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Active control of the diffusion of a circular jet was attempted by application of a secondary film flow around the jet. Sinusoidal acoustic excitation of the film flow was carried out for VR values of 0.5 and 1.0, where VR is the ratio of the film flow velocity to the main jet velocity. For VR = 0.5, the diffusion of the jet was suppressed compared to that of a single jet but it was somewhat enhanced by the acoustic excitation. The acoustic excitation shortened the potential core of the jet; however, the entrainment of the ambient flow was far less than in the case of a single jet, regardless of degree of excitation. For VR = 1.0, diffusion was enhanced by acoustic excitation. Both turbulence intensity and ambient flow entrainment increased downstream of the jet. We conclude that film flow can control diffusion and that acoustic excitation can enhance the diffusion of jet flows. It is worth investigating this mechanism in detail in future studies.

An investigation was carried out into diffusion control for a circular jet using a concentric dielectric barrier discharge plasma actuator, focusing on the effects of electrode size, driving frequency and applied voltage. The actuator was found to induce a flow that was first directed toward the center of the jet, and that was then ejected along the jet central axis. The plasma-induced flow caused an increase in the velocity of the jet, allowing control of velocity fluctuations and the three-dimensional collapse of the jet structure. Increasing the size of the electrode led to an increase in both the volume flow rate and the width of the main jet. In contrast, a smaller electrode caused enhanced contraction of the jet. The results indicated that the actuator provided an effective means of controlling diffusion in the jet.

In this study, an attempt was made to control the diffusion of a round jet using a concentric dielectric barrier discharge plasma actuator. By changing the size of the electrodes, and the input frequency and voltage, it was confirmed that the jet diffusion characteristics could be controlled. By driving the plasma actuator, the induced flow was directed towards the central axis, and then ejected vertically from the wall. This lead to a velocity increase in the circular jet, which allowed control of velocity fluctuations and three-dimensional collapse of the jet structure. By changing the size of the electrode, it was possible to increase the volume flow rate of the main jet by the addition of the plasma induced flow. Decreasing the size of the exposed electrode caused enhanced contraction of the main flow. In contrast, larger electrodes caused the main jet to become wider.