Experimental Investigation of the Generation of a Longitudinal Vortex in a Transverse Synthetic Jet with Different Excitation Frequencies

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In this paper, experimental study was undertaken to investigate the effect of excitation frequency of a synthetic jet on the generation of a longitudinal vortex produced by the interaction between a jet and a crossflow in a wind tunnel. 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. A smoke flow visualization was used to reveal the characteristics of the vortical structures produced by the synthetic jet, and averaged vortical fields were also measured by using hot-wire anemometry during the entire cycle of issuing the synthetic jet. For f=60 Hz, the vortex rings were advected away from an orifice and was deformed. The position where the vortex ring broke down agreed with the position where the half-width of the jet velocity significantly increased. For f=200 Hz, the vortex rings showed wavy movements in the azimuthal direction, and therefore jet velocity profiles did not have a sharp peak in the near field of the orifice exit. A significant difference was observed in the flow field for the synthetic jet issuing into the crossflow for f=60 and 200 Hz. 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.