Non-harmonic excitation of synthetic jet actuators based on electrodynamic transducers

An axisymmetric synthetic jet actuator based on a loudspeaker was tested experimentally. The actuator was driven by a voltage waveform, whose shape was derived from a pulse-width modulated signal. With the duty cycle and frequency of the excitation voltage varied at a constant electrical input power level and fixed nozzle diameter, the momentum flux of the jet (the jet thrust) was measured using precision scales. The maximum of the measured momentum flux was found at the optimum driving frequency and the duty cycle. This experiment was repeated for several input power levels and nozzle diameters, and the resultant optimal driving configurations were compared with adequate results for a harmonically driven actuator with identical geometry. Based on a newly introduced dimensionless nozzle diameter, a criterion was found that states conditions under which it is advantageous to use the suggested non-harmonic excitation.