【作者】 张俊；

【导师】 卢秉恒； 赵万华；

【作者基本信息】 西安交通大学 ， 机械工程， 2009， 博士

【摘要】 在非压力补偿型灌水器中,迷宫型灌水器由于具有结构相对简单、水力性能好、制造成本低等诸多优点而广泛用于滴灌系统,但由于灌水器内部的迷宫流道结构细微弯曲,易发生堵塞,同时又要求具有良好的水力特性,因而水力性能和抗堵性能成为评价其性能优劣的两大重要指标。本文即在此背景下分别研究了迷宫流道灌水器的水力特性,探索了其堵塞机理,并为其水力性能与抗堵性能分别提出了新的评价方法,在此基础上根据二者之间的对立关系建立了一种迷宫流道的多目标结构优化方法。采用数值方法分析迷宫型灌水器的水力特性,计算模型分别选取层流、紊流模型,并进行了结果对比。由迷宫流道内部流体的流态分析得出层、紊流转捩提前,根据这一现象通过分析建立了三角形迷宫流道的特征参数与临界雷诺数之间的数学模型。对三角形和梯形迷宫流道灌水器进行水力性能的实验测试,借此从宏观角度检验数值方法预测水力性能的准确性以及层、紊流模型的适用性。此外,构建了迷宫流道内流体流动特性的可视化测试系统,并利用其可视化流道内部流体的微观流动特性,从微观角度验证数值计算的准确性。在此基础上,综合考虑迷宫流道单元的沿程损失和局部损失,提出以单变量——压力损失系数来评价灌水器水力性能的优劣,克服了以往双变量评价的不足之处。联合采用参数化设计方法和正交实验设计方法分析了迷宫流道特征参数对压力损失系数的影响关系,α影响最大,S/H和H/D其次,D/W影响最小,随后建立了两者之间的数学模型。为验证该评价方法的正确性,以主航道型迷宫流道为例,探索了其特征参数——圆弧半径比与压力损失系数的关系,发现二者呈负相关,该结论与主航道思想是吻合的。分别采用颗粒随机轨道模型和欧拉-欧拉双流体模型分析了灌水器迷宫流道内的液固两相流动规律,得到颗粒在迷宫流道内的运动轨迹以及可能出现沉积的区域,从数值上揭示了迷宫流道发生堵塞的机理,随后由颗粒的沉积和运动轨迹测试实验分别验证采用两种数学模型的液固两相数值计算的正确性。在此基础上提出一种基于颗粒通过率概念的迷宫流道抗堵性能评价方法,结果表明特征参数对颗粒通过率的影响程度为α>D/W>S/H>H/D,采用回归分析方法建立起颗粒通过率与流道特征参数之间的数学模型。将此评价方法用于主航道思想设计的迷宫流道,发现随着圆弧半径比的增大,颗粒通过率也随之增大,这一结论与主航道思想的特点是一致的。针对迷宫型灌水器的水力性能和抗堵性能之间存在的对立性,同时以评价水力性能的压力损失系数和评价抗堵性能的颗粒通过率为优化目标,采用基于NSGA-ΙΙ的多目标遗传优化方法分别求解出了梯形流道和主航道型迷宫流道各特征参数的Pareto最优解集,并可根据决策者的设计权重将其权衡解的求解转化为函数极小值的求解。该方法适用于同形不同尺寸的迷宫流道结构优化,为性能优良的灌水器结构定型提供理论依据。更多还原

【Abstract】 Labyrinth-channel emitters are widely applied in drip irrigation systems for such advantages as simple structure, high hydraulic performance and low manufacture cost among those pressure non-compensating emitters. However, due to their small size of the labyrinth channels, labyrinth-channel emitters are apt to clogging. Hydraulic performance and anti-clogging performance, therefore, are two important factors evaluating the quality of emitters. In this dissertation, the hydraulic characteristic and clogging mechanism of labyrinth channel are analyzed respectively, and new evaluation methods for both hydraulic and anti-clogging performances are developed. Finally, a multi-objective structural optimization model for labyrinth channels is proposed according to the relationship between hydraulic and anti-clogging performance.The hydraulic characteristic of labyrinth-channel emitter is numerically analyzed by both laminar flow and turbulence models respectively, and a comparison is made between the computational results by the two models. The analysis of the flow field distribution in labyrinth channels showed that the transitional Reynolds number from laminar flow to turbulence is much lower than 2300, a mathematic relationship is consequently established between critical Reynolds number and the key parameters of triangular labyrinth channel based on this result. On the other hand, the experiments on hydraulic performance of triangular and trapezoidal channel emitters are carried out to verify the predicted accuracy of numerical analysis from the macroscopical view and the applicability of laminar flow and turbulence model. In addition, the flow visualization system is constructed and the flow field behavior is visualized in labyrinth channels, which verify the accuracy of numerical simulation from microscopical perspective.In an overall consideration of the major and minor losses of labyrinth channel unit, a single variable, pressure loss coefficient (PLC), is presented to evaluate the hydraulic performance of emitters. Parameterized design method and orthogonal experiments method are introduced to study the relationship between the key parameters of labyrinth channel and PLC, the influence degree of each factor ranks as follows:α> S/H > H/D > D/W, and a model is regressed between them using the linear multivariable regression method. In addition, the key parameter of main-flow channels, the ratio of arc radius to the length of straight line, is discussed with PLC in order to validate the evaluation methods. The result shows that the PLC increases as the ratio decreases, which is coincident with the idea of main-flow channel.The liquid-solid two-phase flow in labyrinth channels of emitter is numerically simulated by using the stochastic trajectory model and Eulerian-Eulerian model. The trajectories and potential deposition regions of solid particles are obtained, which can be used to explain the clogging mechanism of labyrinth channels. And then the experiments on particle deposition and particle motion are performed to compare with the analysis of two-phase flow. According to the stochastic trajectory model, an evaluation method for anti-clogging performance of labyrinth channels is proposed by introducing the variable of passage rate of particles (PRP). The analytic results show that the key parameterαis the most important factor on PRP, and then D/W, H/D is least, and another mathematic model between the four key parameters and PRP is regressed. Furthermore, the evaluation method is also tested for main-flow labyrinth channels. The PRP increases as the ratio of arc radius to the length of straight line increases, which is in accord with the design idea of main-flow channels.Considering the contradiction between hydraulic and anti-clogging performance of the labyrinth-channels emitters, PLC evaluating the hydraulic performance and PRP evaluating the anti-clogging performance are chosen as the optimization objectives, and multi-objective genetic algorithm NSGA-II is employed to solve the Pareto fronts of key parameters of trapezoidal and main-flow channels. The trade-off solutions can be obtained by calculating the minimum value of the function according to the weights of equations. This optimization method is well applicable for the labyrinth channels with the same shape but different dimensions, which benefits to the structural finalization of emitters with high performance.更多还原