Behavior Of Synthetic Jets Research Articles

Behavior of Synthetic Jets Generated by Stepped Shaped Slot

Behavior of Synthetic Jets Generated by Stepped Shaped Slot

Vector Control of Synthetic Jets Using an Asymmetric Slot

This paper presents a fundamental study on jet vectoring control by adjusting the dimensionless frequency of synthetic jets over time without changing the injection nozzle shape in actuators. This work involves the introduction of asymmetric slots with various sharp projection lengths in free synthetic jets for various actuator frequencies. The influences of the dimensionless parameters, sharp projection length C, and actuator frequency f* on the behavior of free synthetic jets are experimentally investigated under the same slot width b and Reynolds number Re = 990, and numerical simulations are performed to supplement these experiments. Furthermore, the behavior of synthetic jets is compared with that of continuous jets. The measurements of the velocities for both jet types are performed for the flow visualizations to observe the jet behaviors obtained using the smoke-wire method. The typical flow patterns and the time-averaged velocity distributions of the synthetic jets for various sharp projection lengths and dimensionless frequencies are demonstrated through the experiment. The influence of the dimensionless frequency on the stagnation point near a rigid wall when the inclined synthetic jets form a recirculation flow is also investigated. Furthermore, the degree of the bend of the jets is evaluated based on the change in the jet center's position at a reference downstream cross section. The results show that the jet direction of the synthetic jets induced by the asymmetric slots is related to both the dimensionless sharp projection length and the dimensionless frequency.

Observation of Behavior of Synthetic Jets in Asymmetric Flow Field

Observation of Behavior of Synthetic Jets in Asymmetric Flow Field

An experimental study on the behaviours of circular synthetic jets at low Reynolds numbers

In the work presented in this article, the behaviour of circular synthetic jets issuing into quiescent surrounding fluid at low Reynolds numbers is experimentally studied for potential mixing applications of synthetic jets at micro-scales or in highly viscous fluids. Sugar solutions and silicone oil are used as the flow media in order to achieve the required low Reynolds numbers. The conditions for jet instability, vortex rollup and synthetic jet formation are investigated using both flow visualisation techniques and particle image velocimetry, and the typical behaviour of synthetic jets at a Reynolds number around unity is also illustrated. The roles of Reynolds number, dimensionless stroke length and Stokes number in determining the characteristics of synthetic jets are examined and found to be largely consistent with the finding obtained at higher Reynolds numbers. Finally, a parameter map of synthetic jet flow patterns is produced based on the results from this study, which can be used to aid the choice of synthetic jet operating conditions for specific applications or anticipate if a desired vortex structure can be obtained at a given synthetic jet operating condition.

The behaviour of circular synthetic jets in a laminar boundary layer

AbstractDye flow visualisation of circular synthetic jets was carried out in laminar boundary layers developing over a flat plate at a range of actuator operating conditions and freestream velocities of 0·05 and 0·1ms–1. The purpose of this work was to study the interaction of synthetic jets with the boundary layer and the nature of vortical structures produced as a result of this interaction. The effects of Reynolds number (Re), velocity ratio (VR) and Strouhal number (St) on the behaviour of synthetic jets were studied. At low Re and VR, the vortical structures produced by synthetic jets appear as highly stretched hairpin vortices attached to the wall. At intermediate Re and VR, these structures roll up into vortex rings which experience a considerable amount of tilting and stretching as they enter the boundary layer. These vortex rings will eventually propagate outside the boundary layer hence the influence of the synthetic jets on the near wall flow will be confined in the near field of the jet exit. At high Re and VR, the vortex rings appear to experience a certain amount of tilting but no obvious stretching. They penetrate the edge of the boundary layer quickly, producing very limited impact on the near wall flow. Hence it is believed that the hairpin vortices produced at low Re and VR are likely to be the desirable structures for effective flow separation control. In this paper, a vortex model was also described to explain the mechanism of vortex tilting.

Dye visualisation of inclined and skewed synthetic jets in a cross flow

AbstractDye visualisation of both inclined synthetic jets and skewed synthetic jets was undertaken in a cross-flow experiment and the results were compared with those of normal synthetic jets. The process of vortex roll-up near the orifice exit and how the structure develops and interacts with the cross-flow as it propagates downstream was investigated so as to obtain an understanding of the effect of orifice orientation on the behaviour of synthetic jets. The effects of varying Reynolds number, velocity ratio and Strouhal number due to changes in diaphragm displacements and freestream velocities on the characteristics of synthetic jets were also examined. It is observed that in comparison to the normal jets vortical structures produced by both inclined and skewed jets tend to stay closer to the near wall region where maximum flow control effect is required. In both cases, at a relatively low Reynolds number and velocity ratio the active structures produced by the synthetic jet appear to be hairpin vortices which turn into vortex rings that migrate away from the wall as the Reynolds number and velocity ratio increase. These hairpin vortices are persistent in the near wall region hence are believed to be desirable structures for delaying flow separation.