Laminar Boundary-Layer Response to Spanwise Periodic Forcing by Dielectric-Barrier-Discharge Plasma-Actuator Arrays

An extensive parametric study of the response of a Blasius boundary layer to forcing by spanwise arrays of plasma actuators was performed. The actuator arrays are designed to produce streamwise-oriented vortex pairs, which cause streaks of alternating low and high streamwise velocity. This work is motivated by the closed-loop control of bypass transition. The streaks are measured using hot-wire anemometry over a streamwise distance of approximately 100 boundary-layer thicknesses. The resulting spanwise periodic disturbance velocity is decomposed into spanwise Fourier modes. Typically, at least 90% of the disturbance energy is contained within a mode related to the spanwise spacing of the exposed electrodes and its first three harmonics. Along the streamwise direction, the growth and decay characteristics of the disturbance are considered for various actuator geometries, as well as excitation voltages and frequencies for a freestream velocity of 5m/s. The total disturbance energy is shown to scale with the actuator power consumption. Changes in the excitation voltage influence the energy distribution between Fourier modes due to the effect of voltage on the plasma extent and plasma-induced velocity, which changes the separation between vortices generated by the actuators. The induced disturbance is found to be most closely represented by a single Fourier mode when the electrode width is approximately one-third of the electrode spacing. For the other electrode width, significant energy appears at higher harmonics of the electrode spacing.