New Generation of Synthetic Jet Actuators

Abstract

I N the last 20 years, much attention has been given to developing microfluidic systems [1]. Among them, synthetic-jet actuators (SJA) have been intensely studied recently [2]. Synthetic-jet actuators have many potential applications such as jet vectoring [3,4], boundary-layer control [5,6], combustion control [7], and micro-pumps [8], etc. A synthetic-jet actuator is a zero net mass flux device. Figure 1a shows a typical structure of an existing SJA, which is composed of an exit slot (or orifice) and a diaphragm (or double diaphragms [9]) mounted to enclose a volume of fluid in a cavity. Piezoelectric (PZT) diaphragms are used in most minior microSJAs because of their size, rapid time response, and relatively low power consumption. The PZT-driven SJA also fits within the microelectromechanical system (MEMS) discipline and can be coupled with MEMS sensors, control and logic electronics into a single very lightweight and compact device. Unfortunately, the pressure loading limits to obtain a small deflection of the PZTdiaphragm on the existing SJA requires a high power to drive the PZT-diaphragm when the pressure differential between the base flow (to be controlled by the SJA) and the environment is large. This limits applications of the SJA. In addition, the diaphragm of the existing SJA (as shown in Fig. 1a) has one surface exposed to the fluid drawn from the base flow and the other surface exposed to the environment, which indicates that half of the radiation energy of the vibrating diaphragm is wasted in the environment. Keeping the advantages of a PZT-driven SJA,while resolving themajor problems of pressure loading and energy inefficiency, is the main impetus for designing a new generation SJA. A newSJA prototype is schematically shown in Fig. 1b. It consists of two cavities, a PZT-diaphragm, two exit slots, and a slide block (SB). In the new SJA concept, two adjacent jets are established under the two exit slots and are driven by the motion of the same PZTdiaphragm. The slide block regulates the two jets (as shown in Figs. 1b–1d), and then two adjacent jets merge into a single, larger synthetic jet. In this Note, numerical simulations are conducted to study the new SJA. We include a discussion focused on the novelty and merits of the new SJA in comparison with the existing SJAs.