Computation of the separation of steady and unsteady, incompressible, laminar boundary layers

The unsteady interacting boundary layer equations are integrated, and the effect on finite time singularities is investigated. It is shown that the unsteady interacting boundary layer description delays the appearance of the finite time singularity in the unsteady classical boundary layer solution of the impulsively started cylinder. The breakdown of the interacting solution is characterized by the unlimited growth of a peak in the displacement thickness, but the used meshsize and timestep are too small to decide whether its growth is singular at a finite time or only leads to an unbounded solution for t tends to infinity. The interacting solution for R = 100,000 shows the individualization of a vortex, which is not calculated in the classical solution. It is suggested that the finite time singularity in the classical solution is related to this rapidly growing vortex, which seems to characterize the violently unsteady transition of an unsteady attached flow layer close to the wall to an unsteady detached flow.