Synthetic jet for underwater flow control applications

Abstract

The formation, propagation, and interaction of vortex rings have been the subject of various researchers due to its wide application in nature and day-to-day life. Some of the important applications of vortex rings are volcanic eruption, propulsion of aquatic creatures, sewerage outfalls. As an active device, synthetic jet with a train of large scale coherent structures and zero net mass flow have many practical and industrial applications in flow control.A synthetic jet is generated using a simple cavity with a small orifice at one end and a deformable flexible diaphragm at the opposite end oscillating at different frequency and amplitude. It generates a series of vortex rings due to the changes in the cavity size with diaphragm oscillation. The vortex ring moves away from the orifice exit plane under the influence of self-induced velocity and thus synthesize a jet. Synthetic jet is also called zero net mass flux (ZNMF) system, the net mass transfer through the opening in one cycle is zero but the jet imparts a net transport of momentum to the surroundings.In this work, the aim is to study the characteristics of synthetic jet for various orifice shapes, actuation frequencies and diaphragm displacements. A series of experiments were performed to understand the behavior of circular and rectangular shape synthetic jet in quiescent flow environment. To achieve this, a synthetic jet generation unit mounted on the sidewall of water tank is used. Further, a torpedo shape model with built-in circularsynthetic jet has been designed and developed and the behavior of synthetic jet in crossflow has been investigated. For qualitative study, the bulk flow visualization and laser induced fluorescence (LIF) technique has been used whereas for quantitative measurement, the velocity is measured using hot-film anemometry and Laser Doppler Velocimetry (LDV). Circular orifices of 8, 10 and 13 mm diameter operating at actuation frequencies of 1, 2, 4 and 6 Hz have been used for characterization of circular synthetic jet generation.