Open-loop and closed-loop trailing-edge separation control on a natural laminar flow airfoil

Active Unsteady Flow Control experiments were performed on a Natural Laminar Flow, NLF 0414 airfoil at Re_c = 1.0 × 10⁶. The goal of this study was to control boundary-layer separation across the trailing-edge region of the airfoil in off-design conditions. Both open-loop and closed-loop control approaches were used. Active control of separation was achieved using a series of blowing slots at the x/c = 0.75 location. Open loop control parameters were varied across a parametric range of jet amplitudes, actuation frequencies and duty cycles and performance measurements were acquired to identify the effectiveness of these actuation schemes. PIV measurements were acquired across a horizontal plane near the trailing edge region of the model to understand the effects of actuation on flow separation and the vortex dynamics associated with unsteady actuation. A closed loop controller was developed to vary the actuation parameters in-situ using sensory feedback from the unsteady surface pressure measurements and adaptive modal decomposition methods. This closed-loop system was able to automatically control the extent of separation such that a desired value of C_l was obtained.