Momentum Coefficient as a Parameter for Aerodynamic Flow Control with Synthetic Jets

The influence of periodic excitation from synthetic jet actuators on boundary-layer separation and reattachment over a NACA 0025 airfoil at a low Reynolds number is studied. Flow-visualization results showed a vertical jet pulse accompanied by two counter-rotating vortices being produced at the exit of the simulated slot, with the vortices shed at the excitation frequency. Hot-wire measurements determined the maximum jet velocity for a range of excitation frequencies and voltages, and were used to characterize the excitation amplitude in terms of the momentum coefficient . With the synthetic jet actuator installed in the airfoil, flow-visualization results showed that excitation produces boundary-layer reattachment, with the associated significant reduction in wake width. Wake-velocity measurements were performed to characterize the effect of flow-control excitation amplitude and frequency on airfoil drag and wake topology. The results demonstrate that is the primary governing flow-control parameter. Applying excitation above a specific threshold produced a 50% reduction in drag, significantly affecting wake topology. However, power consumption of a piezoelectric synthetic jet actuator depends substantially on the excitation frequency. Hence, by varying excitation frequency, significant gains in efficiency are possible.