Time-Mean Structure of Axisymmetric Synthetic Jets

Actuators generating synthetic jets are currently receiving increased attention as very promising means for fluid flow control. Necessary for their design are methods for evaluation of time-mean spatial distributions of such quantities as velocity, fluctuation intensity, etc.. An exact analysis is extremely difficult due to the complexity of synthetic jets, which consist of mutually interacting and convoluted vortex rings surrounded by stochastic turbulence, into which they gradually decompose. In ref. [2], authors derived a successful, relatively simple model - in the form of a set of simple ordinary differential equations for similarity-transformed quantities. The solution depends on a dimensionless parameter, which must be found experimentally. In contrast to analogous situation in similarity solutions of other shear flows, the parameter instead of being a constant was found to vary along the jet. In [2], only two sets of experimental data were available for evaluating this variation. The model is corrected and made more reliable in the present paper on the basis of extensive additional experimental evidence. In particular, it is found that in synthetic jets there are two distinctly different regions, the one further downstream exhibiting turbulence structure properties similar - but not identical - to those of steady jets.