Performance Characteristics And Droplet Drift Dynamics Of Irrigation (Fluidic) Sprinklers

This research was supported by the Program for National Hi-tech Research and Development (863program, No.2011AA100506) and Program No.2011GB2C100015of China. Sprinkler irrigation stands out as one of the most versatile methods of irrigation that has enhanced the expansion of irrigation even onto lands categorized as unsuitable for surface irrigation. Several countries, including China, are investing into the development of sprinkler irrigation systems. The complete fluidic sprinkler is a relatively new type of rotating sprinkler head invented in China. It has the prospects of being easy to construct, low-loss of energy and low price. Several theoretical, numerical and indoor studies have been conducted which have helped to improve upon the structural and hydraulic performance of the fluidic sprinkler. However, the assessment of the fluidic sprinkler’s performance on the field under the influence of wind is limited. This study therefore sought to investigate the performance of the fluidic sprinkler on the field, under windy conditions with the goal to give recommendations for improving upon its operational performance. The performance characteristics of the fluidic sprinkler under some performance indicators and factors form the major focus of this research.In the first study, indoor catch-can experiments were performed at varied operating pressures (200,250,300and350kPa) using the fluidic sprinkler and the well-known impact sprinkler (for the purpose of comparative analysis). The goal was to investigate the extent and effect of variation in sprinkler rotation speed on water application intensity in the four quadrants of rotation. The results showed slight variation in rotation time from quadrant to quadrant, albeit, not in constant trend through the quadrants. An inverse relationship between water application intensity and relative standard deviation in rotation time was observed. Among others, the results also showed that averaging four or more radial water distribution profiles, with at least one profile from each of the four quadrants, gives a better approximation of the real situation than using only one radial leg to characterize the distribution pattern for the fluidic sprinkler and for that matter most sprinkler. Overlapped quadrants improved coefficient of uniformity over non-overlapped quadrants. However, slight differences between CU values of overlapped adjacent quadrants were observed for the same configuration of the sprinkler. Proper sprinkler spacing is highly essential to minimize the effect of rotation speed variation on water application.In the second study, a computational model for simulation of sprinkler spacing for optimum uniformity was formulated using MATLAB (Matrix Laboratory). The approach used considers the observation pattern from a single leg sprinkler system as a multidimensional array. Necessary zero arrays are inserted in rows and columns where no water was applied. This leads to a modified array of data which contains the original data set. Overlapped pattern elements are computed by adding corresponding elements of the same or different distribution pattern for desirable sprinkler spacing. The computational model extends application to square, rectangular and triangular layouts of sprinklers. Coefficients of uniformity of four overlapped sprinklers using12different sprinkler spacing’s, simulated by the model were compared with that from measured field data under low wind conditions and same operating conditions. They gave a mean absolute error of1.60%. The model is capable of estimating sprinkler pattern profiles,3D plots of water distribution patterns and sprinkler irrigation performance indices for sprinkler selection and evaluation for improvement. The computational model can serve as a decision support model for sprinkler irrigation layout design to ascertain optimum spacing and layout type for uniform water distribution pattern.The third study focused on the field performance characteristics of the fluidic sprinkler under the influence of wind in both single sprinkler and solid set modes. Water application rates determined through catch-can experiments under different wind speed conditions and operating pressures for both set ups concurrently by means of graduated measuring cylinders were used to calculate the coefficient of uniformity. Statistical analysis, data interpolation and representation in3-D were performed using the ANOVA statistical test, regression, correlation analysis tools in Excel and MATLAB, respectively. Results showed that water application intensities peaked as wind speed exceeded2.3m/s. Wetted surface area reduced significantly with increasing wind speed, ranging from1.8%to25%for wind speeds less than3.5m/s. Under high wind conditions, decreasing sprinkler spacing could not significantly improve uniformity. The CU values ranged from as low as58.8%for the16x18spacing under prevailing wind conditions of above3.5m/s to as high as89%for the 16x16spacing under prevailing wind condition of less than1.5m/s, respectively. The average coefficient of uniformity values for the irrigation events under wind speed less than3.5m/s were, however, encouraging.In the fourth study, a model to quantify and describe the dynamics of wind drift of in-flight droplets was investigated. The modified exponential model for droplet size distribution was used during the simulation. A formulation for calculating the total volume of water drifted in the droplet distribution is reported. The formulation is based on the hypothesis that droplets which travel beyond their characteristic wetted radius are lost to wind drift for a sprinkler under the influence of wind. The sensitivity analysis performed showed that droplet drift was most sensitive to droplet size, followed by initial velocity of projected droplets, wind speed and least sensitive to nozzle height. Smaller diameter droplets drifted greatly, but were in most cases not lost to wind drift compared to the larger droplets. Both down and upwind conditions were simulated to describe the effect of wind direction on range shortening and wind drift. We found out that droplet travel distance increased downwind, but in lesser proportions compared to upwind decrease. It is worthy of note that droplets of smaller diameter (0.05to0.2mm) were extensively drifted compared to the larger droplets (0.5to4.5mm). For example, when the condition was300kPa and2.5m/s, droplets sizes between0.5mm and3.94mm did not travel beyond the characteristic wetted radius even though they were drifted. Only droplets of diameter4.45mm, representing a frequency of0.92%and droplets of diameter less than0.2mm representing a frequency of less than3%of the total number of droplets traveled beyond the wetted radius. The remaining droplets have a higher probability of contributing to distortion of the distribution pattern.Among other things, the main innovations in this dissertation are as followings:Analysis of the wind distortion of the distribution pattern due to wind drift using the percentage coverage area reduction concept. Formulation of the percentage droplet volume drifted beyond the wetted radius for the single leg radial transects. The development of formula and codes for the simulation of sprinkler spacing, layout and droplet travel distance.