【作者】 陈坚祯；

【导师】 李斌；

【作者基本信息】 上海大学 ， 控制理论与控制工程， 2009， 博士

【摘要】 传统电磁流量计在大管径流量测量应用中存在制造和安装成本过高的问题,而插入式电磁流量计结构特点使得它在大管径流量测量中有制造与安装成本低,易于拆卸与维修,一种规格的传感器可用于多种口径管道等突出优点,因而深受用户的欢迎。但也存在仪表精度受流体流场特性影响大,现场需有较长直管段长度等问题。因此,研究提高插入式电磁流量计的性能一直是流量检测领域中重要的课题之一。本文主要进行多电极测量的插入式电磁流量传感器基础研究。插入式电磁流量传感器是以电磁感应为基础和以测量流场分布为前提的流量传感器,权重函数分布、电磁场分布和流场分布对其测量结果的影响是至关重要的。因而必须从流场分布、权重函数和电磁场分布三个方面来研究插入式电磁流量传感器。同时,计算流体力学CFD和有限元计算技术的发展为插入式电磁流量传感器的研究提供了崭新途径,扩展了新的空间和新的方法。利用CFD方法研究传感器几何物理模型,以数值仿真方法分析流场变化对插入式电磁流量传感器的相关影响。总结了传感器测量杆在管道流场中三个特殊的高流速区的特点,为消除流场变化对传感器的影响,提出了一种新型的多电极插入式电磁流量传感器的方案,采用多电极的多点信息测量方法,为解决插入式传感器特性对流场敏感的问题提供了新的途径。本论文的整个工作围绕着新型传感器的关键技术展开研究。首先,叙述总结了插入式电磁流量计测量方面的相关理论基础及研究方法。分析了现有插入式电磁流量计传感器的基本测量方程及测量权重函数、现有插入式电磁流量传感器工作流场的传统Nikuradse模型等经验模型和一般插入式电磁流量计的测量模型。从麦克斯韦方程组的有限元分析方法入手,介绍插入式电磁流量传感器电磁场模型、分析工具和研究方法。对基于CFD的流场数值模拟的方法进行了详细的介绍。详细分析了纳维-斯托克斯方程(简称N-S方程)等基本控制方程、雷诺时均方程及其标准的k-ε模型、大涡模拟方法和壁面函数与近壁模型。并对控制方程的常用求解方法进行了讨论。其次,进行了CFD并行计算平台建设、管道流场分布仿真、钝体绕流仿真和插入式电磁流量传感器的流场仿真等四个方面的研究。在研究并行计算环境的基础上成功搭建了一套微机并行计算集群系统,并对并行计算平台的基本性能进行测试。对管道流场分布进行了仿真,给出了基于CFD模型圆管湍流仿真的流速分布,其与传统Nikuradse模型流速分布较好符合,并能更接近实际流场。钝体绕流仿真则给出了圆柱状、梯形发生体的旋涡产生、脱落的详细过程和发生机理。确定了钝体绕流产生涡街的本质及测量研究方法。进行了插入式电磁流量传感器的流场仿真,从圆柱状插入式电磁流量计传感器对流场影响的角度探讨插入式电磁流量计测量管道流场的方法,提出了用多对电极测量流速及其流场扰动,并给出了传感器测量杆周围的三个高流速特征区域。然后,从流场分布角度进行了多电极插入式电磁流量测量原理的研究分析,讨论了多插入式电磁流量传感器测量和多电极径流速计型插入式电磁流量测量的改进方法,提出了多电极插入式电磁流量传感器测量原理及解决方案。进行了传感器的结构设计及模型研究,建立了电极、流场和磁场的空间关系及其多电极对下的测量原理。同时给出了传感器多点测量的测量方程。论文使用matlab PDE工具的有限元分析方法,分析了普通电磁传感器权重函数、插入式电磁传感器权重函数和插入式电磁传感器工作磁场,在此基础上研究确定了多电极插入式电磁流量传感器的权重函数和磁场实现方案,从理论上确定了设计插入式电磁流量传感器最优工作磁场的方法。最后,为验证本文研究的可行性及实用性,设计制作了多电极插入式电磁流量传感器,并设计实现了信号转换器系统和相应的试验管道系统,在此基础上进行了多电极测量空间关系的试验,对试验数据结果进行分析。实验数据给出了传感器各对电极上的信号大小与流速呈线性关系,显示了三对电极上的信号特征符合三个流速特征区域的变化情况,验证了多电极传感器对流场分布和绕流信号的可测性,为最终降低流场分布对传感器测量的影响,以及提高插入式电磁流量计的性能提供了依据。更多还原

【Abstract】 Traditional electromagnetic flowmeters have significant limitations for meas-uring the flow of large diameter pipelines, while the insertion electromagnetic flowmeter is becoming increasingly popular among users for the same usage with its hightlighting advantages of low price, small weight, easy disassembly and repair as well as good versatility. What’s more, one specification may be used in pipelines of various diameters. However, this kind of flowmeter has its own disadvantages, namely, it’s not only deeply affected by the fluid flow characteristics, but also need to have a longer length of straight pipe at the application scene. Therefore, develop-ing the key technology which improves the performance of insertion electromag-netic flowmeter has been an important subject in flow measurement.This dissertation mainly focuses on the basic study of insertion electromagnetic flow sensor with multi-electrode measurement. Insertion electromagnetic flow sen-sor is based on the electromagnetic induction and the fluid velocity distribution of measuring the flow field. And the distribution of weighting function and electro-magnetism field and flow field play a key role in affecting its measurement result. Thus, the research of insertion electromagnetic flow sensor must be carried out in the three perspectives which are the flow field, the electromagnetic field and the weight function. At present, the development of the finite element technique and CFD (Computational Fluid Dynamics) has provided the brand-new way for the re-search on insertion electromagnetic flow sensor, and has also expanded the new space and the new method for it. The method of CFD is used to study physical model of the sensor geometry, and the numerical simulation is employed to analyze the relevant effects of the flow field change upon the sensor. The characteristics of three special regions of high flow velocity around the sensor staff are summarized. To remove the effects of the flow field change upon the sensor, the feasible design of new Multi-electrode insertion electromagnetic flow sensor is proposed. Adopting technology of the Multi-electrode multi-point measurement, a new way to solve the problem of sensor which is deeply affected by the flow field is provided.This dissertation is carried out around the study of key technologies of the new type sensor. First of all, a summary of the theoretic basis related to the insertion electromagnetic flowmeter and the research methodology are introduced. The basic measurement equation and weighting function of existing insertion electromagnetic flow sensor are analyzed. The empirical models of flow field distribution like tradi-tional Nikuradse model and the measurement model of existing insertion electro-magnetic flowmeter are also analyzed. Based on the finite element method of Max-well equations, the electromagnetic field models of insertion electromagnetic flow-meter and the analysis tools and research methods are introduced. The CFD-based numerical simulation methods of flow field are introduced in detail. The governing equation such as Navier-Stokes (N-S) equation, the Reynolds time-averaged equa-tions and its standard k-εmodel, the Large eddy simulation (LES) method, the wall function and near wall model are analyzed in detail. And the methods of the com-monly used solution to the governing equation are discussed.Secondly, this thesis tries to study the four aspects as follows: the parallel computing platform of CFD, the pipeline flow field distribution simulation, the flow around a bluff body simulation and the insertion electromagnetism flow sensor’s flow field simulation. Based on the research of parallel computing environment, the very excellent parallel computing cluster systems has been built, and the basic per-formance of the parallel computing platform is tested. Based on the CFD turbulent model, the simulation of flow field distribution gives out the velocity profile of pipeline, which is in line with the velocity profile of traditional Nikuradse model perfectly and closer to actual flow field. The Simulations of flow around bluff body show us the cylindrical shape, the trapezoidal body along with the detailed process and the occurrence mechanism which vortex produced and were shedding. The vor-tex production essence of flow around bluff body and the research methods of measurement flow are identified. The measurement methods are discussed from the angle of the simulation of flow field and the influence of cylindrical probe head to the flow field. And then, this dissertation proposes the plan of multi-electrode meas-uring flow velocity and the disturbance of flow. This dissertation also gives out the three characteristic regions of flow velocity around the sensor staff.Then, the dissertation analyzes the measurement principles from the perspec-tive of the flow field distribution. The improved measuring methods of the multi-insertion electromagnetic flowmeter and the multi-electrode radial tachometer type insertion electromagnetic flowmeter are discussed. The measurement principle and solution of multi-parameter and multi-electrode insertion electromagnetism flow sensor are proposed. The study gives the structural design of the sensor and its model study. And the spatial relations among electrode, flow field and magnetic field are established. And the principle of multi-electrodes measuring is given out. The measurement equation of sensor multi-point measuring is presented. Base on the matlab PDE tool’s finite element method analysis, the weighting function of electromagnetic flowmeter sensor and insertion electromagnetic sensor are simu-lated and analyzed. The work magnetic field of insertion electromagnetic sensor are also simulated and analyzed. The research discusses the weighting function and the magnetic field design of the multi-electrode insertion electromagnetic flow sensor. Theoretically, the design method is determined for designing the most superior work magnetic field of insertion electromagnetic flow sensor.Finally, in order to verify the feasibility and practicality of the design, a multi-electrode insertion electromagnetic flow sensor and a signal converter system have been manufactured, and the corresponding experiment pipeline test system has also been set up. Based on this, the experiments on the spatial relations measuring with multi-electrode are carried out, and the results of test data are analyzed. The results confirm that the signal of multi-electrode sensor has linear relationship with the flow rate, and the signal characteristics of three pairs of electrodes are true re-flection of the changes of the three flow rate characteristic regions. The results also confirmed the measurability of multi-electrode sensor which measures the data of flow field distribution and the signal of flow around. All of these provide the basis to reduce the influence of flow field distribution in the sensor measuring finally, and to improve the insertion electromagnetic flowmeter’s performance.更多还原