IUTAM Symposium on Elementary Vortices and Coherent by Shigeo Kida

By Shigeo Kida

Simple vortices – these tubular swirling vortical constructions with targeted vorticity generally saw in several types of turbulent flows – play key roles in turbulence dynamics (e.g. enhancement of combining, diffusion and resistance) and signify turbulence records (e.g. intermittency). as a result of their dynamical value, manipulation of effortless vortices is anticipated to be powerful and priceless in turbulence keep watch over in addition to in building of turbulence modeling. the main complex examine works on trouble-free vortices and similar difficulties have been awarded and mentioned on the IUTAM Symposium in Kyoto, Japan, 26-28 October 2004. This booklet comprises forty contributions offered there, the topics of which conceal vortex dynamics, coherent buildings, chaotic advection and combining, statistical houses of turbulence, rotating and stratified turbulence, instability and transition, dynamics of skinny vortices, finite-time singularity, and superfluid turbulence. The e-book may be valuable for readers of graduate and complex degrees within the box of fluid turbulence.

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1800 ω 2 structures and 1920 s2 structures were extracted from the initial isotropic state and ordered by intensity. The structures contribute 39% and 28%, respectively, to the global variance of vorticity and strain rate while only occupying 13% and 10% of 26 global volume, reflecting the concentrated nature of the fluctuations within. In the sheared state 800 ω 2 and 810 s2 structures were extracted contributing 50% and 38%, respectively to global variance, and 16% and 13% to the volume. The variance-to-volume-ratio is 3 to 1 in both isotropic and sheared states, the average volume of ω 2 and s2 structures increases by 300%, indicating major amalgamation and growth of structures by shear.

Figure 6. 4. The extracted subvolume at each time is shown by the box. 6, then to AR ≈ 1 at St = 1, shortly after which the tube begins a transition to a hairpin vortex. As shown in Figs. 6(c)-(f), the process involves the elongating and flattening of the vortex tube and the bending over and formation of a rather flattened head that is distinct Dynamics of small-scale vorticity and strain-rate structures 29 from a single tube-like leg. As the vortex elongates and bends, the leg of the hairpin remains tube-like with little overlap with the more concentrated strainrate fluctuations.

Shear causes amalgamation of structures and suppresses strain-rate structures between enstrophy structures. Shear enhances “passive” strain-rate fluctuations—strain rate kinematically induced by local vorticity concentrations with negligible enstrophy production—relative to “active,” or vorticity-generating, strain-rate fluctuations. Enstrophy structures separate into “active” and “passive” based on the second eigenvalue of fluctuating strain rate. The time evolution of a shearinduced hairpin enstrophy structure was analyzed.

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