Turbulence and Coherent Structures [back]
Turbulence remains one of the last unsolved problems of classical physics. Although the equations of motion are now known for about two hundred years, a precise understanding, and consequently, a theoretical description of this phenomenon are still lacking. However, turbulent fields turn out not to be purely random. At the same time, they exhibit both a stunning degree of spatio-temporal complexity and coherence.
Two-dimensional Turbulence
For example, two dimensional decaying turbulence can be regarded as an ensemble of interacting patch-like vortices. During the decay process, these structures merge into larger structures with a complicated inner structure.
One of these paradigmatic two-dimensional structures is Lundgren's famous spiral vortex, which is a result of merging process of a strong and several smaller vortices. The small vortices are torn apart by the strong central vortex, only filamentary arms of vorticity remain.
Three-dimensional Turbulence
In three-dimensional turbulence vortex stretching is an important dynamical effect, which causes the emergence of filamentary vortex tubes. These vortices seem to be the dominant flow structures in fully developed, homegeneous and isotropic turbulence.
Each of these vortex filaments produces a spiraling velocity field (indicated by the streamlines), which advects the neighboring structures. Thereby the nonlinear nature of turbulent flows becomes apparent: Vortices create swirling flows, by which they are stretched and advected. The new distribution of vortices then produces a different velocity field and so on ...
Online-Zeitschriften
- Web of Science
- Elsevier (PLA,PhysA,PhysD)
- Elsevier
- Physical Review
- Springer (EPJB,Biol.Cyb.)
- Journal of Physics A
- Europhysics Letters
- Nature
- Annalen der Physik (Annals of Physics-Berlin)
- Nonlinear Phenomena in Complex Systems
- Condensed Matter Preprints (Los Alamos e-Print Archive)
- Zweigbibliothek Physik
- Zeitschriften WWU