Resolvent-analysis-based design of airfoil separation control

We leverage LES and resolvent analysis to design active separation control on a NACA 0012 airfoil. Spanwise-periodic flows over the airfoil at Reynolds number of 23000 are considered at an AoA of 9 deg. Localized unsteady thermal actuation is introduced near the leading edge in an open-loop manner. To provide guidance for effective control, we conduct resolvent analysis on the baseline turbulent mean flow to identify the actuation frequency and wavenumber that provide high energy amplification. The present study also considers the use of a temporal filter (discounting) to limit the time horizon for assessing the energy amplification to extend resolvent analysis for 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. In control cases that achieves full reattachment, we observe drag reduction by up to 49% and lift enhancement by up to 54%.