Adaptive closed-loop separation controlon a high-lift configuration using extremum seeking

We present experimental results on adaptive closed-loop separation control on a 2-D generic high-lift configuration. Because model-based closed-loop flow control suffers from the lack of sufficient simple physical models for this configuration, a non-modell-based control strategy, namely, the gradient-based extremum-seeking scheme, is used here. The controller exploits spanwise distributed pressure measurements and adjusts pulsed jets near the leading edge of the single-slotted flap. The jets are used for flow excitation to suppress separation over the flap at high angles of attack, high deflection angles, or to reattach an already separated flow. Starting from a single-input/single-output design, the extremum-seeking scheme is extended to both a single-input/single-output slope-seeking approach and a multi-input/multi-output approach. Multi-input/multil-output control accounts for spanwise-distributed, small-scale separation phenomena and shows the best performance. Additionally, this case even improves lift gain compared to preliminary open-loop studies. A lift increase is not only observed for angles of attack for which the unactuated flow obviously separates, but as well for smaller angles, which were assumed before to lead to an unseparated flow. Hence, closed-loop results demonstrate the capability of slope-seeking control to adjust the control signal automatically in an energy-efficient sense such that separation is minimized even in the presence of disturbances.