【作者】 Frank Agyen Dwomoh；

【导师】 Yuan Shouqi； Li Hong；

【作者基本信息】 江苏大学 ， Fluid Machinery and Engineering， 2013， 博士

【摘要】 本研究由“国家高技术研究发展计划”(863计划,项目编号：2011AA100506)及“国家农业科技成果转化资金”(2011GB2C100015)资助。喷灌作为适应性较强的灌溉方式之一,应用广范,甚至能应用于地面灌溉不太适宜的场合。因此,包括中国在内的多个国家都致力于喷灌技术的发展。全射流喷头是中国人发明的一种新型旋转式喷头,具有结构简单、能耗低、成本低的优点。虽然已展开了一些理论分析、数值模拟和室内试验研究,有助于从结构和水力性能方面改善全射流喷头,然而,对全射流喷头在田间受风影响时的性能评估研究较为缺乏。因此,本文主要考虑全射流喷头田间有风时的工作情况,研究全射流喷头多指标和影响因素下的性能特征,目的在于提高其工作性能,给出改进途径和方法。论文第一部分是针对不同工作压力下(200、250、300、350kPa)全射流喷头及摇臂式喷头的水力性能进行测试及对比分析,研究喷头旋转一周四个象限内喷头转速对喷灌强度的影响。结果表明：各象限间喷头旋转时间稍有不同,且趋势不一。各象限的喷头旋转时间偏差(标准差)越大,喷灌强度越低。对四条甚至更多的射线上的水量分布进行平均,且每个象限内至少有一条射线包括在内,得到的喷头水量分布比只考虑其中一条射线上水量分布更准确,组合喷灌均匀性比非组合喷灌均匀性更高。喷头同一组合方式下组合喷灌强度也会稍有差异。适宜的喷头间距是减小喷头转速的非均匀性对喷灌强度及水量分布影响的重要因素。论文第二部分,采用MATLAB软件建立了以均匀性为目标的喷头间距计算模型。该方法将单喷头试验得到的水量分布数据作为一个多维向量。为计算方便,在行、列两个方向上对水量未喷洒到的区域以零向量补充,从而对原始数据进行修正。不同喷头间距下的组合喷灌水量分布通过将原始数据与组合时对应区域的水量分布叠加得到。该计算模型可以得出方形、矩形、三角形布置时的喷头水量分布。四个组合喷头的均匀性由室外低风速、相同工作压力下单喷头的水量分布数据换算得到,误差仅为1.60%。该模型可以对单喷头水量喷洒图形、组合喷灌三维水量分布图、喷灌强度等进行估计,以便于喷头的选择及为布置方式或运行条件的改善提供建议。该模型可以作为喷头布置方式的决策模型,以保证最优的喷头间距及布置方式,从而使喷灌均匀性较高。第三部分主要研究在受风速影响下的全射流喷头,包括单喷头和固定式模式两种。通过捕捉确定水的应用率可以通过在不同风速条件和运行压力的实验来实现。通过对量雨筒内水量的测量来计算均匀系数。应用Excel和MATLAB进行方差分析、统计检验、回归、相关分析来分别统计分析、数据插值和3D显示。结果表明,当风速超过2.3m/s时喷灌强度达到峰值。随着风速的增加,湿润面积显著减少,当风速小于3.5m/s时,其范围在1.8%到25%。在强风条件下,减小喷头间距不能提高喷洒均匀性。在间距为16x18且顺行风速大于3.5m/s时,CU值的范围低于58.8%。当风速小于1.5m/s,间距为16x16时,CU值高达89%。灌溉时风速小于3.5m/s时,一般采用平均均匀性系数值。在第四部分研究中,应用了一个模型来定量描述飞行水滴动态风漂移。修正后的指数模型用来模拟水滴大小分布。该研究还提出了一个计算水滴漂流总量的公式。这个公式基于这样一个假设：超出水滴特征湿润半径的水滴飞行被认为是通过风速影响下喷头的漂移损失。灵敏度分析表明,水滴的漂移对液滴尺寸最敏感,其次是水滴的初始速度及风速,对喷嘴高度的敏感性最小。比起大水滴,小直径水滴漂移很大,但在大多数情况下不会损失于风漂移。风速方向对范围缩短及风漂移的影响通过模拟顺风和逆风两种状况来描述。我们发现顺风时润湿半径增加,但逆风时减少的比例很小。值得注意的是,与直径为0.5至4.5mm之间的水滴相比,直径在0.05至0.2mmm之间的水滴大部分产生了漂移。例如：当工作压力为300kPa,风速为2.5m/s时的条件下,水滴直径在0.5至3.94mm之间的水滴并没有导致风漂移损失,尽管它们产生了漂移。只有水滴直径为4.45mm,占水滴总数的0.92%,和水滴直径小于0.2mm,占水滴总数小于3%的的水滴漂移超出它们的特征距离,因此被认为是由于风漂移损失了。其余的水滴主要使水量分布形状产生变形。本文的主要创新点如下：采用覆盖面积减少百分比的概念,分析了风速风向对水量分布变化的影响。在一条射线射程的末端横截面上,建立了水滴漂移模型公式,该模型可准确地模拟喷头的间距、布置方式和水滴的飞行距离。更多还原

【Abstract】 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.更多还原