Time-dependent behavior of a reattaching shear layer

Driver, David M.; Seegmiller, H. L.; Marvin, J. G.

doi:10.2514/3.9722

Cited by 258 publications

(132 citation statements)

References 9 publications

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“…[1][2][3][4][5][6][7][8][9] One of its features is the complexity of turbulent structures. The flow just downstream of the step has a similar flow structure to the plainmixing layer.…”

mentioning

confidence: 99%

Behavior of Separated and Reattaching Flow Formed over a Backward Facing Step.

Rinoie

Shirai

Sunada

2002

Trans. Japan Soc. Aero. S Sci.

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Wind tunnel measurements were done for the separated and reattaching flow formed over a backward-facing step. Turbulent energy and turbulent normal stress balances were estimated from the measured data of mean velocities, Reynolds stresses, and turbulent triple products. The main objective of the experiments is to analyze the turbulent structure inside the reattaching shear layer, including the reverse flow, in detail. The results indicated different turbulent structures in three classified regions of the backward-facing step flow, first the dead air region, second the near wall region just upstream and downstream of the reattachment, and third the separated shear layer region. The second region is the one in which the transverse diffusion by turbulence in the turbulent energy balance equation plays an important role in comparison with other regions. In the reverse flow region just upstream of the reattachment included in the second region, the production term by shear stress, the transverse diffusion term by turbulence, and the advection term similarly help to balance the dissipation term.

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“…[1][2][3][4][5][6][7][8][9] One of its features is the complexity of turbulent structures. The flow just downstream of the step has a similar flow structure to the plainmixing layer.…”

mentioning

confidence: 99%

Behavior of Separated and Reattaching Flow Formed over a Backward Facing Step.

Rinoie

Shirai

Sunada

2002

Trans. Japan Soc. Aero. S Sci.

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“…In the literature, this very low frequency range (n ≤ 0.2) is sometimes attributed to the "flapping" phenomenon (see e.g. in [9]). It is interesting to notice that for the uncontrolled case the spatial extent of this region (with n ≤ 0.2) corresponds fairly well with the extent of the mean secondary recirculation region [5].…”

Section: Resultsmentioning

confidence: 99%

On time‐dependent behaviour of controlled turbulent flow with separation and reattachment

Neumann

2003

Proc Appl Math and Mech

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“…Time series of pressure fluctuations are also shown in Figures 9(a,c). The spectra in the saddle plane have a low-frequency peak due to the flapping of the separated shear-layer, typical of the reattachment region of flows with separation, such as backward facing steps (Eaton & Johnston 1982;Driver et al 1987;Dejoan & Leschziner 2004;Aider & Danet 2006); St = 0.011 for the in-phase alignment, 0.021 for the staggered case. The state of the boundary layer approaching the crest may play a role in this di↵erence, in that in the staggered case, the boundary layer approaching the saddle plane is coming from the upstream lobe.…”

Section: Near-wall Turbulencementioning

confidence: 99%

Large-eddy simulation of three-dimensional dunes in a steady, unidirectional flow. Part 2. Flow structures

Omidyeganeh

Piomelli

2013

J. Fluid Mech.

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This is the accepted version of the paper.This version of the publication may differ from the final published version. We performed large-eddy simulations of the flow over a series of three-dimensional (3D) dunes at laboratory scale. The bedform three-dimensionality was imposed by shifting a standard two-dimensional (2D) dune shape in the streamwise direction according to a sine wave. The turbulence statistics were discussed in Part 1 of this article [M. Omidyeganeh, U. Piomelli, J. Fluid Mech. 721, pp. 454-483, (2013)]. Coherent flow structures and their statistics are discussed concentrating on two cases with the same crestline amplitudes and wavelengths but di↵erent crestline alignments: in-phase and staggered. The present paper shows that the induced large-scale mean streamwise vortices are the primary factor that alters the features of the instantaneous flow structures. Wall turbulence is insensitive to the crestline alignment; alternating high-and low-speed streaks appear in the internal boundary layer developing on the stoss side, whereas over the node plane (the plane normal to the spanwise direction at the node of the crestline), they are inclined towards the lobe plane (the plane normal to the spanwise direction at the most downstream point of the crestline) due to the mean spanwise pressure gradient. Spanwise vortices (rollers) generated by Kelvin-Helmholtz instability in the separated shear-layer appear regularly over the lobe with much larger length scale than those over the saddle (the plane normal to the spanwise direction at the most upstream point of the crestline). Rollers over the lobe may extend to the saddle plane and a↵ect the reattachment features; their shedding is more frequent than in 2D geometries. Vortices shed from the separated shear-layer in the lobe plane undergo a three-dimensional instability while advected downstream, and rise toward the free surface. They develop into a horseshoe shape (similar to the 2D case) and a↵ect the whole channel depth, whereas those generated near the saddle are advected downstream and toward the bed. When the tip of such a horseshoe reaches the free surface, the ejection of flow at the surface causes "boils" (upwelling events on the surface). Strong boil events are observed on the surface of the lobe planes of 3D dunes more frequently than in the saddle planes. They also appear more frequently than in the corresponding 2D geometry. The crestline alignment of the dune alters the dynamics of the flow structures, in that they appear in the lobe plane and are advected towards the saddle plane of the next dune, where they are dissipated. Boil events occur at a higher frequency in the staggered alignment, but with less intensity than in the in-phase alignment. Permanent repository link

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Time-dependent behavior of a reattaching shear layer

Cited by 258 publications

References 9 publications

Behavior of Separated and Reattaching Flow Formed over a Backward Facing Step.

Behavior of Separated and Reattaching Flow Formed over a Backward Facing Step.

On time‐dependent behaviour of controlled turbulent flow with separation and reattachment

Large-eddy simulation of three-dimensional dunes in a steady, unidirectional flow. Part 2. Flow structures

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