Breakdown of steady and unsteady interacting boundary layers

Instabilities encountered in interacting boundary-layer calculations of steady flow past an indented plate, which might be related to the breakdown of the marginal separation, are identified as numerical. It is shown that the unsteady interacting boundary-layer approach delays Van Dommelen's singularity in the classical boundary layer around the impulsively started cylinder. The calculations show the experimentally known individualization of a vortex, after which the solution grows without reaching a steady limit; a process which is likely to be related to dynamic stall.