Performance comparison of four turbulence models for modeling of secondary flow cells in simple trapezoidal channels

Tajnesaie, Mohanna; Nodoushan, Ehsan Jafari; Barati, Reza; Moghadam, Mehdi Azhdary

doi:10.1080/09715010.2018.1469053

Cited by 25 publications

(9 citation statements)

References 30 publications

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“…Some studies have used Large Eddy Simulation (LES) to evaluate the flow in fishways [35,49,51,67] and this model can provide more details about the flow than RANS [68]. However, the turbulence models based on RANS demand lower computational resources and they are much affordable, compared to LES [69] and can simulate adequately larger spatial scales corresponding to the time-averaged flow [68].…”

Section: Governing Equationsmentioning

confidence: 99%

Applications of Computational Fluid Dynamics in The Design and Rehabilitation of Nonstandard Vertical Slot Fishways

Sanagiotto

Rossi

Bravo

2019

Water

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Vertical slot fishways are increasingly common structures for the passage of a wide variety of migratory fish and contribute to the maintenance of fish diversity in fragmented rivers. These structures are designed with several geometric arrangements and, consequently, flow patterns through them can be shaped to present suitable characteristics for the fish species. To aid in the design of vertical slot fishways, a three-dimensional numerical model was used to simulate the flow for different geometric configurations. An existing vertical slot fishway with nonstandard dimensions was initially modeled and validated. This geometry was used as a reference design. Modifications to the reference design, such as the insertion of cylinders, changes in the baffle shape and position of the vertical slots, as possible rehabilitation measures, were proposed and tested. In summary, five different designs were evaluated with several slopes, totaling 17 geometries. Hydraulic parameters, flow patterns, maximum velocities, velocity fields and turbulence kinetic energy in the pools were analyzed. The results indicate that the maximum velocity values were between 9% and 68% higher than those obtained by the theoretical equation. This indicates that maximum velocities can be underestimated for nonstandard vertical slot fishways if a simplified evaluation is conducted. The insertion of cylinders in the region close to the slot reduces the maximum velocity up to 8.2%. The positioning of the vertical slots on alternating sides increases the maximum values of turbulence kinetic energy and the regions subjected to higher values. However, this configuration provided greater energy dissipation and reduction of velocities by up to 27%. Thus, modifications in nonstandard vertical slot fishways can be useful in future design or rehabilitation of existing structures in order to provide velocities and turbulence more friendly for a higher number of fish species.

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Section: Governing Equationsmentioning

confidence: 99%

Applications of Computational Fluid Dynamics in The Design and Rehabilitation of Nonstandard Vertical Slot Fishways

Sanagiotto

Rossi

Bravo

2019

Water

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“…Major suppression of the velocity filament, strong near-bed underflows and multiple stacked filaments, as noted herein, are in accord with hypothesis H2 and reflect control on flow structure by the local channel geometry and hence cannot be replicated using generic theory without detailed investigation of the channel configurations (Hunt et al, 2018;Tajnesaie et al, 2018). Note that the presence of multiple stacked filaments at any one section most probably reflects the fact that distinct memory exists in the flow over length-scales as yet undefined.…”

Section: General Considerationsmentioning

confidence: 52%

“…a total of three filaments; Tracy, 1965;Yang et al, 2012) although one or two of these may dominate the transverse flow field (Hey, 1976). Broad channels in contrast tend to exhibit multiple filaments induced by lateral variation in bed roughness or variation in bathymetry across the section (Nezu and Nakagawa, 1984;Nezu and Nakagawa, 1993b;Cooper and Tait, 2008;Rodriguez and Garcia, 2008;Tajnesaie et al, 2018). Broad channels in contrast tend to exhibit multiple filaments induced by lateral variation in bed roughness or variation in bathymetry across the section (Nezu and Nakagawa, 1984;Nezu and Nakagawa, 1993b;Cooper and Tait, 2008;Rodriguez and Garcia, 2008;Tajnesaie et al, 2018).…”

Section: Resultsmentioning

confidence: 99%

“…The predominance of a single filament for low width-depth ratios is represented by the regression line constrained to an intercept of N equals unity (Figure 8) which is a better fit to the empirical data than a regression constrained to an intercept of N equals three (not shown). Broad channels in contrast tend to exhibit multiple filaments induced by lateral variation in bed roughness or variation in bathymetry across the section (Nezu and Nakagawa, 1984;Nezu and Nakagawa, 1993b;Cooper and Tait, 2008;Rodriguez and Garcia, 2008;Tajnesaie et al, 2018). The 13 examples of broader channels (B/h max > 20; Figure 8) exhibit more than three filaments, but it is not possible with the existing data to demonstrate the specific control of bathymetry and bed roughness on the exact number of flow cells, as B/h max values 850 P. A. CARLING ET AL.…”

Section: Resultsmentioning

confidence: 99%

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Flow structure in large bedrock‐channels: The example of macroturbulent rapids, lower Mekong River, Southeast Asia

Carling

Huang

et al. 2018

Earth Surf Processes Landf

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The rate of bedrock channel incision is key to the understanding of landscape evolution. Theoretical models relate channel incision to sediment transport; the latter conditioned by the bed shear stress. However, theory is deficient in an appreciation of the transverse and vertical flow structure that mediates shear stress for deep, narrow inner‐channels, which often characterize large bedrock rivers. Here we present the detail of the structure of high Reynolds number flows for bedrock‐controlled rapids of the Mekong River, SE Asia. Distinct filaments of high‐velocity flow, separated by regions of slower flow, occur across channels; the numbers of filaments scale linearly with channel width to maximum‐depth (B/hmax) ratios. Inner‐channels with low ratios (B/hmax < 20) exhibit wall‐effected flow structure. Effects include suppressed maximum velocity filaments due to: (i) significant channel‐transverse flow; (ii) strongly‐sheared vertical flow structure; and (iii) significant underflows. Such complex water column flow patterns largely defy theoretical description. Nonetheless near the bed, the vertical velocity distributions often conform to: (i) ‘law‐of‐the‐wall’ logarithmic theory; or (ii) profiles in the near‐bed region and within the transition to outer flow can be described using a log‐wake function. Consequently, for selected velocity profiles it is possible to derive hydraulic parameters suitable for input to incision models. Chezy‐C values are high, indicating low flow resistance, while bed shear stresses remain competent, even during low‐discharges, to transport cobble bedload across low roughness bedrock surfaces. Thus, as competence is high, no blanketing sediment deposits can develop within inner channels to prevent bedrock erosion. Consequently, within similar high competence systems, incision is probably progressive as long as sediment supply is sustained to abrade the bedrock. The landscape modelling implication is that abrasion in this system is supply‐limited and not limited by flow competence. In contrast, a transport‐limited system is likely to evolve to exhibit an alluvial bed. © 2018 John Wiley & Sons, Ltd.

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“…There are also some large-scale simulation (LES) approaches to estimating the flow in fishways, such as Fuentes-Pérez et al (2018) and Quaresma et al (2018). However, RANS simulations have lower computational costs and are more accessible (TAJNESAIE et al, 2018).…”

Section: Turbulence Kinetic Energymentioning

confidence: 99%

Three-dimensional numerical simulation of flow in vertical slot fishways: validation of the model and characterization of the flow

Sanagiotto

Rossi

Lauffer

et al. 2019

RBRH

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Vertical slot fishways allow energy dissipation as a function of the pool, longitudinal slope, baffle and vertical slot design. The mean and turbulent flow patterns in these structures must be compatible with the fish target. The design of these structures is commonly based on previous successful fishways as well as simplified theoretical equations and empirical relationships. To aid in the design of these structures, a three-dimensional hydrodynamic model was used to simulate the flow, and experimental studies were used to validate the model. The mean velocities, pressures and parameters indicative of turbulence were analyzed. The maximum flow velocities were up to 32% higher than the values obtained using a simplified theoretical equation. The evaluation of the volumetric dissipated power indicated that the mean value for the pool was lower than 150 W/m3; however, analysis of the spatial distribution showed that in some areas, the values can exceed 1000 W/m3. The results indicate that the numerical simulation was able to adequately represent the flow considering the computational cost involved. Accordingly, it can be used as a complementary tool for the design of new fishways and for the analysis of modifications in existing ones.

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Performance comparison of four turbulence models for modeling of secondary flow cells in simple trapezoidal channels

Cited by 25 publications

References 30 publications

Applications of Computational Fluid Dynamics in The Design and Rehabilitation of Nonstandard Vertical Slot Fishways

Applications of Computational Fluid Dynamics in The Design and Rehabilitation of Nonstandard Vertical Slot Fishways

Flow structure in large bedrock‐channels: The example of macroturbulent rapids, lower Mekong River, Southeast Asia

Three-dimensional numerical simulation of flow in vertical slot fishways: validation of the model and characterization of the flow

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