Experimental Investigation of a Turbulent Jet Produced by an Oscillating Surface Actuator

A round turbulent water jet produced normal to, and at the center of a resonantly driven piezoceramic actuator is investigated experimentally. The flow is produced without mass injection and is comprised entirely of radially entrained fluid. The jet is created by the formation and disappearance of cavitation bubbles during each oscillation cycle near the actuator surface. It appears that this process produces a series of vortex puffs from radially entrained fluid which coalesce to form the jet. Although the jet results from strong time periodic excitation, its time averaged behavior in the far field is similar to that of a classical turbulent round jet in that the increase its width and decrease in the inverse of its centerline velocity are both linear functions of the distance from the actuator. The time periodic features of the jet are observed throughout the flow field and are superimposed on the mean flow. The transient characteristics of the jet have also been investigated and indicate that it can be manipulated on relatively small time scales suggesting that it may be utilized for control of wall bounded shear flows.