The turbulent near wake of a flat plate at low Reynolds number

Nakayama, A.; Liu, B.

doi:10.1017/s0022112090000647

Cited by 19 publications

(13 citation statements)

References 23 publications

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“…Different boundaries have been suggested for the wake regions in previous literature (Ramaprian et al 1982;Hebbar 1986;Haji-Haidari & Smith 1988). The discrepancy is due to the fact that the scaled centreline velocity depends on the Reynolds number, as the large eddies of the outer layer influence the small-scale mixing within the inner layer (Nakayama & Liu 1990).…”

Section: Discussionmentioning

confidence: 99%

“…They speculated that streamwise vortices along with inrush of fluid from both sides of the plate play a major role in the mixing process. Nakayama & Liu (1990) studied the effect of variation in Reynolds number, and concluded that the larger eddies of the outer layer modulate the small eddies of the centreline region. These studies have explored the statistics of the turbulent fluctuations and the relative scale of the vortical structures, but the type of the coherent structures causing the small-scale mixing is unclear.…”

Section: Introductionmentioning

confidence: 99%

“…In this region, the large eddies in the outer parts of the two boundary layers start to take part in the wake development process, resulting in a gradual exchange of the innerlayer scales to the outer-layer parameters such as wake half-width. The modulation of the small eddies of the centreline region by the larger eddies of the outer layer observed by Nakayama & Liu (1990) can be a part of this conversion process, so that its detailed mechanism requires further investigation. The mixed-fluid contribution within the intermediate wake comprises a transport of turbulent energy away from the centreline while the unmixed-fluid contribution implies a transport of turbulent energy towards the centreline (Andreopoulos & Bradshaw 1980).…”

Section: Introductionmentioning

confidence: 99%

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Counter-hairpin vortices in the turbulent wake of a sharp trailing edge

Ghaemi

Scarano

2011

J. Fluid Mech.

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The unsteady organization and evolution of coherent structures within the turbulent boundary layer and subsequent wake of the sharp symmetric trailing edge of a NACA0012 aerofoil are investigated. The experiments are conducted in an open testsection wind tunnel at Re c = 386 000 based on the aerofoil chord and Re θ = 1300 based on the boundary layer momentum thickness. An initial characterization of the flow field using two-component particle image velocimetry (PIV) is followed by the investigation of the unsteady organization and evolution of coherent structures by time-resolved three-dimensional PIV based on a tomographic approach (Tomo-PIV). The inspection of the turbulent boundary layer prior to the trailing edge in the region between 0.15 and 0.8 δ 99 demonstrated streaks of low-and high-speed flow, while the low-speed streaks are observed to be more coherent along with strong interaction with hairpin-type vortical structures similar to a turbulent boundary layer at zero pressure gradient. The wake region demonstrated gradual deterioration of both the low-and the high-speed streaks with downstream progress. However, the low-speed streaks are observed to lose their coherence at a faster rate relative to the high-speed streaks as the turbulent flow develops towards the far wake. The weakening of the low-speed streaks is due to the disappearance of the viscous sublayer after the trailing edge and gradual mixing through the transport of the remaining low-speed flow towards the free stream. This transport of low-speed flow is performed by the ejection events induced by the hairpin vortices as they also persist into the developing wake. The higher persistence of the high-speed streaks is associated with counter-hairpin vortical activities as they oppose the deterioration of the high-speed streaks by frequently sweeping the high-speed flow towards the wake centreline. These vortical structures are regarded as counter-hairpin vortices as they exhibit opposite characteristics relative to the hairpin vortices of a turbulent boundary layer. They are topologically similar to the hairpins as they appear to be U-shaped but with inverted orientation, as the spanwise portion is in the vicinity of the wake centreline and the legs are inclined at an approximately 60• to the wake axis in the downstream direction demonstrating a strain-dominated topology. The counter-hairpin vortices are partially wrapped around the high-speed streaks and contribute to the wake development by transporting highspeed flow towards the wake centreline. Similar to the hairpin vortices of a turbulent boundary layer, the occurrence of a complete counter-hairpin vortex is occasional while its derivatives (portions of spanwise or quasi-streamwise vortices) are more frequently observed. Therefore, a pattern recognition algorithm is applied to establish characterization based on an ensemble-averaged counter-hairpin vortex. The formation of the counter-hairpin vortices is due to an additional degree of interaction between † Email address for correspondenc...

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Counter-hairpin vortices in the turbulent wake of a sharp trailing edge

Ghaemi

Scarano

2011

J. Fluid Mech.

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“…It can be noted that both v' and uv at the second x-station are higher than those at the first one. This effect has been investigated and discussed by Nakayama and Liu (1990) where they attribute it to a near wake phenomenon. Figure 3.14 shows the decay of the turbulent kinetic energy along the center line of the wake.…”

Section: Validation Of Rfg Proceduresmentioning

confidence: 99%

Large Eddy Simulation of Bubbly Ship Wakes

Yavuz¹,

Smirnov²

2005

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The presence of air bubbles in ship wakes and their dynamic interaction with the turbulent vortical flows create security problems by modifying the hydro-acoustic properties of ship navigation. This study concerns understanding and controlling the mechanisms, which may lead to selective concentration of bubbles to form clusters or clouds and to predict their size distribution and motion. Numerical simulations were conducted using the Large Eddy Simulation (LES) technique in conjunction with a Lagrangian particle tracking (LPT) technique appropriate for dispersed two-phase turbulent flows. In order to cut down on the execution time of LES, the simulation for the flow around the ship model are not considered, instead the simulations started just after the ship where the inlet conditions are prescribed with the help of a newly developed Random Flow Generation (RFG) procedure, and to compute bubble distributions. Moreover, to improve turnaround time of the computations and allow LES of the developing wake in a larger domain, parallel simulation tools are developed and adopted in this study. The turbulence characteristics of ship wakes on a straight tract and a circular tract are investigated using the above mentioned techniques, and processes (e.g. free surface effects, anisotropy, etc.) contributing to turbulence generation are identified, and appropriate sub-grid scale (SGS) models are developed and applied. For the first time, a relatively long developing near wake of three ship lengths was simulated using LES on parallel computers with more than six million nodes.

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“…Large-scale vortex shedding is absent. Other notable experimental investigations of the thin flat plate with a sharp trailing edge include those of Ramaprian et al (1982), Nakayama & Liu (1990), Hayakawa & Iida (1992) and Thomas & Liu (2004). In addition to the experimental investigations mentioned above analytical solutions based on certain simplifying assumptions are provided by Alber (1980).…”

Section: Introductionmentioning

confidence: 99%

Vortex shedding characteristics of the wake of a thin flat plate with a circular trailing edge

Mohan

2018

International Journal of Heat and Fluid Flow

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The turbulent near wake of a flat plate at low Reynolds number

Cited by 19 publications

References 23 publications

Counter-hairpin vortices in the turbulent wake of a sharp trailing edge

Counter-hairpin vortices in the turbulent wake of a sharp trailing edge

Large Eddy Simulation of Bubbly Ship Wakes

Vortex shedding characteristics of the wake of a thin flat plate with a circular trailing edge

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