Effects of nozzle elevation and length on hydraulic performance of negative pressure feedback jet sprinkler

The negative pressure feedback jet sprinkler is a new type of irrigation nozzle independently developed by China. The nozzle is an important part of the sprinkler. Due to the unique water flow of the jet sprinkler, the ejection mechanism is intermittently deflected from left to right, the water will collide with the inner wall of the nozzle, and the collision will cause a large amount of energy loss. Appropriate nozzle parameters are conducive to reducing the head loss and increasing the nozzle range and the uniformity of the combined irrigation. In order to specifically study the influence of nozzle parameters (including elevation angle and length combination) on the hydraulic performance of negative pressure feedback jet sprinklers and find the optimal nozzle parameter combination, the sprinkler comparison tests for negative pressure feedback jet sprinkler and PY210 rocker sprinkler under different nozzle parameters were performed. The main parameters of the PY210 impact sprinkler were the elevation angle of the main and auxiliary nozzles 30°, the length 45 mm×25 mm, and the diameter of the main and auxiliary spray head 4 mm×3 mm. The controlled variable method was used in the test. Namely, keeping the other dimensions of the sprinkler unchanged when studying the influence of different main and auxiliary nozzle elevation angles on the hydraulic performance of the sprinkler. The parameters mainly for the jet mechanism were offset 2 mm, side wall inclination angle 10°, split pitch 28 mm, main and auxiliary nozzle length combination 4.2 cm×4.2 cm, main and auxiliary nozzle spray head 4 mm×4 mm. Similarly, when studying the effect of different nozzle combinations on the hydraulic performance of the jet sprinkler, the elevation angle of the main and auxiliary nozzles was controlled to 30°, and the size of the spray mechanism was the same as the diameter of the main and auxiliary nozzles. At the same time, considering that the main and auxiliary nozzles adopt different elevation angles, the pressure on the nozzles will be asymmetric, which will affect the rotation uniformity of the nozzles. During the tests, the elevation angles of the main and auxiliary nozzles will be synchronized. In order to reduce the test error, the tightness of the rotation mechanism was adjusted by adding or removing plastic gaskets during the test, and then the rotation period of the nozzle was controlled. According to the GB/T 50085-2007, the rotation period was controlled from 3 min to 3.5 min. The specific test scheme design refers to the national standard GB/T 22999-2008. The experimental results showed that with the same nozzle size, the range of the negative pressure feedback jet nozzle was 1-2.5 m farther than the PY210 impact sprinkler under different working pressure and different nozzle parameters. The range of the negative pressure feedback jet nozzle was far because of its unique pulse characteristics, which resulted in the strong pulse turbulence of the outgoing water stream. In the negative pressure feedback jet nozzle, the water distribution of the nozzle showed a good “triangular” distribution in the short range. The water volume distribution showed a “water volume peak” far away from the sprinkler, and as the pressure increases, the “water volume peak” gradually disappeared. The formation of the “convex peak” of water volume is mainly due to the large turbulent kinetic energy of the intermittently ejected water jet from the jet nozzle, which resulted in a larger water droplet at the end, so the end has more water. Finally, based on the measured experimental data, a comprehensive scoring method and an entropy weight method were used. Taking into account the wind resistance of the sprinkler field work and the nozzle cost, the parameters of the main and auxiliary nozzles under the optimal comprehensive score were determined as follows. The length of the main and auxiliary nozzles was 4.2 cm×4.2 cm, when the working pressure was 0.20-0.30 MPa, the elevation angle of the main and auxiliary nozzles was 40°×40° while the working pressure was 0.35 MPa, the elevation angle of the main and auxiliary nozzles was 30°×30°.