Coherent structures in a self-similar adverse pressure gradient turbulent boundary layer

The turbulence statistics and structures of a self-similar adverse pressure gradient turbulent boundary layer (APG-TBL) at the verge of separation are investigated using a direct numerical simulation (DNS). The desired self-similar APG-TBL is achieved by a modification of the far-field velocity boundary condition. The required wall-normal velocity in the far-field to produce the necessary adverse pressure gradient was estimated based on the analytical free-stream streamwise velocity distribution for a flow at the point of separation, and the assumption that the streamlines of the outer flow follow the growth of the boundary layer thickness. The APG-TBL develops over a momentum thickness based Reynolds number upto 12000, and achieves a self-similar region of constant friction coefficient, pressure velocity and shape factor. Turbulence statistics in this region show self-similar collapse when scaled by the external velocity and the displacement thickness. In this study, the coherent structures of a self-similar APG-TBL are investigated by using topological methodology and visualisation techniques.