Spectral analysis of a synthetic jet

In their earlier publications, the present authors discovered a phenomenon, previously not reported, of sudden substantial change in the character and structure of axisymmetric synthetic jets that occurs at the relative axial distance X1*/d∼50. The hypothesis suggested for explanation was the change being associated with the transition from the regime dominated by coherent vortical structures into the flow dominated by stochastic turbulence. To validate the hypothesis, this paper presents frequency spectra at various locations in a synthetic jet generated at the forcing frequency ff = 30 Hz from a d = 4 mm nozzle. The results, a change in the character of the spectra, obviously do corroborate the idea. In addition, the performed analysis of the velocity spectra has lead to several previously not known facts about synthetic jets.