Experiments in laminar flow in a rectangular channel containing a cylindrical rod have
revealed a flow instability in the form of weak pulsations across the gap between the rod and
the channel wall. The instability occurs when the Reynolds number reaches a critical value,
which increases as the gap diminishes. As the Reynolds number is increased, the
pulsations become stronger and develop, first into hairpin-shaped patterns, then into
quasiperiodic laminar vortices, which alternate on either side of the gap. Eventually, the flow …