Breakdown of boundary layers: (I) on moving surfaces; (II) in semi-similar unsteady flow; (III) in fully unsteady flow

Boundary layer breakdown and separation or reattachment are studied for the cases of moving surfaces, semisimilar unsteady flow, and fully unsteady flow. While in the moving surface case the classical steady boundary layer generally admits a logarithmic singularity in the displacement, when breakdown occurs on a downstream-moving surface, the corresponding singularity for an upstream-moving surface can be either logarithmic or of -1/6th form. In certain flows these singularities are locally removable, yielding a breakaway separation or reattachment. Other flows, by contrast, require an interactive strategy.