scholarly journals About bubbles and vortex rings

2015 ◽  
Vol 780 ◽  
pp. 1-4 ◽  
Author(s):  
C. Martínez-Bazán
Keyword(s):  
Vortex Rings ◽  
Complex Mechanism ◽  
Complex Interplay ◽  
Single Vortex ◽  
Vortical Structures ◽  
Turbulent Eddies ◽  
Deformation Dynamics ◽  
Bubble Interaction ◽  
Elongation Process ◽  
Shed Light

Bubble interaction with turbulence has a number of applications in engineering processes and nature. The complex interplay between the vortical structures present in a turbulent flow and the bubbles drives their deformation dynamics, which may lead to bubble rupture under the appropriate conditions. Such a process includes nonlinear interaction among the turbulent eddies and between the eddies and the bubbles. Thus, the coupled evolution of a single vortex ring with a bubble represents an idealized scenario that can provide a framework to shed light on understanding such a common and complex mechanism. Jha & Govardhan (J. Fluid Mech., vol. 773, 2015, pp. 460–497) have performed elegant experiments generating controlled vortex rings and injecting bubbles of known volume. They have reported interesting results on the elongation process of the bubble and its impact on vortex dynamics.

The behaviour of circular synthetic jets in a laminar boundary layer

2005 ◽  
Vol 109 (1100) ◽  
pp. 461-470 ◽  
Author(s):  
S. Zhong ◽  
F. Millet ◽  
N. J. Wood
Keyword(s):  
Boundary Layer ◽  
Velocity Ratio ◽  
Synthetic Jets ◽  
Operating Conditions ◽  
Vortex Rings ◽  
Hairpin Vortices ◽  
Vortical Structures ◽  
Flow Separation Control ◽  
Wall Flow ◽  
Near Wall

Abstract Dye flow visualisation of circular synthetic jets was carried out in laminar boundary layers developing over a flat plate at a range of actuator operating conditions and freestream velocities of 0·05 and 0·1ms–1. The purpose of this work was to study the interaction of synthetic jets with the boundary layer and the nature of vortical structures produced as a result of this interaction. The effects of Reynolds number (Re), velocity ratio (VR ) and Strouhal number (St) on the behaviour of synthetic jets were studied. At low Re and VR , the vortical structures produced by synthetic jets appear as highly stretched hairpin vortices attached to the wall. At intermediate Re and VR , these structures roll up into vortex rings which experience a considerable amount of tilting and stretching as they enter the boundary layer. These vortex rings will eventually propagate outside the boundary layer hence the influence of the synthetic jets on the near wall flow will be confined in the near field of the jet exit. At high Re and VR , the vortex rings appear to experience a certain amount of tilting but no obvious stretching. They penetrate the edge of the boundary layer quickly, producing very limited impact on the near wall flow. Hence it is believed that the hairpin vortices produced at low Re and VR are likely to be the desirable structures for effective flow separation control. In this paper, a vortex model was also described to explain the mechanism of vortex tilting.

Wake Properties of an Oscillating Airfoil Undergoing Small Amplitude Asymmetric Oscillation

2020 ◽  
Author(s):  
Colin Stutz ◽  
Douglas Bohl ◽  
Melissa Green
Keyword(s):  
Small Amplitude ◽  
Single Vortex ◽  
Pitching Motion ◽  
Vortical Structures ◽  
Naca0012 Airfoil ◽  
Reduced Frequency ◽  
Wake Patterns ◽  
Asymmetric Oscillation ◽  
Secondary Vortices ◽  
Equivalent Strength

Abstract The flow around, and in the wake of, pitching airfoils has received renewed interest due to its potential for thrust production at low Reynolds numbers. Past work has centered on the flow fields generated by symmetric pitching of the airfoil. Studies investigating the effects of asymmetric motion are more limited. This work focuses on the wake patterns developed due to asymmetric pitching. Particle Image Velocimetry (PIV) is used to quantify the flow field around a NACA0012 airfoil undergoing small amplitude, high frequency asymmetric pitching. The airfoil is pitched about the quarter chord point with an amplitude of ±4° at reduced frequencies of k = 2.6–5.8 at a Rec = 12000. Pitching symmetries of 50/50, 40/60 and 30/70 are studied, where the symmetry is defined by the fraction of the cycle spent in the pitch down versus pitch up motion. The data show that for the 50/50 (symmetric) motions two alternating sign vortices, with equivalent strength, are formed as expected. The asymmetric cases show that a single vortex is formed during the “fast” portion of the pitching motion. Multiple vortices are formed during the “slow” portion of the pitching motion. The number of secondary vortices and the downstream evolution of the vortices depends on the symmetry value. In some cases they remain isolated but orbit other vortical structures, while in other cases they pair with other vortical structures, and finally when the reduced frequency and asymmetry values are high enough the vortex array shows interaction between cycles.

Dynamics and Instability of a Vortex Ring Impinging on a Wall

2015 ◽  
Vol 18 (4) ◽  
pp. 1122-1146 ◽  
Author(s):  
Heng Ren ◽  
Xi-Yun Lu
Keyword(s):  
Vortex Ring ◽  
Axial Flow ◽  
Core Region ◽  
Vortical Flow ◽  
Vortex Rings ◽  
Flow Transition ◽  
Azimuthal Component ◽  
Vortical Structures ◽  
The Core ◽  
Eddy Simulation

AbstractDynamics and instability of a vortex ring impinging on a wall were investigated by means of large eddy simulation for two vortex core thicknesses corresponding to thin and thick vortex rings. Various fundamental mechanisms dictating the flow behaviors, such as evolution of vortical structures, formation of vortices wrapping around vortex rings, instability and breakdown of vortex rings, and transition from laminar to turbulent state, have been studied systematically. The evolution of vortical structures is elucidated and the formation of the loop-like and hair-pin vortices wrapping around the vortex rings (called briefly wrapping vortices) is clarified. Analysis of the enstrophy of wrapping vortices and turbulent kinetic energy (TKE) in flow field indicates that the formation and evolution of wrapping vortices are closely associated with the flow transition to turbulent state. It is found that the temporal development of wrapping vortices and the growth rate of axial flow generated around the circumference of the core region for the thin ring are faster than those for the thick ring. The azimuthal instabilities of primary and secondary vortex rings are analyzed and the development of modal energies is investigated to reveal the flow transition to turbulent state. The modal energy decay follows a characteristic –5/3 power law, indicating that the vortical flow has become turbulence. Moreover, it is identified that the TKE with a major contribution of the azimuthal component is mainly distributed in the core region of vortex rings. The results obtained in this study provide physical insight of the mechanisms relevant to the vortical flow evolution from laminar to turbulent state.

Deformation and breakup of bubbles interacting with single vortex rings

2021 ◽  
pp. 103734
Author(s):  
F.J. Foronda-Trillo ◽  
J. Rodríguez-Rodríguez ◽  
C. Gutiérrez-Montes ◽  
C. Martínez-Bazán
Keyword(s):  
Vortex Rings ◽  
Single Vortex

scholarly journals Structure of the vortex wake in hovering Anna's hummingbirds ( Calypte anna )

2013 ◽  
Vol 280 (1773) ◽  
pp. 20132391 ◽  
Author(s):  
M. Wolf ◽  
V. M. Ortega-Jimenez ◽  
R. Dudley
Keyword(s):  
Flow Visualization ◽  
Vortex Structure ◽  
Force Production ◽  
Vortex Rings ◽  
Vortex Wake ◽  
Secondary Vortex ◽  
Single Vortex ◽  
Discrete Vortex ◽  
Weight Support ◽  
Calypte Anna

Hummingbirds are specialized hoverers for which the vortex wake has been described as a series of single vortex rings shed primarily during the downstroke. Recent findings in bats and birds, as well as in a recent study on Anna's hummingbirds, suggest that each wing may shed a discrete vortex ring, yielding a bilaterally paired wake. Here, we describe the presence of two discrete rings in the wake of hovering Anna's hummingbirds, and also infer force production through a wingbeat with contributions to weight support. Using flow visualization, we found separate vortices at the tip and root of each wing, with 15% stronger circulation at the wingtip than at the root during the downstroke. The upstroke wake is more complex, with near-continuous shedding of vorticity, and circulation of approximately equal magnitude at tip and root. Force estimates suggest that the downstroke contributes 66% of required weight support, whereas the upstroke generates 35%. We also identified a secondary vortex structure yielding 8–26% of weight support. Lift production in Anna's hummingbirds is more evenly distributed between the stroke phases than previously estimated for Rufous hummingbirds, in accordance with the generally symmetric down- and upstrokes that characterize hovering in these birds.

On the structure of vortex rings from inclined nozzles

2011 ◽  
Vol 686 ◽  
pp. 451-483 ◽  
Author(s):  
Trung Bao Le ◽  
Iman Borazjani ◽  
Seokkoo Kang ◽  
Fotis Sotiropoulos
Keyword(s):  
Vortex Ring ◽  
Vortex Sheet ◽  
Vortex Rings ◽  
Cylinder Wall ◽  
Primary Vortex ◽  
Vortical Structures ◽  
Ambient Flow ◽  
Piston Cylinder ◽  
Axial Stretching ◽  
Vortex Tubes

AbstractWe carry out numerical simulations to investigate the vortex dynamics of laminar, impulsively driven flows through inclined nozzles in a piston–cylinder apparatus. Our simulations are motivated by the need to provide a complete description of the intricate vortical structures and governing mechanisms emerging in such flows as documented in the experiments of Webster & Longmire (Phys. Fluids, vol. 10, 1998, pp. 400–416) and Troolin & Longmire (Exp. Fluids, vol. 48, 2010, pp. 409–420). We show that the flow is dominated by the interaction of two main vortical structures: the primary inclined vortex ring at the nozzle exit and the secondary stopping ring that arises due to the entrainment of the flow into the cylinder when the piston stops moving. These two structures are connected together with pairs of vortex tubes, which evolve from the continuous vortex sheet initially connecting the primary vortex ring with the interior cylinder wall. In the exterior of the nozzle the key mechanism responsible for the breakup of the vortical structure is the interaction of the stronger inclined primary ring with the weaker stopping ring near the longest lip of the nozzle. In the interior of the nozzle the dynamics is governed by the axial stretching of the secondary ring and the ultimate impingement of this ring on the cylinder wall. Our simulations also clarify the kinematics of the azimuthal flow along the core of the primary vortex ring documented in the experiments by Lim (Phys. Fluids, vol. 10, 1998, pp. 1666–1671). We show that the azimuthal flow is characterized by a pair of two spiral saddle foci at the long and short lips of the nozzle through which ambient flow enters and exits the primary vortex core.

scholarly journals A role for circular code properties in translation

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Simone Giannerini ◽  
Diego Luis Gonzalez ◽  
Greta Goracci ◽  
Alberto Danielli
Keyword(s):  
Molecular Mechanisms ◽  
Translation Speed ◽  
Translation Elongation ◽  
Protein Coding ◽  
Coding Sequences ◽  
Initiator Codon ◽  
Circular Codes ◽  
Elongation Process ◽  
Circular Code ◽  
Shed Light

AbstractCircular codes represent a form of coding allowing detection/correction of frame-shift errors. Building on recent theoretical advances on circular codes, we provide evidence that protein coding sequences exhibit in-frame circular code marks, that are absent in introns and are intimately linked to the keto-amino transformation of codon bases. These properties strongly correlate with translation speed, codon influence and protein synthesis levels. Strikingly, circular code marks are absent at the beginning of coding sequences, but stably occur 40 codons after the initiator codon, hinting at the translation elongation process. Finally, we use the lens of circular codes to show that codon influence on translation correlates with the strong-weak dichotomy of the first two bases of the codon. The results can lead to defining new universal tools for sequence indicators and sequence optimization for bioinformatics and biotechnological applications, and can shed light on the molecular mechanisms behind the decoding process.

scholarly journals Value-based attentional capture affects multi-alternative decision making

eLife ◽  
2018 ◽  
Vol 7 ◽  
Author(s):  
Sebastian Gluth ◽  
Mikhail S Spektor ◽  
Jörg Rieskamp
Keyword(s):  
Decision Making ◽  
Original Data ◽  
Complex Interplay ◽  
The Third ◽  
Relative Preference ◽  
Choice Sets ◽  
Human Participants ◽  
Alternative Decision ◽  
Positive Effect ◽  
Shed Light

Humans and other animals often violate economic principles when choosing between multiple alternatives, but the underlying neurocognitive mechanisms remain elusive. A robust finding is that adding a third option can alter the relative preference for the original alternatives, but studies disagree on whether the third option’s value decreases or increases accuracy. To shed light on this controversy, we used and extended the paradigm of one study reporting a positive effect. However, our four experiments with 147 human participants and a reanalysis of the original data revealed that the positive effect is neither replicable nor reproducible. In contrast, our behavioral and eye-tracking results are best explained by assuming that the third option’s value captures attention and thereby impedes accuracy. We propose a computational model that accounts for the complex interplay of value, attention, and choice. Our theory explains how choice sets and environments influence the neurocognitive processes of multi-alternative decision making.

scholarly journals A role for circular code properties in translation

2020 ◽  
Author(s):  
Simone Giannerini ◽  
Alberto Danielli ◽  
Diego Luis Gonzalez ◽  
Greta Goracci
Keyword(s):  
Molecular Mechanisms ◽  
Translation Speed ◽  
Translation Elongation ◽  
Protein Coding ◽  
Coding Sequences ◽  
Initiator Codon ◽  
Circular Codes ◽  
Elongation Process ◽  
Circular Code ◽  
Shed Light

AbstractCircular codes represent a form of coding allowing detection/correction of frameshift errors. Building on recent theoretical advances on circular codes, we provide evidence that protein coding sequences exhibit in-frame circular code marks, that are absent in introns and are intimately linked to the keto-amino transformation of codon bases. These properties strongly correlate with translation speed, codon influence and protein expression levels. Strikingly, circular code marks are absent at the beginning of coding sequences, but stably occur 40 codons after the initiator codon, hinting at the translation elongation process. Finally, we use the lens of circular codes to show that codon influence on translation correlates with the strong-weak dichotomy of the first two bases of the codon. The results provide promising universal tools for sequence indicators and sequence optimization for bioinformatics and biotechnological applications, and can shed light on the molecular mechanisms behind the decoding process.

scholarly journals XX. The potential of an anchor ring.-Part II

1893 ◽  
Vol 184 ◽  
pp. 1041-1106 ◽  
Keyword(s):  
Vortex Ring ◽  
Cross Section ◽  
Steady Motion ◽  
Vortex Rings ◽  
Laplace’S Equation ◽  
Single Vortex ◽  
Laplace's Equation ◽  
The Stability ◽  
Work Done

This paper is a continuation of that at pp. 43-95 suprd , on “The Potential of an Anchor Bing.” In that paper the potential of an anchor ring was found at all external points; in this/its value is determined at internal points. The annular form of rotating gravitating fluid was also discussed in that paper; here the stability of such a ring is considered. In addition, the potential of a ring whose cross-section is elliptic, being of interest in connection with Saturn, is obtained. The similarity of the methods employed, as well as of the analysis, has led me to give in this paper also a determination of the steady motion of a single vortex-ring in an infinite fluid, and of several fine vortex rings on the same axis. In Section I. solutions of Laplace’s equation applicable to space inside an anchor ring are obtained. These results are applied to obtain the potential of a solid ring at internal points, and also of a distribution of matter on the surface of the ring. The work done in collecting the ring from infinity is obtained.

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