Application of empirical mode decomposition based energy ratio to vortex flowmeter state diagnosis

To improve the measurement performance, a method for diagnosing the state of vortex flowmeter under various flow conditions was presented. The raw sensor signal of the vortex flowmeter was adaptively decomposed into intrinsic mode functions using the empirical mode decomposition approach. Based on the empirical mode decomposition results, the energy of each intrinsic mode function was extracted, and the vortex energy ratio was proposed to analyze how the perturbation in the flow affected the measurement performance of the vortex flowmeter. The relationship between the vortex energy ratio of the signal and the flow condition was established. The results show that the vortex energy ratio is sensitive to the flow condition and ideal for the characterization of the vortex flowmeter signal. Moreover, the vortex energy ratio under normal flow condition is greater than 80%, which can be adopted as an indicator to diagnose the state of a vortex flowmeter.

Application of Hilbert-Huang transform to denoising in vortex flowmeter

Due to piping vibration, fluid pulsation and other environmental disturbances, variations of amplitude and frequency to the raw signals of vortex flowmeter are imposed. It is difficult to extract vortex frequencies which indicate volumetric flowrate from noisy data, especially at low flowrates. Hilbert-Huang transform was adopted to estimate vortex frequency. The noisy raw signal was decomposed into different intrinsic modes by empirical mode decomposition, the time-frequency characteristics of each mode were analyzed, and the vortex frequency was obtained by calculating partial mode’s instantaneous frequency. Experimental results show that the proposed method can estimate the vortex frequency with less than 2% relative error; and in the low flowrate range studied, the denoising ability of Hilbert-Huang transform is markedly better than Fourier based algorithms. These findings reveal that this method is accurate for vortex signal processing and at the same time has strong anti-disturbance ability.

INVESTIGATION OF VORTEX SHEDDING INDUCED HYDRODYNAMIC VIBRATION IN VORTEX STREET FLOWMETER

Vortex street flowmeter has been used in steady flow measurement for about three decades The benefits of this type of flowmeter include high accuracy,good linearty,wide measuring range,and excellent reliability However,in unsteady flow measurement,the pressure disturbance as well as the noise from the system or surrounding can reduce the signal to noise ratio of the flowmeter seriously Aimed to use vortex street flowmeters in unsteady flow measurement,the characteristics of the vortex shedding induced hydrodynamic vibration around the prism bluff body in a vortex street flowmeter are investigated numerically and by expriments The results show that the hydrodynamic vibrations with 180° phase shift occur at the axisymmetric points of the channel around the bluff body The most intense vibration occurs at the points on the lateral faces close to the base of the prism The results provide therefore a useful reference for developing an anti interference vortex flowmeter using the different ial sensing technique.

Influence of bluff body shape on wall pressure distribution in vortex flowmeter

To investigate the influence of bluff body shape on wall pressure distribution in a vortex flowmeter,experiments were conducted on a specially designed test section in a closed water rig at Reynolds numbers of 6.2×10 4-9.3×10 4.The cross sections of the bluff bodies were semicircular,square,and triangular shaped,and there were totally 21 pressure tappings along the conduit to acquire the wall pressures.It is found that the variation trends of wall pressures are basically identical regardless of the bluff body shapes.The wall pressures begin to diverge from 0.3D(D is the inner diameter of the vortex flowmeter) in front of the bluff body due to the diversity in shape,and all reach the minimum values at 0.3D behind the bluff body.A discrepancy between the triangular or square cylinder and the semicircular cylinder in wall pressure change is observed at 0-0.1D behind the bluff body.It is also found that the wall pressures and irrecoverable pressure loss coefficients increase with flow rates,and the triangular cylinder causes the smallest irrecoverable pressure loss at a fixed flow rate.

Study on Hydrodynamic Vibration in Dual Bluff Body Vortex Flowmeter

The characteristics of the dual bluff body vortex shedding is investigated, and the possibility to use dual bluff body combinations to strengthen the hydrodynamic vibration around the bluff body objects is explored. The numerical and experimental approaches were utilized to examine the time dependent flow field and the pressure oscillation around the bluff bodies. The numerical data were obtained by the advanced large eddy simulation model. The experiment was conducted on a laboratory scale of Karman vortex flowmeter with 40 mm diameter. It is revealed that the optimized dual bluff body combinations strengthened the hydrodynamic vibration. It was also found that the hydrodynamic vibration with 180° phase difference occurred at the axisymmetric points of circular pipe on the lateral faces of the equilateral triangle-section bluff bodies. Using the dual bluff body configuration and the differential sensing technique, a novel prototype of vortex flowmeter with excellent noise immunity and improved sensibility was developed.

基于CFD的传感器体积对旋进旋涡流量计的影响

针对旋进旋涡流量计的精确测量,使用CFD数值模拟软件,以DN20口径的旋进旋涡流量计作为研究对象,得到了类似于钝体涡街旋涡脱落的现象,并对仿真的可行性进行了深入分析,验证了仿真工作的可靠性.分析比较低流量下不同取压点的压差,得到内流场压差变化规律,确定了DN20流体域的最佳取压点.将压电传感器置于最佳取压点后,使用音速喷嘴装置进行试验.将试验数据与仿真数据进行对比,发现两者之间存在一定的误差.分析其中原因,以小口径壳体内压电传感器自身体积较大为切入点,去除流体域内压电传感器体积,将去除压电传感器体积前后的流体域进行仿真,对结果比较分析,发现去除压电传感器体积后的流体域仿真得到的K值系数与试验值误差较小,说明压电传感器体积对内流场有一定影响,并且压电传感器的探针放置于流量计中会一定程度地增加旋进旋涡流量计的压力损失.

微小口径涡街流量计设计与测量特性研究

涡街流量计是基于流体振荡原理对流量进行测量的流量计,但在低流速下输出的信号很微弱,在实际测量过程中会叠加各种现场产生的噪音。并且目前工业上使用小口径涡街流量计在小流量工况下存在测量局限性,一般最小口径仅到DN15。针对目前涡街流量计存在的问题对DN10及以下的微小口径涡街流量计结构及参数进行研究,以满足工业上的测量新需求。基于模拟仿真计算平台,建立不同尺寸参数的微小口径涡街流量计数值计算模型并进行仿真计算,提出优化的涡街流量计结构尺寸。通过对不同压力监测点的压力波动强度及频率的研究,分析传感器的最佳布置位置。最后以电磁流量计为标准表对所研制的微小口径涡街流量计在微量程段进行了测试,对该被检流量计的误差、精度等参数进行实验,同时对雷诺数与斯特劳哈尔数之间的关系及仪表系数进行分析,结果表明,仿真所获的测量特性与实验测得的特性具有较好的一致性,且该微小口径涡街流量计相对误差优于0.5%,重复性等指标能够满足微量程段内的测量标准。

旋进旋涡与V锥组合计量气液两相流实验研究

目的解决低渗透气田在井间串联、井口混输计量模式下,单井产气、产液量无法准确计量的技术难题。方法基于旋进旋涡流量计和V锥流量计的单相计量原理,通过开展空气-水两相流的室内实验,分析了不同运行压力、气液比以及表观气速下单相流量计的混相计量误差变化规律。借助量纲分析法,分别建立了进动频率和压降与相关无量纲准数的关联公式,并采用室内实验数据分别进行了混相条件下的参数修正,利用两种流量计串联组合的方式,提出了一种适用于低含液率的湿气双参数组合计量模型,并采用延安气田现场的实流数据对模型计算精度进行了验证。结果室内实验时,当湿气体积含液率小于1%时,旋进旋涡进动频率随体积含液率的升高而降低,出现“欠读”现象,而V锥流量计的计量压降随体积含液率的升高而增大,产生“过读”现象。当体积含液率大于1%时,由于气相含液量偏大,造成旋涡进动信号下降规律不明显,从而导致组合计量模型的结果可能出现失真,现场实流测试结果显示,组合计量模型的气相体积流量的平均相对误差为2.029%,液相体积流量的平均相对误差为15.066%,体积含液率的平均绝对误差为0.059%。结论旋进旋涡与V锥流量计的组合计量模型在气相含液量较低时,气相和液相的计量精度可满足现场生产需要,且加工设计成本较低,可以为延安气田排水采气井的气液混相计量提供技术支持。

涡街流量计在高温引气测量中的选型与使用

介绍了涡街流量计的工作原理及实际应用中的选型方法,并对影响涡街流量计测量准确性的因素进行分析。通过对比涡街流量计实际应用中的试验数据,测量结果的误差值在流量测量精度要求的范围内,从而可以看出涡街流量计在发动机引气测量中的可行性和准确性,为后续发动机引气流量等空气流量测量提供方法和依据。

多种介质影响下涡街流量计的计量性能比较

涡街流量计是一种常用的流量测量仪表,用于测量液体、气体等流体介质。涡街流量计在不同介质下的计量性能存在差异,这主要是由于流体介质的可压缩性对涡街流量计的影响。通过理论分析和实流标定实验,研究涡街流量计在不同介质下的计量性能。结果表明,介质的可压缩性和涡街流量计的几何尺寸是影响计量性能的重要因素,不同介质下的涡街流量计需要进行修正。这些研究结果对于涡街流量计在实际应用中的准确测量提供了理论依据和实验指导。

涡街流量计取压方式对检定结果的影响分析

涡街流量计广泛应用于工业管道气体流量的计量。本文对比分析了涡街流量计表前取压和表后取压两种取压方法对检定结果的影响,根据得到的数据提出了减小因取压方式不同造成检定结果差异的措施。

旋进旋涡流量计取压方式对测量结果的影响

本文采用负压法音速喷嘴气体流量标准装置,分析研究了旋进旋涡流量计不同取压方式对测量结果的影响。研究结果表明,表体取压压损最小且表体取压方式的线性度优于表前取压和表后取压。

电磁法检测漩涡频率的涡街流量计

传统的涡街流量计对管径雷诺数ReD<10 4 时的流量不能测量 ,且仪表的耐震性差 ,遇到安装地点震动或管道振动的场合 ,则测量结果经常失真 ,不能保证准确性 ,并且仪表的安装条件苛刻。文中介绍了基于电磁检测法的电磁涡街流量计的原理、设计及如何克服上述缺点的举措。

基于DSP、具有谱分析功能的涡街流量计信号处理系统

本文介绍一种以数字信号处理器 (DSP)为核心、具有谱分析功能的涡街流量计信号处理系统。它采用周期图谱分析方法对涡街流量计中传感器的信号进行数字处理 ,准确计算出信号的频率 ,测出准确的体积流量。它抗干扰能力强 ,保证现场测量精度 ,扩大量程比 ,现场显示 ,并适用于不同口径和测量不同流体的一次仪表。它采用了 DSP。

管壁差压式涡街流量计测量影响因素分析

为了提高涡街流量计的抗干扰性和稳定性并保证测量精度,提出了一种基于管壁差压的旋涡频率检测新方法.在水和空气不同管内流动介质的情况下进行了系统实验.应用旋涡动力学和流体阻抗法,分析了取压位置和引压管频率特性因素对该方法测量性能的影响.实验结果表明,在旋涡发生体下游的一定距离内,取压位置对该方法的斯特劳哈尔数和仪表系数的影响很小,较靠近旋涡发生体迎流面的地方可测流量下限低.引压管的长度应尽量短,并且保证其固有频率与涡街频率相差较大.该方法简便可靠,适应性强,测量下限低.

基于经典谱估计改进方法的涡街流量计

针对涡街流量计高精度、高量程比的要求,在分析涡街信号及其噪声特点的基础上,提出一种采用自适应采样频率和Welch功率谱估计相结合的涡街信号分析处理方法。该方法首先使用经典功率谱估计的FFT算法计算出信号频率的区间范围,然后将信号通过相应截止频率的低通滤波器以防止发生混叠现象,采用信号抽取的方法降低采样频率从而减小频谱的最小频率分辨率,最后采用Welch功率谱估计的方法进行谱分析提高信噪比、减少谱失真。仿真及实验结果表明:所提出的涡街信号处理方法能有效地抑制噪声,实现高精度的功率谱计算,对于提升和改进涡街流量计的性能有良好的效果。

一种新型的光纤光栅涡街流量传感器

采用电子滤波技术、涡街流量传感技术提出了一种不受温度影响的光纤光栅流量测量系统。通过利用光纤光栅作为敏感元件,解决了传统电流量计的本征安全问题。对涡街流量传感信号的特点进行了理论分析,并采用相应的电子滤波技术,从而避免了光纤光栅传感的温度交叉敏感问题。实验验证该传感器的量程达到25L/min,精度为±0.5%F.S。理论分析和实验结果表明,该传感系统具有温度不敏感、本征安全、量程大和精度高等优点。

涡街流量计流场特性的数值仿真研究

由于旋涡产生和脱落机理的复杂性 ,迄今为止对涡街流量计流场的认识几乎全部依赖经验和实验。介绍应用FLUENT6 0计算软件 ,对DN5 0涡街流量计流场进行了数值仿真 ,就旋涡发生体的旋涡脱落频率与实测数据进行了比对。结果表明 ,数值计算结果与实测结果具有很好的一致性。提出了可以根据数值仿真来优化设计涡街流量计结构及选取最佳取压位置的结论。

涡街流量计的研究

涡街流量计是目前发展势头十分良好的流量计,在管道流量测量中得到广泛应用,并已跻身通用流量计之列。但涡街流量计尚属发展中流量计,其理论基础和实践经验较薄弱,在使用中,还会出现一些预想不到的问题。为解决这些问题,国内外科研工作者进行了大量的研究工作,并取得了一定进展。从涡街流量计中旋涡分离、涡街发生体形状、涡街信号检测方法及涡街信号分析和处理几方面对国内外研究现状进行了综述,指出研究中存在的难点及今后的研究方向,并提出一种利用涡街原理的新质量流量测量方法。

双钝体涡街流量计流体振动特性的试验研究

研究了双钝体旋涡脱离的流体动力学特性以及利用双钝体增强流体振动的最佳组合结构。给出了多种钝体组合结构的斯特劳哈尔数的试验结果,表明双钝体结构具有常定的斯特劳哈尔数。用50mm口径涡街流量计进行的试验证明,双钝体组合在一定的条件下能获得理想的旋涡重叠,从而增强流体的振动。在钝体的轴对称点上,还观察到强度和频率相同,相位相差180°的流体振动点,利用优化的双钝体结构和差动传感技术,研制出小流量灵敏度和抗干扰性能很好的新型旋涡流量计。