Stability of finite and infinite von Kármán vortex-cluster streets

Maches, Z.; Bartley, E.; Borjon, J.; Carretero-González, R.

doi:10.1103/physreve.103.032205

Cited by 1 publication

(2 citation statements)

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“…The very early stability analysis of von Kármán, mentioned in § 1, indicated that a street composed of a staggered array of idealised point vortices was stable to first-order two-dimensional disturbances provided the ratio (a/b) of lateral to longitudinal spacing between them was 0.281. However, it was subsequently shown that this system is in fact unstable at the second order of approximation in the disturbance amplitude (Kochin 1939) but, more importantly, that the stability could be critically affected if the vortices are of finite size (and could change shape); see, for example, Saffman & Schatzman (1982) and Maches et al (2021). Such analyses were all in the context of an irrotational, uniform velocity free stream.…”

Section: Final Discussion and Conclusionmentioning

confidence: 99%

“…However, it was subsequently shown that this system is in fact unstable at the second order of approximation in the disturbance amplitude (Kochin 1939) but, more importantly, that the stability could be critically affected if the vortices are of finite size (and could change shape); see, for example, Saffman & Schatzman (1982) and Maches et al. (2021). Such analyses were all in the context of an irrotational, uniform velocity free stream.…”

Section: Final Discussion and Conclusionmentioning

confidence: 99%

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Vortex shedding behind porous flat plates normal to the flow

Cicolin,

Chellini,

Usherwood

et al. 2024

J. Fluid Mech.

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This work examines the influence of body porosity on the wake past nominally two-dimensional rectangular plates of fixed width $D$ in the moderate range of Reynolds numbers $Re = UD/\nu$ (with $U$ the incoming velocity and $\nu$ the kinematic viscosity) between 15 000 and 70 000. With porosity $\beta$ defined as the ratio of open to total area of the plate, it is well established that as porosity increases, the wake shifts from the periodic von Kármán shedding behaviour to a regime where this vortex shedding is absent. This change impacts the fluid forces acting on the plate, especially the drag, which is significantly lower for a wake without vortex shedding. We analyse experimentally the transition between these two regimes using hot-wire anemometry, particle-image velocimetry and force measurements. Coherence and phase measurements are used to determine the existence of regular, periodic vortex shedding based on the velocity fluctuations in the two main shear layers on either side of the wake. Results show that, independent of $Re$ , the wake exhibits the classical Kármán vortex shedding pattern for $\beta <0.2$ but this is absent for $\beta >0.3$ . In the intermediate range, $0.2<\beta <0.3$ , there is a transitional regime that has not previously been identified; it is characterised by intermittent shedding. The flow alternates randomly between a vortex shedding and a non-shedding pattern and the total proportion of time during which vortex shedding is observed (the intermittency) decreases with increasing porosity.

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Section: Final Discussion and Conclusionmentioning

confidence: 99%

Section: Final Discussion and Conclusionmentioning

confidence: 99%