Flow structures and their contribution to turbulent dispersion in a randomly packed porous bed based on particle image velocimetry measurements

2013 ◽  
Vol 25 (11) ◽  
pp. 113303 ◽  
Author(s):  
Vishal A. Patil ◽  
James A. Liburdy
Keyword(s):  
Particle Image Velocimetry ◽  
Particle Image ◽  
Turbulent Dispersion ◽  
Flow Structures ◽  
Porous Bed ◽  
Image Velocimetry

Flow Characteristics of Pressure-Driven Water in Serpentine Micro-Channels

2006 ◽  
Author(s):  
Renqiang Xiong ◽  
J. N. Chung
Keyword(s):  
Particle Image Velocimetry ◽  
Particle Image ◽  
Flow Characteristics ◽  
Flow Structures ◽  
Micro Channel ◽  
Pressure Drops ◽  
Micro Particle Image Velocimetry ◽  
Image Velocimetry ◽  
Micro Channels ◽  
Shape And Size

Flow structures and pressure drops were investigated in rectangular serpentine micro-channels with miter bends which had hydraulic diameters of 0.209mm, 0.395mm and 0.549mm respectively. To evaluate the bend effect, the additional pressure drop due to the miter bend must be obtained. Three groups of micro-channels were fabricated to remove the inlet and outlet losses. A validated micro-particle image velocimetry (μPIV) system was used to achieve the flow structure in a serpentine micro-channel with hydraulic diameter of 0.173mm. The experimental results show the vortices around the outer and inner walls of the bend do not form when Re<100. Those vortices appear and continue to develop with the Re number when Re> 100-300, and the shape and size of the vortices almost remain constant when Re>1000. The bend loss coefficient Kb was observed to be related with the Re number when Re<100, with the Re number and channel size when Re>100. It almost keeps constant and changes in the range of ± 10% When Re is larger than some value in 1300-1500. And a size effect on Kb was also observed.

Two-dimensional shear rate field and flow structures of a pseudoplastic fluid in a stirred tank using particle image velocimetry

2021 ◽  
pp. 117198
Author(s):  
Jenniffer S. Ayala ◽  
Helder L. de Moura ◽  
Rodrigo de L. Amaral ◽  
Francisco de A. Oliveira Júnior ◽  
José R. Nunhez ◽  
...  
Keyword(s):  
Particle Image Velocimetry ◽  
Shear Rate ◽  
Particle Image ◽  
Stirred Tank ◽  
Flow Structures ◽  
Two Dimensional ◽  
Pseudoplastic Fluid ◽  
Image Velocimetry

Laminar vortex rings impinging onto porous walls with a constant porosity

2018 ◽  
Vol 837 ◽  
pp. 729-764 ◽  
Author(s):  
Yang Xu ◽  
Jin-Jun Wang ◽  
Li-Hao Feng ◽  
Guo-Sheng He ◽  
Zhong-Yi Wang
Keyword(s):  
Particle Image Velocimetry ◽  
Vortex Ring ◽  
Particle Image ◽  
Porous Wall ◽  
Hole Diameter ◽  
Vortex Rings ◽  
Flow Structures ◽  
Image Velocimetry ◽  
Porous Walls ◽  
First Time

For the first time, an experiment has been conducted to investigate synthetic jet laminar vortex rings impinging onto porous walls with different geometries by time-resolved particle image velocimetry. The geometry of the porous wall is changed by varying the hole diameter on the wall (from 1.0 mm to 3.0 mm) when surface porosity is kept constant ($\unicode[STIX]{x1D719}=75\,\%$). The finite-time Lyapunov exponent and phase-averaged vorticity field derived from particle image velocimetry data are presented to reveal the evolution of the vortical structures. A mechanism associated with vorticity cancellation is proposed to explain the formation of downstream transmitted vortex rings; and both the vortex ring trajectory and the time-mean flow feature are compared between different cases. It is found that the hole diameter significantly influences the evolution of the flow structures on both the upstream and downstream sides of the porous wall. In particular, for a porous wall with a small hole diameter ($d_{h}^{\ast }=0.067$, 0.10 and 0.133), the transmitted finger-type jets will reorganize into a well-formed transmitted vortex ring in the downstream flow. However, for the case of a large hole diameter of $d_{h}^{\ast }=0.20$, the transmitted vortex ring is not well formed because of insufficient vorticity cancellation. Additionally, the residual vorticity gradually evolves into discrete jet-like structures downstream, which further weaken the intensity of the transmitted vortex ring. Consequently, the transmitted flow structures for the $d_{h}^{\ast }=0.20$ case would lose coherence more easily (or probably even transition to turbulence), resulting in a faster decay of the axial velocity and stronger entrainment of the transmitted jet. For all porous wall cases, the velocity profile of the transmitted jet exhibits self-similar behaviour in the far field ($z/D_{0}\geqslant 6.03$), which agrees well with the velocity distribution of free synthetic jets. With the help of the control-volume approach, the time-mean drag of the porous wall is evaluated experimentally for the first time. It is shown that the porous wall drag increases with the decrease in the hole diameter. Moreover, for a porous wall with a small hole diameter ($d_{h}^{\ast }=0.067$, 0.10 and 0.133), it appears that the porous wall drag mainly derives from the viscous effect. However, as $d_{h}^{\ast }$ increases to 0.20, the form drag associated with the porous wall geometry becomes significant.

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