Control of the separated flow downstream of a two-dimensional fence by low-frequency forcing

Siller, H.; Fernholz, H. H.

doi:10.1007/bf02506066

Cited by 15 publications

(4 citation statements)

References 9 publications

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“…There is, of course, an extensive literature on these latter instabilities and their control. A comprehensive review is provided by Greenblatt & Wygnanski (2000) and it seems that it is control of these (essentially K-H) instabilities which appears to be the most effective in, inter alia, reducing the size of a separated region (see, for example, Siller & Fernholz 1997). Whether the much lower-frequency modes identified by Hudy et al can be controlled remains an open question.…”

Section: Concluding Discussionmentioning

confidence: 99%

The stability of laminar symmetric separated wakes

Castro

2005

J. Fluid Mech.

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Time-dependent computations of the two-dimensional incompressible uniformvelocity laminar flow past a normal flat plate (of unit half-width) in a channel are presented. Attention is restricted to cases in which the well-known anti-symmetric (von Kármán-type) vortex shedding is suppressed by the imposition of a symmetry plane on the downstream plate centreline. With a further symmetry plane at the channel's upper boundary, the only two governing parameters in the problem are the channel half-width, H , and the Reynolds number, Re (based on the body half-width and the upstream velocity, U ). The former is restricted to the range 3 6 H 6 30 and the interest lies in determining the nature of the initial instability which occurs in the separated wake as Re is gradually increased. It is found that for sufficiently large H and at a critical Re, a long-time-scale global (supercritical) instability is initiated, which in its saturated (limit) state takes the form of 'lumps' of vorticity being periodically shed from the tail end of the separated bubble. Stability calculations of corresponding mean flow profiles (typical of those found in the separated wake) are undertaken by examining the impulse response of particular profiles via appropriate solution of the Orr-Sommerfeld equation. The results of this analysis extend those available from related published work and are consistent with the behaviour found from the numerical computations. Taken together, all the results suggest that this type of global instability may be generic to many kinds of separated wakes and, indeed, may provide the fundamental explanation for the very low-frequency oscillations often noticed in fully turbulent wake bubbles.

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Section: Concluding Discussionmentioning

confidence: 99%

The stability of laminar symmetric separated wakes

Castro

2005

J. Fluid Mech.

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“…About 5.76 million (400x96x150) grid points were used to mesh the computational domain of size 37Hx6Hx6.75H. In agreement with the results of experiments conducted by Siller and Fernholz (1997) for similar flow conditions, Orellano and Wengle (2000) show that for ReH=10,500 the optimum forcing Strouhal number is related to the low-frequency movement of the entire separation bubble and not to the instability mode of the SSL.…”

Section: Studies Using Les/dns Modelssupporting

confidence: 72%

Flow around porous barriers

Basnet¹

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This study could not be conducted without the continuous help and enthusiasm of Professor George Constantinescu. I appreciate his valuable support and constant encouragements provided during this period. I am grateful for having a golden opportunity to work with him during my graduate studies at IIHR-Hydroscience and Engineering. I would also like to extend my gratitude to my other adviser, Professor Marian Muste. I wish to thank him for his comments, suggestions, questions, discussions and especially for all the help provided with the experimental part of this study. I would also like to express my appreciation to Professor Jacob Odgaard, Professor William Eichinger and Professor Albert Ratner for their valuable comments and for agreeing to serve on my Ph.D. thesis committee. Lastly, I would like to thank the Iowa Highway Research Board and the Iowa Department of Transportation (IDOT) for supporting this research by funding the project "Optimization of Snow Drifting Mitigation and Control Methods for Iowa Conditions" from January 2011 to December 2014 and all those who voluntarily took some of their own time to help me conducting the field experiments.

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“…A number of studies have provided more complete information on both time-averaged and instantaneous flow structures, which clearly show the unsteady nature of the flow over surface-mounted obstacles [45][46][47]. Few studies have also considered active flow control by periodic suction/blowing upstream to manipulate the length of the recirculation bubble [48,49]. It was found that the length of the recirculation bubble can be considerably reduced when the forcing frequency is close to the frequency of the shear-layer instability.…”

Section: Introductionmentioning

confidence: 99%

Cross-Flow-Induced Vibration of an Elastic Plate

Konstantinidis

2021

Fluids

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The cross-flow over a surface-mounted elastic plate and its vibratory response are studied as a fundamental two-dimensional configuration to gain physical insight into the interaction of viscous flow with flexible structures. The governing equations are numerically solved on a deforming mesh using an arbitrary Lagrangian-Eulerian finite-element method. The turbulent flow is resolved using the unsteady Reynolds-averaged Navier–Stokes equations at a Reynolds number of 2.5×104 based on the plate height. The material properties of the plate are selected so that the structural frequency is close to the frequency of vortex shedding from the free edge of a rigid plate, which is studied initially as the reference case. The results show that the plate tip oscillates back and forth in response to unsteady fluid loading at twice the frequency of vortex shedding, which is attributable to the sequential formation of a primary vortex from the free edge and a secondary vortex near the base of the plate. The effects of the plate elasticity and density on the structural response are considered, and results are compiled in terms of the reduced velocity U* and the density ratio ρ*. The standard deviation of tip displacement increases with reduced velocity in the range 7.1⩽U*⩽18.4, irrespective of whether the elasticity or the density of the plate is varied. However, the average deflection of the plate in the streamwise direction displays different scaling with U* and ρ*, but scales almost linearly with the Cauchy number ∼U*2/ρ*. Interestingly, the synchronization between plate motion and vortex shedding ceases at U*=18.4, and the excitation mechanism in the latter case resembles flutter instability, rather than vortex-induced vibration found at lower U*.

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Control of the separated flow downstream of a two-dimensional fence by low-frequency forcing

Cited by 15 publications

References 9 publications

The stability of laminar symmetric separated wakes

The stability of laminar symmetric separated wakes

Flow around porous barriers

Cross-Flow-Induced Vibration of an Elastic Plate

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