Closed-loop flow control of the oscillations of a free-suspended cylinder at low Reynolds numbers

Helicopters carrying slung loads are plagued by problems in flight stability at moderate speeds. The slung load oscillations are detrimental at full scale flight conditions. The unstable oscillations translate to mission trade-offs and therefore are of interest to overcome. Active flow control technology presents a unique ability to create the necessary aerodynamic stability at low cost, weight, complexity, energy and size. This study is focused on reducing the natural oscillations of a scaled model of a cylindrical slung load suspended in a wind tunnel. The research employs Fluidic-piezoelectric actuators to accomplish the stated objective. The dynamics of the baseline, scaled, uncontrolled model are in good agreement with flight test data. The yaw oscillations characteristics are compared with a spectrum of closed-loop control configurations that were designed and implemented over a range of tunnel speeds. Each configuration commands the actuators to induce fluidic excitation through two miniature openings at the cylinder summit near the side-edges of the finite span cylinder. The experiments demonstrate the feasibility of the solution, presents detailed data and discusses the utility of the technology to solve real world challenges. Future research and application path are also discussed.