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Flow Field Measurements by Particle Image Velocimetry (PIV) Techniques
Published in Je-Chin Han, Lesley M. Wright, Experimental Methods in Heat Transfer and Fluid Mechanics, 2020
With an established history of convective heat transfer measurements in turbulent flows, for years researchers were left to imply how the fluid was moving near the surface. PIV techniques have allowed researchers to first visualize the turbulent flow behavior and now quantify the fluid motion. With improved imaging capabilities, faster and more powerful lasers, and greater computing power (memory and processing speed), PIV techniques have developed rapidly over the past decades. Internal and external flows, high-speed and low-speed flows, stationary and rotating flows have all been investigated using different adaptations of particle image velocimetry. Different challenges arise with each specific flow domain; to understand how to overcome these specific challenges, additional details are available in open literature.Stationary, Internal Flows: Schabacker et al. [9], Suden [10], and Sharma et al. [11]Rotating, Internal Flows: Bons and Kerrebrock [12], Elfert et al. [13], and Coletti et al. [14]External Flows: Gogineni et al. [15], Bernsdorf et al. [16], Aga et al. [17], and Wright et al. [18]
Experimental Methods in Cardiovascular Mechanics
Published in Michel R. Labrosse, Cardiovascular Mechanics, 2018
Particle image velocimetry is an optical velocity measurement technique that uses a laser, digital cameras, and seeding particles. Two consecutive images of the illuminated particles are taken by the high-speed camera. The images are divided into small interrogation regions, typically between 8 × 8 pixels and 64 × 64 pixels in size. A cross-correlation is then applied on the interrogation regions to identify the direction and displacement of the seeding particles. The timing between the two images, or laser pulses, and the estimated displacement lead to the determination of the velocity vector in each interrogation region (Adrian 1991; Keane and Adrian 1992; Raffel et al. 2013). Particle image velocimetry allows for the determination of time-resolved 2D and 3D velocity fields. More recent techniques, such as tomographic PIV (tomo-PIV), allow for direct time-resolved volumetric measurements (Elsinga et al. 2005; Hasler and Obrist 2016). Because PIV is an optical-based technique requiring a transparent fluid, its application is limited to experimental, in vitro, velocity measurements. Its application to cardiovascular flows includes the investigation of flow characteristics in models of the left and right ventricles, the aorta, the pulmonary artery, the left atrium, the carotid artery, and aneurysms of the abdominal aorta. Particle image velocimetry has also been used to investigate the performance of medical devices and surgical procedures, including various heart valves, left ventricular assist devices, and the total cavopulmonary connection.
Velocity
Published in Jochen Aberle, Colin D. Rennie, David M. Admiraal, Marian Muste, Experimental Hydraulics: Methods, Instrumentation, Data Processing and Management, 2017
Jochen Aberle, Colin D. Rennie, David M. Admiraal, Marian Muste
PIV is an optical technique for measuring velocity fields that has revolutionized investigations in experimental fluid mechanics (Adrian, 2005; Westerweel et al., 2013). The most basic implementation of PIV, depicted in Figure 3.7.1, allows two components of the velocity vector to be estimated at discrete points across a 2-dimensional slice of the flow field. This system is referred to as 2C-2D (two components – two dimensions), and it exclusively provides planar measurements of velocity. The key components of a typical PIV system are an illumination source, a digital camera to record the motion of small tracer particles added to the fluid, electronics to synchronize the camera and the light source, and software to analyze the digital images and estimate the displacements (velocities) of the tracer particles.
Low-cost field particle image velocimetry for quantifying environmental turbulence
Published in Journal of Ecohydraulics, 2023
PIV is a non-intrusive flow measurement technique, consisting of four steps: seeding, illumination, recording, and evaluation (Raffel et al. 2018). In brief summary, PIV measurement is done through dispersing small, neutrally-buoyant, reflective particles throughout the flow of interest. These particles are termed “seeds”. This seeded flow is then illuminated using a thin laser sheet to illuminate a plane. Multiple images are captured at a given frame rate using a camera placed perpendicularly to the laser sheet. Consecutive images are paired, and the pairs are evaluated through cross correlation, enabling tracking of particle movement and therefore flow pattern and velocity (Thielicke and Stamhuis 2014; Raffel et al. 2018). Figure 1 shows a general PIV setup. Currently, PIV is largely used in laboratory settings, although past successful efforts have been made to utilize this tool in field settings (Katija and Dabiri 2008; Tritico et al. 2007; Morgan 2013; Jin 2019). Several of these past systems are described here.
Low-cost surface particle image velocimetry for hydraulic model studies
Published in Journal of Applied Water Engineering and Research, 2023
Iverson Italo Siebert, Michael Mannich, Tobias Bleninger
The PIV technique uses a sequence of images of the flow to determine the instantaneous velocity field (Adrian and Westerweel 2011). The PIV image processing algorithms hereby compare two sequential images using cross-correlation methods. The best correlation results in an image displacement, which supposedly is associated to be proportional to the flow velocity (Raffel et al. 1998; Muste et al. 2017). Best results are obtained by seeding the flow particles. Digital image processing, high-resolution cameras, data storage, and processing capacity turn PIV into a quantitative technique with precision like other modern measurement methods. However, the setup and instrumentation, as well as its operation and post-processing efforts, can be significant and costly, especially when considering measurements over the water column which requires laser sheet illumination.
Experimental study on the cyclical jet-flipping in the wall jet scour hole
Published in Journal of Hydraulic Research, 2021
Jin-Hua Si, Siow-Yong Lim, Xikun Wang
Particle image velocimetry (PIV) is an optical technique capable of measuring the whole domain of instantaneous flow fields in a non-intrusive manner. With a PIV system at a sufficiently high recording frequency, Si et al. (2018) captured the real-time flow features in a rapidly developing scour hole generated by a free falling jet on the sediment bed. These advantages of PIV allow for spatial distinction among the vortical structures and a means of tracking such structures in the space and time domains, making it a good candidate to discover the details of the flow during jet-flipping transitions. In the present laboratory study, PIV is used to investigate the real-time flow downstream of a sluice gate over a complete cycle of jet-flipping, i.e. bed jet regime → upward transition → surface jet regime → downward transition → bed jet regime. Typically, this study presents a complex system of dynamic vortices associated with jet-flipping within the momentary transitions between the two jet regimes.