We combine three-dimensional (3D) large-eddy simulations (LES) and resolvent analysis to design active separation control techniques on a NACA 0012 airfoil. Spanwiseperiodic flows over the airfoil at a chord-based Reynolds number of 23, 000 and a freestream Mach number of 0.3 are considered at two post-stall angles of attack of 6 β’ and 9 β’ . Near the leading edge, localized unsteady thermal actuation is introduced in an open-loop manner with two tunable parameters of actuation frequency and spanwise wavelength. For the most successful control case that achieves full reattachment, we observe a reduction in drag by up to 49% and increase in lift by up to 54%. To provide physicsbased guidance for the effective choice of these control input parameters, we conduct global resolvent analysis on the baseline turbulent mean flows to identify the actuation frequency and wavenumber that provide high energy amplification. The present analysis also considers the use of a temporal filter to limit the time horizon for assessing the energy amplification to extend resolvent analysis to unstable base flows. We incorporate the amplification and response mode from resolvent analysis to provide a metric that quantifies momentum mixing associated with the modal structure. By comparing this metric from resolvent analysis and the LES results of controlled flows, we demonstrate that resolvent analysis can predict the effective range of actuation frequency as well as the global response to the actuation input. Supported by the agreements between the results from resolvent analysis and LES, we believe that this study provides insights for the use of resolvent analysis in guiding future active flow control. 4 Case 6-1A βC D = β41%, βC L = +5.1% Case 6-2A βC D = β43%, βC L = +1.2% Case 6-4A βC D = β36%, βC L = +11% 6 Case 6-1B βC D = β40%, βC L = +7.8% Case 6-2B βC D = β44%, βC L = β2.2% Case 6-4B βC D = β41%, βC L = +0.3% 12 Case 6-1C βC D = β38%, βC L = +2.8% Case 6-2C βC D = β37%, βC L = +0.3% Case 6-4C βC D = β30%, βC L = β2.4% 15 Case 6-1D βC D = β2.2%, βC L = +0.4% Case 6-2D βC D = β2.8%, βC L = β0.4% Case 6-4D βC D = +2.8%, βC L = β4.1% 2 Case 9-0A βC D = β35%, βC L = +39% Case 9-1A βC D = β19%, βC L = +28% Case 9-2A βC D = β17%, βC L = +29% 5.5 Case 9-0B βC D = β35%, βC L = +16% Case 9-1B βC D = β38%, βC L = +47% Case 9-2B βC D = β37%, βC L = +53% 12 Case 9-0C βC D = β43%, βC L = +28% Case 9-1C βC D = β46%, βC L = +41% Case 9-2C βC D = β49%, βC L = +37% 16 Case 9-0D βC D = β1.7%, βC L = β3.5% Case 9-1D βC D = +1.9%, βC L = β3.0% Case 9-2D βC D = +0.7%, βC L = β7.4%