【作者】 李琳；

【导师】 邱秀云；

【作者基本信息】 新疆农业大学 ， 水利水电工程， 2008， 博士

【摘要】 我国华北、西北和新疆一带的众多河流都具有高浑浊水的特点,且泥沙粒径极细,小于0.03 mm粒径的泥沙占含沙总量的40%以上,处理起来十分困难。本课题研究的《浑水水力分离清水装置》可以从高含沙浓度的浑水中将水沙(包括0.01mm以下的极细沙和粘粒)分离,并获取清水。与化学处理过程不同的是,该“装置”在获取清水的过程中,不需添加任何化学药剂,也不需任何其它动力、仅靠水流的自身能量就可将水沙分离,因此被称为“绿色环保装置”。该成果可用于自来水厂对浑水进行预处理及灌区水源中的泥沙分离,对环境保护及加速喷、滴灌等先进节水技术的推广应用产生重要影响。为了探求装置的动态水力分离水沙机理,进一步优化“装置”结构形式,为“装置”的推广应用提供理论依据,本文利用试验研究、理论分析和数值模拟三种方法研究“装置”内部弱旋湍流场分布规律、水沙两相流的分离机理以及“装置”相似模化问题。试验研究包括水相流场的测试、水沙分离性能影响因素研究、浑液面的形成对分离性能的影响以及泥沙浓度分布测试。即应用先进的粒子图像测速技术(PIV)测量不同工况下“装置”内的水相流场,揭示了“装置”内的流场的运动规律;运用均匀正交试验和单因素同比试验并结合投影寻踪回归分析法,揭示了“装置”水沙分离的影响因素;观测不同工况下泥沙的絮凝情况,测试不同时间不同工况对应的溢流浓度,揭示了“装置”内泥沙动水絮凝或高浓度下浑液面的形成对“装置”水沙分离效率的影响规律;在“装置”不同位置布置测沙垂线,测试不同工况各测点对应的浓度值,以此验证浑水流场的数值模拟结果的可靠性。数值模拟研究主要包括水相场的湍流模拟和水沙多相流场的模拟。采用了不同的湍流模型RNG k-ε模型和RSM模型封闭时均流动的N-S方程,分别在不同的网格划分方案下对水相场进行数值模拟,详细分析了水相场的三维速度分布及雷诺应力分布规律,并将计算结果与PIV实测值对比。结果表明RSM模型和RNG k-ε模型水相场的数模结果与PIV实测结果吻合均较好,综合考虑计算精度和计算消耗时,可以采用RNG k-ε模型计算“装置”内的弱旋湍流场,而不需采用计算成本较高、耗时较长的RSM模型。对于水沙多相流动的数值模拟,在比较了两相流理论中颗粒运动的描述方法Euler-Euler法和Euler-Lagrangian以及不同方法对应的不同的多相流数学模型后,最终选用Euler-Euler方法中的混合物(Mixture)模型在不同进流量下针对不同泥沙浓度、较宽的粒径分布的非均匀沙和单一粒径的均匀沙多相流场进行数值模拟研究。揭示了不同工况下浑水流场的三维速度、动水压强、紊动强度、泥沙浓度分布以及不同粒径泥沙在“装置”内的分布规律。论文对不同工况下“装置”内泥沙浓度分布的数模结果和试验结果进行了对比,结果表明浑水流场浓度分布规律的数模结果与实测结果较为一致,证明本文采用的水沙多相流Mixture模型可以较准确地计算“装置”内的水沙两相流场,所得结论较为可靠。结合试验研究和数值模拟研究结果,从不同粒径泥沙在”装置”内的分布规律及其所受分离作用力、“装置”内的流场特性、“装置”的结构特点等角度探明了“装置”动态分离水沙的机理,为“装置”的结构和运行工况的优化提供理论指导。最后,在“装置”内的旋转流动中,考虑颗粒在流体中各种受力,包括运动阻力、重力、附加质量力、压强梯度力、Basset力、升力等,忽略低浓度时颗粒间的相互作用,建立了泥沙的运动微分方程。为将模型试验结论推广应用于原型“装置”中,结合水沙两相的运动方程,并根据相似理论中的量纲分析法和方程分析法,推导“装置”相似模化的准则,用以指导“装置”的设计与运行性能预测。更多还原

【Abstract】 Many rivers which lie in the North China and northwest China have the characteristics of high sediment concentration and the sediment particle diameter is very small. It is very difficult to remove the fine sand whose diameter are smaller than 0.03mm and quality occupies 40% of the total quality. The turbid water hydraulic separation device is able to separate sediment (consists of fine sand and clay grain) and extract clear water from turbid water of high sediment concentration. It only relies on the water self-contained energy under dynamic conditions. In the process of separation, no any chemical is needed and no external energy is provided. So it is known as the green environmental protection device. The device can be applied in the running water factory to pretreat the turbid water, and also provide good source of water for the advanced water conservation technology such as spray and drip irrigation. In order to find out the water-sediment separation mechanism under dynamics conditions and make optimization for the structure of the device as well as provide principle basis for the application, experiment studies and numerical simulations as well as theoretical analysis are used to research the rule of weak swirling turbulent flow field and the water-sediment separation mechanism and the scaling rules of the device.The contents of experimental research consist of four sections. The first part is experiment studies for clean water flow field under different incoming discharge which is conducted by Particle Image Velocity(PIV). The results of tests have revealed the flow characteristics in the device. Secondly, the uniform orthogonal designs method with the projection pursuit regression(PPR) method to deal with the measured data, and single factor experiments have both been utilized to find out the main factors influencing on the water-sediment separation efficiency of the device. The third part is experiment studies about observing the sediment flocculation and testing the sediment concentration of the overflowing water at different time in the device with different incoming discharges and sediment concentrations. The results have promulgated the influence of silt hydrodynamic flocculation or the formation of interface between clean water and turbid water due to silt flocculation under high sediment concentration on the separation efficiency of the device. The last section is to study the sediment volume fraction distribution rule in the device. The test points were arranged at different positions of the device, and then the sediment concentration of each one was measured. The results of the tests can be used to verify the multiphase flow numerical simulation results.The numerical simulation research mainly includes the clean water turbulent flow field simulation and the water sediment multiphase flow field calculations. Numerical simulations were conducted for the single-phase (clear water) flow field in the device by applying the RNG k-εmodel and the Reynolds-stress model with the different schemes of grid division. According to the computational results, the characteristics of radial, tangential and axial velocity and Reynolds-stress are analyzed in detail, and the calculation results are contrasted with the experimental data by PIV. The results show that both models can accurately predict the flow field, with a comprehensive consideration of simulation precision and time consumption, we can simulate the flow field of the device by applying RNG k-εmodel, which is less time consuming than the Reynolds-stress model.Nowadays, in the solid-liquid two phase flow theory, there are two methods to describe the solid particle movement. They are Euler-Euler and Euler-Lagrangian method, respectively. After the two methods and their corresponding computational models have been compared with each other in detail, the Eulerian model-Algebraic Slip Mixture Model was selected for simulating the two-phase (water &sediment) flow field in the device. The flow field characteristics of the device are predicted by means of computational fluid dynamics technology under different operating conditions including different inlet sediment concentration, different inlet discharges as well as uniform graded sediment and non-uniform graded sediment. The results have revealed the characteristic and the distribution rules of three-dimensional velocity, dynamical pressure, intensity, sediment concentration as well as the different grain diameter sediment and the simulation results are in good agreement with the experimental data. The results show that it is reasonable and accurate to use the Mixture model for the water& sediment two-phase flow field of the device.Combining with the experiment and simulation results, the mechanism for that the sediment is separated from the turbid water with high sediment concentration is clarified from the different views such as considering the separation forces acting on the different particle size sediment, the flow field characteristics of the device and the particular structure of the device, which can provide instructions for making optimization in the structure or operation conditions.Finally, considering synchronously the drag force, gravity force, adjunctive mass force, pressure gradient force, Basset force, lift force, Magnus force, Saffman force, and neglecting the interation between particles at the low inlet sediment concentration, the movement differential equations for the sediment was established. In order to apply the model experiment conclusions on the prototype device and instruct its design, Combing with the three-dimensional time average control equations for the water and sediment movement equations, the scaling rules is derived to according to dimensional analysis method of similarity theory and Equation analytic method.更多还原