3D and 2D experimental views on the flow field of gas-evolving electrode cold model for electrolysis magnesium

In the magnesium electrolysis process, chlorine gas bubbles release at the surfaces of anode and affect electrolyte flow patterns. This paper presents an experimental apparatus to simulate the flow field induced by chlorine gas evolution at the gas-evolving electrodes of magnesium electrolysis cell. The three-dimensional flow structures were determined by using volumetric three-component velocimetry (V3V) technique, which has the ability to capture the out-of-plane velocity component. The three-dimensional flow structures in the region with a depth about 120 mm can be obtained. To achieve this, approximately 15,000 three-dimensional velocity vectors were detected in the flow measurements and constituted the three-dimensional flow field, which eliminated the perspective error caused by the out-of-plane motion in Particle Image Velocimetry (PIV) method. In experiments, comparisons are made between the V3V and PIV results. The in-of-plane velocities data obtained by V3V technique have the same trend with the PIV results, and V3V provides more details in the third direction for the flow field accurately.     

PIV measurements of the time-averaged flow velocity downstream of flow conditioners in a pipeline

The flow downstream of three different flow conditioners, a tube bundle and two perforated plates, was investigated by measuring the time-averaged, axial velocity component with Particle Image Velocimetry (PIV). The conditioners were exposed to the flow disturbed by a 90° out-of-plane double-bend. The experiments were performed with air flow through a pipeline of 100 mm i.d. and at Reynolds numbers between 100 000 and 200 000. The axial development of the velocity profiles, without and with conditioner, is documented, and the performance of the three devices in conditioning the disturbed flow can be compared. Particular attention is given to the determination of time-averaged velocity values by means of PIV.     

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。     

迷宫型灌水器水沙两相流场分析及结构改进

为了解决迷宫型灌水器微细流道容易堵塞的问题,针对其复杂的微细流道结构(实际尺寸在0.8～1.2 mm之间),根据灌水器工作时灌溉水中存在过滤不掉的沙粒的实际情况,首先应用计算流体力学(Computational fluid dynamics, CFD)数值计算的方法,进行灌水器整体迷宫流道水砂两相流数值模拟,根据其流动场分析其堵塞的结构因素。同时应用粒子图像测速(Particle image velocimetry, PIV)技术,搭建灌水器流道流动场微PIV测试台,测量实际尺寸大小的微流道中流动场和粒子运动状况,得到其流动场流线图和粒子运动轨迹图,并通过灌水器的抗堵塞性能试验,验证了迷宫型灌水器微流道中流动场和粒子状况分析计算的正确性。针对流道中存在的容易引起堵塞的流动滞止区进行结构优化改进,试验结果表明,应用改进的结构可提高迷宫型灌水器的抗堵塞性能。     

水平安装文丘里管低压湿气测量模型

在低压高流速工况下,对文丘里管的湿气测量虚高数学模型进行理论和试验研究.由动量方程出发,推导文丘里管用于湿气测量的理论计算式.在天津大学低压油、气、水三相流试验装置上,对管径比为0.404 8、0.55、0.7的文丘里管进行大量湿气试验,分析压力、滑差及液相含率对文丘里湿气测量虚高的影响,提出一个新的文丘里管低压湿气测量半经验模型公式,达到较高的测量精度.通过对不同管径比的试验数据的分析比较,得出管径比为0.55的文丘里管信号具有较小分散性的结论.     

河流水面成像测速研究进展

大尺度粒子图像测速(LSPIV)是一种用于测量大面积(数百平方米)水体表面流速的非接触式全场流速测量技术。不仅可用于常规条件下明渠紊动特性和时均特性的研究,更具有极端条件下河道水流监测的应用潜力。然而受复杂现场环境的影响,该技术在天然河流的应用中面临着诸多挑战。从水流示踪方式、流场图像采集、水面目标增强、运动矢量估计、时均流场重建、水面流场定标及不确定度评估七个方面综述了国内外对河流水面成像测速(RSIV)方法的研究进展。通过对现有方法的总结和讨论,提出改进技术方法的研究需求,以使其成为水动力学和水文学中有力的测量工具。     

利用PIV研究超声波引起的微流动现象

利用微观粒子图像测速技术(Micro-PIV)定量研究了位于两块载波片之间的微量液体在压电陶瓷超声换能器(PZT)的激振作用下而产生的微流动现象,超声换能器的激振频率为1.3 MHz,超声功率为1~5 W／cm2,微量流体的体积为5μL。试验中利用Micro-PIV系统测量了微量流体在不同超声功率下的流场结构。试验结果表明,微量流体在功率超声的激振下,在垂直于超声振动的方向上存在平面旋涡结构,而且声流的最大速度与超声强度成正比。     

Phase discrimination and a high accuracy algorithm for PIV image processing of particle–fluid two-phase flow inside high-speed rotating centrifugal slurry pump

PIV technology is an efficient and powerful measurement method to investigate the characteristics of fluid flow field. But for PIV particle image post-processing, some problems still exit in two-phase particles discrimination and velocity field algorithm, especially for high-speed rotating centrifugal slurry pump. In this study, through summarization and comparison of the various phase discrimination methods, we proposed a two-phase identification method based on statistics of gray-scale level and particle size. The assessment of performance through experimental PIV images shows that a satisfying effect for particle identification. For high speed rotation of the impeller, a combination of adaptive cross-correlation window deformation algorithm and multistage grid subdivision is presented. The algorithm is applied to experimental PIV images of solid–liquid two-phase flow in a centrifugal slurry pump, the results show that the algorithm in the present study has less pseudo vector number and more matching particle pairs than those of fixed window and window translation methods, having the ability to remove pseudo vector efficiently. It confirmed that the algorithm proposed in the present study has good performance and reliability for PIV image processing of particle–fluid two-phase flow inside high-speed rotating centrifugal slurry pump.     

Particle Image Velocimetry Measurement of the Flow Field in the Play of the Drilling Pump Valve

The failure of a drilling pump is always due to the break of the drilling pump valve, which is one of the most important but also the weakest parts of the drilling pump. Over the decades, the degradation of drilling pump valves has been investigated extensively and various failure mechanisms have been proposed. However, no experimental test on the fluid has been successfully performed to support some of these mechanisms. In this paper, tests of the flow within the valve play are carried out to investigate the factors resulting in the failure of the valve. In the tests, particle image velocimetry(PIV) technology is employed to measure the flow field distribution of the valve play in the model. From these tests, the distributions of velocity and vorticity of fluid in various valves with different valve angles and different valve lifts are obtained, from which the features of flow fields are derived and generalized. Subsequently, a general rule of the influence of valve angles and valve lifts on the flow velocity is concluded according to chart analyses of maximal velocities and mean velocities. Finally, an analysis is made on the possibility of valve failure caused by erosion and abrasion in a working valve, with the application of the failure mechanisms of drilling pump valves. PIV measurement improves the study on the failure of the drilling pump valve, and the results show good agreement with previous computational fluid dynamics(CFD) simulations.     

基于PIV测量的涡轮流量计响应分析

应用粒子成像测速技术获得了涡轮流量计叶片入口流场的速度分布信息,并基于该测量结果,运用T-G模型理论得出流量计的响应.通过与以往所采用的几种典型的入口速度分布计算得到的结果比较分析表明,基于PIV测量的结果更接近于涡轮流量计的真实响应.还比较分析了涡轮入口速度分布对涡轮流量计响应的影响机理,相关结果可望为改进涡轮流量计响应的计算分析方法以及优化设计提供有价值的参考.     

分离涡流场数值仿真的参数影响研究

分离涡流场普遍存在于工业现场,数值仿真和试验研究在分离涡研究中相辅相成。数值仿真控制方程存在多个参数,某些参数变化对仿真结果有很大影响。以二维后向台阶流场、圆管后向台阶流场和圆管楔形流场为例,借助粒子图像测速技术和数值仿真方法,对参数变化影响进行研究。使用切应力运输(Shear stress transport,SST)k-ω湍流模型对分离涡流场进行数值仿真,理论推导得到SST k-ω湍流模型参数a_1变化对三种具有分离涡的流场数值仿真结果的影响。研究结果认为参数a_1越大,回流区长度越小。通过数值仿真验证理论推导结论。并通过比较模型参数变化对数值仿真结果的影响,认为圆管楔形流场与二维后向台阶流场、圆管后向台阶流场具有相似流场特性。根据粒子图像测速技术观测结果,优化模型参数a_1的设置。     

采用自定位原理的三维流场速度测量

本文介绍了采用沿不同方向扫描拍摄方式 ,利用成熟的二维 PIV技术进行相关分析的三维流场速度测量方法 ,以及三维速度场合成中 ,利用二维速度场的冗余信息进行定位的自定位原理。文中还介绍了这两种方法用于 Bénard- Rayleigh对流场测量的实验     

沟槽数量对泰勒涡流稳定性的影响

用粒子图像测速技术(Particle image velocimetry,PIV)对光滑壁面和沟槽数量为18的模型内的流场进行测量,初步获得沟槽的存在对于环隙内流场的影响规律;同时利用数值计算获得沟槽数量为18的模型内的流场分布,通过对比试验结果和数值模拟结果,验证数值计算方法可靠性。通过数值计算研究沟槽数量0、6、12、18模型内的流场分布,在比较沟槽模型与光壁模型环隙内的速度场和涡量场的基础上,得出以下结论：较少的沟槽数量增加了泰勒涡的轴向尺寸,随着沟槽数的增加,沟槽结构对流场影响不断加剧,环隙内最大径向速度和轴向速度均有不同程度的增加;对比不同轴向位置的流场分布,发现沟槽区域内存在明显的旋涡流动,不同轴向位置沟槽内的流体存在着进出环隙内的运动。     

空调器室外机流场和噪声特性

针对分体空调室外机空气侧流场和声场的特点,采用计算流体动力学(CFD)的方法对该系统的气体流动进行数值模拟。详细分析了轴流风扇流道内部和出口的速度分布,并利用激光微粒图像测速(PIV)手段,验证数值模拟结果,模拟结果与PIV测量值吻合较好。在CFD数值模拟的基础上,运用Lowson模型预估系统的离散频率噪声,预估值与测量值吻合较好。CFD技术能够有效地分析室外机空气侧流场特性,并为进行气动声学分析提供依据。