Three-dimensional MHD simulations of the electromagnetic flowmeter for laminar and turbulent flows

The interaction between an electrically conducting fluid and an external magnetic field in an ideal cylindrical electromagnetic flowmeter is numerically investigated for both laminar and turbulent flows. Induced electric potential in the fluid, and the difference in potential at the measuring electrodes are directly obtained by including MHD effects in the CFD simulations. Fully developed laminar and turbulent flows are simulated. The computed electric potential difference on the electrodes agrees with analytical values for small Hartmann number cases, where the induced Lorentz force is small. Turbulent flow produces a more uniform electric potential distribution in the flow meter cross-section than laminar flow. These integrated MHD/CFD simulations couple the MHD effect with flow dynamics without deriving a weighting function with an assumed velocity profile, which will be necessary for electromagnetic flow meters when the Hartmann number is not small.     

Theoretical study of vertical slug flow measurement by data fusion from electromagnetic flowmeter and electrical resistance tomography

Electrical resistance tomography (ERT) can be used to obtain the conductivity distribution or the phase distribution of gas/liquid flows (e.g. slug flow). Using proper parameter models and flow regime identification models, the measurement of phase size, void fraction, and pattern recognition can be realized. Electromagnetic flowmeters have been used to measure conductive single-phase liquid flows. However, neither ERT nor electromagnetic flowmeters (EMF) can provide accurate measurement of gas/liquid two-phase flows. This paper presents an approach to fuse the information from ERT and an electromagnetic flowmeter. A model for the measurement signal from the electromagnetic flowmeter has been developed based on the flow pattern and the phase distributions, which are obtained from the reconstructed images of ERT, aiming to reduce the measurement error of the electromagnetic flowmeter and enhance the measurement accuracy. Through the simulation research of virtual current density distribution, the feasibility of fusion of electromagnetic flowmeter and ERT to measure gas/liquid two-phase vertical slug flow is verified. By theoretical analysis, the relationship between the output of electromagnetic flowmeter and flow parameters is established. The electrical potential difference of the electromagnetic flowmeter, average velocity, volume flow rate and gas void fraction between the bubble size and location are also investigated. The fusion approach can be used to measure vertical slug flows.     

Numerical investigation on the installation effects of electromagnetic flowmeter downstream of a 90° elbow–laminar flow case

An electromagnetic flowmeter installed downstream of a 90° elbow to measure the flowrate of laminar flow is numerically simulated to investigate installation effects by varying the location of the electromagnetic flowmeter at a distance up to 22D from the elbow, and the angle between the electrodes plane and the symmetry plane of the elbow at ϕ=0, 45 and 90°. Effects of the curvature radius (R_c) and the Reynolds number (Re) based on a diameter D are also scrutinized in the range of 400≤Re≤1500 and R_c=1.5D and 3.0D.For the simulation of an electromagnetic flowmeter, a commercial code FLUENT(ver. 4.4) is applied for flow field analyses and a three-dimensional numerical code is developed for analyzing the magnetic field. The developed code adopts a finite volume method to solve a Poisson-type voltage equation for the magnetic field.It is found that the deviations of the flow signal due to the disturbance from the elbow is strongly dependent on the pattern of axial velocity contours. Cases for ϕ=45° are found to permit significantly better measurement accuracy in comparison with ϕ=0° and ϕ=90°, and the effect of the curvature on the optimum installation distance depends on the Reynolds number. The present numerical simulation method is found to be a useful tool for the performance analysis of the electromagnetic flowmeter.     

A numerical model for simulating separated gas-liquid two-phase flow with low GVF in a V-cone flowmeter

One of the relatively new types of differential pressure flowmeters is the V-Cone (conical or cone) meter. In addition to having many advantages over other types, this flowmeter can also be used in multiphase flows. In the last few decades, many numerical works have been presented for single-phase flows. But in the discussion of two-phase flow, most of the available works are related to experimental research. Therefore, in this paper, the separated two-phase flow with a low gas volume fraction (GVF) has been numerically investigated. For this purpose, an unstructured grid and finite volume numerical method were used. In order to model the two-phase flow and turbulence, the existing approaches were compared. According to the results obtained, the volume of fluid (VOF) method for simulating two-phase flow and the Realizable k-ε model for turbulence modeling lead to better results than other investigated models. Also, by stimulating the flow with the aforementioned methods, it was found that the accuracy of the pressure calculation decreases with the reduction of the superficial velocity and volume fraction of the gas. Furthermore, for a more detailed analysis, the superiority of the Realizable k-ε turbulence model compared to other investigated models was proved quantitatively.     

A new velocity estimation method using spectral identification of noise

In all measurement techniques one seeks accuracy and precision. In ultrasonic Doppler velocimetry, those qualities strongly depend on signal to noise ratio of the Doppler signal and on the performance of the velocity estimator. The most widely used estimation method in ultrasonic coherent Doppler velocimetry is the pulse pair method. Its success is due to the computation efficiency of the algorithm combined to an unbiased estimator. Unfortunately, for a wide range of experimental fluid flows, the pulse pair estimation is less efficient, especially for clear water or concentrated mud where the signal to noise ratio can be very low, or for highly turbulent flows where the Doppler signal has a broad spectrum. Our approach is based on the treatment of the Doppler spectral information. It uses a simple parametric identification inspired by theoretical models and experimental observations. It acts through noise subtraction and subsequent cutting. Thus, we have developed a fast velocity estimation algorithm superior to the pulse pair one in terms of accuracy. The robustness of the method was evaluated by adding different levels of white Gaussian noise to an experimental Doppler signal. The results demonstrate an increase of noise immunity up to one decade compared to the pulse pair method.     

Numerical modeling and experimental verification of a low fluid flow inductive flowmeter

The article discusses modeling procedures to capture the physical and chemical processes present in operational measurement with a high-precision inductive flowmeter. In this context, a theoretical model and a numerical solution are proposed. Exploiting the combined finite element method (FEM) and the finite volume method (FVM), we prepared numerical models of multiple variants of the flowmeter and computed the output voltage on the device's electrodes. The model joins together the magnetic, electric, and current fields; a flow field; and a physical-chemical nonlinear ion model. The results were obtained by means of the FEM/FVM in ANSYS software and verified via experimental testing.     

Statistical modeling and signal reconstruction processing method of EMF for slurry flow measurement

According to the experimental data, an amplitude probability density function (PDF) model of the slurry flow signal is built up for electromagnetic flowmeter (EMF) by the method combining statistical analysis with numerical fitting, in order to reveal the effect of slurry noise on the flow signal and describe the features of slurry flow signal. Based on this model, a signal reconstruction processing algorithm is proposed to deal with the output signal of EMF sensor for realizing the slurry flow measurement. At the same time, the high-low voltage switching mode based square-wave excitation method is presented for EMF so as to reduce the slurry noise interferences. A slurry-type EMF transmitter is developed with a DSP chip – TMS320F28335, to implement the signal processing algorithm and control function. Finally water flow calibrations and slurry flow experiments are conducted to verify the reliability and stability of the method and system. Experimental results show that its measurement accuracy of water flow is better than 0.5%, and its steady-state volatility of paper slurry is less than 3%, and its dynamic response time is less than 4 s.     

利用钻孔垂向流计算多层含水层参数方法探讨

论述了在揭露多层含水层的钻孔中,利用地下水同位素示踪仪测定孔内垂向水流流速和流向计算多层含水层参数的基本原理,并经工程实例检测证实测试方法可行,参数计算精度可靠。     

数字信号处理技术在科氏质量流量计中的应用

科氏质量流量计是目前应用范围最广、发展速度最快的流量计之一。数字信号处理技术是科氏质量流量计的核心技术,直接决定其测量精度、测量稳定性等性能指标;而流量传感器输出信号的数学模型是信号处理的依据和基础。国内外学者提出了多种信号处理方法,但是,没有根据不同的信号模型和不同的应用场合对各种信号处理方法进行比较和评价。为此,根据不同数字信号处理方法的特征量提取原理,分析了其具有的优缺点。针对科氏质量流量计单相流、批料流与气液两相流测量这3种典型应用场合中存在的关键技术问题,依据随机游动信号模型、突变信号模型和自回归滑动平均(ARMA)信号模型,分别从计算精度、响应速度、收敛性、抗干扰能力和对参数变化的敏感度等方面,对不同信号处理方法进行考核和对比,确定了3种典型应用场合下,解决关键技术问题,性能最佳的数字信号处理方法。     

Flow measurement with an electromagnetic flowmeter in two-phase bubbly and slug flow regimes

In order to investigate the characteristics of an electromagnetic flowmeter in two-phase flow, an alternating-current electromagnetic flowmeter was designed and manufactured. The signals and noise from the flowmeter under various flow conditions were obtained, and analyzed in comparison with the flow patterns observed with a high-speed charge-coupled device camera.

An experiment with void simulators, in which a rod-shaped non-conducting material was used, was carried out to investigate the effect of bubble position and void fraction on the flowmeter. Two-phase flow experiments, encompassing bubbly to slug flow regimes, were conducted with a water–air mixture.

The simple relation ΔU_TP=ΔU_SP/(1−), relating the flowmeter signal between single-phase flow and two-phase flow, was verified with measurements of the potential difference and the void fraction for a bubbly flow regime. Due to the lack of homogeneity in a real two-phase flow, the discrepancy between the relation and the present measurement increased slightly with increasing void fraction and superficial liquid velocity j_f.

Whereas there is no difference in the shape of the raw signal between single-phase flow and bubbly flow, the signal amplitude for bubbly flow is higher than that for single-phase flow at the same water flow rate, since the passage area of the water flow is reduced. In the case of slug flow, the phase and the amplitude of the flowmeter output show dramatically the flow characteristics around each slug bubble and the position of the slug bubble itself. Therefore, the electromagnetic flowmeter shows a good possibility of being useful for identifying the flow regimes.     

High-precision Coriolis mass flowmeter for bulk material two-phase flows

For measuring or dosing purposes in gas/solid two-phase flows (non-pressurized and pressurized systems) a mass flux measurement device based on the Coriolis principle has been developed. The Coriolis flowmeter developed is applicable for on-line measurements of the mass flux, showing a fast response time to load variations and measuring accuracies of ±1% of the actual measured value. The Coriolis flowmeter was successfully tested in pilot and industrial plants. Different granular materials, such as coal dust, quartz sand, feldspar, plastic granulates and foodstuffs have been measured already. In practice, the Coriolis flowmeter has shown reliable operation in various applications in process engineering. The integration of the Coriolis flowmeter into advanced control systems for feeding or dosing purposes opens new possibilities for on-line control and exact dosing of gas/solid two-phase flows.     

A new method of seamless land navigation for GPS/INS integrated system

For the last few years, integrated navigation systems have been widely used to calculate positions and attitudes of vehicles. The strapdown inertial navigation system (SINS) provides velocity, attitudes and position information, whereas the global positioning system (GPS) provides velocity and position information. A method using neural network (NN) and wavelet-based de-noising technology is introduced into the SINS/GPS/magnetometer integrated navigation system, because system accuracy may decrease during GPS outages. When the GPS is working well, NN is trained using the velocity and position information provided by SINS as input and the corresponding errors as output. Wavelet multi-resolution analysis (WMRA) is also introduced to de-noise the errors, the desired output of NN. Test results showed that velocity accuracies improved using NN, but other accuracies remained poor. By re-training NN with WMRA, the system accuracies improved to the level of using normal GPS signal. In addition, NN trained with WMRA also improved the approximation to the actual model, further enhancing alignment accuracy.     

Installation effects on ultrasonic and electromagnetic flowmeters: a model-based approach

The paper describes the basic ideas of a model-based installation-effects analysis method and presents results from a collaborative research programme being conducted at the National Institute of Standards and Technology (NIST) in Gaithersburg, MD, USA, and at Tampere University of Technology in Finland. The analysis method is based on a combination of flow modelling and flowmeter modelling. In this paper, installation effects on electromagnetic and travel-time-difference ultrasonic flowmeters are discussed. The installation cases are single elbow and double elbow out-of-plane piping configurations. The results show that significant shifts from ‘ideal’ meter performance can occur in such disturbed flow conditions. The flowmeter modelling results also show that these significant shifts can be reduced by altering the operational arrangements and performance characteristics of the meters. It is concluded that such flowmeter modelling can be very useful in: (1) redesigning flowmeters to make them less susceptible to installation effects, (2) constructing new meters, or (3) arranging special meter configurations to deal with specific disturbed flows.     

Study on a new electromagnetic flowmeter based on three-value trapezoidal wave excitation

Excitation technology plays an important part in the field of electromagnetic flowmeter (EMF). The form of the magnetic field directly determines the characteristics of the flow signal. No breakthrough has been made on the excitation technology since the invention of sinusoidal wave excitation, rectangular wave excitation, and double-frequency excitation. In this paper, firstly a new three-value trapezoidal wave excitation with transient responses is proposed. Then the signal model is established, and the verification experiments are carried out. Finally, flow calibration experiments and comparative experiments on the trapezoidal wave excitation are conducted on the experimental platform. The experiment results show that the electromotive force output by the EMF based on three-value trapezoidal wave excitation is linearly related to the flow velocity. When the flow velocity is 0.257 m/s, the relative error is only 1.635%. When the flow velocity reaches 2.133 m/s, the relative error is reduced to 0.432%. The three-value trapezoidal wave excitation with the transient analysis satisfies the requirements of the EMF with high accuracy. The research also shows that the excitation frequency has a great influence on the measurement accuracy of the EMF based on three-value trapezoidal wave excitation.     

基于流—固耦合的汽车减振器动态特性仿真分析

对减振器的流—固耦合建模和求解技术进行研究。基于多求解器的流—固耦合方法,建立精度较高的阻尼阀流场网格模型和叠加阀片有限元接触模型,并联合有限体积法和有限元法对减振器流—固耦合模型进行求解和分析,获取了减振器的速度特性和示功图,对阻尼阀内部压力场、速度场进行详细分析,对叠加阀片非线性动力学特性进行分析。仿真结果表明:由于高速油液对阻尼阀壁面的冲击作用,阻尼阀核心区域的压力场急剧变化;阀片在开启和关闭瞬间,速度有一个跳跃,这使得节流通道迅速变化,具体表现为开阀点附近的速度特性曲线向下弯折。因此,阻尼阀核心区域的流场网格模型和叠加阀片的接触模型对仿真精度影响最大。计算中考虑了油液的湍流流动,阀片的接触滑移和大挠度变形,使得流—固耦合模型尽可能地贴近物理事实,仿真结果与试验吻合较好。     

Flow measurement method of complex flow in heat exchange casing

Fluid plays an important role in engineering application and the accurate control of the carrier is the premise of energy efficient conversion and management, such as the primary air volume of the boiler, the reactor inlet flowrate, the amount of oil and air intake of internal combustion engine, etc. Therefore, flowmeter plays an important role in energy conversion and management. In this work, a high-low frequency combined with reflection-penetration synchronization flowmeter was designed to measure the flowrate in casing device based on the characteristics of different frequencies of sound. The flowrate calculation method of casing device is given and verified by numerical simulation. The results show that the flowrate of different flow states can be calculated accurately by using the high-low frequency combined with reflection-penetration synchronization method. At the same time, the method can also be used in electromagnetic wave, optical and other fields.     

电磁轴承磁场计算的磁路法优化

介绍电磁轴承磁场计算和转子受力特性分析的磁路法和有限元法。基于上述两种方法,详细地计算了考虑铁磁材料磁阻及其非线性因数的电磁轴承磁场,讨论了两种方法计算结果的差异。参考有限元法的计算结果,对计算电磁轴承磁场的磁路法进行了优化。优化后的电磁轴承磁路法简单、准确,具有工程应用价值。     

管坯电磁胀形磁场特性及磁压力分布

电磁成形理论涉及电磁学与塑性动力学,磁压力研究是其理论研究的基本问题之一。采用有限元法是提高磁压力求解精度的有效途径,而确定求解区域及其边界上的磁场特性又是有限元方法的关键问题。采用解析方法求解管坯与线圈同轴放置时的磁场,确定了有限元的求解区域及该求解区域边界上的磁场特性。在此基础上通过有限元计算得到了螺线管线圈和阶梯形线圈胀形时的磁场场景和磁压力分布,并通过管坯自由胀形试验验证了磁压力分布。     

循环流化床颗粒团多参数的光散射测量方法

针对循环流化床床内颗粒团动态参数和行为特性的测量问题,提出了基于光散射原理的颗粒团运动速度、高度与浓度等多参数同时在线测量方法,利用该方法对二维冷态循环流化床试验台开展颗粒团参数测量,获得了颗粒经测量区造成的光强衰减信号,通过对上下测量单元光强信号进行互相关分析可获得颗粒团运动速度参数;对信号进行低通滤波,根据低频信号极值点时间差及运动速度测量结果,得到颗粒团高度参数;同时根据光强衰减程度计算颗粒团的浓度参数。由此实现了基于光散射原理的循环流化床床内颗粒团运动速度、高度与浓度多参数同时在线测量,测量结果显示,在典型工况下,提升管中心区域颗粒团运动速度较为稳定,平均速度为3.81 m/s,近壁面区域颗粒团运动速度有较大波动且出现负值,平均速度为0.65 m/s;中心区域颗粒浓度较近壁面区域小;中心区域颗粒团高度主要分布在20～40 mm区间,近壁面区域颗粒团高度主要分布在30～60 mm区间。这为循环流化床内颗粒团的形成、结构及其运动研究提供了一种有效的测量手段。     

耐磨气固两相流离心风机的理论研究与开发

分析了气固两相流风机的使用背景和存在的问题，通过对固粒穿过湍流和层流边界层时造成叶片磨损的比较，建立了风机叶片附近流场特性与磨损之间的关系，说明叶片附近流场的湍化程度高能减轻固粒对叶片的磨损，而由计算表明叶片表面加肋条能提高流场的湍化程度，因而能减轻磨损。在理论研究的基础上，通过固粒对壁面的冲击角与冲击速度对磨损率影响的实验研究，设计了耐磨风机，经实际运行，耐磨效果很好。