Spanwise Structures in a 2-D Synthetic Jet

A two dimensional isolated zero net mass flux jet, or synthetic jet, was investigated experimentally using Particle Image Velocimetry (PIV) and hot-wire anemometry. The evolution of counter-rotating spanwise coherent structures was explored for different jet orifice aspect ratios. Two synthetic jet configurations were tested, both driven by piezo-ceramic disks, for actuation frequencies of 300 and 917Hz, with various length- and time-scales, Reynolds numbers and several stroke lengths (between 5 to 50 times the slit width). The velocity and vorticity fields were measured in planes along and across the slit. Analysis of the spanwise extent of the jet demonstrates a unique flow pattern, where the flow near the jet exit plane is initially two-dimensional, while farther downstream the vortex pair lines develop secondary counter-rotating streamwise structures, where the streamwise and spanwise spacing between them vary with stroke length and formation frequency.