New Trends in Experimental Turbulence Research

Laufer, John

doi:10.1146/annurev.fl.07.010175.001515

Cited by 160 publications

(55 citation statements)

References 18 publications

(26 reference statements)

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“…;Brown and Roshko 1971, 1974 where such structures having been almost obscured by previous correlation measurements. Prior to the more recent recognition of the role of coherent structures in turbulent free shear flows, it was widely thought that such flows were independent of initial and environmental conditions (Townsend 1956, Laufer 1975. The experiments of Crow and Champagne (I971) and Binder and Fa vre-Marinet (1973) pointed out the distinct possibilities of controlling the downstream development of the jet flow oscillations via the upstream forcing of the large-scale coherent structure.…”

Section: Sknimsted 1948)mentioning

confidence: 99%

Contributions to the Understanding of Large-Scale Coherent Structures in Developing Free Turbulent Shear Flows

Liu

1988

Advances in Applied Mechanics

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Section: Sknimsted 1948)mentioning

confidence: 99%

Contributions to the Understanding of Large-Scale Coherent Structures in Developing Free Turbulent Shear Flows

Liu

1988

Advances in Applied Mechanics

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“…The intermittent transfer of momentum by coherent structures of turbulence is manifest by velocity fluctuations, and is linked to short-term variations in near-bed stresses (Heathershaw, 1974;Laufer, 1975). This is evident in the turbulent "bursting" process (Kline et al, 1967;Kline, 1974, 1975), which is a critical mechanism for production of turbulent kinetic energy (Dey et al, 2012;Schoppa and Hussain, 2002).…”

Section: Introductionmentioning

confidence: 99%

“…This is in essence a repeatable and hence coherent convective entrainment process (Nielsen, 1992) that is observed in both regular (at half cycle) and irregular wave conditions (O'hara Murray et al, 2012;O'hara Murray et al, 2011;Thorne et al, 2003). Where vortex pairs may develop, sediments may be violently ejected much higher (several orders of a ripple height) than classically described (Williams et al, 2007).The intermittent transfer of momentum by coherent structures of turbulence is manifest by velocity fluctuations, and is linked to short-term variations in near-bed stresses (Heathershaw, 1974;Laufer, 1975). This is evident in the turbulent "bursting" process (Kline et al, 1967; Kline, 1974, 1975), which is a critical mechanism for production of turbulent kinetic energy (Dey et al, 2012;Schoppa and Hussain, 2002).…”

mentioning

confidence: 99%

Wave-induced coherent turbulence structures and sediment resuspension in the nearshore of a prototype-scale sandy barrier beach

Kassem

Thompson

Amos

et al. 2015

Continental Shelf Research

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Abstract:The suspension of sediments by oscillatory flows is a complex case of fluid-particle interaction. The aim of this study is to provide insight into the spatial (time) and scale (frequency) relationships between wave-generated boundary layer turbulence and eventdriven sediment transport beneath irregular shoaling and breaking waves in the nearshore of a prototype sandy barrier beach, using data collected through the Barrier Dynamics Experiment II (BARDEX II). Statistical, quadrant and spectral analyses reveal the anisotropic and intermittent nature of Reynolds' stresses (momentum exchange) in the wave boundary layer, in all three orthogonal planes of motion. The fractional contribution of coherent turbulence structures appears to be dictated by the structural form of eddies beneath plunging and spilling breakers, which in turn define the net sediment mobilisation towards or away from the barrier, and hence ensuing erosion and accretion trends. A standing transverse wave is also observed in the flume, contributing to the substantial skewness of spanwise turbulence. Observed low frequency suspensions are closely linked to the mean flow (wave) properties. Wavelet analysis reveals that the entrainment and maintenance of sediment in suspension through a cluster of bursting sequence is associated with the passage of intermittent slowly-evolving large structures, which can modulate the frequency of smaller motions. Outside the boundary layer, small scale, higher frequency turbulence drives the suspension. The extent to which these spatially varied perturbation clusters persist is associated with suspension events in the high frequency scales, decaying as the turbulent motion ceases to supply momentum, with an observed hysteresis effect. The suspension of sediment in turbulent flows is a complex case of fluid-particle interaction, governed by shear stresses (momentum exchanges) at the bed and within the benthic boundary layer (BBL). Defining the physical processes which dictate the resuspension of sediments in coastal and estuarine settings is fundamental for accurate predictions of bed morphology evolution (Van Rijn et al., 2007), and has profound implications for the biogeochemical processes that shape their local ecology (Thompson et al., 2011). It is also a prerequisite to quantifying erosion and deposition trends, and hence guiding engineering applications such as beach nourishment, defence schemes against erosion and flooding, maintenance of marine infrastructure and waterways, and aggregate dredging. There is a genuine need for better, robust models of suspended sediment transport in the coastal zone (Aagaard and Jensen, 2013). In a vision paper on future research needs in coastal dynamics, Van Rijn et al. (2013) highlighted the pressing need for research to support such models, focusing in particular on sand transport in the shoreface (non-breaking waves), surf and swash zones; employing field and controlled laboratory experiments.The mobilisation of sediments in the nearshore and shoreface is dominated b...

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“…Il ne semble pas non plus exister de consensus concernant l'origine de ces structures dans les écoulements sur lit lisse en chenal de laboratoire. Pour certains auteurs (FALCO, 1977 ;BROWN et THOMAS, 1977 ;KOMORI étal., 1989 ;NEZU et NAKAGAWA, 1993 ;KIM et ADRIAN, 1999), les structures à grande échelle sont le résultat de la croissance et de l'amalgame de structures d'éjection dans l'écoulement alors que pour d'autres (LAUFER, 1975 ;PRATURY et BRODKEY, 1978 ;YALIN, 1992), il semble plutôt que les structures à grande échelle contrôlent l'éjection du fluide provenant de la souscouche visqueuse près du lit. Dans un écoulement sur lit de graviers, des mesures de vitesse ont révélé que les structures à grande échelle peuvent durer plusieurs secondes et qu'elles possèdent une longueur de 2 à 5 fois la profondeur de l'écoulement (BUFFIN-BÉLANGER ef al., 2000a).…”

Section: -Introductionunclassified

Interactions entre les structures d'échappement et les structures à grande échelle dans l'écoulement turbulent des rivières à lit de graviers

Buffin‐Bélanger¹,

Roy²,

Levasseur³

2005

rseau

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Dans les rivières graveleuses, il est établi que les structures d'échappement formées dans la zone de recirculation à l'aval d'amas de galets génèrent d'intenses échanges turbulents. Le mécanisme responsable de l'échappement demeure par contre mal connu. Peu d'études sur la dynamique des structures d'échappement ont été réalisées dans des écoulements où le nombre de Reynolds est élevé comme c'est le cas en rivières. De plus, les connaissances actuelles ne tiennent pas compte des découvertes récentes sur la turbulence en rivière à lit de graviers où on a observé des structures de forte et de faible vitesse occupant toute la profondeur de l'écoulement et pouvant durer plusieurs secondes. Ces structures à grande échelle devraient jouer un rôle sur le mécanisme d'échappement étant donné l'influence de la vitesse ambiante sur la dynamique de la zone de recirculation. Nous rapportons les résultats de deux expériences originales sur les liens dynamiques entre les structures à grande échelle et le mécanisme d'échappement en aval d'un amas de galets. La première expérience repose sur l'analyse de corrélations croisées entre des séries de vitesses obtenues au sommet et à l'aval proximal d'un amas de galets. Les résultats montrent que les fortes fluctuations dans le sens de l'écoulement au sommet de l'obstacle sont liées, quelques instants plus tard, à de fortes fluctuations vers l'amont dans la zone de recirculation. La seconde expérience utilise la visualisation des structures d'échappement et la mesure simultanée des vitesses de l'écoulement. L'analyse combinée des images vidéo et de séries de vitesse suggère une relation entre le passage des structures à grande échelle et les manifestations de l'échappement. Ces résultats nous permettent de présenter un modèle où, lors du passage d'un front de haute vitesse, une structure d'échappement se développe et prend de l'expansion vers le lit et vers la surface en se propageant vers l'aval alors que, lors du passage d'un front de faible vitesse, elle s'élève vers la surface de manière plus cohérente. Cette étude propose un nouveau mécanisme d'échappement et révèle le rôle que joue la structure de l'écoulement ambiant sur le développement de structures dans les cours d'eau à lit graveleux.The flow structure in a gravel-bed river is closely related to the presence of protruding clasts and of pebble clusters. It is well known that shedding motions from the lee side of large clasts and clusters are a recurrent process that explains the strong exchanges of momentum in river flows. However, shedding has yet to be fully characterised for high Reynolds number flows such as those found in gravel-bed rivers. Moreover, our current understanding of shedding mechanisms does not include the recent discovery that large-scale flow structures in the form of high- and low-speed wedges occupy the entire flow depth over a gravel-bed river. From two original experiments, this paper investigates the influence of these wedges on the nature of shedding in the lee of a pebble cluster. The interactions b...

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New Trends in Experimental Turbulence Research

Cited by 160 publications

References 18 publications

Contributions to the Understanding of Large-Scale Coherent Structures in Developing Free Turbulent Shear Flows

Contributions to the Understanding of Large-Scale Coherent Structures in Developing Free Turbulent Shear Flows

Wave-induced coherent turbulence structures and sediment resuspension in the nearshore of a prototype-scale sandy barrier beach

Interactions entre les structures d'échappement et les structures à grande échelle dans l'écoulement turbulent des rivières à lit de graviers

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