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Formation of vortices and its significance in fully developed turbulence

by admin last modified 2007-06-04 20:53

Prof. T.Kambe, Dept. of Physics, Univ. of Tokyo; Science Council of Japan.

What Meeting
When 2007-06-14
from 16:00 to 16:55
Where Tallinn Mechanics Seminar: B101, Akadeemia tee 21
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Turbulence is regarded as a dynamical system of considerably many degrees of freedom. It is an irregular flow field, fluctuating both spatially and temporally, and evolving autonomously under nonlinear mechanism of field dynamics (without external force). There are structures in turbulence, sometimes called intermittency. It is well-known that statistical laws of velocity differences at two points are non-Gaussian, characterized with negative skewness (third-order moment) of longitudinal velocity difference. The negative skewness is responsible for enhancement of enstrophy (an average of squared vorticity).

In turbulence, there exists a certain mechanism by which vortex lines are stretched on the average. A Burgers vortex is formed in a velocity field of negative skewness. A number of strong vortices in the form of slender objects are observed in experiments and computer simulations carried out at high Reynolds numbers. Some of observed statistical properties of fully developed turbulence such as scaling laws of structure functions of longitudinal velocity differences can be predicted by random distribution of Burgers vortices.

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