Flow control of a rectangular jet by DBD plasma actuators

The utility of a dielectric barrier discharge (DBD) plasma actuator as a spread controller for a rectangular jet was investigated in this study. A rectangular nozzle (75 × 10 mm) was used and actuators were placed on the longer sides of the nozzle exit. Unsteady actuation of actuators was achieved by changing the modulation frequency, duty ratio, and phase difference. Flow visualization and velocity measurements showed that the spread of the rectangular jet is controllable by the DBD plasma actuator. When the actuators are operated in the same phase, the jet width depends on the modulation frequency rather than on the duty ratio. The jet width becomes larger than the base case when the dimensionless modulation frequency is less than approximately 1.36. When the actuators are operated in the opposite phase, the jet width strongly depends on the duty ratio at a modulation frequency of less than approximately 0.682. The largest spread in x-y plane appeared when the dimensionless modulation frequency was 0.125; the duty ratio was 10%, and the phase difference was π. The modulation frequency was approximately equivalent to 1/8 of the natural frequency of the base case. In this scenario, an alternative vortex grows near the nozzle exit and the jet width in x-y plane becomes approximately 3 times larger than that of the base case. The smallest spread in the x-y plane appeared when the dimensionless modulation frequency was 1.59 and the duty ratio was 30%. Definite vortex shedding was suppressed and small-scale structures emerged near the nozzle exit. The jet width in the x-y plane was approximately 20% smaller than that of the base case.