largest radius of throw under 200kPa than DFS and D3000.The mean value of the coefficient of discharge was 0.58,0.70 and 0.75,for CFS,D 3000 and DFS,respectively.The comparison of velocity distribution showed that the maximum frequency value was obtained at velocities of 1 m/s for each combination.Velocities for DFS and D3000 droplets were similar but not identical.Overall,CFS tends to give greater velocities than DFS or D3000.Individual spray sprinkler water distributions were mathematically overlapped to calculate the combined uniformity coefficient?CU?.Maximal combined CUs of 81.83,81.2,and 80.83%were found for the DFS,D3000,and CFS,respectively.Both the DFS and D3000 were found to have greater CU values than the CFS,which indicates that the DFS and D3000 provided a better water distribution pattern than the CFS at low pressure.The study can give a reference to the operation for saving water and cost reduction.