Vectoring of parallel synthetic jets: a parametric study

Abstract

The vectoring of a pair of parallel synthetic jets can be described using five dimensionless parameters: the aspect ratio of the slots, the Strouhal number, the Reynolds number, the phase difference between the jets and the spacing between the slots. In the present study, the influence of the latter four on the vectoring behaviour of the jets is examined experimentally, using particle image velocimetry. Time-averaged velocity maps are used to give a qualitative description of the variations in vectoring for a parametric sweep of each of the four parameters independently. A diverse set of vectoring behaviour is observed in which the resulting jet can be merged or bifurcated and either vectored towards the actuator leading in phase or the actuator lagging in phase. Three performance metrics are defined to give a quantitative description of the vectoring behaviour: the included angle between bifurcated branches, the vectoring angle of the total flow and the normalized momentum flux of the flow. Using these metrics, the influence of changes in the Strouhal number, Reynolds number, phase difference and spacing are quantified. Phase-locked maps of the swirling strength are used to track vortex pairs. Vortex trajectories are used to define three Strouhal number regimes for the vectoring behaviour. In the first regime, vectoring behaviour is dominated by the pinch-off time, which is written as function of Strouhal number only. In the second regime, the pinch-off time is invariant and the vectoring behaviour slightly changes with Strouhal number. In the third regime, given by the formation criterion, no synthetic jet is formed. Vortex positions at a single phase, shortly after creation of the lagging vortex pair, are used to propose a vectoring mechanism. This vectoring mechanism explains the observed qualitative and quantitative variations for all four parameters.

Jet vectoring using secondary Coanda synthetic jets

“…Furthermore, regarding the interaction of multiple jets, Berk et al (2016) experimentally investigated the vectoring behavior of a pair of parallel synthetic jets. Upon revealing that the vectoring of a pair of parallel synthetic jets is dominated by five parameters-the aspect ratio of the slots, Strouhal number, Reynolds number, phase difference between the jets, and spacing between the slots-they parametrically examined the influence of those parameters, neglecting the aspect ratio of the slots, on the vectoring behavior of the jets.…”

Interaction and vectoring of parallel rectangular twin jets in a turbulent boundary layer

“…Similarly, Berk et al (2016) experimentally observed that for two orifices close enough, the resulting jet from the interaction process can either be merged, bifurcated or vectored towards the actuator FIG. 1 Interactions between parallel synthetic jet actuators in quiescent flow, adapted from Luo and Xia (2008) and Berk et al (2016). (a) Enhancement mechanism which occurs in the absence of a phase difference between the two jets and (b) Vectoring mechanism associated with the introduction of a phase difference.…”

“…1b). Berk et al (2016) observed that the vectoring angle, γ, increased with phase difference up to the point where the merged jet becomes fully attached to the surface. When β is increased such that the jets are completely out of phase, a reduction in vectoring and flow rate is observed since the fluid ejected from one orifice is ingested into the adjacent orifice (Luo and Xia, 2008).…”

“…In the absence of a crossflow, two key parameters dictate the interaction and evolution of parallel synthetic jets: (i) the spacing between the orifices, s, and (ii) the phase difference between the jets, β (Berk et al, 2016;Luo and Xia, 2008;Smith and Glezer, 2005;Watson et al, 2003). In such a configuration, Luo and Xia (2008) found that the interaction between the jets lead to two types of mechanism based on the initial operating conditions, namely, an enhancing mechanism and a vectoring mechanism (Fig.…”

“…In spite of such pertinence, lim-ited literature is available on two or more parallel jets in a crossflow. There has been extensive research carried out in understanding the interaction of parallel twin jets in quiescent flow (Berk et al, 2016;Luo and Xia, 2008;Smith and Glezer, 2005) and twin jets arranged in an in-line configuration in a crossflow, i.e., the orifices are placed one behind another, in a linear pattern (Honami and Motosuke, 2012;Wen et al, 2015Wen et al, , 2016Yu et al, 2006). However, the added complexity of parallel jetjet interactions with a crossflow is still unexplored in a detailed and systematic parametric approach.…”