Dandelion seeds stay afloat with the help of vortex pairs

Scilight ◽  
2021 ◽  
Vol 2021 (34) ◽  
pp. 341101
Author(s):  
Anashe Bandari
Keyword(s):  
Vortex Pairs

Widnall instabilities in vortex pairs

2003 ◽  
Vol 15 (7) ◽  
pp. 1861-1874 ◽  
Author(s):  
Denis Sipp ◽  
Laurent Jacquin
Keyword(s):  
Vortex Pairs

Heat Transfer and Flow Phenomena in a Swirl Chamber Simulating Turbine Blade Internal Cooling

1998 ◽  
Author(s):  
C. R. Hedlund ◽  
P. M. Ligrani ◽  
H.-K. Moon ◽  
B. Glezer
Keyword(s):  
Heat Transfer ◽  
Turbine Blade ◽  
Flow Characteristics ◽  
Leading Edge ◽  
Internal Cooling ◽  
Vortex Pairs ◽  
Nusselt Numbers ◽  
Swirl Chamber ◽  
Flow Phenomena ◽  
Energy Balances

Heat transfer and fluid mechanics results are given for a swirl chamber whose geometry models an internal passage used to cool the leading edge of a turbine blade. The Reynolds numbers investigated, based on inlet duct characteristics, include values which are the same as in the application (18000–19400). The ratio of absolute air temperature between the inlet and wall of the swirl chamber ranges from 0.62 to 0.86 for the heat transfer measurements. Spatial variations of surface Nusselt numbers along swirl chamber surfaces are measured using infrared thermography in conjunction with thermocouples, energy balances, digital image processing, and in situ calibration procedures. The structure and streamwise development of arrays of Görtler vortex pairs, which develop along concave surfaces, are apparent from flow visualizations. Overall swirl chamber structure is also described from time-averaged surveys of the circumferential component of velocity, total pressure, static pressure, and the circumferential component of vorticity. Important variations of surface Nusselt numbers and time-averaged flow characteristics are present due to arrays of Görtler vortex pairs, especially near each of the two inlets, where Nusselt numbers are highest. Nusselt numbers then decrease and become more spatially uniform along the interior surface of the chamber as the flows advect away from each inlet.

scholarly journals Two-vortex equilibrium in the flow past a flat plate at incidence

2014 ◽  
Vol 755 ◽  
pp. 50-61 ◽  
Author(s):  
Luca Zannetti ◽  
Alexandre Gourjii
Keyword(s):  
Flat Plate ◽  
Symmetric Equilibrium ◽  
Equilibrium Conditions ◽  
Kutta Condition ◽  
Vortex Pairs ◽  
Flow Past ◽  
Equilibrium Configurations ◽  
Asymmetric Flows ◽  
Asymmetric Equilibrium ◽  
Total Circulation

AbstractThe two-dimensional inviscid incompressible steady flow past an inclined flat plate is considered. A locus of asymmetric equilibrium configurations for vortex pairs is detected. It is shown that the flat geometry has peculiar properties compared to other geometries: (i) in order to satisfy the Kutta condition at both edges, which ensures flow regularity, the total circulation and the force acting on the plate must be zero; and (ii) the Kutta condition and the free vortex equilibrium conditions are not independent of each other. The non-existence of symmetric equilibrium configurations for an orthogonal plate is extended to more general asymmetric flows.

What happens to the vortex structures when the rising bubble transits from zigzag to spiral?

2017 ◽  
Vol 828 ◽  
pp. 353-373 ◽  
Author(s):  
Jie Zhang ◽  
Ming-Jiu Ni
Keyword(s):  
Angular Velocity ◽  
Magnetic Fields ◽  
Physical Mechanism ◽  
Critical Value ◽  
Theoretical Explanation ◽  
Vortex Structures ◽  
Direct Numerical Simulations ◽  
Vortex Pairs ◽  
Spiral Path ◽  
Rising Bubble

It has been demonstrated by many experiments carried out over the last 60 years that in certain liquids a single millimetre-sized bubble will rise within an unstable path, which is sometimes observed to transit from zigzag to spiral. After performing several groups of direct numerical simulations, the present work gives a theoretical explanation to reveal the physical mechanism causing the transition, and the results are presented in two parts. In the first part, in which a freely rising bubble is simulated, equal-strength vortex pairs are observed to shed twice during a period of the pure zigzag path, and this type of motion is triggered by the amounts of streamwise vorticities accumulated on the bubble interface, when a critical value is reached. However, when the balance between the counter-rotating vortices is broken, an angular velocity is induced between the asymmetric vortex pairs, driving the bubble to rise in an opposite spiral path. Therefore, although there is no preference of the spiral direction as observed in experiments, it is actually determined by the sign of the stronger vortex thread. In the second part, external vertical magnetic fields are imposed onto the spirally rising bubble in order to further confirm the relations between the vortex structures and the unstable path patterns. As shown in our previous studies (Zhang & Ni, Phys. Fluids, vol. 26 (10), 2014, 102102), the strength of the double-threaded vortex pairs, as well as the imbalance between them, will be weakened under magnetic fields. Therefore, as the vortex pairs become more symmetric, the rotating radius of the spirally rising bubble is observed to decrease. We try to answer the question, put forward by Shew et al. (2005, Preprint, ENS, Lyon), ‘what caused the bubble to transit from zigzag to spiral naturally?’

scholarly journals ERRATUM: "FRACTAL TRACER PATTERNS IN OPEN HYDRODYNAMICAL FLOWS: THE CASE OF LEAPEROGGING VORTEX PAIRS"

Fractals ◽  
1995 ◽  
Vol 03 (02) ◽  
pp. 403-404
Author(s):  
Á. Péntek ◽  
T. Tél ◽  
Z. Toroczkai
Keyword(s):  
Vortex Pairs

scholarly journals Dust trapping in vortex pairs

2010 ◽  
Vol 239 (18) ◽  
pp. 1789-1797 ◽  
Author(s):  
Jean-Régis Angilella
Keyword(s):  
Dust Trapping ◽  
Vortex Pairs
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