Proposed method for reconstructing velocity profiles using a multi-electrode electromagnetic flow meter
Proposed method for reconstructing velocity profiles using a multi-electrode electromagnetic flow meter
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DOI：
10.1088/0957-0233/25/7/075301
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发表时间：
2014-05
影响因子：
2.4
通讯作者：
L. E. Kollár;G. Lucas;Zhichao Zhang
中科院分区：
文献类型：
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作者：
L. E. Kollár;G. Lucas;Zhichao Zhang
提出了一种利用测量得到的多电极电磁流量计(EMFM)边界附近的电势分布重建速度剖面的解析方法。该方法基于离散傅里叶变换(DFT)，并在MatLab中实现。该方法假定管段内的速度分布为六阶多项式的叠加。每个多项式分量沿管道截面平面中的特定方向定义。对于在均匀磁场中得到的电势分布，该方向对于二次和高阶分量不是唯一的；因此，对于重建的速度分布，存在多种可能的解。提出了一种选择最优速度剖面的方法。它适用于单相流或两相流，需要测量非均匀磁场中的电势分布。对于可能的解，使用权值计算了该非均匀磁场中的电势分布。然后，计算出的电势分布与实测值最接近的速度分布提供了最优解。通过重建由多项式函数定义的人工速度剖面，证明了该方法的可靠性。其次，基于文献的结果，使用不同两相流中的速度分布来定义输入速度场。在所有情况下，都使用COMSOL多物理来模拟EMFM的物理规范并模拟测量；因此，COMSOL模拟产生了流管内圆周上的电势分布。这些电势分布作为分析方法的输入。重建的速度分布与输入的速度分布吻合较好。本文所描述的方法最适用于分层流动，而不适用于目前形式的轴对称流动。它的新颖之处在于它不仅提供了平均流速，而且提供了圆形管段内的速度分布作为空间坐标的解析函数。
An analytical method is developed for the reconstruction of velocity profiles using measured potential distributions obtained around the boundary of a multi-electrode electromagnetic flow meter (EMFM). The method is based on the discrete Fourier transform (DFT), and is implemented in Matlab. The method assumes the velocity profile in a section of a pipe as a superposition of polynomials up to sixth order. Each polynomial component is defined along a specific direction in the plane of the pipe section. For a potential distribution obtained in a uniform magnetic field, this direction is not unique for quadratic and higher-order components; thus, multiple possible solutions exist for the reconstructed velocity profile. A procedure for choosing the optimum velocity profile is proposed. It is applicable for single-phase or two-phase flows, and requires measurement of the potential distribution in a non-uniform magnetic field. The potential distribution in this non-uniform magnetic field is also calculated for the possible solutions using weight values. Then, the velocity profile with the calculated potential distribution which is closest to the measured one provides the optimum solution. The reliability of the method is first demonstrated by reconstructing an artificial velocity profile defined by polynomial functions. Next, velocity profiles in different two-phase flows, based on results from the literature, are used to define the input velocity fields. In all cases, COMSOL Multiphysics is used to model the physical specifications of the EMFM and to simulate the measurements; thus, COMSOL simulations produce the potential distributions on the internal circumference of the flow pipe. These potential distributions serve as inputs for the analytical method. The reconstructed velocity profiles show satisfactory agreement with the input velocity profiles. The method described in this paper is most suitable for stratified flows and is not applicable to axisymmetric flows in its present form. Its novelty is that it provides not only a mean flow velocity, but a velocity distribution in a circular pipe section as an analytical function of the spatial coordinates.