The mixing layer perturbed by dielectric barrier discharge

The effects of dielectric barrier discharge (DBD) plasma actuators on a low-speed incompressible turbulent mixing layer are studied experimentally. Both alternating current (ac) and nanosecond (ns) pulse driven plasma are examined in an effort to elucidate the control mechanism for each actuator as well as the general physics governing momentum versus thermal perturbations. Boundary layer suction is employed to analyze the influence of initial conditions on each method. The efficacy of ac-DBD plasma actuators, which function through electrohydrodynamic effects, is found to be dependent on initial mixing layer conditions and frequency. Forcing waveform and amplitude also play a significant role, but are held constant here. Results qualitatively agree with previous literature employing mechanical flaps and sinusoidal waveforms showing the validity of the experiment. Ns-DBD plasma, which is believed to function via thermal effects, is found to produce a slight stabilizing effect that is accompanied by weak fluctuations of the most amplified frequency. The stabilization is unexpected and primarily dependent on the initial conditions and plasma on-time since the employed forcing frequencies behave similarly. These effects are only observed in burst mode forcing. No measureable changes are found using single pulse forcing. The ns-DBD generated pressure waves seem to have no effect on the mixing layer growth. In the context of past studies this suggests that the efficacy of ns-DBD plasma actuators, and likely thermal perturbations in general, is heavily dependent on the scale of energy deposition relative to the initial shear layer conditions. Accordingly, typical amplitude scaling arguments in flow control must be refined for energy deposition actuators.