Space flow channel design of rotary sprinkler and hydraulic performance experiments at low pressure

A rotary sprinkler has been commonly used in a wide spray pattern in various irrigation systems, depending on the nozzle type, flow rate, and water pressure. The broad working pressure range of the sprinkler can require uniform water distribution, increased wetted radius, and stable operation under low pressure. In this study, a novel spatial structure of the flow channel was designed in the rotary sprinkler suitable for low pressure. The structure was greatly contributed to the increased driving force of sprinkler rotation, whereas, the outlet structure of the spatial channel was to promote the wetted radius and spraying uniformity. A numerical simulation was conducted to widen the rated working pressure range of the sprinkler using a computational fluid dynamics (CFD) software, where the elevation angle of the space flow channel, the offset angles of the middle and outlet section were taken as the factors, while the average speed, and the rotation driving force of the outlet as the indexes. The hydraulic performance was then evaluated under the structural parameters of the space flow channel. A comparative experiment was performed on the hydraulic performance between the low-pressure rotary and Nelson sprinkler. The results show that the average velocity at the outlet of the nozzle in the spatial channel and the uniform velocity distribution were closely related to the wetted radius of the sprinkler. The larger average velocity at the outlet was a benefit to the wetted radius of the sprinkler. The uniform velocity distribution maintained the water jet near the jet core area in the air, further improving the wetted radius of the sprinkler. A stable working range was better under the stable operation of sprinkler, and the greater driving force at low pressure. There was a relatively uniform velocity distribution of the flow field in Schemes 1, 5, 7, and 9, where the variation range of velocity at the outlet section was less than 40%, indicating the large average velocity. Therefore, Schemes 1, 5, 7, and 9 were conducive to the water jet near the jet core area for the better-wetted radius of the sprinkler. Schemes 2, 4, and 7 presented the larger average outlet speed of flow rate than others, where the maximum occurred in Scheme 7. An optimum parameter combination of spatial channel structure was obtained as follows: the offset angles of the outlet and middle section were 3.0°, and 3.5°, respectively, and the elevation angle of the spatial channel was 30°. The significant level of each factor on the average velocity of the nozzle outlet was ranked in descending order: the elevation angle of the spatial channel, the offset angle of the middle section, and the offset angle of the outlet section. The influence degree of each factor on the rotating driving force of the nozzle was also ranked in the descending order of the middle section offset angle, spatial channel elevation angle, and outlet section offset angle. An optimal pressure of 150 and 200kPa was achieved, where the wetted radius of the rotary sprinkler remained basically unchanged, indicating a more stable operation, a more uniform water distribution, and a higher uniform coefficient than before. Consequently, the maximum uniform coefficients were 74% and 86% under the working pressure of 150 and 200kPa, respectively, when the rotary sprinkler was arranged in the square combination.