Understanding the interaction between unsteady streamwise vortices with a separated shear layer for novel flow control solutions.

Aircraft performance at high angles of attack, either during high-lift maneuvers or in gusty conditions is impacted by flow separation. Vortex generators have been widely used as a passive flow control solution to alleviate separation. Recent advances in active control provide opportunities for enhanced separation control, especially when the incoming boundary layer is unsteady or transitional. Understanding the interaction of unsteady disturbances with passive and active vortex generators, and the influence of the generated unsteady streamwise vortices with the dynamics of a separated shear layer and the separation bubble is key for advancing separation control. In this talk, we explore these questions in the well-studied setting of a backward-facing step. Large-eddy simulations are performed on a low to moderate Reynolds number inflow imposed with artificial disturbances representative of a transitional boundary layer and study their interaction, with passive and active vortex generators. The magnitude and frequency of forcing of the inflow and the active vortex generator are varied to generate different mean and the fluctuating components of the streamwise vorticity and the results are examined from a vorticity dynamics point of view.