scholarly journals A Fluid Motion Estimator for Schlieren Image Velocimetry

2006 ◽  
pp. 198-210 ◽  
Author(s):  
Elise Arnaud ◽  
Etienne Mémin ◽  
Roberto Sosa ◽  
Guillermo Artana
Keyword(s):  
Fluid Motion ◽  
Schlieren Image ◽  
Image Velocimetry

scholarly journals Volumetric quantification of fluid flow reveals fish's use of hydrodynamic stealth to capture evasive prey

2014 ◽  
Vol 11 (90) ◽  
pp. 20130880 ◽  
Author(s):  
Brad J. Gemmell ◽  
Deepak Adhikari ◽  
Ellen K. Longmire
Keyword(s):  
High Speed ◽  
Prey Capture ◽  
Fluid Motion ◽  
Three Dimensional ◽  
Trophic Levels ◽  
Small Fish ◽  
Major Pathway ◽  
Image Velocimetry ◽  
Highly Sensitive ◽  
Volumetric Quantification

In aquatic ecosystems, predation on zooplankton by fish provides a major pathway for the transfer of energy to higher trophic levels. Copepods are an abundant zooplankton group that sense hydromechanical disturbances produced by approaching predators and respond with rapid escapes. Despite this capability, fish capture copepods with high success. Previous studies have focused on the predatory strike to elucidate details of this interaction. However, these raptorial strikes and resulting suction are only effective at short range. Thus, small fish must closely approach highly sensitive prey without triggering an escape in order for a strike to be successful. We use a new method, high-speed, infrared, tomographic particle image velocimetry, to investigate three-dimensional fluid patterns around predator and prey during approaches. Our results show that at least one planktivorous fish ( Danio rerio ) can control the bow wave in front of the head during the approach and consumption of prey (copepod). This alters hydrodynamic profiles at the location of the copepod such that it is below the threshold required to elicit an escape response. We find this behaviour to be mediated by the generation of suction within the buccopharyngeal cavity, where the velocity into the mouth roughly matches the forward speed of the fish. These results provide insight into how animals modulate aspects of fluid motion around their bodies to overcome escape responses and enhance prey capture.

Stereoscopic Particle Image Velocimetry Analysis of Healthy and Emphysemic Alveolar Sac Models

2011 ◽  
Vol 133 (6) ◽  
Author(s):  
Emily J. Berg ◽  
Risa J. Robinson
Keyword(s):  
Particle Image Velocimetry ◽  
Particle Image ◽  
Fluid Motion ◽  
Three Dimensional ◽  
Flow Fields ◽  
Stereoscopic Particle Image Velocimetry ◽  
Recirculating Flow ◽  
Image Velocimetry ◽  
Flow Speeds ◽  
Healthy Lung

Emphysema is a progressive lung disease that involves permanent destruction of the alveolar walls. Fluid mechanics in the pulmonary region and how they are altered with the presence of emphysema are not well understood. Much of our understanding of the flow fields occurring in the healthy pulmonary region is based on idealized geometries, and little attention has been paid to emphysemic geometries. The goal of this research was to utilize actual replica lung geometries to gain a better understanding of the mechanisms that govern fluid motion and particle transport in the most distal regions of the lung and to compare the differences that exist between healthy and emphysematous lungs. Excised human healthy and emphysemic lungs were cast, scanned, graphically reconstructed, and used to fabricate clear, hollow, compliant models. Three dimensional flow fields were obtained experimentally using stereoscopic particle image velocimetry techniques for healthy and emphysematic breathing conditions. Measured alveolar velocities ranged over two orders of magnitude from the duct entrance to the wall in both models. Recirculating flow was not found in either the healthy or the emphysematic model, while the average flow rate was three times larger in emphysema as compared to healthy. Diffusion dominated particle flow, which is characteristic in the pulmonary region of the healthy lung, was not seen for emphysema, except for very small particle sizes. Flow speeds dissipated quickly in the healthy lung (60% reduction in 0.25 mm) but not in the emphysematic lung (only 8% reduction 0.25 mm). Alveolar ventilation per unit volume was 30% smaller in emphysema compared to healthy. Destruction of the alveolar walls in emphysema leads to significant differences in flow fields between the healthy and emphysemic lung. Models based on replica geometry provide a useful means to quantify these differences and could ultimately improve our understanding of disease progression.

Single-pixel resolution velocity/convection velocity field of a supersonic jet measured by particle/schlieren image velocimetry

2020 ◽  
Vol 61 (6) ◽  
Author(s):  
Yuta Ozawa ◽  
Takuma Ibuki ◽  
Taku Nonomura ◽  
Kento Suzuki ◽  
Atsushi Komuro ◽  
...  
Keyword(s):  
Velocity Field ◽  
Supersonic Jet ◽  
Convection Velocity ◽  
Schlieren Image ◽  
Pixel Resolution ◽  
Image Velocimetry ◽  
Single Pixel

Breaking and broadening of internal solitary waves

2000 ◽  
Vol 413 ◽  
pp. 181-217 ◽  
Author(s):  
JOHN GRUE ◽  
ATLE JENSEN ◽  
PER-OLAV RUSÅS ◽  
J. KRISTIAN SVEEN
Keyword(s):  
Solitary Waves ◽  
Wave Breaking ◽  
Wave Speed ◽  
Wave Amplitude ◽  
Fluid Velocity ◽  
Fluid Motion ◽  
Constant Density ◽  
Image Velocimetry ◽  
The Waves

Solitary waves propagating horizontally in a stratified fluid are investigated. The fluid has a shallow layer with linear stratification and a deep layer with constant density. The investigation is both experimental and theoretical. Detailed measurements of the velocities induced by the waves are facilitated by particle tracking velocimetry (PTV) and particle image velocimetry (PIV). Particular attention is paid to the role of wave breaking which is observed in the experiments. Incipient breaking is found to take place for moderately large waves in the form of the generation of vortices in the leading part of the waves. The maximal induced fluid velocity close to the free surface is then about 80% of the wave speed, and the wave amplitude is about half of the depth of the stratified layer. Wave amplitude is defined as the maximal excursion of the stratified layer. The breaking increases in power with increasing wave amplitude. The magnitude of the induced fluid velocity in the large waves is found to be approximately bounded by the wave speed. The breaking introduces a broadening of the waves. In the experiments a maximal amplitude and speed of the waves are obtained. A theoretical fully nonlinear two-layer model is developed in parallel with the experiments. In this model the fluid motion is assumed to be steady in a frame of reference moving with the wave. The Brunt-Väisälä frequency is constant in the layer with linear stratification and zero in the other. A mathematical solution is obtained by means of integral equations. Experiments and theory show good agreement up to breaking. An approximately linear relationship between the wave speed and amplitude is found both in the theory and the experiments and also when wave breaking is observed in the latter. The upper bound of the fluid velocity and the broadening of the waves, observed in the experiments, are not predicted by the theory, however. There was always found to be excursion of the solitary waves into the layer with constant density, irrespective of the ratio between the depths of the layers.

Fluid Motion Induced by Spark Plasma: Development of Particle Image Velocimetry Measurements

2016 ◽  
Author(s):  
Bhavini Singh ◽  
Lalit K. Rajendran ◽  
Matthew Giarra ◽  
Sally P. Bane ◽  
Pavlos Vlachos
Keyword(s):  
Particle Image Velocimetry ◽  
Particle Image ◽  
Fluid Motion ◽  
Image Velocimetry ◽  
Spark Plasma

scholarly journals Time-resolved sphere and fluid motions in turbulent boundary layers

2021 ◽  
Vol 1 (1) ◽  
Author(s):  
Yi Hui Tee ◽  
Ellen K. Longmire
Keyword(s):  
Coherent Structures ◽  
Fluid Motion ◽  
Terminal Velocity ◽  
Stereoscopic Particle Image Velocimetry ◽  
Wall Friction ◽  
Time Resolved ◽  
Image Velocimetry ◽  
Slow Moving ◽  
Lift Off ◽  
Streamwise Distance

This paper extends the study by Tee et al. (2020) to investigate the effect of large coherent structures on motion of spheres with specific gravities of 1.006 (P1) and 1.152 (P3) at Reτ = 670 and 1300 (d+ = 56 and 116). The sphere and fluid motions are tracked simultaneously via 3D particle tracking and stereoscopic particle image velocimetry over the streamwise-spanwise plane, respectively. With sufficient mean shear, sphere P1 lifts off of the wall upon release before descending back towards the wall at both Reτ. It typically accelerates strongly over a streamwise distance of less than one boundary layer thickness before approaching an approximate terminal velocity. By contrast, the denser sphere P3 does not lift off upon release but mainly slides along the wall. At lower Reτ where wall friction is stronger, this sphere translates with unsteady velocity, significantly lagging the local fluid. The streamwise velocities of both spheres correlate strongly with the fast- and slow-moving zones that approach and move over them. In most runs, both spheres lag the local coherent structures and travel with either fast- or slow-moving zones throughout the observed trajectories. Vortex shedding, which is most prevalent for sphere P3 at Reτ = 670, is also important. The sphere spanwise motion is prompted by wall friction, spanwise fluid motion, and/or meandering of the coherent structures, and spheres do not appear to migrate preferentially into slow-moving zones.

scholarly journals Propulsive design principles in a multi-jet siphonophore

2018 ◽  
Author(s):  
Kelly R. Sutherland ◽  
Sean P. Colin ◽  
John H. Costello ◽  
Brad J. Gemmell
Keyword(s):  
High Speed ◽  
Swimming Performance ◽  
Dimensional Space ◽  
Fluid Motion ◽  
Three Dimensional ◽  
Flow Parameters ◽  
Image Velocimetry ◽  
Summary Statement ◽  
High Pressure Region ◽  
Three Dimensional Space

AbstractCoordination of multiple propulsors can provide performance benefits in swimming organisms. Siphonophores are marine colonial organisms that orchestrate the motion of multiple swimming zooids for effective swimming. However, the kinematics at the level of individual swimming zooids (nectophores) have not been examined in detail. We used high speed, high resolution microvideography and particle image velocimetry (PIV) of the physonect siphonophore, Nanomia bijuga, to study the motion of the nectophores and the associated fluid motion during jetting and refilling. The integration of nectophore and velum kinematics allow for a high-speed (maximum ~1 m s−1), narrow (1-2 mm) jet and rapid refill as well as a 1:1 ratio of jetting to refill time. Overall swimming performance is enhanced by velocity gradients produced in the nectophore during refill, which lead to a high pressure region that produces forward thrust. Generating thrust during both the jet and refill phases augments the distance travelled by 17% over theoretical animals, which generate thrust only during the jet phase. The details of velum kinematics and associated fluid mechanics elucidate how siphonophores effectively navigate three-dimensional space and could be applied to exit flow parameters in multijet underwater vehicles.Summary statement:Colonial siphonophores produce high speed jets and generate forward thrust during refill using a flexible velum to achieve effective propulsion.

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