Numerical simulations of cellular secondary currents and suspended sediment transport in open-channel flows over smooth-rough bed strips

Choi, Sung-Uk; Park, Moonhyeong; Kang, Hyeongsik

doi:10.1080/00221686.2007.9521820

Cited by 9 publications

(3 citation statements)

References 19 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Near the side walls, the surface vortex was much stronger and larger than in the smooth bed case, almost obliterating the bottom vortex. Tominaga et al (1989) did not provide any clear explanation about the mechanisms responsible for the maintenance of secondary circulation in the central region of the channel; instead they speculated about the possibility of slight irregularities in the bed roughness which could produce an effect similar to the presence of alternating smooth and rough stripes (Mclean, 1981;Studerus, 1982;Nezu and Nakagawa, 1993;Choi et al, 2006). This paper presents a new set of data on the 3D flow structure observed in a straight open channel flow over a rough, flat bed.…”

Section: Closed Channelmentioning

confidence: 94%

Laboratory measurements of 3-D flow patterns and turbulence in straight open channel with rough bed

Rodríguez

García

2008

Journal of Hydraulic Research

102

View full text Add to dashboard Cite

Laboratory experiments have been carried out in order to study secondary circulation and flow variability in straight open channel flows over a rough bed. 3D flow velocities and turbulence characteristics were measured using a micro Acoustic Doppler Velocimeter. Two flow conditions were analyzed, with aspect ratios b/ h (width over depth) of 8.5 and 6.3, respectively. These two cases cannot be classified in principle as narrow (b/ h < 5) or wide (b/ h > 10) channel flows, but exhibited well defined secondary flows in the whole cross section. Bed shear stresses and turbulence patterns were consistent with the secondary flow cellular circulation. These results contradict the general perception that secondary circulation cells die out at a distance of b > 2.5 h from the walls. The behavior was attributed to the bed roughness (k s /h ∼ 0.1) and to the difference in roughness between bed and walls, the latter being much smoother. The results allowed for quantification of hydrodynamic variability in terms of secondary velocities (5% of mean flow velocity), cores of high streamwise velocities (10% higher than surrounding flow) and bed shear stress (20% oscillation with respect to cross sectional averaged value). All these patterns are consistent with the very few results reported in the literature for similar roughness conditions. These results can be used to assess the background flow conditions existing in a straight channel with a plane bed, before the addition of pools and riffles as part of a restoration strategy for streams that have been channelized and do not present the flow variability needed to enhance habitat conditions. RÉSUMÉ Des expériences de laboratoire ont été effectuées en vue d'étudier la circulation secondaire et la variabilité des écoulements en canal rectiligne à surface libre sur un lit rugueux. Les vitesses 3D et les caractéristiques de la turbulence ont été mesurées en utilisant un micro Vélocimètre Acoustique Doppler. Deux conditions d'écoulement ont été analysées, avec des rapports b/ h (largeur sur profondeur) de 8.5 et de 6.3, respectivement. Ces deux cas ne peuvent pas être classifiés en principe en tant qu'écoulement en canal étroit (b/ h < 5) ou large (b/ h > 10), mais ils comportaient des écoulements secondaires bien définis dans toute la section transversale. Les efforts de cisaillement de lit et les configurations de turbulence étaient conformes à la circulation cellulaire de l'écoulement secondaire. Ces résultats contredisent l'idée reçue de cellules de circulation secondaire s'éteignant à une distance des parois de b > 2.5 h. Ce comportement a été attribué à la rugosité de lit (k s /h ∼ 0.1) et à la différence de rugosité entre le lit et les parois, celles-ci étant beaucoup plus lisses. Les résultats ont permis de quantifier la variabilité hydrodynamique en termes de vitesses secondaires (5% de la vitesse moyenne d'écoulement), de noyaux de courant à vitesses élevées (10% de plus que l'écoulement environnant) et d'effort de cisaillement de lit (20% d'oscillation par rapport à la val...

show abstract

Section: Closed Channelmentioning

confidence: 94%

Laboratory measurements of 3-D flow patterns and turbulence in straight open channel with rough bed

Rodríguez

García

2008

Journal of Hydraulic Research

102

View full text Add to dashboard Cite

show abstract

“…In order to be able to represent the effects of turbulence anisotropy on secondary circulation (i.e., Prandtl type 2 secondary circulation) a Reynolds Stress Model (RSM) was used to close Equation (1). Although the magnitude of secondary circulation associated with turbulence anisotropy may be small in rivers with irregular boundaries as compared with that associated with channel scale effects such as pressure gradients [59,60], it may be significant for more regular geometries or in far field situations with fewer channel scale effects [61][62][63][64][65]. Representing such effects require a Reynolds Stress Model [66].…”

Section: Numerical Simulationmentioning

confidence: 99%

A Numerical Study of the Influence of Channel-Scale Secondary Circulation on Mixing Processes Downstream of River Junctions

Lyubimova

Lepikhin

Parshakova

et al. 2020

Water

View full text Add to dashboard Cite

A rapid downstream weakening of the processes that drive the intensity of transverse mixing at the confluence of large rivers has been identified in the literature and attributed to the progressive reduction in channel scale secondary circulation and shear-driven mixing with distance downstream from the junction. These processes are investigated in this paper using a three-dimensional computation of the Reynolds averaged Navier Stokes equations combined with a Reynolds stress turbulence model for the confluence of the Kama and Vishera rivers in the Russian Urals. Simulations were carried out for three different configurations: an idealized planform with a rectangular cross-section (R), the natural planform with a rectangular cross-section (P), and the natural planform with the measured bathymetry (N), each one for three different discharge ratios. Results show that in the idealized configuration (R), the initial vortices that form due to channel-scale pressure gradients decline rapidly with distance downstream. Mixing is slow and incomplete at more than 10 multiples of channel width downstream from the junction corner. However, when the natural planform and bathymetry are introduced (N), rates of mixing increase dramatically at the junction corner and are maintained with distance downstream. Comparison with the P case suggests that it is the bathymetry that drives the most rapid mixing and notably when the discharge ratio is such that a single channel-scale vortex develops aided by curvature in the post junction channel. This effect is strongest when the discharge of the tributary that has the same direction of curvature as the post junction channel is greatest. A comprehensive set of field data are required to test this conclusion. If it holds, theoretical models of mixing processes in rivers will need to take into account the effects of bathymetry upon the interaction between river discharge ratio, secondary circulation development, and mixing rates.

show abstract

“…Open-channel flows with lateral variations have been studied under diverse conditions: shallow mixing layers, where the flow is characterized by a lateral velocity difference with no roughness changes [2,4,26]; smooth-to-rough roughness variation due to compound channels, where the lateral velocity difference is driven mainly by the difference in the flow depth [6,14,21,22,27]; and finally, the most directly relevant case, flows with lateral transition between completely smooth and rough beds [3,17,28] and between smooth and vegetation patches [12,19,30]. Rough-to-rougher transitions, however, have to our knowledge not yet been considered.…”

Section: Introductionmentioning

confidence: 99%

Lateral bed-roughness variation in shallow open-channel flow with very low submergence

et al. 2019

View full text Add to dashboard Cite

Quantifying turbulent fluxes and secondary structures in shallow channel flows is important for predicting momentum and mass transfer in rivers as well as channel capacity and associated water levels. Here, we focus on the flow over a lateral bed-roughness variation with very low relative submergence of the roughness elements, h∕k = {3, 2, 1.5} , where h is the flow depth and k is the roughness height. Measurements were performed in a 1.1 m wide and 26 m long glass flume whose bed was fitted with cubes arranged in two regular side-by-side patterns with frontal densities f = 0.2 and 0.4 to create a rough-to-rougher variation. Measurements were performed using stereoscopic PIV in two orthogonal planes, in a vertical transverse plane spanning the two roughness types, and in a longitudinal one at the interface between the roughness types. The results show that the bulk velocity difference between the two sides of the channel increases with decreasing h/k. Also, contrary to what is observed at high relative submergence with smooth-to-rough transitions, higher bulk velocities occur on the side with higher roughness. This difference is increasing as the flow becomes shallower and is shown to be due to increasing effective depths ratios, leading to increasingly lower friction factor ratios with lower friction factors on the high-velocity but rougher side. Although increasing streamwise momentum transfer at the interface is needed as h/k decreases, the turbulent and secondary circulation transfer of momentum is increasingly inhibited. A globally-driven secondary-circulation at h∕k = 3 ceases for lower h/k and roughness-scale circulation becomes dominant. Also, even the increased global shear does not lead to large-scale Kelvin Helmholtz instabilities structures. However, the relative importance of the roughness difference on the flow is augmented as the flow becomes shallower and momentum transfer due to lateral dispersive stresses increases.

show abstract

Numerical simulations of cellular secondary currents and suspended sediment transport in open-channel flows over smooth-rough bed strips

Cited by 9 publications

References 19 publications

Laboratory measurements of 3-D flow patterns and turbulence in straight open channel with rough bed

Laboratory measurements of 3-D flow patterns and turbulence in straight open channel with rough bed

A Numerical Study of the Influence of Channel-Scale Secondary Circulation on Mixing Processes Downstream of River Junctions

Lateral bed-roughness variation in shallow open-channel flow with very low submergence

Contact Info

Product

Resources

About