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Vectoring of parallel synthetic jets: a parametric study

Published online by Cambridge University Press:  09 September 2016

Tim Berk ,
Guillaume Gomit  and
Bharathram Ganapathisubramani
Tim Berk
Affiliation:
Aerodynamics and Flight Mechanics Research Group, University of Southampton, Southampton SO17 1BJ, UK
Guillaume Gomit
Affiliation:
Aerodynamics and Flight Mechanics Research Group, University of Southampton, Southampton SO17 1BJ, UK
Bharathram Ganapathisubramani*
Affiliation:
Aerodynamics and Flight Mechanics Research Group, University of Southampton, Southampton SO17 1BJ, UK
*
†Email address for correspondence: G.Bharath@soton.ac.uk
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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.

JFM classification

Flow Control: Flow Control Wakes/Jets: Jets Vortex Flows: Vortex interactions

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Type
Papers
Information
Journal of Fluid Mechanics , Volume 804 , 10 October 2016 , pp. 467 - 489
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Copyright
© 2016 Cambridge University Press 

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Berk et al. supplementary movie

Phase-locked vorticity map, showing vortex trajectories for the St = 0.02 case, corresponding to figure 7a.

Download Berk et al. supplementary movie(Video)
Video 1.2 MB

Berk et al. supplementary movie

Phase-locked vorticity map, showing vortex trajectories for the St = 0.06 case, corresponding to figure 7b.

Download Berk et al. supplementary movie(Video)
Video 1.3 MB