Evolving strategies for active flow control

About fourty years ago – according to (Rechenberg, 1994) – Rechenberg and Schwefel came up with the idea of evolution strategies for flow optimization. Since then advances in computer architectures and numerical algorithms have greatly decreased computational costs of realistic flow simulations, and today Computational Fluid Dynamics (CFD) is complementing flow experiments as a key guiding tool for aerodynamic design. Of particular interest are designs with active devices controlling the inherently unsteady flow fields, promising potentially drastic performance leaps. Here we demonstrate that CFD-based design of active control strategies can benefit from evolutionary computation. We optimize the flow past an actively controlled circular cylinder, a fundamental prototypical configuration. The flow is controlled using surface-mounted vortex generators; evolutionary algorithms are used to optimize actuator placement and operating parameters. We achieve drag reduction of up to 60 percent, outperforming the best methods previously reported in the fluid dynamics literature on this benchmark problem.