Various phenomena on a water vortex in a cylindrical tank over a rotating bottom

Flows in a cylindrical tank over a rotating bottom are investigated by laboratory experiments. Despite the axisymmetry of the experimental setup, various anisotropic phenomena are observed. The slow rotation of the bottom disk induces a circular flow according to the axisymmetric environment, but polygonal vortices form under faster rotation. Between these two vortex flow states, the flow undergoes a transition with clear hysteresis during which the elliptical shape assumed under faster rotation is retained when the rotation is subsequently slowed to rates that previously supported axisymmetric flow. Sloshing is also observed; here, a calm circular flow state alternates with an oscillation of the water surface along the sidewall of the container. A phase diagram showing the phenomena observed under different combinations of the initial water depth at rest and the rotation rate of the bottom disk is developed following thorough experimental testing over a wide range of parameter values. The features of the dependences of the range for each phenomenon to occur on these parameters are also elucidated.