Experimental study of the formation and scaling of a round synthetic jet

Abstract

The flow field from a piston-cylinder synthetic jet actuator was investigated in detail over a range of dimensionless stroke values, L∘∕D∘, and Reynolds numbers, ReU∘. In each of the test flows examined, only one of these dimensionless groups was varied. The flow fields were examined using particle image velocimetry measurements in a plane bisecting the jet. A slug flow model was used to determine scaling parameters for the jet flow field. In the near-field of the orifice, the flow was dominated by the vortex ring formed during the expulsion phase of the actuator cycle, and the flow field scaled exclusively on the actuator stroke, L∘. For distances from the orifice greater than L∘, the flow field resembled a conventional, round turbulent jet. The resemblance was not complete as the synthetic jet had a faster spreading rate with a correspondingly more rapid decline in the mean centerline velocity. The dimensionless jet momentum was comparable at the higher stroke values for the same Reynolds numbers, and the jet momentum increased with Reynolds number. It is apparent from this work that the slug flow model provides suitable scaling parameters for the near- and far-field regions of a synthetic jet flow. Moreover, the study conclusively demonstrates that the dimensionless stroke, L∘∕D∘, uniquely identifies a synthetic jet flow.