Direct Numerical Simulation of Non-Linear Transitional Stages in an Experimentally Investigated Laminar Separation Bubble

This paper details a joint numerical and experimental effort to investigate a transition process in a laminar separation bubble, with the emphasis being put on the numerical contribution. A laminar separation bubble is formed if a laminar boundary layer separates in a region of adverse pressure gradient on a flat plate and undergoes transition, leading to a reattached turbulent boundary layer. Development of disturbances during the transition process in such a separation bubble is studied by means of direct numerical simulation with controlled disturbance input. Focus is put on the stage of non-linear development of these perturbations, for which a detailed comparison between numerical and experimental results is given. Beside physical phenomena like shear-layer roll-up and vortex shedding, computational aspects such as the performance of the numerical code on supercomputers are treated.