Jet Velocity and Acoustic Excitation Characteristics of a Synthetic Jet Actuator

Abstract

The effect of the excitation frequency of synthetic jet actuators on the mean jet velocity issuing from an array of circular orifices is investigated experimentally, focusing on the acoustic excitation characteristics of the actuator’s cavity. Two cavity configurations are considered. In the first configuration, synthetic jets are generated by exciting a single, large cavity having an array of sixteen orifices via sixteen piezoelectric elements. In the second configuration, the cavity volume of the first configuration is divided into eight isolated compartments, each with two orifices and two piezoelectric elements. Several distinct resonant peaks were observed in the frequency response of the synthetic jet actuator built with a single large-aspect-ratio cavity, whereas the case of compartmentalised cavities exhibited a single resonant peak. Acoustic simulations of the large-aspect-ratio-cavity volume showed that the multiple peaks in its frequency response correspond to the acoustic standing-wave mode shapes of the cavity. Due to its large aspect ratio, several acoustic mode shapes coexist in the excitation frequency range aside from the Helmholtz resonance frequency. When the actuator’s cavity volume is compartmentalised, only the Helmholtz resonance frequency is observed within the excitation frequency range.

Multiphysics Modeling of a Synthetic Jet Actuator in Operation

“…The noise generated by SJAs is maximized when the actuation frequency matches the Helmholtz frequency or the mechanical resonance of the diaphragm. Arafa et al [6] showed that at higher harmonics, noise generation could be lower at a minimal cost to the jet's performance. For the purposes of the current work, however, only frequencies near the Helmholtz frequency were considered.…”

“…Excessive noise generation can be a critical design drawback, especially in applications such as transportation, where noise reduction is a focus. Arafa et al [6] found that when designing SJA arrays, an excitation frequency away from the cavity acoustic modes should be used to ensure uniform mean jet velocity across the array. They achieved this target by dividing the SJA cavity into isolated sections.…”

Recent Advances in Fluid Mechanics: Feature Papers, 2022

“…In general, SJAs are smaller than an aircraft's wingspan, and as a result, they are used in an array form. Arafa et al [10] experimentally studied the effect of the excitation frequency of SJAs on the mean jet velocity issuing from an array of circular orifices. They focused on the acoustic excitation characteristics of the actuator's cavity.…”