<p>The synthetic jet actuator is a very promising candidate for active control of separated flows over airfoils. Commonly, the synthetic jet is introduced to the flow field via exciting a cavity to force an oscillatory zero-mass flow through an orifice and into the boundary layer region. The efficiency of synthetic jet in controlling a separated flow depends mainly on its capability of injecting higher momentum into the flow. Therefore, the effect of excitation frequency on the mean jet velocity of a synthetic jet is experimentally investigated in this work. In the present investigation, the focus has been placed on synthetic jets emanating from an array of circular orifices, rather than a single orifice, because of its applicability in covering a long-span airfoil. The array investigated in the present work consists of 16 circular orifices, having a 3.42 mm diameter each and covering a span of 300 mm. The jets are generated by exciting a unified cavity, of 300 mm length, via 16 piezoelectric elements. Hotwire measurements at the orifice exit show that the mean jet velocity varies with the excitation frequency. Several distinct resonant peaks were observed in the frequency response in the range of 300 to 2300 Hz, when excited by a 150 V excitation amplitude (peak-to-peak). Originally, it was thought that these peaks correspond to the Helmholtz resonance frequency and mechanical resonance of the piezoelectric elements, but the results showed several peaks. Acoustic simulations of the cavity showed that these peaks correspond to acoustic mode shapes of the cavity. Due to the high-aspect ratio of the cavity, several acoustic mode shapes exist&nbsp;in the excitation frequency range aside from the Helmholtz resonance frequency. Spanwise hotwire measurements above the orifices show a variation in the mean jet velocity that corresponds to the excited acoustic mode.</p>

Frequency Response of Synthetic Jets Emanating From an Array of Circular Orifices

Paper Proceedings: https://asmedigitalcollection.asme.org/FEDSM/FEDSM2021/volume/85284

ASME 2021 Fluids Engineering Division Summer Meeting (FEDSM2021)

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