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Particle tracking velocimetry (PTV) is one of the latest and most powerful flow visualization techniques, using numerous cameras to track flow tracers in two or three dimensions. This book provides a review of both experimental and computational aspects of PTV for academic and industrial researchers and engineers.

Transparent exopolymer particles (TEP), a major component of coral mucus, are responsible for particle aggregation. These particles contribute substantially to the carbon cycle in coral reefs, and serve as an energy source for bacteria and other microorganisms. Water flows and induced turbulent mixing control material exchange between the coral canopy and the surrounding water, which is critical for coral health. However, how these factors affect TEP release by coral colonies has yet to be evaluated. Using a recirculating flume, we assessed TEP release by branching Acropora coral colonies and associated bacterial growth in the water column under different unidirectional flows. Changes in TEP and bacterial concentrations after 24-h incubation were quantified for flow speeds of 0, 5, 10, and 30 cm/s. Particle image velocimetry (PIV) measurements provided an estimate of turbulent mixing efficiency above the coral canopy. TEP and bacterial concentrations in the water column increased after 24 h of incubation. The increase in TEP and bacterial concentrations were 6.2–9.3 times and 3.4–5.1 times higher in the absence of flows, respectively, than mean values under water flows. Although mixing efficiency increased linearly with mean flow speeds, TEP release and bacterial growth differed only marginally at flows ranging from 5–30 cm/s. Detailed flow measurements combined with evaluation of TEP release suggest that the complex geometry of corals facilitates efficient material exchange at a range of flow speeds, and highlight the importance of considering these factors when estimating coral reef biogeochemistry.

The present paper aims at establishing the synthetic jet technology capabilities in controlling the von Kármán street behind a circular cylinder. The circular cylinder, placed in an open-circuit wind tunnel, presents a slot in its rear position, through which the synthetic jet is issued. The Reynolds number, based on the circular cylinder diameter and the free-stream velocity, is equal to 4600 and the von Kármán street is characterized, in the baseline configuration (i.e. without synthetic jet), by a shedding frequency of 16.2 Hz. Several synthetic jet operating conditions are tested. Therefore, the effects of the momentum coefficient ($C_{\\mu } = 5.4$%, 10.8% and 21.6%) and the dimensionless frequency ($f^{+} = 0.49$, 0.98 and 1.96) on the von Kármán street behaviour can be analysed. Instantaneous two-dimensional in-plane velocity fields are measured in a plane containing the synthetic jet slot axis using multigrid/multipass cross-correlation digital particle image velocimetry. These measurements have been used to investigate the mean flow quantities and turbulent statistics of the phenomenon. In addition, the wake extent and behaviour (i.e. symmetric or asymmetric) are analysed as well as the drag coefficient, for each configuration. The extent of the wake region decreases as the momentum coefficient and/or the dimensionless frequency increase, while the symmetric/asymmetric wake behaviour is found to be governed by a different control parameter: the synthetic jet Reynolds number based on its impulse. As regards the drag coefficient, a maximum reduction, of approximately 35%, is found for the configuration at $C_{\\mu }=10.8\\,\\%$ and $f^{+}=0.98$.

Operator choices, both in acquiring the video and data and in processing them, can be a prominent source of error in image‐based velocimetry methods applied to river discharge measurements. The Large Scale Particle Image Velocimetry (LSPIV) is known to be sensitive to the parameters and computation choices set by the user, but no systematic comparisons with discharge references or intercomparisons have been conducted yet to evaluate this operator effect in LSPIV. In this paper, an analysis of a video gauging intercomparison, the Video Globe Challenge 2020, is proposed to evaluate such operator effect. The analysis is based on the gauging reports of the 15 to 23 participants using the Fudaa‐LSPIV software and intents to identify the most sensitive parameters for the eight videos. The analysis highlighted the significant impact of the time interval, the grid points and the filters on the LSPIV discharge measurements. These parameters are often inter‐dependent and should be correctly set together to strongly reduce the discharge errors. Based on the results, several automated tools were proposed to reduce the operator effect. These tools consist of several parameter assistants to automatically set the orthorectification resolution, the grid and the time interval, and of a sequence of systematic and automatic filters to ensure reliable velocity measurements used for discharge estimation. The application of the assisted LSPIV workflow using the proposed tools leads to significant improvements of the discharge measurements with strong reductions of the inter‐participant variability. On the eight videos, the mean interquartile range of the discharge errors is reduced from 17% to 5% and the mean discharge bias is reduced from −9% to 1% with the assisted LSPIV workflow. The remaining inter‐participant variability is mainly due to the user‐defined surface velocity coefficient α. Key Points Video‐based river discharge measurements are sensitive to both measuring conditions and user‐defined parameters and options The sensitivity of Large Scale Particle Image Velocimetry discharge computations to operator choices is quantified through a video streamgauging intercomparison Proposed automatic settings and spurious velocity filters efficiently reduce discharge biases and inter‐operator variability

Background In this paper, we introduce an image analysis approach for spatiotemporal segmentation, quantification, and visualization of movement or contraction patterns in 2D+t and 3D+t microscopy recordings of biological tissues. The development of this pipeline was motivated by the observation of contraction waves in the extra-embryonic membranes of the red flour beetle Tribolium castaneum . These contraction waves are a novel finding, whose origin and function are not yet understood. The objective of the proposed approach is to analyze the dynamics of the extra-embryonic membranes in order to provide quantitative evidence for the existence of contraction waves during late stages of embryonic development. Results We apply the pipeline to live-imaging data of Tribolium embryonic development recorded with light-sheet fluorescence microscopy. The proposed pipeline integrates particle image velocimetry (PIV) for quantitative movement analysis, surface detection, tissue cartography, and algorithmic identification of characteristic movement dynamics. We demonstrate that our approach reliably and efficiently detects contraction waves in both 2D+t and 3D+t recordings and enables automated quantitative analyses, such as measuring the area involved in contractile behavior, wave duration and frequency, spatiotemporal location of the contractile regions, and their relation to the underlying velocity distribution. Conclusions The pipeline will be employed in future work to conduct a large-scale characterization and quantification of contraction wave behavior in Tribolium development and can be readily adapted for the identification and segmentation of characteristic tissue dynamics in other biological systems.

As tools and techniques to measure experimental granular flows become increasingly sophisticated, there is a need to rigorously assess the validity of the approaches used. This paper critically assesses the performance of particle image velocimetry (PIV) and particle tracking velocimetry (PTV) for the measurement of granular flow properties. After a brief review of the PIV and PTV techniques, we describe the most common sources of error arising from the applications of these two methods. For PTV, a series of controlled experiments of a circular motion is used to illustrate the errors associated with the particle centroid uncertainties and the linear approximation of particle trajectories. The influence of these errors is then examined in experiments on dry monodisperse granular flows down an inclined chute geometry. The results are compared to those from PIV analysis in which errors are influenced by the size of the interrogation region. While velocity profiles estimated by the two techniques show strong agreement, second order statistics, e.g. the granular temperature, display very different profiles. We show how the choice of the sampling interval, or frame rate, affects both the magnitude of granular temperature and the profile shape determined in the case of PTV. In addition, the determined magnitudes of granular temperature from PIV tends to be considerably lower when directly measured or largely overestimated when theoretically scaled than those of PTV for the same tests, though the shape of the profiles is less sensitive to frame rate. We finally present solid concentration profiles obtained at the sidewalls and and examine their relationship to the determined shear rate and granular temperature profiles.

Stroke has emerged as the primary contributor to morbidity and mortality in patients undergoing treatment with Left Ventricular Assist Devices (LVADs), possibly arising from the turbulent flow and elevated wall shear stresses generated in these devices. A minimally invasive LVAD (LifeheART) has been proposed to address these issues, employing an intra-aortic location and a shaftless impeller design. The current study uses Particle Image Velocimetry (PIV) flow visualization, carried out in a Cardiovascular Mock Circulation Loop (CMCL), to identify the velocity distribution at the pump outlet in order to validate the developed CFD model. Subsequently, the model evaluates the blood shear stress distribution and blood damage index. The results showed that the calculated viscous shear stress (VSS) and the blood damage index of the LifeheART prototype is significantly lower than the published data for current clinically available devices, confirming the potential utility of the new design to improve patient outcomes.

The airfoil DU91‐W2‐150 was investigated in the Low Speed Low Turbulence Tunnel at the Delft University of Technology to study unsteady aerodynamics. This experimental study tested the airfoil under a wide range of angles of attack (AoA) from 0° to 310° at three Reynolds numbers (Re $$ \\mathit{\\operatorname{Re}} $$ ) from 2×105 $$ 2\\times 1{0}^5 $$to 8×105 $$ 8\\times 1{0}^5 $$ . Pressure on the airfoil surface was measured and particle image velocimetry (PIV) measurements were conducted to capture the flow field in the wake. By examining the force coefficient and comparing the wake contours, it shows that an upwind concave surface provides a higher load compared to a convex surface upwind case, highlighting the critical role of surface shape in aerodynamics. When comparing separation at specific locations along the chord for all three Re $$ \\mathit{\\operatorname{Re}} $$values, it is observed that as Re $$ \\mathit{\\operatorname{Re}} $$increases, separation tends to occur at lower AoA, both for positive stall and negative stall. The examination of the aerodynamic force variation indicates that, during reverse flow, fluctuations are more pronounced compared to forward flow. This is owing to separation occurring at the aerodynamic leading edge (geometric trailing edge) in reverse flow. In terms of vortex shedding frequency, the study found a nearly constant normalized Strouhal number (St $$ St $$ ) of 0.16 across various Re $$ \\mathit{\\operatorname{Re}} $$and AoA values in fully separated regions, indicating a consistent pattern under these conditions. However, a slight increase in St $$ St $$ , between 0.16 and 0.20, was observed for AoA values exceeding 180°, possibly due to the convex curvature of the airfoil in the upwind direction. In conclusion, this research not only corroborates previous findings for small AoA values but also adds new data on the aerodynamic behavior of the DU91‐W2‐150 airfoil under large AoA values, offering various perspectives on the effects of surface curvature, Re $$ \\mathit{\\operatorname{Re}} $$ , and flow conditions on key aerodynamic parameters.

Time-varying force/moment measurements and digital particle image velocimetry (DPIV) were conducted to reveal the influence of an advance ratio $J$ on an insect-like flapping wing. A scaled-up robotic model and a servo-driven towing tank were employed to investigate nine individual $J$ cases – $J=0$ (hovering), 0.0625, 0.1250, 0.1875, 0.25, 0.50, 0.75, 1.0 and $\\infty$ (gliding motion) – at a high Reynolds number ( $Re\\sim 10^{4}$ ). At $J\\leqslant 0.25$ , the aerodynamic forces slightly increased from those in hover ( $J=0$ ). The centres of pressure in these cases were concentrated in the outboard section, and the leading-edge vortices (LEVs) grew more conically than those in hover. Spanwise cross-sectional DPIV indicated that the wings generated more balanced downwashes, which effectively supported the slight lift increments in this range. At $J>0.25$ , a drastic force drop appeared as $J$ increased. The DPIV results in the $J=0.5$ case clearly showed a strong trailing-edge vortex on the outboard trailing edges encroaching into the upper surface, which had been occupied by the LEV for lower  $J$ . The LEV vorticity was noticeably weakened, and coherent substructures with substantial turbulence accompanied this vorticity. In the $J=1.0$ case, such encroachment was extended to 50 % of the section, and the LEV outboard became significantly irregular. The near-wake structures also showed that the $J=1.0$ case had the narrowest downwash area, with unstable root and tip vortices, which reflected considerable attenuation in the lift enhancements. It was of note that all of these vortical behaviours were clearly distinguishable from aspect ratio ( $AR$ ) effects. The $J$ even played a similar role to that of the $AR$ in the Navier–Stokes equation. These findings clearly indicated that the $J$ could be an independent quantity governing the overall vortical system and lift enhancing mechanism on a flapping wing of a flapping-wing micro air vehicle.

A Lean Premixed Prevaporized (LPP) low-emission combustor which is applied with the combustion technology of staged lean fuel is developed. To study the cold flow dynamics and the combustion performance of the LPP combustor, both experimental tests using the Particle Image Velocimetry (PIV) to quantify the flow dynamics and numerical simulation using the Fluent software are conducted respectively. To investigate the emissions of the LPP combustor, four kinds of inlet conditions (viz. 7%, 30%, 85% and 100% F∞ (Thrust Force)) were conducted using numerical simulation. Numerical results are in good agreement with the experimental data. Results show that:1) a Primary recirculation zone (PRZ), a Corner recirculation zone (CRZ) and a Lip recirculation zone (LRZ) exist in the LPP combustor, and the velocity gradients between pilot swirling flow and primary swirling flow have contributed to the exchanges of mass, momentum and energy. 2) With the decrease of thrust force, NO mass fraction, CO2 mass fraction and total pressure losses at the exit of LPP combustor fall gradually. 3) Thermal NO formation rate closely relate to the zone area where gas temperature overruns 1900K and the maximum temperature in LPP combustor. 4) The combustion performance of the LPP combustor proposed in this paper is very well, and through comparative analysis with four kins of typical gas tubine combustor, the NO emission is very low and is equivalent to the CAEP6 43.87%.