Further studies of unsteady boundary layers with flow reversal

One set of calculations was performed using the first order, time dependent turbulent boundary layer equations, and extended earlier work by Nash and Patel to a wider range of flows. Another set of calculations was performed for laminar flow using the time dependent Navier-Stokes equations. The results of the calculations confirm previous conclusions concerning the existence of a regime of unseparated flow, containing an embedded region of reversal, which is accessible to first order boundary layer theory. However, certain doubts are cast on the precise nature of the events which accompany the eventual breakdown of the theory due to singularity onset. The earlier view that the singularity appears as the final event in a sequence involving rapid thickening of the boundary layer and the formation of a localized region of steep gradients is called into question by the present results. It appears that singularity onset is not necessarily preceded by rapid boundary layer thickening, or even necessarily produces immediate thickening.