Separated rows structure of vortex streets behind triangular objects

Kim, Ildoo

doi:10.1017/jfm.2018.993

Cited by 6 publications

(1 citation statement)

References 26 publications

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“…The flowing soap film channel [1][2][3] is an attractive tool of experiment in testing the formation, self-organization, and evolution of vortices in two-dimensional flow, because it is easy to handle, convenient to visualize, and inexpensive. Because of these advantages, there are many research papers using soap film channels to investigate various phenomena including the wake structure [5][6][7], fluid-structure interaction [8,9], and turbulence [10][11][12][13][14].…”

Section: Introductionmentioning

confidence: 99%

The effect of menisci on vortex streets on soap film flows

Kim

2023

Physics of Fluids

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In soap film experiments, the insertion of an external object is necessary to produce vorticity. However, this insertion causes local thickness changes, or simply meniscus, near the object. Because the meniscus formation may alter the flow near the object, the characterization of a meniscus is of considerable importance for the accurate interpretation of data. In this study, we insert cylindrical cones made of aluminum, titanium, and glass to measure the size of the menisci by using a long-range microscope. In all material tested, we find that the size of the meniscus is less than 0.2 mm, much shorter than the capillary length. In addition, by comparing the formation of vortex streets behind objects of different materials, we conclude that the meniscus acts as an added length to the size of the object itself. This added length effect can be non-negligible if the size of an object is comparable to the size of a meniscus.

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Section: Introductionmentioning

confidence: 99%

The effect of menisci on vortex streets on soap film flows

Kim

2023

Physics of Fluids

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Evolution of a quasi-two-dimensional shear layer in a soap film flow

Korlimarla

Vorobieff

2020

Physics of Fluids

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A quasi-two-dimensional shear layer is produced by merging two gravity-driven flows of soap film at different average velocities. The Kelvin–Helmholtz instability dominates the evolution of the shear layer, similar to what is observed in three-dimensional shear layers. However, the constraints that effectively limit the flow to two spatial dimensions have a considerable influence on the development of secondary instabilities and transition to turbulence. Nearly 40 cm downstream in the flow, two two-dimensional instabilities are observed, namely, vortex-pairing and secondary Kelvin–Helmholtz instability. The development of secondary instabilities and transition to turbulence in the flow is also affected by the interaction of the flowing soap film with boundary layers forming in the air surrounding the flowing soap film in the direction normal to the plane of the film. This becomes apparent when the flow is analyzed quantitatively in terms of the mixing interface length and fractal dimension. Initially, the mixing interface length grows exponentially with the downstream distance; however, beyond a certain distance, the growth stops. For the fractal dimension of the mixing interface in our quasi-two-dimensional shear layer, we have observed a peak value of 1.27 as compared to 1.34 reported in the literature for a corresponding section of a three-dimensional shear layer. For scales larger than ∼1 cm, interaction with air begins to dominate as the leading mechanism of dissipation. Coupling with boundary layers in air near the soap film drains energy from the large flow features and apparently “freezes” its evolution, producing “fossil” turbulence at large downstream distances.

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Stability of a reverse Karman vortex street

et al. 2021

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The reverse vortex street differs from the ordinary Karman vortex street in the direction of the rotation of the vortices. Such a street is formed behind the oscillating airfoils in the flow. It is of interest in connection with studies of the aerodynamics of flapping wings. It is known that the vortex wake behind a symmetric airfoil performing symmetric oscillations in a certain range of parameters becomes asymmetric, which leads to the appearance of a nonzero average lift. Reasons of the symmetry violation are associated with the instability of the reverse vortex street, but the mechanism of this instability is currently not well understood. In this work, the analysis of the stability of the reverse vortex street is carried out on the basis of the theory developed by Karman for infinite rows of point vortices. In contrast to the Karman model, in this work, semi-infinite rows with periodically arising new vortices at their ends are considered. This is the first time this model has been used. It is shown that the periodic appearance of new vortices radically affects the characteristics of the street stability. It is found that the violation of the symmetry of the reverse vortex street is associated with its instability to bending perturbations, while the ordinary Karman vortex street behind the body is unstable to varicose perturbations. Regions of instability are determined.

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Separated rows structure of vortex streets behind triangular objects

Cited by 6 publications

References 26 publications

The effect of menisci on vortex streets on soap film flows

The effect of menisci on vortex streets on soap film flows

Evolution of a quasi-two-dimensional shear layer in a soap film flow

Stability of a reverse Karman vortex street

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