Sensors and Actuators A 105 (2003) 229–236 Numerical simulation of micro-fabricated zero mass-flux jet actuators S.G. Mallinson a,∗ , C.Y. Kwok b , J.A. Reizes a a Faculty of Engineering, University of Technology Sydney, Broadway NSW 2007, Australia b Department of Electrical Engineering and Telecommunications, University of New South Wales, Kensington NSW 2052, Australia Received 5 July 2002; received in revised form 19 March 2003; accepted 23 March 2003 Abstract Computational fluid dynamics can play an important role in the design of microelectromechanical systems (MEMS)-based actuators, allowing an investigation of the underlying physical behavior of devices before proceeding to expensive manufacturing processes. Here, we present the results of a series of numerical simulations of synthetic jet actuators, so-called because they synthesize jets from the working fluid. The primary characteristic of these actuators is that over a cycle, the net mass flux is zero, yet the mean momentum flux is non-zero. The simulations consider both the internal and external flow-fields of a micro-scaled device, with the membrane motion specified using a simplified structural analysis. Key features of the flow in the external, orifice and cavity regions are presented and discussed. The actuator output is observed to vary linearly with a non-dimensional input parameter, and this may guide the design of flow control systems that use synthetic jet actuators. Finally, our fabrication strategy for a MEMS-based synthetic jet actuator is presented. © 2003 Elsevier B.V. All rights reserved. Keywords: Numerical simulation; Actuators; Fluid mechanics; Synthetic jets; Microfabrication 1. Introduction Microelectromechanical systems (MEMS)-based flow control devices have been proposed to improve the flow quality in a range of fluid mechanical systems [1,2]. Here, we employ computational fluid dynamics (CFD) to in- vestigate the flow produced by one of these devices, the synthetic jet actuator. This consists of a membrane located on one wall of a small cavity, which has an orifice in an- other face, typically opposite the membrane (see Fig. 1). The membrane is forced to oscillate, with fluid being ex- pelled through the orifice as the membrane moves upwards. The flow separates at the edge of the orifice, inducing a vortex ring that moves outwards under its own momentum. When the membrane moves downwards, fluid is entrained into the cavity. If the vortex ring is sufficiently distant from the orifice, it is not influenced by the entrainment of fluid into the cavity. Thus, over a single period of oscillation of the membrane, whilst there is zero net mass-flux into or out of the cavity, there is also a non-zero mean momentum flux. This momentum flux is, effectively, a jet that has been synthesized from the ambient fluid [3]. ∗ Corresponding author. Present address: Silverbrook Research, 393 Darling St., Balmain NSW 2041, Australia. Fax: +61-298-1867-11. E-mail address: sam.mallinson@silverbrookresearch.com (S.G. Mallinson). Micro-fabricated synthetic jet actuators have been the sub- ject of experimental investigation [4], however, earlier nu- merical studies of synthetic jet actuator flows have focused almost exclusively on macro-sized actuators. These studies employed either a wall normal boundary condition at the orifice exit plane [5,6], a pressure boundary condition at the bottom of the cavity [7], a moving piston [8–10], or a mov- ing membrane [11,12]; note that only the last of these ac- curately represents the physical situation, and that the other methods were used to simplify the computational problem. The wall normal boundary condition has been found to pro- vide very good agreement with experimental data in the far-field, where the jet seems to behave largely as a turbulent jet (see Fig. 2), but was unable to reproduce key features of the near-field flow. The studies that considered the cav- ity and orifice regions all predicted a similar outflow to that shown in Fig. 1. Here, we will employ the moving mem- brane boundary condition, as it more closely represents the physical situation than the other options. 2. Simulation methodology It was not possible to micro-fabricated circular geome- tries in our laboratories, and so we have chosen to use square cavities and orifices. To model the flow generated by such micro-fabricated synthetic jet actuators correctly would 0924-4247/$ – see front matter © 2003 Elsevier B.V. All rights reserved. doi:10.1016/S0924-4247(03)00204-8