HighlightsExperiments were conducted to investigate the hydraulic performance of the solid-set rotating sprinkler.The effects of nozzle shape and working pressure on the droplet characteristics and kinetic energy of the rotating sprinkler were analyzed.The circular nozzle has a large wetting radius and large droplet size.Use of a non-circular nozzle could result in higher irrigation uniformity and lower kinetic energy imparted to the soil surface by water droplets under low working pressures.Abstract. Reducing the working pressure of sprinklers can effectively reduce sprinkler irrigation energy requirements. However, the reduction in working pressure and variation of nozzle shape inevitably lead to changes in the hydraulic performance of the sprinkler. To evaluate the spray characteristics of selected non-circular (the shape of the nozzle opening was asymmetric) and circular nozzles at low pressure, experiments were conducted to investigate the effects of working pressure, nozzle shape, and nozzle diameter on flow rate, radius of throw, water application rate, droplet size, droplet velocity of the rotating sprinkler, and kinetic energy of the water droplets impacting on the soil surface. The coefficients of irrigation uniformity were calculated for the non-circular and circular nozzles under different rectangular sprinkler spacing and working pressures. The results show that the flow rates of the non-circular and circular nozzles were equal under the same working pressure and with the same nozzle size, while the throw radius of the circular nozzle was longer than that of the non-circular nozzle. The circular nozzle produced a larger droplet size than the non-circular nozzle did. Since the droplet size and kinetic energy per unit droplet volume increased along the radius of throw, and the peak water application rate of the circular nozzle was located near the perimeter of the radius of throw, the peak specific power impact on the soil surface by the water droplets of the circular nozzle was greaterspecifically, 1.26 to 1.97 times that of the non-circular nozzle. With the increase in working pressure, the peak values of specific power and water application rate decreased. The irrigation uniformity coefficients of the non-circular and circular nozzles were more than 85% within the recommended pressure range of the manufacturer when the sprinkler spacing was less than 11 m. It was easier to obtain higher irrigation uniformity and lower impact kinetic energy under low working pressure when using a non-circular nozzle. Keywords: Application rate, Irrigation uniformity, Kinetic energy, Sprinkler irrigation, Working condition.

The characteristics of spray droplets are important for calculating the hydraulic performance of sprinklers. In order to evaluate the effects of working pressure and nozzle diameter on the near ground droplet characteristics of the Nelson R33 sprinkler, an experiment was conducted to test the droplet size and velocity by using a two-dimensional video disdrometer (2DVD). Based on the water application rate, droplet diameter and velocity, the kinetic energy was calculated. The results show that there is an exponential positive correlation between the range and the volume-weighted mean particle size of droplets (VMD). The average kinetic energy of a single droplet fits well with the power function model. Under the minimum pressure of 200 kPa, the diameter and kinetic energy of droplets are large, and the peak values are 5.67 mm and 0.0092 J, which are 1.14 to 1.62 times and 1.18 to 5.68 times those of other working conditions, respectively. When the nozzle diameter is the smallest (4.4 mm), the droplet diameter and peak kinetic energy are 1.12 to 1.58 times and 1.02 to 1.26 times higher than 4.8 and 5.2 mm. Therefore, it is not recommended to work under the condition of less than 250 kPa, and a small-diameter nozzle should be selected while ensuring uniform kinetic energy.

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HighlightsA hydraulic model was used to determine the value of the equivalent length for evaluating local emitter head losses in drip laterals.Dimensional analysis was used to develop an equation for predicting the equivalent length.The effects of the design variables on the equivalent length were investigated.The accuracy of the equation was validated by a previous experiment and an alternative hydraulic model.Abstract. The equivalent length is widely used in current hydraulic models to estimate local emitter head losses for the analysis and design of drip irrigation laterals. The accurate evaluation of the equivalent length is therefore required in the lateral design procedure. In this study, a finite element model was used to develop an equation to predict the equivalent length. Eight design variables were selected, and 32 lateral cases were generated using the orthogonal design. The total local head loss in the 32 laterals were firstly calculated using the local head loss coefficient multiplied by the kinetic head. The solutions were considered as exact values and being equivalent to friction head losses, and the equivalent length was computed using the Darcy-Weisbach equation. Dimensional analysis and regression procedures were then used to obtain the prediction equation related to the selected variables. The results show that the converted equivalent lengths accurately estimated the local head losses in the 32 laterals. The local head loss coefficient was the most important factor for the equivalent length, followed by the lateral diameter. The effects of the lateral inlet pressure head, flow exponent, nominal flow rate of emitter, number of emitter, emitter spacing and lateral slope were not significant. Two models were developed to predict the equivalent length, and to calculated the total local head losses. The results demonstrated satisfactory agreement with the measured value available in a previous experimental study, with RMSE = 0.202 and 0.162 m for the full and simplified model, respectively. The percent error between the measured and calculated total head losses using simplified model was from -16.5% to 14.8%, and the Camargo and Sentelhas coefficient c was higher than 0.98. The equations were therefore capable for evaluating the local head loss in the hydraulic design of drip irrigation laterals. Keywords: Dimensional analysis, Finite element method, Hydraulic design, Pressure head, Uniformity.