Acoustical analysis of sound generated by synthetic jet actuators

Piezoelectrically driven synthetic jet actuators (SJA) are useful in various applications such as flow control, heat transfer and camera lens cleaning. This paper aims to better understand the fundamental sound generation mechanisms of synthetic jet actuators and investigate methods for the noise reduction and vibration control. The SJAs tested in this paper are driven by sinusoidal signals at frequencies ranging between 100 and 600 Hz, and can produce pulsated air jets at high velocity, up to 100 m/s. The sound generated by these devices, generally tonal and rich in harmonics, was modeled as the superposition of two monopoles associated with the breathing mode of the diaphragm and of the pulsated jet. Component analyses showed that the two monopoles cancelled each other partially depending on their amplitudes and phase relationship. A computational aeroacoustic model of the SJAs was built using PowerFLOW, a computation fluid dynamic simulation software. Simulation results were compared with jet velocities measured with a hot-wire anemometer and flow patterns were analyzed. Active and passive control methods were investigated, and a sound quality analysis was performed in order to reduce the overall radiated sound power and improve sound quality.