Experimentally Observed Instability of a Laminar Ekman Flow in a Rotating Basin

In studying the axi-symmetric flow induced by source-sink distributions in a rotating cylindrical basin in the absence of radial barriers, a highly organized pattern of instability has been observed in the laminar Ekman layer along the bottom of the basin. The instability manifests itself in the form of almost perfectly concentric cylindrical sheets or curtains of water which rise as sharply defined vertical jets from the Ekman layer and penetrate the entire depth of fluid. A less sharply defined downward motion between the curtains completes the circulation celis thus developed. At some maximum critical radius, the curtains usually disappear, and the flow at larger radii is a stable, laminar Ekman flow. Quantitative observations of ring spacing and critical radius are reported for experiments in which angular velocity, flow rate, viscosity and total depth of water were varied over experimentally available ranges.