Experimental closed-loop control of flow separation over a plain flap using slope seeking

Abstract

Slope seeking control is implemented to suppress flow separation occurring on a plain flap progressively deflected at $$Re_{\mathrm{c}}=2\times 10^{6}$$ . The flap is equipped with pulsed blowing slots that are actuated by a square signal whose duty cycle is adapted by the so-called slope seeking algorithm in order to minimise the injected momentum while maintaining the flow attached whatever the flap deflection angle. Thirteen hot-film sensors are chordwise distributed on the flap. They measure the wall shear stress fluctuations that are used to calculate in real time a series of correlation coefficients. This method constitutes a way to determine whether the flow is separated or not within the context of flow separation control. Finally, a modification of basic slope seeking algorithm is proposed to improve its convergence rate without compromising stability.