Visualization of Lagrangian fluid transport of a vortex ring based on time-resolved PIV

Journal of Visualization - We carry out experiments on vortex ring flows submerged underwater which are generated by a pulsatile circular jet with the stroke ratio of 10. The pulsatile Reynolds...     

Visualization studies using PIV in a cylindrical tank with and without vortex suppressor

Vortexing occurs during draining from tanks which reduces the rate of outflow. The phenomenon is augmented by initial rotation. The use of a vortex suppressor in a circular tank prevents vortexing. The reasons for the suppression of the vortexing are not clear. In this paper quantitative flow visualization results using PIV are presented which bring out the flow structure under various conditions. The suppressor leads to a faster decay in the rotational component.     

Visualization and PIV measurement of the flow around and inside of a falling droplet

Although the phenomena related to the multiphase flow can be found in many kinds of industrial and engineering applications, the physical mechanism of the multiphase flow has not been investigated in detail. The major reason for the lack of data in the multiphase flow lies in the difficulties in measuring the flow quantities of the multiple phases simultaneously. Presently, the visualization and the PIV measurement have been carried out about the both phases of the liquid-liquid two-phase flow. The difference in the refractive indices makes the visualization in the vicinity of the boundary of the multiple phases very difficult. In this study, the refractive index of the aqueous phase has been equalized to that of the oil phase by adjusting the concentration of the aqueous solution. As for the surrounding fluid, silicon oil is chosen and as for the droplet, the aqueous solution of glycerol is prepared whose refractive index matches that of silicon oil. Both phases are seeded with neutrally buoyant particles. The droplet is slightly colored with Rhodamine B so that the position of the invisible droplet can be identified. The difference in the background brightness in both phases helps PIV algorithm in distinguishing the motions in each phases. The results show the details of the flow structures both around and inside of a falling droplet simultaneously.     

Flow visualization and PIV measurement of flow field around a darrieus rotor in dynamic stall

The flow field around a Darrieus rotor in dynamic stall is studied by flow visualization and PIV measurements. The visualization is carried out by dye injection technique while the phase averaged velocity distributions around the blade are measured by PIV combined with a conditional imaging technique. The results indicate the appearance of dynamic stall phenomenon due to the shedding of two pairs of vortices from the blade during one rotation of the rotor. These stall vortices are produced by the separation of flow over the inner surface of the blade and the formation of roll-up vortices from the outer surface. The second stall vortices develop along the blade and strongly interact with the flow field near the blade, affecting the aerodynamic performance of the rotor.     

Unsteady flow visualization at part-load conditions of a radial diffuser pump: by PIV and CFD

The present study provides flow visualization on complex internal flows in a radial diffuser pump under part-load conditions by using the three-dimensional Navier-Stokes code CFX-10 with Detached Eddy Simulation (DES) turbulence model. Particle Image Velocimetry (PIV) measurements have been conducted to validate numerical results. The CFD results show good agreements with experimental ones on both the phase-averaged velocity fields and turbulence field. The detailed flow analysis shows that no separation occurs at 0.75Q_des although a low-velocity zone develops on the rear impeller suction side. Steady flow separations are observed on the impeller suction sides at 0.5Qdes but with different onsets and amounts. When reducing the flow rate to 0.25Q_des, CFD predicts different types of back flows in the impeller region, including steady leading edge separations, rotating vortex in the impeller wake region, and back flow on the impeller pressure side.     

Flow visualization and scanning PIV measurement of three-dimensional structure in near field of strongly buoyant jet

Abstract  

The near-field structure of strongly buoyant jet issuing from a square nozzle at low Froude and Reynolds numbers is studied by using LIF flow visualization and time-resolved scanning PIV. These experimental techniques allow the visualization of unsteady three-dimensional flow phenomenon occurring in the near-field of strongly buoyant jet. It is found that the buoyant jet is unstable to the positive buoyancy forces, which promote the inflow motion near the nozzle exit. The surrounding low temperature fluid moves into the nozzle inside along the nozzle corner and mixes with the high temperature fluid deep into the nozzle. Then, the flow pattern inside the nozzle becomes highly complex to promote the laminar to turbulent transition of the jet. The statistical flow characteristics of the strongly buoyant jet are evaluated from the scanning PIV measurement, and the result indicates the presence of axisymmetric distributions of mean flow and velocity fluctuations in the circle of diameter equal to the square side of the nozzle.     

Quantitative visualization of high-Schmidt-number turbulent mixing in grid turbulence by means of PLIF

Abstract  

Quantitative visualization of high-Schmidt-number scalar fields has been performed in grid turbulence by means of a planar laser-induced fluorescence (PLIF) technique. The Reynolds number based on a mesh size of the grid is 2500 and the Schmidt number of the scalar is around 2100. To correct for the effects of various spatiotemporal variations such as quantum yield, a recently proposed correction method was introduced in the present experiment. In the present work, a PLIF experiment in combination with a calibration region installed outside of the test section is proposed. Visualizations of the instantaneous fluctuating scalar field suggest that mushroom-like structures accompanied by a pair of stirring structures, called engulfments, exist and contribute to large-scale scalar transfer. Visualization of the scalar dissipation field in the horizontal plane suggests that accumulation of the filament structures, which can be related to the mixing transition, locally exists around large-|c| regions, where |c| is the absolute value of the instantaneous fluctuating concentration. Thus, accumulation of the filament structures should be considered in the development of a turbulent mixing model for high-Schmidt-number scalar transfer.     

Recent progress in flow visualization techniques toward the generation of fluid art

This paper describes recent progress in flow visualization techniques from the viewpoint of visual art incorporating fluid motion. The images of fluid art introduced here are categorized into four groups: the reflected or refracted patterns of free surface motion in nature and in a controlled environment, the coherent turbulent phenomena of fluid flow, and the fluid motion induced by the physical properties of fluids. It is shown that flow visualization techniques, which were originally developed in the field of engineering, have been successfully applied to the creation of artistic images.     

水洞流场PIV显示与分析系统离轴测试校正

粒子图像测速技术(PIV)通过测量被测流场截面上每一位置点的速度,获得整个被测流场的信息.在PIV一般应用中所使用的照明激光片光与成像CCD装置的拍摄方向是垂直的,在某些应用场合受测试条件的限制,需要采用离轴方式进行测量,此时CCD成像方向与照明的激光片光不垂直,而是有一定夹角.离轴测试方式将对PIV系统的光学成像系统、示踪粒子选择和粒子图像处理带来影响.实验采用Scheimpflug离轴聚焦的方法对表面镀银高反射率的示踪粒子进行成像,通过调整成像透镜与CCD像面的夹角可获得清晰的粒子成像,并利用网格校正板和软件计算处理等方法有效校正了由于离轴测试带来的影响.     

Visualization of the human body toward the navigation diagnosis with the virtualized human body

In this article we present the visualization of the human body basing upon the X-ray CT and MR images. Topics and examaples of images rendered by the computer are all selected from the studies in the authors’ laboratory during about twenty years. Topics are classified into four groups. First we introduce a few historical pictures of cross section images, and the surface of bones and the skull. Second, the selected pictures in the surgical simulation system NUCSS (=Nagoya University Craniofacial Surgical Simulation system) we developed are shown. This system was for the simulation of the craniofacial surgery of the skull and the orthopedic surgery of the hip joint. This was the pioneering work which showed the potential of computer aid in surgery based upon 3D CT images about ten years in advance of the present rapid extention of the computer aided surgery. One of the earliest work to visualize the performance of the soft tissue — rendering of the cut skin is also included. Third, the virtualized endoscope system is presented in detail. The images of both the inside and the outside view of the bronchus, the vessel and the stomach are shown here with the introduction to the new concept of the navigation diagnosis. Finally the navigation through an Egyptian mummy is added.     

Planar velocity visualization in high-speed wedge flow using Doppler Picture Velocimetry (DPV) compared with Particle Image Velocimetry (PIV)

A technique for visualizing a velocity field in an entire plane has been developed by taking ‘Doppler Pictures’ using Michelson interferometry. With the Doppler Picture Velocimetry (DPV), information about the instantaneous and local velocities of tracers passing through a light sheet is available. The technique for taking and processing the Doppler pictures has been improved recently and the state-of-the-art of the DPV method will be described with an application in high-speed fluid flows showing the velocity distribution in a light sheet plane crossing a supersonic wedge flow generated in the high-energy shock tunnel STB of ISL. A comparison with Particle Image Velocimetry (PIV) velocity visualizations is also presented.     

运载火箭试验数据管理及可视化系统设计

针对现有运载火箭试验数据管理及可视化系统依赖于第三方功能插件,未实现纯浏览器端三维模型渲染及交互,系统对运行环境依赖性强、部署和维护成本高等问题,设计了基于JavaScript框架ExtJS和WebGL框架three.js的运载火箭试验数据管理及可视化系统。首先基于B/S架构设计了系统总体框架,然后针对二维图形数据传输延迟问题设计了基于Web Worker的数据读取方案,最后针对浏览器端三维模型渲染需求提出了基于VTK模型的转换算法,设计了三维模型渲染及交互方案。试验结果显示,本系统不依赖于运行环境和功能插件,能实现浏览器端二维图形和三维模型渲染及流畅交互,为兼容国产化操作系统、降低部署和维护成本创造了条件。     

PIV系统水洞流场测量准确度与误差分析

为了改进粒子图像测速技术,分析限制PIV系统测量准确度的因素.利用PIV系统分析比较了水洞中无模型和圆球模型两种环境下的流场.6 m/s水速下,无模型流场测量PIV系统测量准确度优于1.3%.通过比较标准球模型流场理论值和测量结果,表明,所测量区域内大部分区域的测量准确度均优于2%,在球模型边界与靠近连接杆位置,误差达到6%~8%左右.对造成PIV测量误差的原因进行了探讨,为系统改进提供了参考.     

基于数据驱动的航天器三维可视化系统设计

航天器数据庞大繁杂,为了给设计人员提供快速检验设计思想的便捷工具,对基于数据驱动的航天器三维可视化系统进行了研究。在分析航天器可视化系统特点的基础上,提出系统功能要求,继而提出了基于数据驱动的三维可视化系统构建方案,介绍了可视化系统组成、核心模块关系。在基于MFC框架及Vega Prime为主的开发的前提下,对系统模块划分进行了研究,给出模块功能和实现方案。为了提升系统展示效果,对消息缓冲与插值延迟、特效集成与驱动机制、相机管理和场景切换等关键技术提出了优化设计方案,使之更加适应航天器可视化展示需求。设计系统较传统可视化系统展示更为流畅,场景视角切换更为智能。系统已应用于多个航天器研发工作中,应用效果证明系统具有良好的通用性和实用性,具有一定的推广价值。