scholarly journals Response of a columnar vortex to a wrapped vortex loop

1999 ◽  
Vol 7 ◽  
pp. 280-291
Author(s):  
J. S. Marshall
Keyword(s):  
Vortex Loop ◽  
Columnar Vortex

Loss of Superconducting Phase Coherence inYBa2Cu3O7Films: Vortex-Loop Unbinding and Kosterlitz-Thouless Phenomena

2001 ◽  
Vol 87 (12) ◽  
Author(s):  
Jürgen Kötzler ◽  
Detlef Görlitz ◽  
Sven Skwirblies ◽  
Axel Wriedt
Keyword(s):  
Phase Coherence ◽  
Superconducting Phase ◽  
Vortex Loop

Characteristics of Dynamic Forces Generated by a Flapping Butterfly and its Wake Structure

2017 ◽  
Author(s):  
Masaki Fuchiwaki ◽  
Kazuhiro Tanaka
Keyword(s):  
Flow Field ◽  
Butterfly Wing ◽  
Vortex Loop ◽  
Insect Wing ◽  
Fluid Forces ◽  
Insect Wings ◽  
Piv Measurement ◽  
Dynamic Forces ◽  
Butterfly Wings ◽  
The Relationship

A typical example of the flow field around a moving elastic body is that around butterfly wings. Butterflies fly by skillfully controlling this flow field, and vortices are generated around their bodies. The motion of their elastic wings produces dynamic fluid forces by manipulating the flow field. For this reason, there has been increased academic interest in the flow field and dynamic fluid forces produced by butterfly wings. A number of recent studies have qualitatively and quantitatively examined the flow field around insect wings. In some such previous studies, the vortex ring or vortex loop formed on the wing was visualized. However, the characteristics of dynamic forces generated by the flapping insect wing are not yet sufficiently understood. The purpose of the present study is to investigate the characteristics of dynamic lift and thrust produced by the flapping butterfly wing and the relationship between the dynamic lift and thrust and the flow field around the butterfly. We conducted the dynamic lift and thrust measurements of a fixed flapping butterfly, Idea leuconoe, using a six-axes sensor. Moreover, two-dimensional PIV measurement was conducted in the wake of the butterfly. The butterfly produced dynamic lift in downward flapping which became maximum at a flapping angle of approximately 0.0 deg. At the same time, the butterfly produced negative dynamic thrust during downward flapping. The negative dynamic thrust was not produced hydrodynamically by a flapping butterfly wing because a jet was not formed in front of the butterfly. The negative dynamic thrust was the kicking force for jumping and the maximum of this kicking force was about 6.0 times as large as the weight. On the other hand, the butterfly produced dynamic thrust in upward flapping which was approximately 6.0 times as large as the weight of the butterfly. However, the attacking force by the abdomen of the butterfly was included in the dynamic thrust and we have not yet clarified quantitatively the dynamic thrust produced by the butterfly wing.

A sufficient condition for the instability of columnar vortices

1983 ◽  
Vol 126 ◽  
pp. 335-356 ◽  
Author(s):  
S. Leibovich ◽  
K. Stewartson
Keyword(s):  
Numerical Solutions ◽  
Three Dimensional ◽  
Azimuthal Velocity ◽  
Unstable Wave ◽  
Sufficient Condition ◽  
Asymptotic Results ◽  
Specific Flow ◽  
Columnar Vortex ◽  
Swirl Velocity ◽  
Inviscid Instability

The inviscid instability of columnar vortex flows in unbounded domains to three-dimensional perturbations is considered. The undisturbed flows may have axial and swirl velocity components with a general dependence on distance from the swirl axis. The equation governing the disturbance is found to simplify when the azimuthal wavenumber n is large. This permits us to develop the solution in an asymptotic expansion and reveals a class of unstable modes. The asymptotic results are confirmed by comparisons with numerical solutions of the full problem for a specific flow modelling the trailing vortex. It is found that the asymptotic theory predicts the most-unstable wave with reasonable accuracy for values of n as low as 3, and improves rapidly in accuracy as n increases. This study enables us to formulate a sufficient condition for the instability of columnar vortices as follows. Let the vortex have axial velocity W(r), azimuthal velocity V(r), where r is distance from the axis, let Ω be the angular velocity V/r, and let Γ be the circulation rV. Then the flow is unstable if $ V\frac{d\Omega}{dr}\left[ \frac{d\Omega}{dr}\frac{d\Gamma}{dr} + \left(\frac{dW}{dr}\right)^2\right] < 0.$

Three-dimensional, unsteady vortex loop dynamics

1985 ◽  
Author(s):  
S. BATILL ◽  
T. DOLIGALSKI
Keyword(s):  
Three Dimensional ◽  
Vortex Loop ◽  
Loop Dynamics

Nonlinear dynamics of the elliptic instability

2010 ◽  
Vol 646 ◽  
pp. 471-480 ◽  
Author(s):  
NATHANAËL SCHAEFFER ◽  
STÉPHANE LE DIZÈS
Keyword(s):  
Nonlinear Dynamics ◽  
Numerical Simulations ◽  
Shear Layer ◽  
Rapid Growth ◽  
Vortex Core ◽  
Nonlinear Evolution ◽  
Core Size ◽  
Layer Formation ◽  
Vortex Loop ◽  
Weakly Nonlinear

In this paper, we analyse by numerical simulations the nonlinear dynamics of the elliptic instability in the configurations of a single strained vortex and a system of two counter-rotating vortices. We show that although a weakly nonlinear regime associated with a limit cycle is possible, the nonlinear evolution far from the instability threshold is, in general, much more catastrophic for the vortex. In both configurations, we put forward some evidence of a universal nonlinear transition involving shear layer formation and vortex loop ejection, leading to a strong alteration and attenuation of the vortex, and a rapid growth of the vortex core size.

The nucleation of vorticity by ions in superfluid 4 He I. Basic theory

1984 ◽  
Vol 311 (1518) ◽  
pp. 433-467 ◽  
Keyword(s):  
High Pressure ◽  
Potential Barrier ◽  
Superfluid Helium ◽  
Recent Observation ◽  
Critical Value ◽  
Vortex Loop ◽  
Quantum Tunnelling ◽  
Vortex Loops ◽  
Very High ◽  
Vortex Nucleation

A theory is developed of vortex nucleation by an ion moving in superfluid helium at a low temperature. It is shown that production of a vortex loop attached to the side of the ion becomes energetically possible when the velocity of the ion exceeds a critical value, but that nucleation is impeded by the presence of a small potential barrier. The predicted critical velocity is close to that observed experimentally, at least at high pressure. Nucleation of an encircling vortex ring, considered some years ago by Schwarz & Jang (Phys.Rev. A8,3199 (1973)), probably becomes possible only at a higher velocity, and it is impeded by a large potential barrier. It is shown that for vortex loops the potential barrier can probably be overcome at a rate consistent with experiment either by quantum tunnelling at the lowest temperatures or thermally, by absorption of a single roton, at higher temperatures. Possible explanations of the recent observation by Bowley et al . {Phil. Trans. R. Soc. Lond. A307, 201 (1982)) that at high pressure the rate of vortex nucleation falls off at very high velocities are discussed.

Sign in / Sign up

Export Citation Format

Share Document