Abstract:
This paper presents the three-dimensional
characteristics of coherent fine scale eddies related
to their axis in homogeneous isotropic turbulence in
order to understand the detailed features of the fine
scale eddy in turbulence. The coherent fine scale
eddy and their axis are identified by an auto tracking
algorithm from the Direct Numerical Simulation
(DNS) database, where DNS is performed based on a
spectral method. It is shown that the axis of each fine
scale eddy contains several nodes, in which these
nodes are identified by the minima of second
invariant (Q) of the velocity gradient tensor on the
axis. It is also shown that the number of nodes
increases for strong and relatively long eddy but it
decreases for weak and short eddy. At each node the
axis bends with a large angle. The maximum
azimuthal velocity and axial velocity of coherent fine
scale eddy show relatively large fluctuations along
their axis, while the diameter is nearly constant
along the entire axis of the fine scale eddy. The
coherent fine scale eddies have large advection
velocity but the dissipation rate along the axis of the
eddy is not so large.
