Laminar flow instability in a rectangular channel with a cylindrical core

Abstract

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 becomes turbulent, albeit preserving a quasiperiodic vortical structure. Within the present experimental range, the Strouhal number of the pulsations increases with increasing Reynolds number. The instability process is discussed in the context of previous analyses of low-speed streak instability of wall-bounded flows and transition to turbulence.