scholarly journals Characterization of hop-and-sink daphniid locomotion

2019 ◽  
Vol 41 (2) ◽  
pp. 142-153 ◽  
Author(s):  
A N Skipper ◽  
D W Murphy ◽  
D R Webster
Keyword(s):  
Flow Field ◽  
Particle Image ◽  
Power Stroke ◽  
Time Resolved ◽  
Image Velocimetry ◽  
Recovery Stroke ◽  
Self Similar ◽  
Energy Dissipated ◽  
Good Agreement

Abstract This study characterizes the hop-and-sink locomotion of Daphnia magna, a zooplankton species widely studied in a variety of biological fields. Time-resolved tomographic particle image velocimetry (tomo-PIV) is used to obtain 3D kinematics and flow field data with high spatial and temporal resolution. The kinematics data show that the daphniid’s velocity quickly increases during the power stroke, reaching maximum accelerations of 1000 body lengths/s2, then decelerates during the recovery stroke to a steady sinking speed. The hop-and-sink locomotion produces a viscous vortex ring located under each second antennae. These flow structures develop during the power stroke, strengthen during the recovery stroke, and then decay slowly during the sinking phase. The time records of vortex circulation are self-similar when properly normalized. The flow fields were successfully modeled using an impulsive stresslet, showing good agreement between the decay of circulation and a conceptual model of the impulse. While no relationships were found between kinematics or flow field parameters and body size, the total energy dissipated by the daphniid hop-and-sink motion was found to scale exponentially with the vortex strength.

scholarly journals Particle Image Velocimetry for in vitro characterization of Paravalvular Leakage of TAVR-sealing concepts

2021 ◽  
Vol 7 (2) ◽  
pp. 668-671
Author(s):  
Samuel Höing ◽  
Finja Borowski ◽  
Jan Oldenburg ◽  
Sabine Illner ◽  
Alper Öner ◽  
...  
Keyword(s):  
Particle Image Velocimetry ◽  
Flow Field ◽  
Particle Image ◽  
Aortic Annulus ◽  
Piv Measurements ◽  
Paravalvular Leakage ◽  
Transcatheter Aortic Valve ◽  
Image Velocimetry

Abstract Paravalvular leakage (PVL), defined as the leakage between the aortic annulus and a transcatheter aortic valve replacement (TAVR), is verifiably associated with short- and long-term clinical outcome, especially with increased mortality. Therefore, with the ambition to reduce or even prevent PVL of next generation TAVR, it is necessary to extend the hemodynamic understanding of PVL. This study presents an in vitro flow measurement method to localize PVL during hydrodynamic characterization of TAVR and furthermore presents different design features, socalled outer skirt, to reduce PVL. Particle image velocimetry (PIV) measurements were performed for flow field assessment during hydrodynamic characterization of TAVR. Additionally, two different sealing concepts were developed to reduce PVL. The skirts were manufactured from polymeric-nonwoven and sued to pericardium-based TAVR-prototype. The prepared TAVR-prototypes were then deployed in a pathophysiological model of the aortic root with a calcification nodule of 2 mm according to ISO 5840:2021. To assess PVL, the flow field and the regurgitation volume was measured. The PIV measurements showed a clearly visible leakage jet between the TAVR-prototypes without skirt and the pathophysiological aortic annulus model. Jet velocities of up to 0.5 m/s were measured depending on presence or configuration of a PVL-preventing skirt. When implanted in the physiological annulus model without calcification nodule, PVL was hardly recognizable. The regurgitation volume of a TAVR-prototype without skirt at 5 l/min was 36.26±1.89 ml (n = 10). The developed and manufactured polymeric-nonwoven skirts reduced PVL from 37.67±1.17 ml to 18.36±1.8 ml (n = 10, TAVR-skirt-design1) and from 46.97±1.07 ml to 17.85±1.29 ml (n = 10, TAVR-skirt-design2) at 5 l/min. The localization of PVL during hydrodynamic characterization by means of PIV was successful. The sealing concepts developed in this work were very effective and led to a PVL-reduction of the tested TAVR prototypes of about 50% to 70%.

Time-Resolved Particle Image Velocimetry Measurements of Nonreacting Flow Field in a Swirl-Stabilized Combustor Without and With Porous Inserts for Acoustic Control

2014 ◽  
Vol 137 (4) ◽  
Author(s):  
Joseph Meadows ◽  
Ajay K. Agrawal
Keyword(s):  
Particle Image Velocimetry ◽  
Flow Field ◽  
Particle Image ◽  
Direct Injection ◽  
Combustion Noise ◽  
Turbulent Structures ◽  
Time Resolved ◽  
Turbulence Structures ◽  
Image Velocimetry ◽  
Acoustic Instabilities

Combustion noise and thermo-acoustic instabilities are of primary importance in highly critical applications such as rocket propulsion systems, power generation, and jet propulsion engines. Mechanisms for combustion instabilities are extremely complex because they often involve interactions among several different physical phenomena such as unsteady flame propagation leading to unsteady flow field, acoustic wave propagation, natural and forced hydrodynamic instabilities, etc. In the past, we have utilized porous inert media (PIM) to mitigate combustion noise and thermo-acoustic instabilities in both lean premixed (LPM) and lean direct injection (LDI) combustion systems. While these studies demonstrated the efficacy of the PIM concept to mitigate noise and thermo-acoustic instabilities, the actual mechanisms involved have not been understood. The present study utilizes time-resolved particle image velocimetry (PIV) to measure the turbulent flow field in a nonreacting swirl-stabilized combustor without and with PIM. Although the flow field inside the annulus of the PIM cannot be observed, measurements immediately downstream of the PIM provide insight into the turbulent structures. Results are analyzed using the proper orthogonal decomposition (POD) method and show that the PIM alters the flow field in an advantageous manner by modifying the turbulence structures and eliminating the corner recirculation zones and precessing vortex core (PVC), which would ultimately affect the acoustic behavior in a favorable manner.

scholarly journals Spectral characteristics of turbulent boundary layers – comparison of Particle Image Velocimetry and Thermal Anemometry

2019 ◽  
Vol 213 ◽  
pp. 02034 ◽  
Author(s):  
Klára Jurčáková ◽  
Radka Kellnerová ◽  
Pavel Procházka ◽  
Pavel Antoš
Keyword(s):  
Particle Image Velocimetry ◽  
Boundary Layers ◽  
Particle Image ◽  
Spectral Characteristics ◽  
Experimental Methods ◽  
Turbulent Boundary Layers ◽  
Time Resolved ◽  
Image Velocimetry ◽  
Normal Distance ◽  
Good Agreement

Flow in turbulent boundary layers over various rough surfaces was measured by the time-resolved particle image velocimetry and the thermal anemometry. The experimental methods showed very good agreement in both mean and spectral characteristics taking into account each method limitations. The spectral characteristics supported the attached eddy hypothesis. The most energetic structures were growing with the wall-normal distance and they achieved sizes equal to 3 to 8 boundary layer depths.

Natural Convection Around a Horizontal Heated Square-Section Cylinder in an Enclosure: Visualization and Dynamic Characterization of Instabilities by Particle Image Velocimetry

2008 ◽  
Author(s):  
Gillian Leplat ◽  
Philippe Barricau ◽  
Philippe Reulet ◽  
Pierre Millan
Keyword(s):  
Particle Image Velocimetry ◽  
Particle Image ◽  
Three Dimensional ◽  
Dynamic Characterization ◽  
Steady Regime ◽  
Time Resolved ◽  
Unsteady Regime ◽  
Image Velocimetry ◽  
Side Walls

Consider an air-filled square cavity with cold top and bottom walls, adiabatic side walls and a centered heated sharp-edged source (a square-section cylinder). An unstable behavior has been highlighted previously while studying the effects of confinement (with different cylinder sizes) on the topology of the flow. A transition occurs from a bi-dimensional, steady regime to a three-dimensional, unsteady regime when the aspect ratio reaches the value of 0.4 for a Rayleigh number of 5.74 × 104. Time-resolved 2D particle image velocimetry is used to characterize the dynamics of the flow in this configuration. The evolution of the instability is particularly investigated.

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