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In this study, a disk-type bluff body was installed at the upper part of a nozzle exit, and the circular jet inside the nozzle was controlled using a dielectric barrier discharge (DBD) plasma actuator (DBD-PA). The effects of the changes in the excitation frequency of the jet induced by the DBD-PA on the jet diffusion were elucidated. The experiments included visualization of the jet cross-section, particle image velocimetry analysis, and velocity measurements using an I-type hot-wire anemometer. When the DBD-PA was driven at a specific burst frequency (900–1400 Hz), a lock-in phenomenon occurred, in which the frequency of vortices generated in the initial jet coincided with the burst frequency. This lock-in phenomenon suppressed the merging of vortices by generating vortices at regular intervals. When vortex merging was suppressed, the jet was less likely to be entrained into the recirculation flow generated by the bluff body, thereby increasing the downstream jet width and average flow rate.

In this study, two dielectric barrier discharge plasma actuators (DBD-PAs) are driven at different times to control a circular jet flow. DBD-PA was installed inside a nozzle and on a disk-shaped bluff body above the nozzle. A vortex was generated in the jet using DBD-PA in the nozzle, and the development of the vortex was controlled using the DBD-PA installed in the disk-shaped bluff body above the nozzle. The two DBD-PAs were driven with a time lag based on the time the vortex reached the bluff body. The findings reveal that the vortices did not pair with each other when the DBD-PA of the bluff body was slightly delayed from the timing of the occurrence of the vortex on the circulating flow side. When the vortices did not pair, the flow was not entrained in the circulating flow, causing the jet width to widen. The vortices paired with each other when the DBD-PA of the bluff body was driven at the same time as or long after the occurrence of the vortex on the circulating flow side. When the vortex pair with each other, they collapse quickly after pairing, and the jet width narrows, as the flow is entrained in the circulating flow. The difference in jet width downstream of the bluff body was found by driving the two DBD-PAs installed inside the nozzle and on the bluff body at different times.

In this study, a double-tube burner nozzle with a DBD-PA (dielectric barrier discharge plasma actuator) and flame holder was employed to regulate the lifted flame. The flame holder held the lifted flame and the DBD-PA regulated the lifted flame to suppress the lifted flame’s vertical oscillation. To form a lifted flame, pseudo-biogas, a mixture of CH4 and CO2 in the ratio of 6:4, was jetted out through an inner nozzle and air through an annular nozzle. To control the air jet and prevent the lifted flame’s vertical oscillation, the DBD-PA was installed inside an annular nozzle. The DBD-PA was driven intermittently at regular intervals to produce a tangential flow in the same direction as the jetting gas, and the flame holder was placed above the nozzle outlet on the nozzle center axis. The finding indicated that by driving the DBD-PA at the slightly lower frequency than the frequency of the naturally shedding vortices in the free jet, the lifted flame’s vertical oscillation can be reduced by collapsing the jet’s vortex ring at a steady position and with a steady cycle. By impeding the lifted flame’s vertical oscillation, it is forecasted to reduce the blowout of the lifted flame and combustion noise.