A PIV study of synthetic jets with different orifice shape and orientation

PIV measurements have been undertaken on synthetic jets with rectangular orifices of different aspect ratios and circular orifices of different inclination angles in quiescent conditions. The results were compared with those from normal circular synthetic jets so as to examine the effects of orifice shape and orientation on the characteristics of synthetic jets. The results show that increasing aspect ratio leads to an initially higher axial velocity at the exit of the orifice. Although the synthetic jet with a high aspect ratio appears to be two-dimensional when they just form, they are highly unstable and experience subsequent "axis swapping" between the major and minor axis of the jet. It is also found that an increase in orifice inclination angle results in a higher jet exit velocity and more asymmetrical roll-up of vortex rings which undergo rapidly self reorganization to form axisymmetric structures further downstream. Overall, although synthetic jets with a higher aspect ratio or inclination angle possess higher initial momentum and vorticity than equivalent normal circular jets, this additional energy tends to be dissipated rapidly due to the need for the distorted vortex rings to rearrange themselves into more stable structures. Further investigations will be carried out to extend the present study to boundary layers and separated flows so as to assess the potential of rectangular jets and inclined jets in producing more effective flow structures that can delay flow separation on high lift systems. © 2004 by University of Manchester.