Synthetic jet flow
A synthetic jet is a pulsating jet flow actuated by an oscillating diaphragm. The device consists of a membrane (such as that of a speaker), cavity, and orifice, as shown in Figure 1 (a). In suction phase, external fluid enters the cavity, then in the blowing phase it is released through the orifice and forms a propagating vortex ring with a trailing jet. (Figure 1b) Synthetic jets have an interesting feature of being able to generate linear momentum flux without net mass flux. Due to the pulsating flow characteristic with large-scale coherent structures, synthetic jet devices have shown good performance in active flow control (e.g. lift generation, drag reduction, and separation control) and heat transfer enhancement (e.g. impingement cooling). We have investigated the flow structure of free and impinging synthetic jets with regards to various characteristic parameters such as Reynolds number and dimensionless stroke length. Phase-locked particle image velocimetry (PIV) is used to analyze the phase-averaged flow fields and vortex dynamics. We are also examining the interaction of multiple synthetic jets.
Figure 1. (a) Schematic diagram of synthetic jet actuator and (b) vorticity contours by Q-criterion [1].