Dynamic Response of a Free Jet to the Activation of a Single Synthetic Jet

The transitory behavior of an axisymmetric free jet (Re U e = 6600) with a single synthetic jet, inclined at a 30° angle with respect to the main jet centerline, was investigated experimentally using PIV. The dynamic response of the main jet was measured immediately following the activation of the synthetic jet. The synthetic jet was driven at a frequency of 1000 Hz, which corresponds to a Strouhal number of 0.16 (within the range of unstable modes of the free jet). Three-dimensional flow renderings were calculated from multiple two-dimensional measurement planes to explore the complex three-dimensional flow field resulting from the interaction. Using this technique, it was shown that the transitory response is highly three-dimensional and occurs within the first four synthetic jet actuation cycles. Moreover, the synthetic jet's effect on the main jet flow field is felt throughout the measurement domain after only two synthetic jet cycles. Measurements of the streamwise vorticity showed that the interaction results in the formation of counter-rotating streamwise vortices that are formed on the side closer to the synthetic jet due to the bending of the main jet both inward and in the downstream direction. From these results, it can be inferred that the response of the main jet to the actuation is directly linked with the response of the synthetic jet to the activation signal.