SUMMARY

The dynamics of transitory flow attachment effected by pulsed actuation on the separated flows over a 2-D airfoil model are investigated experimentally. Actuation on time scales that are an order of magnitude shorter than the characteristic convective time scale is effected by momentary pulsed jets that are generated by a spanwise array of combustion-based actuators integrated into the airfoil. In the preliminary work, this flow control approach was applied to control of static and dynamic stall on a nominally 2-D airfoil. On a static airfoil, a single actuation pulse leads to a strong transitory change in the circulation about the airfoil that is manifested by severing of the separated vorticity layer and the subsequent shedding of a large-scale stall vortex. Successive actuation pulses extend the flow attachment and enhance the global aerodynamic performance. When the airfoil is undergoing time-periodic pitch oscillations beyond its static stall margin, staged actuation coupled to the airfoil’s motion can lead to an increase in lift over most of the cycle including at angles of attack that are below stall. The actuation also leads to enhanced pitch stability with reduced “negative damping” that are typically associated with the onset of dynamic stall.

The proposed research will focus on three-dimensional aspects of transient flow control on static and dynamically pitching 2-D airfoils. Of particular interest is the evolution of the interface between the actuated and unactuated flow domains and the formation of streamwise vorticity, and the corresponding time-dependent aerodynamic forces and moment. Various actuation schemes and the spanwise structure of the flow will be investigated using multi-plane PIV measurements.