Feedback control using extremum seeking method for drag reduction of a 3D bluff body

The flow around a modified Ahmed body with a curved rear section is studied at Re > 2. 10(6) and a line of vortex generators (VG) is used as actuators. By varying the angle a of the VG we observe an optimal value of a defining a minimum of aerodynamic drag and correspondingly a maximum base pressure coefficient. As this optimum value is shown to be Reynolds dependent we use an extremum control strategy for the system to find this optimal condition autonomously. It consists of the synchronous detection of the response measured in either the base pressure signal or in the drag and a slow sinusoidal modulation of the angle of the VG. It is finally demonstrated that the closed-loop system is robust and reacts successfully to unpredictable changes in the external flow conditions.