Turbulence Structures in Flow over Two-Dimensional Dunes

Stoesser, Thorsten; Braun, Carsten; García-Villalba, Manuel; Rodi, W.

doi:10.1061/(asce)0733-9429(2008)134:1(42)

Cited by 125 publications

(127 citation statements)

References 36 publications

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“…[25] The water flow module of the numerical model had been tested previously against velocity measurements for a number of cases, for example flow in a natural river [Olsen and Stokseth, 1995] and flow over a sand dune [Stoesser et al, 2006]. The water surface computation was tested by Tritthart and Gutknecht [2007] against field measurements from another part of the Danube River.…”

Section: Resultsmentioning

confidence: 99%

Three‐dimensional CFD modeling of morphological bed changes in the Danube River

Fischer-Antze¹,

Olsen

Gutknecht

2008

Water Resources Research

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[1] The bed changes in a section of the river Danube were computed using a 3-D computational fluid dynamics model. A time series of discharges during the flood in 2002 was used. The results compared reasonably well with regular bed level surveys before and after the flood. The Danube River section was 6 km long and located between Vienna and the Austrian-Slovakian border. The fully three-dimensional numerical model solved the Navier-Stokes equations using the k-epsilon turbulence closure. Nonuniform sediment transport was computed using the formulas of Wu et al. (2000b), considering hidingexposure algorithms. Both bed deformation and sorting processes were calculated. A number of parameter sensitivity tests were carried out on roughness values, parameters in the sediment transport capacity formula, parameters in the hiding-exposure formulas, critical Shields number, and variations in the formulas for the effect of a sloping bed. Additionally, the sediment inflow to the section was varied together with investigations of physical parameters such as vegetation and groyne structures. The results were most sensitive to the Shields number for critical movement of the sediments. An error analysis was performed to give a quantitative assessment of the parameter sensitivity tests.

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Section: Resultsmentioning

confidence: 99%

Three‐dimensional CFD modeling of morphological bed changes in the Danube River

Fischer-Antze¹,

Olsen

Gutknecht

2008

Water Resources Research

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“…The top surface is assumed to be rigid and free of shear stress: the vertical velocity is set to zero, as are the vertical derivatives of the streamwise and spanwise velocity components. The surface deformation is reported to be small, less than 2% of the flow depth in experiments (McLean et al 1994;Kadota & Nezu 1999;Maddux et al 2003b,a) and simulations (Yue et al 2006;Stoesser et al 2008) of 2D and 3D dunes, and it was shown that the free surface response to the 3D dune bed is 2D (Maddux et al 2003b;Omidyeganeh & Piomelli 2013). Therefore, the free-slip condition is expected to have small e↵ects on the statistics and on the evolution of significant structures.…”

Section: Problem Formulationmentioning

confidence: 98%

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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“…The condition at the free surface is represented by a zero shear stress, assuming that the fluid surface is stable during the disinfection process [36,38], viz. …”

Section: Governing Equations and Boundary Conditionsmentioning

confidence: 99%

Spiral-shaped reactor for water disinfection

Soukane

Ait-Djoudi

Naceur

et al. 2016

Desalination and Water Treatment

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Chlorine based processes are still widely used for water disinfection. The disinfection process for municipal water consumption is usually carried out in large tanks, specifically designed to verify several hydraulic and disinfection criteria. The hydrodynamic behavior of contact tanks of different shapes, each with an approximate total volume of 50,000 m 3 , was analyzed by solving turbulent momentum transport equations with a computational fluid dynamics (CFD) code, namely ANSYS fluent. Numerical experiments of a tracer pulse were performed for each design to generate flow through curves and investigate species residence time distribution for different inlet flow rates, ranging from 3 m 3 ·s -1 to 12 m 3 ·s -1 . A new nature inspired Conch tank design of which shape follows an Archimedean spiral was then developed. The spiral design is shown to strongly outperform the other tanks designs for all the selected plug flow criteria with an enhancement in efficiency, less short-circuiting and an order of magnitude improvement in mixing and dispersion. Moreover, following the intensification philosophy, after 50% reduction of its size, the new design retains its properties and still gives far better results than the classical shapes.

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Turbulence Structures in Flow over Two-Dimensional Dunes

Cited by 125 publications

References 36 publications

Three‐dimensional CFD modeling of morphological bed changes in the Danube River

Three‐dimensional CFD modeling of morphological bed changes in the Danube River

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

Spiral-shaped reactor for water disinfection

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