Velocity field measurements and visualization are applied to a sink vortex of water (with a free surface on top) produced in a cylindrical tank rotating about the vertical axis. The controlling parameters are the rotating rate of the tank (0.2 and 0.4 rad s(sup -1)) and the volume flux of a water withdrawn from a hole at the center of the bottom (50 and 150 cu cm s(sup -1)). It is found that a Rankine-like vortex is produced in the steady state when the volume flux of water withdrawn from the hole is large. When the volume flux is small, however, the conservation of the angular momentum around the central axis of the vortex is not established. A simple theoretical model that assumes Ekman boundary layer on bottom plate turns out to reproduce successfully the nonconservation of angular momentum. The injection of fluorescence dye at the periphery of the cylindrical tank reveals that the water introduced at the periphery of the tank descends to the bottom along the side wall and flows to the center of the tank in the boundary layer at the bottom of the tank. However, the dye ascends in a thin vertical layer around the core of the vortex suggesting that the upward flow is formed surrounding the sink vortex. When a rotation rate of the tank is reduced from 0.4 rad s(sup -1) to 0.2 rad s(sup -1) with keeping the withdrawal rate of the water (to maintain a vortex) constant, horizontal plumes appear near the side wall because of the inertial instability. They penetrated a limited extent into the interior region, so that there appears a mixing layer near the periphery of the tank. At the same time nearly-axisymmetric disturbances develop from the bottom boundary layer and intrude into the interior region.

資料番号: AA0047776015

レポート番号: JAXA-SP-04-002