Formation Criterion for Synthetic Jets

TitleFormation Criterion for Synthetic Jets
Publication TypeJournal Article
Year of Publication2005
AuthorsHolman, R., Y. Utturkar, R. Mittal, B. Smith, and L. Cattafesta
JournalAIAA Journal
Date PublishedOCT

A formation criterion for synthetic jets is proposed and validated. A synthetic jet actuator is a zero-net mass-?ux device that imparts momentum to its surroundings. Jet formation is de?ned as the appearance of a time-averaged outward velocity along the jet axis and corresponds to the generation and subsequent convection or escape of a vortex ring. It is shown that over a wide range of operating conditions synthetic jet formation is governed by the jet Strouhal number Sr (or Reynolds number Re and Stokes number S). Both numerical simulations and experiments are performed to supplement available two-dimensional and axisymmetric synthetic jet formation data in the literature. The data support the jet formation criterion 1/Sr = Re/S2 > K, where the constant K is approximately 1 and 0.16 for two-dimensional and axisymmetric synthetic jets, respectively. In addition, the dependence of the constant K on the normalized radius of curvature of a rounded ori?ce or slot is addressed. The criterion is expected to serve as a useful design guide for synthetic jet formation in ?ow control, heat transfer, and acoustic liner applications, in which a stronger jet is synonymous with increased momentum transfer, vorticity generation, and acoustic nonlinearities.