Formation of vortices and its significance in fully developed turbulence
Prof. T.Kambe, Dept. of Physics, Univ. of Tokyo; Science Council of Japan.
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
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.