Flow Characteristics and Novel Applications of Synthetic Jets - A Review

Synthetic jets, often abbreviated as 'SJs' or 'Synjets' are a type of Zero Net Mass Flux (ZNMF) jets which have gained popularity due to their ability to transfer momentum without transferring mass. This property distinguishes SJs from their counterpart traditional continuous jets. Over a stretch of time, SJs have been employed extensively in applications such as active flow control, impingement heat transfer, miniature electronics cooling, etc. However, researchers are now slowly extending the frontiers of SJ research and making efforts to utilize excellent properties of SJs in novel applications such as AUVs, marine systems, bio-inspired propulsion systems, etc. This paper strives to identify the gaps in the current research and the areas which have remained unexplored yet. The article begins with a discussion of the origin of SJs i.e. 'acoustic streaming'. The resulting segments talk about the formation criteria and the recent works employing various configurations of orifices and cavities. The paper discusses critical concepts such as JIF, volumetric efficiency, and propulsive efficiency of synthetic jets. It is followed by the introduction of novel flow control systems employing SJs such as gurney flaps, bumps, and electroactive synthetic jets. Finally, the most innovative applications of SJs such as AUVs, UAVs, jetting cavities. Pulsatile jet flows found in jellyfish, cephalopod, squid and salp have been discussed in great detail. The exhaustive discussion on future prospects strives not only to provide reader with comprehensive insights into SJs, but also to motivate future researchers to overcome the gaps identified in this paper.