Flat vs. curved rigid-lid LES computations of an open-channel confluence

Ramos, Pedro Cunha; Schindfessel, Laurent; Pêgo, João Pedro; Mulder, Tom De

doi:10.2166/hydro.2019.109

Cited by 18 publications

(12 citation statements)

References 18 publications

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“…Large eddy simulation (LES) was applied by Ramos et al ( 2019) [39] on four openchannel confluence flows through the using of a frictionless rigid-lid to treat the free-surface. The simulation was carried out on a flat rigid-lid for three of the confluences with different elevations while the fourth simulation was conducted on a curved rigid-lid which is closer to the true free surface flow, and the experimental data of Weber et al (2001) [16] were used.…”

Section: Asymmetrical Shapedmentioning

confidence: 99%

Review and Comparison of Numerical Simulations of Secondary Flow in River Confluences

Shaheed

Yan

Mohammadian

2021

Water

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River confluences are a common feature in natural water resources. The flow characteristics in confluences are complicated, especially at junction areas between tributaries and the main river. One of the typical characteristics of confluences is secondary flow, which plays an important role in mixing, velocity, sediment transport, and pollutant dispersion. In addition to the experimental and field studies that have been conducted in this area, the development of computational fluid dynamics has allowed researchers in this field to use different numerical models to simulate turbulence properties in rivers, especially secondary flows. Nowadays, the hydrodynamics of flows in confluences are widely simulated by using three-dimensional models in order to fully capture the flow structures, as the flow characteristics are considered to be turbulent and three-dimensional at river junctions. Several numerical models have been recommended for this purpose, and various turbulence models have been used to simulate the flows at confluences. To assess the accuracy of turbulence models, flows have been predicted by applying different turbulence models in the numerical model and the results have been compared with other data, such as field, laboratory, and experimental data. The purpose behind these investigations was to find the suitable model for each case of turbulent flow and for different types of confluences. In this study, the performances of turbulence models for confluences are reviewed for different numerical simulation strategies.

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Section: Asymmetrical Shapedmentioning

confidence: 99%

Review and Comparison of Numerical Simulations of Secondary Flow in River Confluences

Shaheed

Yan

Mohammadian

2021

Water

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“…Grading of the cell size is adopted, yielding a higher resolution in the confluence zone and a smooth transition between the different blocks. Our mesh sensitivity analysis shows that a coarser resolution than adopted in this paper will miss the secondary currents, like it is reported for another open-channel confluence in Ramos et al (2019a), and in open-channel flows in general, by Talebpour and Liu (2019). Therefore, special care was devoted to the mesh independence in terms of secondary flow results.…”

Section: Computational Meshmentioning

confidence: 59%

“…To treat the free surface, the rigid-lid approach will be adopted, implying that the free surface is replaced by a frictionless and impermeable upper boundary of the computational domain. More specifically, the curved rigid-lid approach described in Ramos et al (2019a) is adopted in the present work. The curved shape of the upper domain boundary is defined by the location of a virtual free surface which would cause a hydrostatic pressure field identical to the time-averaged pressure field predicted on a flat rigid-lid in a preceding LES simulation.…”

Section: Boundary Conditionsmentioning

confidence: 99%

Numerical study of the flow and passive scalar transport in an open-channel confluence with a flat and a degraded fixed bed

Jin¹,

Ramos²,

Schindfessel³

et al. 2020

River Flow 2020

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Confluences are important junctions in fluvial and artificial networks of open-channels, as they regulate the mixing phenomena of substances transported by the merging flows, as well as the scour and deposition phenomena. This paper aims at contributing to the study of how the bed morphology, such as the presence of a scour hole and a depositional bar, influences the flow and mixing phenomena at a T-shaped open-channel confluence. By means of Large Eddy Simulations (LES) of flow and passive scalar transport, a comparative numerical study is carried out of two fixed bed cases, i.e. a flat one and a degraded one, which were investigated earlier experimentally in the lab and numerically with a RANS based solver by Tang et al. (2018). The spatial focus of the present paper is not exclusively devoted to the Confluence Hydrodynamics Zone, but also extends somewhat further downstream (i.e. up to 10 post-confluence channel widths W d downstream of the upstream confluence corner). For the investigated flow condition with a dominant incoming flow from the upstream main channel, the recirculation zone in the degraded bed case is found to be significantly shorter and less wide or even absent near the bed, yielding differences in the contraction of the main channel flow and in the secondary flow. Nevertheless, the non-uniformity of passive scalar mixing was found to be very similar up to 3.5W d . Further downstream, the flat bed case shows a slightly higher mixing rate, which does not seem to be related to differences in secondary flow patterns, but rather to differences in turbulence levels.

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“…Part of the value of our results stems from the systematic comparison among the outcomes of many computations in various settings. Conversely, Ramos et al (2019) pointed out recently that a high mesh resolution remains necessary for 3‐D computations to capture secondary flows. As a consequence, conclusions requiring systematic comparisons could not have been reached based on a limited number of high‐resolution 3‐D simulations.…”

Section: Introductionmentioning

confidence: 99%

Numerical Insights Into the Effects of Model Geometric Distortion in Laboratory Experiments of Urban Flooding

Erpicum

Mignot

et al. 2020

Water Resources Research

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Geometrically distorted scale models have been a valuable tool for physical modeling of urban flooding in a network of streets. However, little is known so far about the bias induced in such cases by the model geometric distortion. Here, we use 2‐D computational modeling to provide a first systematic quantification of this bias in the case of a synthetic urban layout. The bias is found to be generally small, with the maximum deviations of the upscaled flow depth and discharge partition from the corresponding values of the undistorted model being around 10% in the case of relatively rapid and shallow flow conditions. When the geometric distortion is increased, the computations reveal a nonmonotonous pattern of the flow variables (depth, discharge partition, and size of flow separation zones), which results from a competition between declining frictional losses and growing local losses in the model. These findings may guide the design of distorted scale models of urban flooding and assist the interpretation of laboratory observations for assessing flood protection measures, for process understanding or for validating computational modeling.

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Flat vs. curved rigid-lid LES computations of an open-channel confluence

Cited by 18 publications

References 18 publications

Review and Comparison of Numerical Simulations of Secondary Flow in River Confluences

Review and Comparison of Numerical Simulations of Secondary Flow in River Confluences

Numerical study of the flow and passive scalar transport in an open-channel confluence with a flat and a degraded fixed bed

Numerical Insights Into the Effects of Model Geometric Distortion in Laboratory Experiments of Urban Flooding

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