Effect of controlling the Large-Scale Motions on the Separation Region*

In wall-bounded turbulent boundary layer flows, a significant portion of the Turbulent Kinetic Energy (TKE) and Reynolds Shear Stress is carried by large spatial and temporal coherent structures. These structures are termed Large-Scale or Very Large-Scale motion (LSM/VLSM). They have the potential to increase near-wall mixing and re-energize the boundary layer if moved closer to the wall. In this work, we study the effect of targeted manipulation of LSMs and interaction with a separation region for separation delay. We employ direct numerical simulation of laminar boundary layer flow over a flat plate where we introduce LSMs modeled as a series of hairpin vortices. The simulations are performed with the synthetically generated hairpins as well as by using the velocity data from experimentally generated hairpins as an inflow condition. The LSMs are steered using a localized Gaussian force field which acts like an actuator that induces downwash to move them closer to the wall.