Experimental study on rotational speed and uniformity of rotary damping nozzle

A sprinkler is one of the most important components in irrigation. Existing studies have systematically revealed the effects of some factors, such as the sprinkler disc structure, nozzle diameter, and working pressure on the hydraulic performance of the sprinklers. Among them, the rotational speed uniformity of the rotating-damped sprinklers can play a crucial role in the stable water distribution, leading to the uniform irrigation in the sprinkler systems. However, the fluctuations of the rotating speed can cause the uneven distribution of the water, thus reducing the crop growth and water use efficiency. Therefore, this study aims to explore the influence of the damping grease viscosity on the rotational speed uniformity of the rotating-damped sprinklers. The key influencing factors on the rotational speed uniformity were also determined to improve the sprinkler performance and irrigation quality. The research object was then used as the R3000 rotating-damped sprinkler with the damping greases of different viscosities. A systematic investigation was implemented to clarify the influence of the damping grease viscosity on the hydraulic performance of the sprinkler. An emphasis was put on the effects of the different working parameters and sprinkler disc structures on the rotational speed stability. The low-cost, low-vibration, constant-speed sprinklers were obtained to replace the low-pressure impact ones. The sprinklers were equipped with the improved damping grease No.1 and No.2 (where No.1 and No.2 referred to the original damping grease modified by the addition of silica micropowder at the mass-volume fractions of 15% and 20%), and imported damping grease. Two loading levels were intended to tune the viscosity and damping behavior under operating conditions. Rotational speed was measured in real time using a Hall sensor. A series of experiments was conducted at different temperatures, sprinkler disc structures, and working pressures. Experimental results demonstrated that the Grease No.2 with 20% silica micropowder delivered the best performance under a variety of operating scenarios. The superior rotational-speed stability and operational robustness are also exhibited among the formulations. Taking the brown sprinkler disc as an example, the rotational speed fluctuation for the No.1, No.2, domestic, and imported damped sprinklers were 1.186%-8.503%, 0.075%-1.769%, 0.717%-8.455%, and 0.182%-2.287%, respectively, under low temperature and low pressure, such as 10°C and 103 kPa. Notably, the No.2 damped sprinkler exhibited the smallest variation in the rotational speed fluctuation, thereby performing closest to the imported sprinkler. The rotational stability was also surpassed that of the imported sprinkler under these specific conditions. Furthermore, the rotational speed fluctuation ranges were 1.252%-9.783%, 0.611%-3.990%, 0.488%-5.476%, and 0.065%-3.574%, respectively, for the same four sprinkler types with the brown disc under high temperature and high pressure, such as 30 °C and 137 kPa. Once again, the No.2 damped sprinkler shared the lowest fluctuation of the rotational speed. The better performance was comparable to that of the imported sprinkler. In summary, the optimal modifications of the Grease No.2 were fully achieved in the better performance of the No.2 damped sprinkler. There was the long-term stability of the No.2, domestic and imported damping grease under high pressure over extended periods. After continuous operation for 9 h at a working pressure of 207 kPa, the average rotational speeds of the sprinklers with the three types of damping grease were 3.80, 10.33, and 4.81 r/min, respectively, with the average rotational speed fluctuation rates of 3.66%, 10.78%, and 0.97%, respectively. The performance of the No.2 grease sprinkler was closest to that of the imported grease sprinkler, compared with the domestic ones. However, the rotational speed of the No.2 grease sprinkler was lower, due to its slightly higher viscosity, compared with the imported ones. According to the high viscosity of Grease No.2 at low temperatures and its viscosity reduction at elevated temperatures, the proportion of the silica micropowder can be expected to optimize the stability under high-temperature and long-duration operating.