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Turbulence and Shear Flow Phenomena -1 First International Symposium

ISBN Print: 1-56700-135-1

THREE-DIMENSIONAL FEATURES OF COHERENT FINE SCALE EDDIES IN TURBULENCE

Аннотация

Three-dimensional structure of coherent fine scale eddies in turbulence is investigated by using a DNS database of a homogeneous isotropic turbulence. The axes of coherent fine scale eddies are determined and characteristics are clarified. The axis has several nodes which are identified as the minima of second invariant on the axis. Along the axis, maximum azimuthal velocity and axial velocity show relatively large fluctuations, while diameter is nearly constant. At each node, the axis bends with a large angle. Magnitude of advection velocity and direction of movement of the coherent fine scale eddy also change at these nodes. Probability density function of length of the segment between neighboring nodes shows a peak at the length of Taylor micro scale. The segment length shows a strong correlation with the maximum second invariant and increases with the increase of the second invariant with a 1/2-2/3 power. Probability density function of advection velocity of each segment of the axis shows a peak at 1.25 times of r. m. s. velocity fluctuation, which means that coherent fine scale eddies are very active in turbulence.
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