Changes in the flow regime between a stationary disk and a rotating disk

The principal results of an experimental study, which show that the flow between two (stationary and rotating) coaxial disks has a boundary-layer-type structure near each of the walls (a Cochran boundary layer on the rotating disk and a Boedewadt boundary layer on the stationary disk), and which allow the determination of a critical instability or transition range, are presented and discussed. The fluctuation rate of the radial and azimuthal components of a velocity vector is measured by laser velocimetry, and the local mass-transfer coefficient is determined by a polarographic technique. It is shown that significant velocity fluctuations exist near the stationary wall, whether or not there is flow instability in the vicinity of the rotating disk.