A synthetic jet device is a tool for generating a jet, and a synthetic jet actuator is a useful tool for active flow control. For separation control, it is necessary to clarify the periodic behavior of a synthetic jet. This study investigates the effect of excitation frequency f of a synthetic jet on the behavior of a vortex ring and the generation of a longitudinal vortex produced by the interaction between a jet and a crossflow. A significant difference was observed in the flow field for the synthetic jet issuing into the crossflow for f = 60 and 200 Hz. For f = 200 Hz, the propagated vortex rings were observed further downstream, and a longitudinal vortex was not generated. In addition, the vortex rings passed through the boundary layer. For f = 60 Hz, a longitudinal vortex produced by the interaction between the jet and crossflow was observed. It was confirmed that longitudinal vortices were observed for f = 60 Hz but not for f = 200 Hz. The generation of longitudinal vortices was affected by the excitation frequency of the synthetic jet.

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