Numerical experiments in separating and reattaching flows

We report high-order implicit large Eddy simulations of flows around flat plates with massive flow separation and reattachment. The aim is to provide evidence of the influence of relevant flow parameters such as the geometry of the leading-edge corner, the presence of a trailing-edge flow separation, and of a flow coupling between the two sides of the plate. The results reveal that flows with right-angled corners develop taller flow recirculations, which promote very-slow instability of the bubble itself. This large-scale unsteadiness is then found to be the basis of negative turbulence production mechanisms that in turn enhance the height of the bubble itself, thus closing a self-sustained cycle. The absence of these phenomena in flows with smooth leading-edge corners is also found to explain their high sensitivity to free-stream turbulence. The observed behaviors may have strong repercussions for theories and closures of separating and reattaching flows and should be carefully taken into account in control strategies used in the applications.