【作者】 孙志强；

【导师】 张宏建；

【作者基本信息】 浙江大学 ， 控制科学与工程， 2007， 博士

【摘要】 流体在管道内的流动几乎存在于所有工业生产过程和设备之中。作为热量、质量、动量传递和参与化学反应的主要介质，流体的流动状态及其参数的变化对生产过程有着至关重要的影响。及时掌握管内流体流动状态并准确测量其参数，是有效控制生产操作、优化生产过程的必备条件之一。然而，工业生产中流体种类繁多、工作条件复杂，虽然目前已有多种流体参数测量方法和仪表，但是仍然存在大量的实际问题急待解决。一直以来，流体状态的获取及其参数的测量都是过程检测与控制领域的一大公认难题。涡街是粘性流体在一定条件下绕过非流线型柱体时产生的一种特殊的流动现象。越来越多的研究显示出，涡街与其所在的流场状态密切耦合，涡街特性能够在很大程度上反映流体流动状况。因此，涡街特性作为一个包含大量流动信息的“富流场信息源”，通过对其采用合适的信号检测和处理方法，可以实现对管内流体的流动分析和参数检测。尽管这一课题的理论和实际意义均十分重大，但是该领域的研究成果还相当有限。因此，在这一前沿交叉方向上开展研究工作，不但能够有力推动过程参数检测理论和技术的发展，同时也将为尚在迅速发展中的流体力学旋涡理论注入新的活力。本论文紧紧围绕基于涡街特性的管道内流体流动分析与参数检测这一核心目标开展研究，独创性地利用涡街尾流中特定位置处的管壁差压对单相流和气液两相流的流动特性进行了系统的分析，深入刻画了涡街特性与其所处流场状态的耦合关系，并在此基础上，成功实现了流量和流型等关键参数的有效检测。本论文完成的主要工作和创新点如下：(1)根据涡街流动的基本特性，首次提出了基于管壁处静压波动信号的非侵入式涡街流动特性检测新方法——“管壁差压法”。通过采用RNG k-ε模型对管内涡街流场的三维数值模拟，论证了管壁差压法的可行性，着重描绘了管内卡门涡街的产生和脱落过程，重点分析了静压和速度等流动参数随涡街脱落的演变情况，针对不同的检测目的设计了周向式和轴向式两种管壁差压法，研制了配套的信号处理系统。(2)基于管壁差压法提取的涡街特性，成功地实现了管道内单相流体流量的准确测量。通过从管壁差压信号中提取涡街频率，根据涡街频率与流速的关系获得了管内流体的体积流量，形成了一种检测更稳定、抗干扰性更强、测量下限更低的“管壁差压式涡街流量计”；分析了干扰噪声、取压位置、引压管等因素对管壁差压式涡街流量计测量性能的影响，评定了测量系统的不确定度，提出了相应的克服措施，优化了管壁差压式涡街流量计的测量性能；基于渐缩渐扩管原理，有效地拓展了管壁差压式涡街流量计的测量下限。(3)创新性地提出了基于涡街信号统计特征的流动分析的思想及方法，并实现对部分管道内流体流动状态的诊断。通过对涡街信号的功率谱和高阶谱分析，提出了“功率谱式涡街能量比”，为涡街流量计检测元件位置的优化提供了依据，并以双谱幅度最大值为特征参数，揭示了涡街信号的非高斯性随流量的变化情况，深化了人们对涡街流动现象的认识；利用固有模态分解技术提取了非平稳状态下涡街信号的固有模态函数，提出了“EMD式涡街能量比”，实现了定量判断管内涡街流动是否处于正常单相流动状态。(4)首次研究了气液两相流涡街和气液两相流绕流的管壁差压特性，定量判别了气液两相流涡街的稳定性，揭示了流型对气液两相流绕流压降的影响。以气液两相流涡街周向管壁差压信号为基础，提出了一个基于管内平均流速和涡街频率的量纲为1的涡街稳定性指数，利用该指数可实现对管内气液两相流涡街的稳定性的定量判断，发现体积含气率对气液两相流涡街的稳定性起主要作用；通过轴向管壁差压法测量了气液两相流绕流近尾流区的动态压降，讨论了气液两相流绕流动态压降与流型之间的关系，结果表明，气液两相流绕流的动态压降特性对于流型具有很大的依赖性。(5)提出了基于气液两相流绕流频域特征的流型识别方法，并成功地应用于垂直管中气液两相流流型的识别。通过对气液两相流绕流周向管壁差压信号频域特征的量化处理，分析了频域特征参量与流型之间的关系，设计了一个三层前馈人工神经网络，以气液两相流绕流周向管壁差压信号的量化频域特征作为输入，以数值化的流型作为输出，采用BP算法进行训练。该方法对于垂直上升管内的单相水、泡状流、弹状流和混状流有较好的识别效果，准确率接近90％。(6)基于气液两相流涡街特性，创新性地提出了涡街—文丘里联合法和单涡街流量计法，实现了气液泡状流流量和含气率等关键参数的测量。通过分析管壁差压式涡街流量计在气液泡状流中的性能和不确定度，提出了以涡街流量计和文丘里管作为测量元件的“涡街—文丘里联合法”，建立了以涡街频率和文丘里差压为被测量的测量模型，该方法对气液泡状流质量流量的测量相对误差可达±5％；通过建立涡街周向管壁差压信号频率和幅度与被测流体的关系，使用单个涡街流量计实现了对气液泡状流流量和体积含气率的双参数测量，该方法对气液泡状流流量和体积含气率的测量相对误差分别为±5％和±10％，可以满足大量工业实际应用的要求。本论文以涡街特性这一学术思想为主线，在一个统一的框架内集中解决了单相流流量测量与状态诊断、气液两相流流型识别与参数测量等过程检测基本问题。以上研究成果得到了国内外同行的广泛认可和正面评价，目前已经和即将在Measurement Science & Technology、Sensors & Actuators A Physical、Measurement、Flow Measurement & Instrumentation、Chemical Engineering Communications等本领域权威学术刊物上发表相关论文30余篇，申请和授权国家专利7项，并且部分研究成果还受到了国内一些著名仪表厂家的关注，正在商议相关合作和技术转让等事宜。这些研究成果丰富和发展了过程参数检测理论和技术，对涡街特性向实际工程的应用必将产生重要的推动作用，同时，对流体力学旋涡理论等相关交叉领域的发展也将起到积极的促进作用。更多还原

【Abstract】 The fluid flow in conduits is almost seen in all variety of industrial processes andfacilities. As the main medium for heat, mass, momentum transfer and chemicalreaction, the fluid flow state and its parameters are crucial to the quality of productionprocesses. Knowing about the fluid flow state in time with pertinent parametersmeasured accurately is one of the necessities for effective control and optimization ofproduction operations. However, due to the wide variety of fluids and the complex ofworking conditions, although numbers of methods and instruments for fluid parametermeasurement have been devised, there still exist many urgent practical problems to besolved. For all the time, it is well recognized that acquisition of fluid flow state andmeasurement of its parameters is one of the most difficult problems in the area ofprocess measurement and control.The vortex street is a special flow phenomenon which occurs under uncertainconditions when viscous fluids flow around bluff bodies. More and more researcheshave shown that there is a close coupling relationship between a vortex street and theflow state in which it sheds, and the characteristics of the vortex street can reflect itsfluid flow state to a significant extent. Therefore, through applying proper acquisitionand processing approaches to the vortex street signals, a flow-information-intensivesource, analysis and measurement of the fluid flow in conduits can be partiallyrealized. However, so far studies on this topic are fairly limited despite its importancein both theory and practice. Undoubtedly, investigations on this interdisciplinaryfrontier area will promote the development of process measurement theory andtechnology, and at the same time they may also motivate the rapid-evolving theory ofvortex in fluid mechanics.In this dissertation, investigations on the analysis and measurement of the fluidflow in conduits using the characteristics of a vortex street were carried out. Theproperties of single-phase and gas-liquid two-phase flows were analyzedsystematically based on the duct-wall differential pressure obtained at certainpositions in the vortex wake. The coupling relationship between the vortex street andits flow state was studied thoroughly, and some key fluid parameters including flowrate and flow pattern were measured successfully. The main contributions andinnovations of this dissertation are summarized as follows:(1) Based on the essential characteristics of a vortex street, the duct-walldifferential pressure method (DDPM), a new non-intrusive approach for detectingvortex signals using the static pressure fluctuation on the duct wall, was put forwardfor the first time. Three-dimensional numerical simulations of the pipe vortex flowfield were performed adopting the RNG k-εmodel, on the basis of which thefeasibility of the DDPM was demonstrated primarily. The focus was placed ondepicting the generation and shedding of the Karman vortex street, and the analyses ofthe evolution of the static pressure and velocity with the vortex shedding process wereemphasized. Circumferential and axial DDPMs were devised for various detectionpurposes, and corresponding signal processing systems were also developed.(2) The flowrate of single-phase flows in conduits were accurately measuredthrough the vortex street characteristics extracted from the DDPM. According to therelationship between the vortex frequency and flow velocity in a vortex street, theflowrate was obtained via the frequency extracted from the DDPM signals, and thusthe DDPM vortex flowmeter was taken form with stable performance, stronganti-disturbance ability and low measuring limit. The influence of noise, pressuresampling position and tube on the performance of the DDPM vortex flowmeter wasdiscussed, the uncertainty of the measuring system was evaluated, and measures toreduce the uncertainties were recommended to optimize the measurement. Moreover,the lower measuring limit of the DDPM vortex flowmeter was further extended by theuse of a converging-diverging conduit.(3) The idea and techniques of flow analysis using the statistical characteristicsof vortex street signals was presented, on the basis of which partial fluid flow states inconduits were diagnosed properly. The power spectrum based vortex energy ratio wasput forward through the power spectrum analysis, which could be used as a criterionfor selecting the optimal position of vortex flowmeter sensing element. The maximumvalue of bispectrum from higher-order statistical analysis revealed the relationship ofthe non-Gaussian degree and the flowrates, which contributes to a more in-depthunderstanding of the vortex street phenomenon. Furthermore, the intrinsic modefunctions of vortex street sigals under non-steady states were drawn using the empirical mode decomposition (EMD) technique, and then the EMD vortex energyratio was brought forward to realize the quantificationally judge whether the vortexstreet was shed in a normal single-phase flow.(4) The characteristics of the DDPM signals acquired from gas-liquid two-phasevortex streets and flows around a cylinder were studied, the stability of the gas-liquidtwo-phase vortex street was determined quantificationally, and the influence of flowpattern on the pressure drop in the flow around a cylinder was explored. Based on theDDPM signals of a gas-liquid two-phase vortex street, a new dimensionless stabilityindex using the average velocity and vortex frequency was put forward toquantificationally judge the stability of a gas-liquid two-phase vortex street, and it isfound that the volume void fraction has the dominant effect on the stability. At thesame time, the dynamic pressure drops in the flow around a cylinder were measuredwith the axial DDPM, the relationship between the dynamic pressure drop and theflow pattern was discussed, and results show that the dynamic pressure drop mainlydepends upon the flow pattern.(5) An approach for the flow pattern identification using the frequency domaincharacteristics of gas-liquid two-phase flow around a cylinder was proposed, whichwas applied to vertical upward gas-liquid two-phase flows successfully. After thequantification processing of the DDPM signal frequency domain characteristics ofgas-liquid two-phase flow around a cylinder, the relationship between the frequencydomain characteristics parameters and the flow patterns was investigated. Athree-layer feed-forward neural network was designed and trained through theback-propagation learning algorithm, which adopted frequency domain characteristicsparameters as inputs and numerical-valued flow patterns as output. It is proved thatthis approach predicts the single water, bubble, slug and churn flows in a verticalupward pipe successfully with an accuracy rate up to about 90%.(6) Based on the characteristics of gas-liquid two-phase vortex streets, the vortexflowmeter-Venturi tube combinative method and the single vortex flowmeter methodwere introduced, which realized the measurement of some key parameters of bubbleflows including the flowrate and void fraction. After analyzing the performance anduncertainty of the DDPM vortex flowmeter in gas-liquid bubble flows, the vortexflowmeter-Venturi tube combinative method using the vortex flowmeter and the Venturi tube as measuring cells was put forward, the measurement model based on thevortex frequency and the Venturi differential pressure was established, and it showsthat the relative errors of this method for the mass flow measurement of bubble flowsare within±5%. Furthermore, the flowrate and volume void fraction of bubble flowswere obtained using a single DDPM vortex flowmeter through the relationshipbetween the frequency and amplitude of the circumferential DDPM signal, and resultsdemonstrate that the relative errors of the flowrate and volume void fraction of bubbleflows are within±5% and±10% respectively, which indicates the broad applicabilityof this method to large numbers of engineering fields.This dissertation solves the primary problems of flow measurement and statediagnosis for single-phase flow, flow pattern identification and parameter estimationfor gas-liquid two-phase flow in a unified framework based on the idea of vortexstreet characteristics. The above research results have obtained broad recognitions andpositive appraisals. Nearly thirty related papers on these results have been publishedor accepted for publication by authoritative journals including Measurement Science& Technology, Sensors & Actuators: A. Physical, Measurement, Flow Measurement &Instrumentation, Chemical Engineering Communications etc. Seven national patentshave been applied or authorized, and parts of the researches have received attentionsfrom some renowned national instrument manufacturers who are negotiating with theauthor for cooperation and technique transfer at present. These researches willcontribute to the development of process measurement theory and technology, canadvance the application of vortex street characteristics to practical engineering, andmay also motivate the progress of their related interdisciplines such as the vortextheory in fluid mechanics.更多还原