Explorations of the apparent Weissenberg effect in water

The puzzling phenomenon in which water is observed to suddenly climb partially up a vertical rotating shaft whose tip was initially just in contact with the free surface is explored. This phenomenon occurs when the rotational rate is increased above a certain threshold. In an attempt to make some progress on understanding the phenomenon, it is explored by detailed observations and by varying parameters of the problem. Observations are presented with the aid of photographs of the surface waves and of tracer particle path elements. The effect of varying the shaft diameter, immersion of depth of the shaft tip into the water, and the effect of varying some fluid properties are investigated. In addition, extraneous effects such as irregularities in the driving mechanism and shaft, external disturbances of the fluid, and vessel size are eliminated as possible causes of the phenomenon. Despite these explorations of characteristics of the phenomenon, we have not found a satisfactory explanation of it. Another interesting instability was also observed. The water near the fluid surface in the undisturbed state flows radially outward in a regulary laminar fashion. However, small disturbances of the fluid can cause shedding of vortices whose axes are in the tangential direction and which are swept outward.