The Effect of C-D Riblets on the Shed Vorticity of an Unsteady Wing

When birds flap their wings, separated flow structures such as leading- (LEV) and trailing-edge vortices (TEV) are manipulated to enhance flight. The herringbone pattern on bird feathers is speculated to aid control of shed flow structures. Bio-inspired Converging-Diverging (C-D) riblets have been applied to attached wall flows in which spanwise circulation promoted fluidic mixing and energy transfer between the near-wall region and the freestream. No evidence of how this phenomenon affects the characteristics of separated flow structures has been presented in literature. We aim to address this gap by applying C-D riblets on an unsteady airfoil. Smooth and riblet textured NACA 0012 airfoils are actuated in water to achieve dynamic flow separation. LEVs and TEVs shed by the airfoil are tracked using particle image velocimetry. We hypothesize that the momentum mixing effect of C-D riblets and variation of actuation parameters can be leveraged to modify the size, strength, and circulation of shed vorticity. Work in passive flow control has made great strides; however, literature is devoid of content regarding unsteady wing maneuvers. We seek to address this gap and provide a stepping-stone for applications in low-Re flight and bio-inspired flows.