Calculations of unsteady turbulent boundary layers with flow reversal

The present studies relate to incompressible time-dependent flow over a two-dimensional surface which is flat or of large radius. The paper reports the results of a series of computational experiments aimed at studying the characteristics of time-dependent turbulent boundary layers with embedded reversed-flow regions. A calculation method, developed earlier by the authors and their co-workers, was extended to boundary layers with reversed flows for this purpose. The calculations were performed for an idealized family of external velocity distributions, and covered a range of degress of unsteadiness. The results confirmed those of previous studies in demonstrating that the point of flow reversal is nonsingular in a time-dependent boundary layer. However, a singularity was observed to develop downstream of reversal, under certain conditions, accompanied by the breakdown of the boundary-layer approximations.