粒子图像测速(PIV)技术的发展

在流场显示测量技术中，粒子图像测速(PIV)技术占有相当重要的地位，本文重点介绍了PIV的测试原理及应用要求，并以TSI公司开发的PIV系统为例对DPIV系统的构成作了概括，同时指出了PIV技术的未来发展方向。     

电驱动微流体粒子图像测试系统

为了研究微米量级管道机械特性对小雷诺数流体运动传质机理的影响,建立了电驱动微流体粒子图像测试系统,系统包括倒置荧光显微镜、致冷图像传感器、微流体驱动高压电源及微流场位移矢量识别算法.通过实验测试及理论分析给出了系统的关键技术参数;通过测量示踪粒子表面电荷特性,以消除粒子电泳运动对电驱动流体PIV方法产生的测量偏差;测量了水力直径为30μm微管道中电渗流场,测量结果与理论分析的塞状流型一致;分析了布朗运动、粒子电泳运动以及相关算法误差,对粒子图像测速方法不确定度的影响.     

微流场可视化测速技术及其应用

介绍了一种针对微观流场检测数字粒子图像测速技术，通过添加荧光显微装置，改进激光入射与照明方式及聚焦平面控制，解决了微观检测的关键问题。对微流体器件中几种典型微管道进行了理论与试验研究，并定量对比与分析了仿真与试验结果，结果显示Micro—PIV是适合于微米级流场检测的有效试验手段。     

基于PIV的泥泵叶轮内颗粒相对速度场的研究

泥泵是挖泥船的核心设备,泥泵性能与叶轮内泥砂颗粒的运动密切相关。本文采用PIV(粒子图像测速)测量技术,分别对中砂(粒径0.2~0.4 mm)和粗砂(粒径0.8~1 mm)在叶轮内的运动速度进行了测量。研究表明:中砂颗粒沿流道的相对速度变化趋势与液相相似,均在流道前半段出现高速区,在后半段出现低速区,且中砂颗粒的相对速度值均高于液相;而粗砂颗粒在叶轮流道内相对速度值变化较小,在流道前半段低于液相,在后半段与液相相差不大。     

离心泵偏置短叶片叶轮内部流动的粒子图像速度测量

对三副短叶片不同偏置的低比转数复合叶轮离心泵,应用粒子图像速度仪分别测试大流量、设计流量和小流量三种工况下长短叶片叶轮同一叶槽内的瞬时流场.分析叶槽内相对速度矢量、速度等值线的特征,揭示短叶片不同偏置时的速度分布规律.研究三副长短叶片复合叶轮出口处径向速度、切向速度、相对速度和相对液流角沿圆周的分布,测得与三副叶轮相对应的泵外特性曲线.测量结果表明,分流短叶片不同偏置对叶槽内流场的影响差异明显,当短叶片进口相对出口向压力面偏转时,叶轮出口相对速度分布很不均匀,短叶片工作面出口存在较大的低速区;与之相反,当短叶片进口相对出口向吸力面偏转时,叶轮出口速度分布较均匀,并且泵的扬程与流量曲线明显右移,大流量时,效率显著提高.     

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.     

Experimental assessment on the performance of hot wire anemometry in and around a permeable medium by comparison with Particle Image Velocimetry

The air flow through a test section partially obstructed by a permeable array of wires was measured simultaneously by Hot Wire Anemometry (HWA) and Particle Image Velocimetry. The objective of the study was the assessment of the suitability of HWA for the measurement of flow velocities amid and adjacent to groups of small obstacles. In the present case the obstacles are set in a regular array configuring a highly permeable structure. The probe was placed at three characteristic positions: in the free flow close to the wire array, inside the permeable medium, and at the interface between the permeable structure and the free flow. The measurements were performed with the hot wire operating under natural convection and mixed convection heat transfer, and operating the hot wire at different overheat ratios. Natural convection plumes extending over several permeable volume elements were detected when the hot wire was under natural convection, in some cases reaching velocities up to 60 mm/s downstream from the hot wire position. For low velocity flows, natural convection can be regarded as a flow velocity offset, which becomes negligible at local velocities higher than 0.03 m/s. For higher velocities, in the mixed convection regime, the intrusivity of the HWA probe becomes relevant. Furthermore, the flow in the test section used in the study presents a linear instability that produces velocity fluctuations. Availing ourselves of this phenomenon we verified the dynamic response of the HWA at the lowest velocity where the flow shows periodic fluctuations; for a local mean velocity of (0.131 ± 0.012) m/s the HWA showed a satisfactory dynamic response up to 20 Hz.     

粒子追踪测速(PTV)技术及其在多相流测试中的应用

粒子追踪测速即PTV方法是近年来受到较多关注的一种多相流全场测试技术。本文通过文献综述总结了该方法的最新进展,涵盖了其试验装置构成、多相流图像数据的处理、粒子匹配算法的分类及特点等专题内容,着重对粒子匹配进行了讨论。最后结合工程应用实例分析了使用该方法时应注意的问题。     

Spectral Method of Detection of Laser Doppler Velocimeter Signals in Turbulent Flows

A spectral method of detection of laser Doppler velocimeter signals in turbulent flows is proposed. The method is based on estimating the signal/noise ratio adapted to the width of the power spectral density of the signal and comparing its value with the recognition threshold. Numerical simulations show that the error of the signal/noise ratio estimates is 1% for different velocities of the turbulent flow. Physical experiments aimed at measuring turbulent aerodynamic processes show that the proposed method offers a possibility of eliminating the errors of calculating the mean value and the velocity deviation equal to 15 and 78% by means of eliminating the signals with low signal/noise ratios from the processing system. Application of the proposed method also ensures lower nonuniformity of the signal/noise ratio estimates than that ensured by the famous method developed by Tropea for a wide range of turbulent velocities.     

双流道泵内非定常流动数值模拟及粒子图像测速测量

为探讨双流道泵内部的非定常流动机理,采用Fluent软件,基于滑移网格技术、 湍流模型计算了一双流道泵在不同工况下的内部流动,并将计算结果与粒子图像测速仪(Particle image velocimeter, PIV)实测结果进行比较。结果表明：计算所得双流道泵内部流场符合叶轮机械内部流动的一般规律,且与PIV实测结果总体变化趋势一致;由于双流道泵结构特殊,其进口处的流动状态与普通叶轮相差较大,出口处的流动状态与普通叶轮类似;叶轮进口处,流体基本沿流道吸力面流动,流道工作面上的相对速度很小,存在严重的脱流和旋涡;叶轮出口处,压力面和吸力面的速度趋于相等,射流—尾迹现象并不明显;由于叶轮—蜗壳动静干涉,两个叶轮流道内的静压分布有所不同;同一流道内,静压随着半径的增加而逐步增大,压力面侧静压大于吸力面侧;蜗壳流道内静压随半径增大,最大静压值在隔舌处。此项研究不仅加深了人们对双流道泵内非定常流动图画的理解,从而进一步完善双流道泵设计方法,同时也可为其他类型泵的内流研究提供借鉴。     

An improvement of the Space-Time Image Velocimetry combined with a new denoising method for estimating river discharge

The Space-Time Image Velocimetry (STIV) is a time-averaged velocity measurement method, which takes river surface images as the analysis object, and detects the Main Orientation of Texture (MOT) in a generated Space-Time Image (STI) to obtain one-dimensional velocities on the water surface. The STIV has great potential in real-time monitoring of river flow owing to its high spatial resolution and low time complexity. However, the generated STI contains a lot of noise and interference texture, which is inevitable in practical applications. The practicality of the STIV is severely limited by the low-quality STI. To solve this problem, a denoising method based on the filtering technology is proposed and combined with different texture detection algorithms in this paper. The accuracy of this method is verified through a comparative field experiment with an impellor-style current meter. The experimental results show: (1) By using this new denoising method, the robustness and accuracy of the STIV are significantly improved no matter what kind of texture detection algorithm is adopted; (2) Among all the texture detection algorithms, the FFT-based STIV combined with the new denoising method performs best. The relative errors of the surface velocities are controlled within 6%, and the relative errors of the discharges are controlled within ±4%.     

单片机定时器T2在T法测速中的应用

针对采用T法测速时存在的两个转速脉冲之间耐间间隔测量不便的问题,采用AT89C52单片机的定时器T2进行测量.阐述了定时器T2工作原理,介绍了利用定时器T2实现T法测速的具体实现方式,采用C语言编程,可应用于低速重载设备转速测量系统中.     

A New Method to Visualize Grease Flow in a Double Restriction Seal Using Microparticle Image Velocimetry

A new method to visualize and quantify grease flow in between two sealing lips or, in general, a double restriction seal is presented. Two setups were designed to mimic different types of seals; that is, a radial and an axial shaft seal. The flow of the grease inside and in between the sealing restrictions was measured using microparticle image velocimetry. The results show that grease flow due to a pressure difference mainly takes place close to the rotating shaft surface with an exponentially decaying velocity profile in the radial direction. Consequently, contaminants may be captured in the stationary grease at the outer radius, which explains the sealing function of the grease.     

适用于现场的非线性频谱分析技术

本文从辨识算法和硬件设计上综合考虑,论述了非线性频谱分析仪的设计过程。设计中综合使用数字和模拟的方法,解决了数据采样折叠噪声、非线性频谱分析方法建立等核心问题。最后,详细给出了应用试验。试验结果表明,整个仪器简洁高效,已经达到可以推广应用于工程试验研究的程度。     

基于小波的磨粒图像融合方法研究

针对油液磨粒检测需要,基于彩色空间变换和小波分析理论,研究磨粒多聚焦图像融合方法。该方法采用邻域梯度特征因子取大法来选取多聚焦图像清晰区域的低频系数,以进行低频融合系数的确定;采用建立新系数带以及系数取大法来进行高频融合小波系数的选取。分析小波基和分解层数对磨粒多聚焦图像融合效果的影响,结果表明,在分解层数为5时,采用db4、sym4、bior2.4小波基进行磨粒多聚焦图像融合均可获得较好的融合效果。     

一种混合降噪方法在辐射图像降噪处理中的应用

在强辐射的环境中,采集的图像包含多种噪音,主要为椒盐噪声和高斯噪声,而遥操作的可靠性与高效性则在很大程度上依赖于采集图像的质量,图像去噪至关重要。对于辐射图像,采用了一种将多重中值滤波和第二代曲波变换相结合的混合降噪方法,从而较好地去除噪音、保护细节。其具体过程是:首先运用改进后的多重中值滤波对辐射图像进行去噪,再将初步处理后的辐射图像进行Wrapping快速离散曲波变换,然后再对每个子带的系数计算阈值并根据阈值对系数进行处理,最后进行曲波逆变换得降噪图像。辐射图像的仿真实验结果表明,提出的方法能较好地降低噪点并保护边缘,从而获得更好的视觉效果。     

深窄间隙焊接技术在大厚度构件材料焊接中的应用研究

窄间隙焊接技术作为一种高效焊接方法以其大大降低熔敷量和节约制造时间的优点,使其在大厚度构件制造中具有广阔的应用前景,但是焊接过程的稳定性及侧壁熔合等缺陷的存在,成为影响构件高品质制造的关键问题。利用深窄间隙埋弧焊接方法成功制造了外径尺寸为2 500 mm,厚度达150 mm的转子模拟件,采用多层双道焊接方法,实现了良好的侧壁熔合效果,且未发现夹杂等缺陷,表面该焊接接头具有较高的成形质量。基于该焊接接头开展冲击韧度、拉伸等力学性能试验,表明该接头的力学性能完全满足使用需求。从而验证了深窄间隙焊接技术在大厚度核电转子焊接中应用的可靠性。     

Experimental Study of Lubricating Grease Flow inside the Gap of a Labyrinth Seal Using Microparticle Image Velocimetry

In this study, the flow of lubricating greases in a labyrinth seal geometry is studied using microparticle image velocimetry (µPIV). The aim is to evaluate the grease velocity distribution inside the gap of a labyrinth seal and to find a relationship between the grease consistency and the transferred speed from the rotating ring in order to choose the correct grease as a sealing medium. In addition, the grease flow characteristics are important for the understanding of fracture due to grease layer displacement. For these purposes, four greases with different rheological properties were used in µPIV experiments. It was found that the grease consistency plays a crucial role in speed development as well as the grease composition and presence of a slip effect at the grease–rotating wall interface.     

湍流通道中椭球形微粒的受力分析

微粒运动和沉降对柴油机排气微粒的测量、废气再循环系统的正常工作以及微粒的净化捕集等具有重要的影响。微粒形态决定了其在湍流通道中的受力,而微粒受力对湍流通道中微粒的运动及其沉降具有重要的作用。建立椭球形微粒的运动学方程和动力学方程以及湍流场中椭球形微粒的受力及力矩模型;利用所建模型对湍流通道中椭球形微粒的受力及力矩进行研究,着重对微粒形态的变化对微粒受力的影响进行分析。研究结果表明,对于亚微米级和微米级微粒来说,微粒形态对微粒受力具有重要的影响;微粒形态的变化一方面会造成微粒受力及力矩的变化,另一方面也有可能对曳力、布朗力、升力以及热泳力等不同作用力在微粒受力中所处的地位产生一定的影响。研究结果对于加深柴油机微粒在湍流通道中运动及沉降规律的理解具有重要的意义。     

最小二乘法在尘埃粒子计数器中的应用

分析了导致尘埃粒子计数器标定过程非常复杂的原因,提出将最小二乘法用于尘埃子计数器标定过程中的方法,有利于提高仪器标定的一致性并降低劳动强度,文中给出了用量小二乘法对国产激光尘埃粒子计数器进行标定的实验结果。