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Search Results: 1 - 10 of 262 matches for " PIV "
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The hemodynamic study for growth factor evaluation of rupture cerebral aneurysm followed up for five years  [PDF]
Masahiro Kojima, Keiko Irie, Seiichi Ikeda, Toshio Fukuda, Fumihito Arai, Yuichi Hirose, Makoto Negoro
Journal of Biomedical Science and Engineering (JBiSE) , 2012, DOI: 10.4236/jbise.2012.512A112
Abstract:

Computer-based simulations are essential for clarifying the hemodynamics of brain aneurysms. Since cerebrovascular disease is often fatal, it is strongly desirable to predict its progression. While previous studies have clarified the initiation mechanism of aneurysms, their growth mechanism remains unclear. Consequently, it is difficult to develop a diagnostic system for predicting aneurysm rupture. This study seeks to clarify the mechanism of aneurysm growth by identifying significant hydrodynamic factors. We focus on a single ruptured aneurysm that was followed up for five years. Computer simulations and fluid dynamic experiments with silicone vessel models were performed. To confirm the reliability of data in the computer simulations, we conducted particle image velocimetry measurements in steady flow. We then performed computer simulations for pulsatile conditions to determine an effective index for aneurysm growth. We obtained good agreement between the trends in the obtained computer simulation and experimental data. Numerical simulations for pulsatile flow in three models revealed that aneurysms grew in regions having a low wall shear stress, a low aneurysm formation indicator, and a high oscillatory shear index.

Mixing Enhancement in a Coaxial Jet Mixer  [PDF]
Valery Zhdanov, Egon Hassel
Advances in Materials Physics and Chemistry (AMPC) , 2012, DOI: 10.4236/ampc.2012.24B035
Abstract: Experimental investigations of mixing in a coaxial jet mixer have been carried out applying Particle Image Velocimetry (PIV) and Planar Laser Induced Fluorescence (PLIF) methods simultaneously. A developed turbulent jet of an aqueous solution of Rhodamine 6G issued from the nozzle was mixed with co-flow water. Velocity and scalar fields were studied quite far downstream flow to control the formation of a quasi homogeneous mixture. The intensity of mixing was varied by mouthpieces with rectangular and triangular vortex generators of different sizes installed in the nozzle. The formation length of the quasi homogeneous mixture was reduced about 10 jet diameters by the tabs. The triangular tabs were more effective than the rectangular ones.
A Micromixer Using the Chaos of Secondary Flow: Rotation Effect of Channel on the Chaos of Secondary Flow  [PDF]
Yasutaka Hayamizu, Shinichiro Yanase, Shinichi Morita, Shigeru Ohtsuka, Takeshi Gonda, Kazunori Nishida, Kyoji Yamamoto
Open Journal of Fluid Dynamics (OJFD) , 2012, DOI: 10.4236/ojfd.2012.24A021
Abstract: The micromixer, which has a rotor with a curved channel, is studied experimentally. The secondary flow in a curved channel of rectangular cross-section is investigated using PIV (Particle Image Velocimetry) and LIF (Laser Induced Fluorescence) methods. Two walls of the channel (the inner and top walls) rotate around the center of curvature and a pressure gradient is imposed in the direction of the exit of the channel. The non-dimensional channel curvature δ=a/R is taken to be about 0.1, where 2a is the width of the channel, R the curvature radius of the channel. Other non-dimensional parameters concerned are the Dean number De=Reδ1/2, the Reynolds number Re=qdh/v, where q is the mean flow velocity in the channel axis direction, ν the kinematic viscosity, dh the hydraulic diameter of the channel, and the Taylor number Tr=2(2δ)1/2Ωa2/(δv), where Ω is the angular velocity of the rotor. Photographs of the flow in a cross-section at 180° downstream from the curved channel entrance are taken by changing the flux (De) at a constant rotational speed (Tr) of the channel walls. It is found that good mixing performance is obtained in the case of De≤0.1|Tr| and for that case secondary flows show chaotic behaviors. And then we have confirmed the occurrence of reversal of the mean axial flow.
A Review of Particle Image Velocimetry for Fish Migration  [PDF]
S. M. Sayeed-Bin-Asad, T. Staffan Lundstr?m, A. G. Andersson, J. Gunnar I. Hellstr?m
World Journal of Mechanics (WJM) , 2016, DOI: 10.4236/wjm.2016.64011
Abstract: Understanding the flow characteristic in fishways is crucial for efficient fish migration. Flow characteristic measurements can generally provide quantitative information of velocity distributions in such passages; Particle Image Velocimetry (PIV) has become one of the most versatile techniques to disclose flow fields in general and in fishways, in particular. This paper firstly gives an overview of fish migration along with fish ladders and then the application of PIV measurements on the fish migration process. The overview shows that the quantitative and detailed turbulent flow information in fish ladders obtained by PIV is critical for analyzing turbulent properties and validating numerical results.
Scanning PIV Method and Its Application to the Calorimetry of Ground Source Heat Pump Systems  [PDF]
Shumpei Funatani, Shinya Amano, Tetsuaki Takeda, Koji Toriyama
Journal of Flow Control, Measurement & Visualization (JFCMV) , 2018, DOI: 10.4236/jfcmv.2018.61005
Abstract: Ground source heat pump (GSHP) systems that use a direct expansion method?are expected to have higher energy-saving performance than conventional air conditioning systems. The heat transfer rate is evaluated by measuring the temperature, humidity, and flow rate at the indoor unit of the GSHP system. However, it is difficult to evaluate the flow rate by measuring the flow velocity distribution at the outlet of the indoor unit. In this study, the Scanning PIV method is proposed to improve the accuracy of the flow rate measured by hot wire anemometers. The flow rates obtained by the hot wire anemometers were 60.6% and 15.2% higher than those from the PIV method during cooling and heating operation, respectively. Compensation formulas are generated using the results of the Scanning PIV method to correct the measurements from the hot wire anemometers. This compensation formula reduced the error generated by the nonuniformity of velocity distribution. It was 60.6% to 2.5% in cooling operation and 15.2% to 0.9% in heating operation, respectively. The compensation formulas were applied to evaluate the performance of a GSHP system, and the result shows that the GSHP system provides improved performance stability compared to traditional air conditioning systems.
Characterization of Flow Structures Induced by Highly Rough Surface Using Particle Image Velocimetry, Proper Orthogonal Decomposition and Velocity Correlations  [PDF]
L. R. Andersson, I. A. S. Larsson, J. G. I. Hellstr?m, P. Andreasson, A. G. Andersson, T. S. Lundstr?m
Engineering (ENG) , 2018, DOI: 10.4236/eng.2018.107028
Abstract: High Reynolds number flow inside a channel of rectangular cross section is examined using Particle Image Velocimetry. One wall of the channel has been replaced with a surface of a roughness representative to that of real hydropower tunnels, i.e. a random terrain with roughness dimensions typically in the range of ≈10% - 20% of the channels hydraulic radius. The rest of the channel walls can be considered smooth. The rough surface was captured from an existing blasted rock tunnel using high resolution laser scanning and scaled to 1:10. For quantification of the size of the largest flow structures, integral length scales are derived from the auto-correlation functions of the temporally averaged velocity. Additionally, Proper Orthogonal Decomposition (POD) and higher-order statistics are applied to the instantaneous snapshots of the velocity fluctuations. The results show a high spatial heterogeneity of the velocity and other flow characteristics in vicinity of the rough surface, putting outer similarity treatment into jeopardy. Roughness effects are not confined to the vicinity of the rough surface but can be seen in the outer flow throughout the channel, indicating a different behavior than postulated by Townsend’s similarity hypothesis. The effects on the flow structures vary depending on the shape and size of the roughness elements leading to a high spatial dependence of the flow above the rough surface. Hence, any spatial averaging, e.g. assuming a characteristic sand grain roughness factor, for determining local flow parameters becomes less applicable in this case.
Investigation of Unsteady Flow Fields for Flow Control Research by Means of Particle Image Velocimetry  [PDF]
Reinhard Geisler, Andreas Schr?der, Jürgen Kompenhans
Journal of Flow Control, Measurement & Visualization (JFCMV) , 2014, DOI: 10.4236/jfcmv.2014.22007
Abstract: Unsteady three-dimensional flow phenomena must be investigated and well understood to be able to design devices to control such complex flow phenomena in order to achieve the desired behavior of the flow and to assess their performance, even in harsh industrial environments. Experimental investigations for flow control research require measurement techniques capable to resolve the flow field with high spatial and temporal resolution to be able to perceive the relevant phenomena. Particle Image Velocimetry (PIV), providing access to the unsteady flow velocity field, is a measurement technique which is readily available commercially today. This explains why PIV is widely used for flow control research. A number of standard configurations exist, which, with increasing complexity, allow capturing flow velocity data instantaneously in geometrical arrangements extending from planes to volumes and in temporal arrangements extending from snapshots to temporarily well resolved data. With increasing complexity these PIV systems require advancing expertise of the user and growing investment costs. Using typical problems of flow control research, three different standard PIV systems will be characterized briefly. It is possible to upgrade a PIV system from a simple planar to a “high end” tomographic PIV system over a period of time, if sufficient PIV expertise can be built up and budget for additional investments becomes available.
多级网格迭代的图像变形算法在PIV中的应用
Iterative Multigrid Image Deformation Method for PIV
 [PDF]

陈槐, 钟强, 李丹勋, 王兴奎
International Journal of Fluid Dynamics (IJFD) , 2013, DOI: 10.12677/IJFD.2013.12006
Abstract:

本文简述了多级网格迭代的图像变形算法的发展,重点介绍了多级网格迭代算法与图像变形算法匹配进行流场分析的基本原理及计算步骤。对算法的各主要环节进行了详细的讨论,包括相关系数峰值拟合方法,图形变形的速度场插值方法,亚像素点灰度插值方法,数据剔错方法及窗函数的应用。
This paper presents a brief introduction of the iterative multigrid image deformation method which combines iterative multigrid approach and image deformation approach for PIV. Major components of the method are discussed in detail, including correlation peak finding algorithms, interpolation schemes, velocity interpolation schemes, outlier detection schemes and weighting windows.

Velocity Measurement by PIV Using W-Shaped Scanning Light Sheet  [PDF]
Shumpei Funatani, Tetsuaki Takeda, Koji Toriyama
Journal of Flow Control, Measurement & Visualization (JFCMV) , 2015, DOI: 10.4236/jfcmv.2015.31004
Abstract: This study proposes a three-dimensional (3D) particle image velocimetry (PIV) method using W- shaped light sheet and color PIV with a digital SLR camera. The uncertainty of the velocity measurement was also studied and it was acceptable. The spatial resolution of the z-direction has much room for improvement by increasing the number of cameras. When applied to the velocity distribution measurement of a thermal vertical buoyant plume, the proposed 3D PIV method is found to be very effective for studying thermal structures and well suited for measuring the airflow velocity field.
湍流混合层流场的PIV测量
郭富德,陈斌,王智伟,郭烈锦,张西民
工程热物理学报 , 2008,
Abstract: 本文使用PIV对在竖直通道内放置一个特殊设计的隔板所形成的湍流混合层流动进行测量,高低侧速比为4:1,基于两股流体速度差和管道水力半径的Re数范围4400~158400。发现混合层中大涡拟序结构的尺度随雷诺数的增加而增大,而后又随雷诺数的继续增大而减小,气泡的加入会延缓或阻碍大涡拟序结构的发展。对雷诺应力、湍流强度、涡量、旋涡强度在混合层流场内随雷诺数的变化和分布规律进行分析,发现混合层内雷诺应力、湍流强度、涡量及旋涡强度均集中分布在隔板下游一个较窄的锥形区域内,雷诺应力和湍流强度随雷诺数的增大先增大后减小,随离开隔板距离的增大而减小.涡量及旋涡强度随雷诺数的增大而增加,随离开隔板距离的增大而减小.
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