The project will employ a multi-modal approach to study the flow physics and nonlinear dynamics of turbulent separation bubbles (TSBs), which occur when a turbulent boundary layer (TBL) separates from the wall and reattaches further downstream. We will focus on both natural (unperturbed) as well as perturbed TSBs produced by an adverse pressure-gradient (APG), yet devoid of configuration-dependent curvature effects, with the particular objective of gaining physical insights required for the future development of efficient, flow-physics based control strategies. Our specific objectives are to employ: (1) wind-tunnel experiments to induce separation of a turbulent boundary layer (103 < Reθ < 104) and subsequent reattachment on a flat plate model; (2) simulations (DNS for Reθ < 500, wall-resolved LES for 500 < Reθ < 1500, and a new wall-modeled LES approach for Reθ > 1500) to provide data/insights that complement the experiments; (3) dynamical systems modeling employing Extended Dynamic Mode Decomposition and Resolvent Analysis to explore the flow-physics and nonlinear dynamics underlying the appearance and scaling of distinct time-scales observed; (4) explore various methods to perturb the TSB in a controlled manner to dissect the nonlinear dynamics. Studying the TSB under the effect of controlled perturbations will elucidate the mechanisms that generate and govern the observed breathing and shedding modes, reveal their nonlinear coupling, and provide strategies for future effective control efforts. In the current study, unsteady perturbations will be introduced by modulating the APG as well as oscillating a fence upstream of the separation point. Steady perturbations that modify the wall-streak spacing will also be employed to examine the effect of this feature on the dynamics of the TSB. Finally, sudden initiation and termination of the APG will be used to study the transient response of the TSB.