Optimization Design And Experimental Study For The Low Pressure Rotating Sprinklers

This research is one of the main contents of China National High-tech Program “Precision sprinkling irrigation technology and product”(Project No.2011AA100506)and the National Nature Science Foundation of China “ Study on the jet flow fragmentation mechanism and model of gas-liquid phases fluidic sprinkler”.Sprinklers are the key equipment of sprinkler irrigation system,and lowering the working pressure of sprinklers is one of the ways to reduce the energy consumption of the system.Rotary sprinkler is a new kind of variable speed sprinkler,and lowering the working pressure could cause some problems,such as hydraulic performance gets worse and sprinkler rotates unstable.Therefore,it is of great significance to optimize the structure of the rotary sprinkler.In this paper,theoretical analysis,experimental research and numerical simulation are used to study the new kind of variable speed sprinkler.The main research contents and results were as follows:(1)The structure and working principle of low-pressure rotary sprinkler were analyzed,and the influence of key parameters of damping mechanism on the hydraulic performance of the sprinkler was studied.The results showed that the rotating speed decreases gradually as the increase of the width of the gear,and the magnitude of the reduction was becoming larger under the same condition.Considering the hydraulic performance of the sprinkler,the best parameter of the gear width in the damping mechanism was 4mm,which the rotating speed was 0.94 r/min,the wetted radius was 11.8m and the combination uniformity coefficient was above 80%.(2)Numerical simulation and experimental research were applied to analyze the influence of outlet section shape on the internal flow field and hydraulic performance of sprinklers.The results showed that the optimal outlet section of the rotary sprinkler was inverted U shape,and the hydraulic performance of it was better than others.Taking 200 kPa as an example,the wetted radius of sprinkler with the inverted U shape nozzle was the longest,reached 12.2m,the ending average raindrop diameter was smallest,which was 4.81 mm,and the combination uniformity coefficient was 85.8% at the best combination distance 1.2R.(3)An orthogonal array was selected to study the influence of geometrical parameters on the hydraulic performance of sprinklers.The primary and secondary order of geometrical parameters which affect the comprehensive evaluation index of wetted radius and combined uniformity coefficient of low-pressure rotary sprinkler was achieved by comprehensive weighted mark method and range analysis method,which was elevation angle of outlet,arc length of flow passage,deflection angle of flow channel and shape of outlet.The best geometrical parameters of low-pressure rotary sprinkler was got,which the shape of outlet was inverted U,deflection angle of flow channel is 4.5 degree,arc length of passage shape is 29 mm and elevation angle of outlet is 19 degree.(4)PIV test method was applied to analyze the internal flow field,and comparing the inner field of optimized sprinkler with the original one.The results showed that the growth rate of the main jet velocity of optimized sprinkler was 1.03~1.19 times of that before optimization under the same pressure.The main jet velocity at the same position was 1.16~1.34 times of that before optimization as the working pressure increased.The hydraulic performance of optimized sprinkler was measured,and comparing it with the original one’s.The results showed that the hydraulic performance of optimized sprinkler was better than original one’s.Taking 175 kPa as an example,the wetted radius decreased 2.54%,while the best combination distance increased 8.33%,the uniformity coefficient increased 18.8% at the best combination distance and the ending average raindrop diameter decreased 12.5%.(5)Based on the fuzzy comprehensive evaluation method,the original and optimized sprinklers were evaluated.The evaluation index mainly included the wetted radius reduced coefficient,the combined uniformity coefficient,the irrigation water utilization,the variations of hit intensity coefficient and the specific gravity coefficient of raindrop diameter.The results showed that the comprehensive evaluation result of optimized sprinkler was better than the original one.