Turbulent Elliptic Wakes

Kiya, Masaru; Abe, Y.

doi:10.1006/jfls.1999.0248

Cited by 25 publications

(20 citation statements)

References 27 publications

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“…The mentioned shedding of the vortex structures generated in the gap upstream of the miniflap into the wake region were the shear layer is generated, fulfill the conditions of a specific perturbation acting on the region were the shear layer is generated and therefore able to influence the shape and evolution of vortex structures. The studies of Kiya et al (1986;1999a and describe interesting aspects of the response of a shear layer perturbed by vortices which also corroborate the asymmetric behavior detected in our experiments. Experimental procedures and results discussion -The models were located in the wing tunnel between two panels, in order to assure a close approximation to two-dimensional flow over the model.…”

Section: Abstract -The Present Research Analyzes the Asymmetry In Thesupporting

confidence: 76%

Low Speed Turbulent Boundary Layer Wind Tunnels

Lerner¹,

Boldes²,

Leo³

et al. 2011

Wind Tunnels and Experimental Fluid Dynamics Research

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Section: Abstract -The Present Research Analyzes the Asymmetry In Thesupporting

confidence: 76%

Low Speed Turbulent Boundary Layer Wind Tunnels

Lerner¹,

Boldes²,

Leo³

et al. 2011

Wind Tunnels and Experimental Fluid Dynamics Research

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“…These characteristic frequencies are denoted by f 1 and f 2 respectively and the Strouhal numbers are St 1 and St 2 . As in the experiments of Kiya & Abe (1999), depending on the hot-wire position, one or both frequencies are measured. The recurrent probe positions A, A ′ , B, B ′ , C and C ′ used in the plane x * = 2.5 are presented in figure 18(b).…”

Section: Oscillating Global Modesmentioning

confidence: 99%

“…Over more complex geometries, global modes may also be observed but their frequencies and structures are slightly different. Kiya & Abe (1999) depicted the impact of the as-pect ratio on the vortex shedding in the wake of elliptical and rectangular normal flat plates. Two peaks of energy are observed in the power spectrum of velocity signals at Strouhal numbers between 0.05 and 0.15 depending on the aspect ratio.…”

Section: Introductionmentioning

confidence: 99%

Turbulent wake past a three-dimensional blunt body. Part 1. Global modes and bi-stability

2013

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The flow around the three-dimensional blunt geometry presented in the work of Ahmed, Ramm & Faitin (Tech. Rep., 1984) is investigated experimentally at $\mathit{Re}= {U}_{0} H/ \nu = 9. 2\times 1{0}^{4} $ (where ${U}_{0} $ is free-stream velocity, $H$ the height of the body and $\nu $ viscosity). The very large recirculation on the base responsible for the dominant part of the drag is characterized. The analyses of the coherent dynamics of the wake reveal the presence of two very distinctive time scales. At long time scales ${T}_{l} \sim 1{0}^{3} H/ {U}_{0} $, the recirculation region shifts between two preferred reflectional-symmetry-breaking positions leading to a statistically symmetric wake; the sequence of these asymmetric states is random. This bi-stable behaviour is independent of the Reynolds number but occurs only above a critical value of ground clearance. At short time scales ${T}_{s} \sim 5H/ {U}_{0} $, the wake presents weak coherent oscillations in the vertical and lateral directions. They are respectively associated with the interaction of the top/bottom and lateral shear layers; when normalized by the height and width of the body, the Strouhal numbers are close to 0.17. These results suggest an alternate shedding associated with the vertical oscillation and a one-sided vortex shedding in the lateral direction with an orientation linked to the current asymmetric position. Finally, the impact of these coherent wake motions on the base pressure is discussed to motivate further drag reduction strategies.

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“…A “turbulence‐in‐a‐box” picture, described in section 2.1, probably presents better analogies and leads to better insight as to what might be important quantities to measure in the plasma sheet and to extract via data analysis. Another insightful and physically motivated analogy is a turbulent wake [ Smits and Dussauge , 1996; Evangelinos and Karniadakis , 1999; Kiya and Abe , 1999; Bourdon and Dutton , 1999]. In the work of Borovsky et al [1998a], several phenomena that are common between fluid wakes in the laboratory and the Earth's magnetotail were pointed out, in particular the downtail flow reversal and the attached twin vortices in an averaged flow pattern.…”

Section: Plasma Sheet Turbulence: Present Thinkingmentioning

confidence: 99%

MHD turbulence in the Earth's plasma sheet: Dynamics, dissipation, and driving

Borovsky¹

2003

J. Geophys. Res.

183

177

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[1] The turbulent flows and tangled magnetic fields of the Earth's plasma sheet are explored theoretically and by means of ISEE-2 plasma and magnetic-field measurements. The goal is to obtain a basic understanding of (1) the dynamics, (2) the driving, and (3) the dissipation of the turbulence. Dynamically, the turbulence of the plasma sheet appears to be a turbulence of eddies, rather than a turbulence of Alfven waves or other MHD modes. In this respect, it is similar to the two-dimensional turbulence of the solar wind. Previously published statistical arguments that the correlation length (= integral scale = eddy size) of the turbulence fluctuations in the plasma sheet is ' eddy $ 1.6 R E are confirmed by analyzing plasma sheet magnetic-field measurements during two special ''sweeping'' intervals that follow the passage of interplanetary shocks. For dissipation of the turbulence, two mechanisms appear to be important. The first is a cascade of energy in the turbulence to small spatial scales, where internal dissipation at non-MHD spatial scales should occur. The second mechanism is electrical coupling of the turbulent flows to the resistive ionosphere, which introduces a ''quasi-viscosity'' to the plasma sheet. This quasi-viscosity is complicated owing (1) to a time delay associated with Alfventransit-time coupling (introducing a viscoelasticity to the turbulence), (2) to a scalesize dependence of the coupling (introducing a hypoviscosity), and (3) to a dependence of the coupling on the sign of the flow shear (introducing a sign-vorticity effect). For the coupling of the plasma sheet turbulence to the ionosphere, retarded-time Reynolds numbers R* are derived to describe the importance of the resulting dissipation (quasiviscosity) and a Deborah number D is derived to describe the importance of the time lag (elasticity). The difference of the plasma sheet turbulence from homogeneous turbulence is discussed; this dissimilarity is owed to (a) dissipation at all wave numbers in the plasma sheet, (b) the presence of boundaries, and (c) the limited range of spatial scales that will allow scale-invariant dynamics. A better description of the plasma sheet turbulence would be ''turbulence in a box'' or a turbulent wake.

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Turbulent Elliptic Wakes

Cited by 25 publications

References 27 publications

Low Speed Turbulent Boundary Layer Wind Tunnels

Low Speed Turbulent Boundary Layer Wind Tunnels

Turbulent wake past a three-dimensional blunt body. Part 1. Global modes and bi-stability

MHD turbulence in the Earth's plasma sheet: Dynamics, dissipation, and driving

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