【作者】 陈洁；

【导师】 李斌；

【作者基本信息】 上海大学 ， 控制理论与控制工程， 2010， 博士

【摘要】 涡街流量计是20世纪60年代末期发展起来的一种基于流体振动原理的流量计。在特定的流动条件下,一部分流体动能转化为流体振动,其振动频率与流速有确定的比例关系。涡街流量计是一种比较新型的速度式流量仪表,它具有可靠性高、压力损失小、量程比宽等优点,因此被广泛应用于化工、石油、冶金、轻工、食品等流程工业中。涡街流量计在低流速下输出的信号很微弱,仪表在应用现场又会叠加上各种复杂的噪声,因此如何扩展它的量程测量下限一直是流量界的研究热点,它对提高涡街流量计的性能以及增强其应用性有重要的意义。本论文主要完成了以下的工作:1.通过对涡街流量计的原理和发展现状的介绍,讨论了一系列跟论文相关的理论基础,包括流体力学基础和CFD仿真基础,以及一些常用的时域和频域的信号处理方法在跟踪涡街信号时的缺陷。这些介绍为论文后面章节的具体研究提供了理论指导,并引出了本文所研究的主要课题:如何实现低流速下对涡街信号的准确捕捉以提高涡街流量计测量的量程比。2.从流体力学方程出发,用CFD方法给出几个典型的涡街仿真模型,用RSM模型对涡街传感器进行二维圆柱绕流仿真,得到旋涡稳定分离的仿真曲线,并得到检出器上阻力和升力关系。论文按照实际涡街流量计传感器的结构尺寸,用LES模型对旋涡分离与行进过程进行了仿真,验证了在检出器上涡街信号的频率与发生体上一致,且满足流速和信号频率的关系。这为我们后续信号处理方法的研究提供了最直观的理论依据。3.从分析总结低流速时涡街流量计中的动量流量、流速、频率和幅值的关系出发,推导出了涡街动量流量关系和涡街信号的动量一致性关系,然后提出了本论文的核心理论:基于动量流量跟踪的涡街信号处理方法,并进一步论述了用一组二阶非线性滤波器组对低流速下涡街信号进行调理放大的技术方法。形成了一整套基于动量流量跟踪的涡街信号处理方法及其相关技术。该方法能够在信号幅值随频率平方增长时,通过低通滤波器组转折频率的动态调整使输出信号幅值基本固定,确保后级数字采集器有效捕捉到信号脉动频率。4.为完善实际涡街流量计仪表系统对高、低流速的信号处理要求,考虑当流量逐渐增大时,由于检出器输出信号出现饱和,它的幅值不再随信号频率呈平方关系增长,因此本文提出了仪表系统的双通道信号处理实现方法。该方法将传统中、高流速段的信号处理方法与低流速下基于动量流量的信号处理方法相结合,对不同特点的信号作分段处理,并根据频率与幅值特征设计了通道切换依据,同时满足了各流速下对涡街信号精确测量的要求。5.具体讨论和设计了双通道原理的宽量程涡街流量计的软硬件实现方案,以及产品化功能设计,实现了量程比为1:40的宽量程涡街流量计样机。6.对所设计的涡街流量计样机进行了实验室验证以及校准检定实验,对实验得到的重复性、线性等参数进行了分析和总结。此外,本文还用不确定性理论探讨了系统的稳定性和标定精度。更多还原

【Abstract】 Vortex flowmeter is a kind of oscillator flowmeter developed from the end of 1960s. Under definite flow condition, some kinetic energy of the fluid transfers to flow oscillation and the oscillator frequency is proportional to the flow velocity. This novel velocity-type flowmeter has its advantages of high stabilization, low pressure loss and wide measurement range, which is widely used in chemical industry, petroleum, metallurgy, light industry, food industry and other flow industry. At low flow rate, the signal amplitude of the vortex flowmeter is very slim and many kinds of noises will add on it in application. So it is still a hot spot on how to widen the measurement range with high accuracy. It is meaningful to research the vortex character under different fluid conditions and create a new method to pick up the vortex signal in wide flow range.The main researches of this thesis are listed below:1. The thesis firstly introduces the principle of vortex flowmeter and its state of development. A series of theory related to the flowmeter is then cited, including the foundation of hydromechanics and the method of CFD simulation. The disadvantage of traditional methods based on time domain and frequency domain are also discussed. All the introduction and analysis above provide instructions to the following chapters, which also clarify the main research of this thesis: how to tracking the vortex signal at low flow rate to enhance the measure ratio.2. It is presented how to simulate the phenomenon of Karman Vortex Street when fluid passes the meter by CFD software. With the parameters measured on the product of generator and detector separating sensor, the relationship of the lift force on different parts of the sensor is clearly presented. The CFD simulation results validate the character of vortex output signal on the detector.3. Vortex flowmeter momentum relation, amplitude consistency relation and frequency-amplitude restriction are discussed in the thesis. Then the creative signal processing method based on momentum flow is put forward. According to the relationship of signal amplitude and its frequency, the module of non-linear filter is designed, which will ensure to exactly capture the real vortex pulsation even in low flow velocity with all kinds of noises. 4. The thesis then puts forward the two-channel signal processing method to realize the signal measurement over the whole flow range. With the flow volume increasing, the output of the amplifier will be saturated and momentum flow relation is no longer met. So it is necessary to combine one channel of traditional vortex signal processing method in high flow velocity with the other of momentum-flow signal processing method in low flow velocity to ensure the measurement accuracy in the whole range. Meanwhile the criterion of the channel shift is created in the thesis according to the signal character.5. The solution of the signal processing method is presented in the thesis. The hardware and software functions are introduced of the wide range flowmeter. The prototype is able to at last realize the flow measurement with the measure ratio of 1:40.6. Online Verification tests are done both in lab and in calibration field with this prototype of wide range flowmeter. The test results on meter error, repeatability and linearity are discussed in this thesis. Further, the system uncertainty is also taken into consideration to analyze the meter’s capability.更多还原