Control of Flexible 3-D Wing Bending Motion by Prescribed Spanwise Circulation*

Controlled interactions between a 3-D flexible wing and the embedding cross flow are explored in wind tunnel investigations for effecting tunable structural and aeroelastic characteristics to control its bending motion by regulating the spanwise aerodynamic loads using distributed bleed actuation.  Air bleed driven by pressure differences between the airfoil’s pressure and suction surfaces through surface ports and its interior and is regulated by surface louvers on the pressure surface. The effects of time varying sectional bleed on spanwise and streamwise vorticity concentrations over a 3-D flexible wing, their advection into its near wake, and the mechanisms of spanwise spreading of the response to the actuation are explored using high speed 2-D and stereo PIV measurements. The temporal variations of the spanwise vorticity flux over each of the pressure and suction surfaces are used to assess the effects of unsteady actuation on the circulation of the spanwise vorticity. The balance between spanwise concentrations of streamwise and spanwise vorticity in the near wake is used to evaluate the unsteady circulation as a surrogate of temporal and spatial variations of the load along the wing and their dependence on the applied actuation.