Experimental detection of a periodically forced turbulent boundary layer separation

Wind tunnel experiments are conducted to investigate the effect of periodic blowing over a non-slotted NACA-type flap equipped with seven pulsed slots. The tests are performed at Re ≃ 3 × 106 for different deflection angles ranging from 2° to 35°. Wall-mounted hot-films are chordwise distributed on the flap. The purpose of the experiments is to assess the ability of wall shear stress signals to detect flow separation with and without periodic control, and to be used as reliable feedback information in a closed-loop control framework. Laser beam tomoscopy is first used to visualize flow structures with and without flow control. Two separation criteria based on higher-order statistical moments of hot-film signals are proposed to detect flow separation. They present the advantage of being independent of the free-stream velocity. The two criteria are finally practised to follow the steady-state response of the system and determine its static map local gradient.