Ultrasound flow mapping of complex liquid metal flows with spatial self-calibration

Investigating the complex interaction of electrically conductive fluids and magnetic fields is relevant for a variety of applications from basic research in magnetohydrodynamics (MHD) to modeling of industrial processes involving metal melts, such as steel casting and crystal growth. However, experimental studies in this field are often limited by the performance of flow instrumentation for opaque liquids. Commercially available measurement systems usually lack the ability to provide a time-resolved imaging of transient flow structures. We present an ultrasound array Doppler velocimeter (UADV) for flow mapping in opaque liquids near room temperature. It is modular and flexible regarding its measurement configuration, for instance it allows capturing two velocity components in two planes (2d–2c) of 67×67 mm² with a frame rate of 30 Hz. It uses up to 9 linear arrays with 25 ultrasound transducers each driven in a parallelized time division multiplex (TDM) scheme. A FPGA-based signal processing allows a continuous realtime operation of the measurement system. Combining the single-component velocity data of each linear array to a 2d–2c flow field demands precise knowledge of the relative geometric position of the transducer arrays. We present a novel method that performs a spatial self-calibration by a mutual time of flight measurement, significantly reducing alignment errors. A measurement example of a magnetically stirred flow of GaInSn in a rectangular container is given. The UADV is applied to experiments in the context of manufacturing crystalline silicon ingots for photovoltaics.     

用激光外差技术高精度测量目标速度

搭建了外差探测实验平台,分别选用漫反射目标及类简谐运动模型作匀转速运动及变速运动的测量目标,应用激光外差探测技术实现了对匀转速运动及变速运动物体的速度测量.在匀转速测量过程中,同时采用外差探测法和振幅调制法测量了漫反射目标正负两个方向转动的速度,共得到133组不同的转速结果.通过调整实验系统,亦实现了对类简谐运动目标的...     

Use of gas bubbles for ultrasound Doppler flow velocity profile measurement

Ultrasonic velocimetry based on the Doppler shift effect accurately provides quasi-instantaneous flow fields for fluids with a sufficiently high acoustic scattering level. However, ultrasonic velocity instruments are known to perform poorly in clear water with low acoustic scattering level, which are frequent conditions in laboratory applications. This work confirms a technique to solve the problem by seeding the flow with micro hydrogen bubbles, generated by means of electrolysis.This paper investigates the influence of gas bubbles density on the quality of the ultrasound Doppler based velocity profiles in an open channel flow. The bubbles are generated by electrolysis of water using different magnitudes of electrical current. The estimation of the number of bubbles in the measurement volume confirms that the bubble diameter is similar to that of the wire used for electrolysis. This enables to determine the minimum density of gas bubbles needed to obtain a reasonably good echo and therefore an accurate velocity profile.     

临床超声技术中造影剂的应用

本文介绍了超声造影剂的发展历史、作用机理以及相关新技术的应用,并概括了目前超声造影剂主要的临床应用领域及今后的发展方向。     

Simultaneous velocity profile and temperature profile measurements in microfluidics

Simultaneous non-intrusive temperature and velocity measurements in flows are of high technological interest, e. g. to study the heat transfer in microfluidic environments. However, a measurement system that offers a low velocity uncertainty and micrometre spatial resolution as well as highly accurate temperature measurements in a single device has not been demonstrated so far. In this work, this problem is solved by combining a Laser Doppler Velocity Profile Sensor (LDV-PS) with Laser-Induced Fluorescence (LIF). Seeding particles are employed, that contain the fluorescent dyes uranine and rhodamine B. The multiple dye approach eliminates the influence of the droplet size. Relative velocity uncertainties of down to 0.4% and a temperature uncertainty of down to 0.24 ${}^{\circ }$C with a spatial resolution of $10\mathrm{\mu }\mathrm{m}$ are achieved in a demonstration air flow experiment. The method has the potential to be optimised for different temperature ranges and uncertainty requirements, making it applicable on a wide range of thermal flows like fuel cells or microbioreactors. A better understanding of heat exchange processes can improve the energy efficiency of microfluidic devices.     

光电非接触式表面流速测量

针对水工物理模型试验中尚无简单易行的表面流速测量方法,提出了一种新型光电非接触式表面流速直接测量法。在对光束入射水体后散射光强度公式进行推导的基础上,根据水体浅层泥沙浓度的统计继承效应,得出了经上下游浅层泥沙调制的散射光强成相关特性的结论。根据上下游散射光的相关特性,推导了流速测量公式,并分析了上下游测量间距、水流流速、采样率对测量结果的影响。搭建了实验系统,在6种不同标定流速下,分析了不同含沙量对测量精度的影响。实验结果表明,在0～50kg/m36种不同含沙量情况下,实测流速与标定流速的一致性均较好,但水体在10～50kg/m3适量含沙情况下,测量精度较不含沙情况有所提高,测量绝对误差均小于0.1m/s,相对误差能控制在8%以内。     

基于虚拟仪器的互相关流速测量系统设计

采用计算机模拟与实验相结合的方式,建立了基于虚拟仪器平台的互相关测量系统。系统采用LabVIEW函数选板中信号运算部分提供的互相关和自相关函数模块,设计了使用函数互相关、极性互相关和差动自相关3种算法实现互相关流速测量的程序。使用随机信号对上述3种算法进行验证,并对计算结果进行比较,验证结果表明互相关和差动自相关算法较为理想。     

Ultrasound measurement of large bubbles rising in angled slug pipe flows

This study details the problem of the ultrasonic detection of large bubbles rising rapidly in an upward gas–liquid two-phase pipe flow and proposes a new method to solve the problem. The proposed method uses two types of information, namely the echo intensity reflected by large bubbles and the Doppler frequency, which have different features in interface detection. The method using the Doppler frequency performs well in the detection of large bubbles regardless of the interface condition, whereas the method using the echo intensity has trouble in detecting an uneven interface. In contrast, the information of the echo intensity guarantees high accuracy of the interface detection even if that of the Doppler frequency has low accuracy for the detection owing to many small bubbles existing in the liquid film. Here, the two methods are combined to overcome their problems, and a validation test confirms that the results of the combined method agree well with the results of image processing. As demonstrations of the proposed method, the slug frequency, velocity, and airflow rate of large bubbles in an air-lift pump are obtained. The results confirm that the proposed method can be adopted for the high velocity of slug flow in various applications.     

声学法炉内温度场与速度场协同测量方法研究

实时监测炉内燃烧温度场和烟气速度场是保证锅炉安全、经济运行的重要手段,声学法测物理场被认为是一种非侵入性和有效的测量方法。本文提出了一种基于声波法的炉内温度场和烟气速度场的协同测量新方法,建立了基于径向基函数的多物理场重建模型,采用Tikhonov正则化算法求解不适定问题,同时考虑了声波的折射效应对物理场的重建影响。采用典型的炉内物理场模型进行了数值模拟,模拟结果表明,本文方法能够很好的协同重建温度场和速度场。当考虑声线弯曲时能够显著提高各物理场的重建质量。算法具有较好的适应性和良好的抗噪性能,重建精度较高,标准均方根误差在10%以下。模拟实验平均计算时间为31.4 s,可保证炉内声学测量的实时性。声学法协同测量多物理场可为优化炉膛燃烧过程提供依据。     

光学互相关测速系统设计与验证

针对两相流颗粒运动速度测量及基于互相关原理设计了双光路激光测速系统。采用搭建的变频电机带动绕丝产生已知旋转线速度的装置开展光学互相关测速验证实验。通过测量绕丝经双光路激光的光强衰减信号,再对两路信号进行互相关分析,从而得到测点绕丝旋转线速度。以电机转速计算的测点绕丝线速度作为参考值进行测量精度验证,得到光学互相关测速方法的测量相对误差在6%以内,验证了光学互相关测速方法的准确性。     

光声血流速度测量方法及研究进展

光声成像因其独特的成像原理,兼顾了功能性和分辨率,对诊断和处理心血管疾病具有十分重要的意义。通过对光声血流速度测量进行综述,系统介绍了光声多普勒、光声显微成像和光声相关谱三个原理下的血流速度测量原理及具体应用,以期对此领域的研究人员的研究提供参考。     

Estimation of uncertainty of mean velocity of flue gas in a conduit as determined by the traverse method within the gravimetric measurement of particulate concentration

In gravimetric measurements of dust emissions from industrial technological plants, the required mean gas velocity in a conduit is often determined by Pitot traverse method. It is commonly seen as a method giving good approximate values of mean gas velocity, although the actual rate of this approximation is not considered in the analysis of measurement results. It was seen that there was a need to establish what magnitude of error might occur in practice due to the small number of measurement points and typical non-uniformity of the gas velocity profiles in conduits of rectangular cross-section. The calculations were based on the concept of treating a measurement plane as one consisting of a set of elementary planes. The elementary gas velocity profiles in these elementary planes were simulated, the mean velocity for these profiles were calculated based on point velocity values, and the measurement uncertainty of this mean velocity determined. This uncertainty results in the uncertainty of the mean velocity across the entire measurement plane. It appears that, depending on the number of measurement points and gas velocity profile non-uniformity, the value is not small and is of the order of several percent, and hence needs to be taken into account in the budget of the combined uncertainty of mean velocity, which in turn contributes to the uncertainty of gas volumetric flow rate and dust pollutant mass flow rate.     

Investigations of electrically driven liquid metal flows using an ultrasound Doppler flow mapping system

This paper presents a combined experimental and numerical study of the properties of a liquid metal flow inside a cylinder driven by the application of a strong electrical current. The interaction between the electric current running through the melt and the corresponding induced magnetic field produces so-called electro-vortex flows. We consider here a configuration of two parallel pencil electrodes immersed at the free surface. Velocity measurements were performed by means of the Ultrasound Doppler method. A linear array of 25 singular transducers was used to determine the two-dimensional pattern of the vertical flow component. Numerical simulations of the magnetohydrodynamic (MHD) problem were conducted to calculate the Lorentz force, the Joule heating and the induced melt flow. Experimental and numerical results reveal a complex three-dimensional flow structure of the liquid metal flow. In particular, two pronounced downward jets are formed below both electrodes. The flow structure appears to be symmetrical with respect to two vertical cross sections being perpendicular to each other and one of the two planes contains the electrodes. The comparison between the experimental data and the numerical results shows a very good agreement.     

基于几何光学的图像矫正法在圆管PIV实验中的应用研究

粒子图像速度技术被广泛用于流体流动测量,介质折射率差异使光在圆管壁面发生偏折,导致图像失真,直接影响速度测量精度。本文建立了光学折射的物理模型,得到圆形管道中物点和图像点之间的函数关系进而得到矫正后图像的像素坐标,使用双线性插值算法得到像素灰度值重建出矫正后的粒子图像,最后根据多重网格迭代算法计算管内速度场。分别对流体进行管内静态流体与管内层流速度场测量实验,对比了光学矫正箱法、线性矫正以及基于光学模型的畸变矫正方法误差。结果表明,本文提出的基于几何光学的图像矫正方法精度优于光学矫正箱法和线性矫正方法,并通过静态与流动实验充分验证了所建立几何光学模型的准确性和有效性。     

激光测距与光速测量实验方法研究

本文给出了采用相位式进行激光测距的实验原理,根据相位式激光测距原理提出了一种激光测距实验方法。在此基础上,通过对实验方法的调整,同时实现了对光速的测量,并对距离测量和光速测量测量的结果进行了误差分析。     

Application of video imagery techniques for low cost measurement of water surface velocity in open channels

Developments in digital video recording technology make the video imagery tools more popular for velocity measurement in water flows. This has especially been of large interest due to its inherent advantage of non-contact nature which is quite handy in extreme flow conditions. Particle Image Velocimetry (PIV), Particle Tracking Velocimetry (PTV) and Large Scale Particle Tracking Velocimetry (LSPTV) are applied to free surface channel flow for water surface velocity measurement. Experiments are conducted to measure either a single point velocity applying PTV or velocity profiles across the channel width applying PIV on the water surface in a rectang typical velocities of nearly 1 andular tilting flume for various flow conditions. Technical issues regarding tracer particle size and type, travel distance, lighting, recording speed, camera position, image distortion and state of flow are discussed. Measured data is compared to computational results obtained from a numerical model involving a non-linear turbulence model capable of predicting turbulence driven secondary flows. Confirmation of reasonable match between computational and experimental results whereby applying mutual collaboration of them for discharge measurement has been attested. In addition to discharge, boundary roughness has also been predicted as an outcome of the numerical solution.     

An experimental study on the distribution of the drop size and velocity in asymmetric impinging jet sprays

Distributions of the drop size and velocity in an asymmetric impinging jet are investigated by injecting water and a sodium carbonate (Na₂CO₃) solution, which simulates the mixing process in impinging jet sprays of liquid oxidizer and liquid fuel for liquid propellants. The liquid sheet formed from the impinging jet is visualized and the drop size distributions are obtained by using image processing for the visualized images. The drop size distribution of the asymmetric impinging jets is fitted to the Rosin-Rammler distribution function. The obtained drop size distributions according to the azimuth angle in the impinging jet are compared with the theoretical predictions of previous research. The experimental results of the drop size distributions are located between the two curves obtained from the theoretical predictions by treating each jet in the asymmetric impinging jets as an independent wall-impinging jet. PIV images using a double-exposure method were processed to obtain the drop velocity vector in the impinging jets. Whether the drops shedding from the edge of the asymmetric impinging jets occurs radially or tangentially is also investigated from the PIV results.     

Flow measurement using free over-fall in generalized trapezoidal channels based on one velocity point method

A free over-fall offers the possibility of being used as a flow measuring device in hydraulic structures with a single depth measurement of the end section. Due to its practical importance, considerable attention has been paid to investigate free over-falls for different channel cross-sections using various approaches. This paper presents a new theoretical approach for computing the end depth ratio (EDR) relationship for the generalized trapezoidal channel cross-sections at free over-falls in sub critical flow regimes from which the end depth discharge (EDD) can be computed. The generalized trapezoidal channel is a geometric shape that is defined mathematically with a single equation where five widely known prismatic channel cross-sectional shapes can be generated (trapezoidal, inverted triangular (Δ), rectangular, parabolic, and triangular). This suggested theoretical approach uses one velocity point at the geometric center of the end section based on the energy and the continuity equations. Relevant experimental and theoretical results were utilized in order to examine the suggested method through the statistical measuring indices (percentage difference and the correlation coefficient (R²)). The computed results show very close agreements with the earlier works. Furthermore, simple equations are also generated using the regression curve fitting technique in order to estimate the direct discharges (Q) using the end depth (y_e) for each of the above mentioned channel cross-sections.     

水平管道中瓦斯爆炸火焰传播速度测量

在煤炭工业中, 瓦斯爆炸事故经常发生, 造成了巨大的人员伤亡以及材料性能的破坏. 在研究瓦斯爆炸机理过程中, 火焰前端传播速度是最重要的因素之一. 根据中北大学水平管道实验装置设计了一套火焰速度测量系统, 用于研究在密闭管道内圆环障碍物的数量和阻塞比对火焰传播速度的影响. 结果表明, 障碍物对瓦斯爆炸产生的火焰具有明显的加速作用. 随障碍物数量和阻塞比的增加, 火焰加速更加明显且持续更剧烈. 其中, 障碍物数量对火焰加速持续的作用更大, 而障碍物阻塞比的作用不明显.