Vortex ring bifurcation and secondary structures in a finite-span synthetic jet

Straccia, Joseph; Farnsworth, John

doi:10.1017/jfm.2020.616

Cited by 6 publications

(1 citation statement)

References 56 publications

(167 reference statements)

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“…Similar to biological jetters, our vortex generator produces a nonlinear time-varying exit velocity profile and has a finite volume capacity, which limits the maximum stroke length that the device can attain more than in classical piston cylinder arrangements. It bears similarities with synthetic jet actuators (Lawson & Dawson, 2013; Shuster & Smith, 2007; Straccia & Farnsworth, 2020; Van Buren, Whalen, & Amitay, 2014). We experimentally study the vortex ring formation using time-resolved velocity field measurements.…”

Section: Introductionmentioning

confidence: 99%

Lagrangian analysis of bio-inspired vortex ring formation

Baskaran

Mülleners

2022

Flow

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Pulsatile jet propulsion is a highly energy-efficient swimming mode used by various species of aquatic animals that continues to inspire engineers of underwater vehicles. Here, we present a bio-inspired jet propulsor that combines the flexible hull of a jellyfish with the compression motion of a scallop to create individual vortex rings for thrust generation. Similar to the biological jetters, our propulsor generates a nonlinear time-varying exit velocity profile and has a finite volume capacity. The formation process of the vortices generated by this jet profile is analysed using time-resolved velocity field measurements. The transient development of the vortex properties is characterised based on the evolution of ridges in the finite-time Lyapunov exponent field and on local extrema in the pressure field derived from the velocity data. Special attention is directed toward the vortex merging observed in the trailing shear layer. During vortex merging, the Lagrangian vortex boundaries first contract in the streamwise direction before expanding in the normal direction to keep the non-dimensional energy at its minimum value, in agreement with the Kelvin–Benjamin variational principle. The circulation, diameter and translational velocity of the vortex increase due to merging. The vortex merging takes place because the velocity of the trailing vortex is higher than the velocity of the main vortex ring prior to merging. The comparison of the temporal evolution of the Lagrangian vortex boundaries and the pressure-based vortex delimiters confirms that features in the pressure field serve as accurate and robust observables for the vortex formation process.

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Section: Introductionmentioning

confidence: 99%

Lagrangian analysis of bio-inspired vortex ring formation

Baskaran

Mülleners

2022

Flow

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Probing dynamics of elliptical vortex rings via direct vorticity measurements with digital inline holography

Li,

Hong

2024

Exp Fluids

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Vortex–wall interactions in elliptic impinging synthetic jets

Xu,

Fan,

Wang

2024

Physics of Fluids

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Vortex structures and flow scenarios of noncircular vortex rings impinging onto walls were studied by conducting a large eddy simulation. Three orifice aspect ratios, ARs = 3, 5, and 7, and six dimensionless orifice-to-wall distances, in the range H = 0.71–1.90, were considered for elliptic impinging synthetic jets. At H = 0.95–1.19, the results exhibit different flow scenarios from those of circular vortex rings, which directly interact with the wall to produce a secondary vortex ring. New scenarios are attributed to mutual interactions between the primary vortex ring, the arc-shaped vortex, the wall, and the arc-shaped vortex is unique to noncircular vortex rings. These scenarios are further divided into two categories depending on whether the primary vortex ring can merge with the arc-shaped vortex, which is strongly affected by their separation distance and circulation ratio at the onset of vortex–wall interactions. For small separation distance and circulation ratio, the primary vortex ring swallows the arc-shaped vortex, leading to a strong crescent-shaped secondary vortex or a secondary vortex ring at different ARs. However, as the separation distance or circulation ratio increases, the interactions between the primary vortex ring and arc-shaped vortex weaken so that the latter escapes from entrainment by the primary vortex ring, leading to a weak crescent-shaped vortex. Finally, an AR-H map is constructed to illustrate the flow scenarios for all the cases. These findings provide new insights into the intricate dynamics of noncircular ring–wall interactions and may help us understand the heat transfer performance of noncircular impinging synthetic jets.

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Vortex ring bifurcation and secondary structures in a finite-span synthetic jet

Abstract: Abstract

Cited by 6 publications

References 56 publications

Lagrangian analysis of bio-inspired vortex ring formation

Lagrangian analysis of bio-inspired vortex ring formation

Probing dynamics of elliptical vortex rings via direct vorticity measurements with digital inline holography

Vortex–wall interactions in elliptic impinging synthetic jets

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