Affiliations: Graduate School of Engineering, Hokkaido University,
N13W8, Sapporo, 060-8628, Japan. E-mail: tasaka@eng.hokudai.ac.jp | Graduate School of Science, Hokkaido University,
N10W8, Sapporo, 060-0810, Japan | Research Institute for Electronic Science, Hokkaido
University, N12W6, Sapporo, 060-0812, Japan
Abstract: This study aims to clarify the relationship between the deformation
of a free surface and flow transition in a "switching
phenomenon" process. In a flow driven by a rotating disk in a
cylindrical open vessel, the free surface irregularly changes its shape from
axisymmetric to nonaxisymmetric and vice versa with repeating up-and-down
motion (so-called "switching phenomenon"). The flow
under the free surface was visualized by anisotropic flakes. When the free
surface assumes a parabolic shape, the flow is distinguished by three regions;
local circulation region, rigid vortex region and meridional circulation
region. The flow transition in the switching phenomenon was shown by snapshots
and movies of the visualized flow; the flow near the free surface is laminar
even if the shape of the free surface changes to nonaxisymmetric during the
time at which the free surface attaches to the bottom of the vessel. After the
free surface detaches from the disk, the flow near the free surface becomes
turbulent. When the free surface changes to axisymmetric while descending to
the bottom, the flow changes from turbulent to laminar flow and the local
circulation region reemerges at the center of the vessel.
