Low Reynolds Number Flow Control Over an Airfoil Using Synthetic Jet Actuators

The influence of periodic excitation from synthetic jet actuators, SJA, on boundary layer separation and reattachment over a NACA 0025 airfoil at a low Reynolds number is studied. All experiments were performed in a low-turbulence recirculating wind tunnel at a Reynolds number of 100000 and angle of attack of α = 0°. Mounted just below the surface of the airfoil, the SJA consists of four (32.77mm diameter) piezo-electric ceramic diaphragms positioned in a single row. Flow visualization and hot wire tests were conducted with the SJA outside of the airfoil to characterize the exit flow. Results from flow visualization show 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. Based on flow visualization results, the length scales of successive vortices were used to estimate the exit velocities. Hot-wire measurements determined the maximum jet velocity for a range of excitation frequencies (f = 50H_z–2.7kHz) and voltages (V_p–p = 50V–300V), which was used to characterize the excitation amplitude in terms of the momentum coefficient (c_μ). With the SJA installed in the airfoil, preliminary flow visualization results show a reattachment of the boundary layer and a significant reduction in wake width.