An experimental study on the behaviours of circular synthetic jets at low Reynolds numbers

In the work presented in this article, the behaviour of circular synthetic jets issuing into quiescent surrounding fluid at low Reynolds numbers is experimentally studied for potential mixing applications of synthetic jets at micro-scales or in highly viscous fluids. Sugar solutions and silicone oil are used as the flow media in order to achieve the required low Reynolds numbers. The conditions for jet instability, vortex rollup and synthetic jet formation are investigated using both flow visualisation techniques and particle image velocimetry, and the typical behaviour of synthetic jets at a Reynolds number around unity is also illustrated. The roles of Reynolds number, dimensionless stroke length and Stokes number in determining the characteristics of synthetic jets are examined and found to be largely consistent with the finding obtained at higher Reynolds numbers. Finally, a parameter map of synthetic jet flow patterns is produced based on the results from this study, which can be used to aid the choice of synthetic jet operating conditions for specific applications or anticipate if a desired vortex structure can be obtained at a given synthetic jet operating condition.