Novel quadruple synthetic jet device: Flowfield and acoustic behavior

This paper reports on an experimental investigation of the flowfield and acoustic behavior of an innovative quadruple synthetic jet device operated in different configurations. The device consists of four resonant cavities, each driven separately by a loudspeaker in such a way that it is possible to implement any configuration in terms of the frequency, amplitude, and initial phase angle of the exit velocities of the four embedded jets. Here, the main goal is to investigate the effect of varying the phase delay between the ejection strokes of the single synthetic jets. At first, a calibration procedure of the driving signals is designed in order to ensure that the four jets have the same exit conditions, except for a desired phase shift. Second, four different configurations are investigated at fixed values of the Reynolds and Strouhal numbers of each synthetic jet, equal to 4000 and 0.2, respectively. Stereoscopic particle image velocimetry measurements highlight the central role of the near-field large-scale coherent vortex structures in determining the flow behavior. Far-field noise measurements show that, by introducing a phase shift between the jet exit velocities, a significant noise reduction can be obtained (up to 23.9% for the examined configurations).