Suppression of fluctuating lift on a cylinder via evolutionary algorithms: Control with interfering small cylinder

A generalized model-free method to optimize parameters for open-loop and closed-loop control in fluid mechanics applications is presented. A multi-objective evolutionary algorithm (MOEA) is employed to minimize the oscillating lift caused by vortex shedding from a cylinder of diameter D via the insertion of a secondary control cylinder of diameter D/8. The first objective of the algorithm is to minimize the fluctuating force coefficient $CLRMS$⁠, while the second objective is to minimize the actuation power required to drive the control cylinder. Experiments are carried out in a free surface water channel at Re_D = 12 500 and verified for robustness to changes in Reynolds number at Re_D = 17 000. The control cylinder is prescribed a position as well as a periodic sinusoidal motion in two dimensions. The MOEA efficiently handles the larger optimization parameter space, with the final solution suppressing $CLRMS$ by over 90% using near-zero actuation power. Further, the MOEA inherently provides a sensitivity study as to the influence of the different parameters and also in which spatial area the greatest influence is expressed. The dynamics of the optimal suppression case are compared to those of the baseline case (no control cylinder) using phase averaged and mean particle image velocimetry and direct force measurements.