Large-eddy simulation of three-dimensional dunes in a steady, unidirectional flow. Part 1. Turbulence statistics

Omidyeganeh, Mohammad; Piomelli, Ugo

doi:10.1017/jfm.2013.36

Cited by 57 publications

(68 citation statements)

References 58 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The Crank-Nicolson scheme is used for the wall-normal di↵usive terms, and the Adams-Bashforth scheme for all the other terms. The pressure is obtained from the solution of a Poisson equation, which is discussed in Omidyeganeh & Piomelli (2013). The code is parallelized using the Message-Passing Interface and the domain-decomposition technique, and has been Radhakrishnan et al 2006Radhakrishnan et al , 2008Omidyeganeh & Piomelli 2011, 2013.…”

Section: Problem Formulationmentioning

confidence: 99%

“…A full description of the geometry and 3D parameters of the crestline (amplitude A and wavelength ) can be found in Omidyeganeh & Piomelli (2013). The computational configuration is sketched in Figure 1.…”

Section: Problem Formulationmentioning

confidence: 99%

“…Note that in large sand-bed alluvial channels dunes may possess low-angle lee side and intermittent separation of the flow at the crest (Roden 1998;Best & Kostaschuk 2002); here we study typical dune models with an angle of repose slip face where the flow permanently separates at the crest (Roden 1998;Kostaschuk 2000). In the first part of this paper (Omidyeganeh & Piomelli 2013), the past research on two-and three-dimensional dunes was reviewed, and thus here we limit ourselves to a brief summary.…”

Section: Introductionmentioning

confidence: 99%

“…The mean flow has been studied experimentally (Allen 1968;Maddux et al 2003b,a;Venditti 2007) and numerically (Omidyeganeh & Piomelli 2013). Although some features of the flow are common with the flow over 2D dunes (e.g., the separation at the crest, reattachment on the bed, and deceleration/acceleration over the lee/stoss side), the 3D mean flow significantly alters the turbulence characteristics.…”

Section: Introductionmentioning

confidence: 99%

“…In addition to the relation between boundary shear stress and turbulence statistics with three-dimensionality of dunes, the relation of instantaneous features of vortical structures to the geometrical parameters of 3D dunes must be studied to explore the morphology mechanics and channel resistance in rivers, and to understand bed deformation mechanism (Best 2005a). In the first part of this article (Omidyeganeh & Piomelli 2013), we performed a controlled investigation of simple sinusoidal crestline deformations and analyzed the e↵ect of geometrical parameters of the crestline on the mean-flow characteristics. Here, in the second article, we study the e↵ect of the three-dimensionality on the turbulent structures near the bed, in the separatedshear layer, and in the bulk flow.…”

Section: Introductionmentioning

confidence: 99%

See 4 more Smart Citations

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

Omidyeganeh

Piomelli

2013

J. Fluid Mech.

Self Cite

View full text Add to dashboard Cite

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

show abstract

Section: Problem Formulationmentioning

confidence: 99%

Section: Problem Formulationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

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

Omidyeganeh

Piomelli

2013

J. Fluid Mech.

Self Cite

View full text Add to dashboard Cite

show abstract

Effect of bed permeability and hyporheic flow on turbulent flow over bed forms

Blois

Best

Smith

et al. 2014

Geophys. Res. Lett.

View full text Add to dashboard Cite

This paper uses particle imaging velocimetry to provide the first measurements detailing the flow field over a porous bed in the presence of bed forms. The results demonstrate that flow downstream of coarse-grained bed forms on permeable beds is fundamentally different to that over impermeable beds. Most significantly, the leeside flow separation cell is greatly modified by jets of fluid emerging from the subsurface, such that reattachment of the separated flow does not occur and the Reynolds stresses bounding the separation zone are substantially lessened. These results shed new light on the underlying flow physics and advance our understanding of both ecological and geomorphological processes associated with permeable bed forms. Water fluxes at the bed interface are critically important for biogeochemical cycling in all rivers, yet mass and momentum exchanges across the bed interface are not routinely incorporated into flow models. Our observations suggest that ignoring such exchange processes in coarse-grained rivers may overlook important implications. These new results also provide insight to explain the distinctive morphology of coarse-grained bed forms, the production of openwork textures in gravels, and the absence of ripples in coarse sands, all of which have implications for modeling and prediction of sediment entrainment and flow resistance.

show abstract

Observations of Coherent Flow Structures Over Subaqueous High‐ and Low‐ Angle Dunes

2017

View full text Add to dashboard Cite

Large‐scale coherent flow structures (CFSs) above dunes are the dominant source of flow resistance and constitute the principal mechanism for sediment transport and mixing in sand bed river and estuarine systems. Based on laboratory observations, CFS formation has been previously linked to flow separation downstream of high‐angle dunes with lee slopes of ~30°. How CFSs form in natural, deep rivers and estuaries where dunes exhibit lower lee slopes and intermittent flow separation is not well understood. Here we present particle image velocimetry measurements from an experiment where dune lee slope was systematically varied (30°, 20°, and 10°), while other geometric and hydraulic parameters were held constant. We show that CFSs form downstream of all three dune geometries from shear layer vortices in the dune lee. The mode of CFS formation undergoes a low‐frequency oscillation with periods of intense vortex shedding interspersed with periods of rare vortex shedding. Streamwise alignment of several vortices during periods of intense shedding results in wedge‐shaped CFSs that are advected above the dune stoss side. Streamwise length scales of wedge‐shaped CFS correspond to large‐scale motions (LSMs). We hypothesize that the advection of LSM over the dune crest triggers the periods of intense shedding in the dune lee. LSMs are weaker and smaller above low‐angle dunes; however, the low‐frequency oscillation in CFS formation periods persists. The formation of smaller and weaker CFS results in a reduction of flow resistance over low‐angle dunes.

show abstract

Large-eddy simulation of three-dimensional dunes in a steady, unidirectional flow. Part 1. Turbulence statistics

Cited by 57 publications

References 58 publications

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

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

Effect of bed permeability and hyporheic flow on turbulent flow over bed forms

Observations of Coherent Flow Structures Over Subaqueous High‐ and Low‐ Angle Dunes

Contact Info

Product

Resources

About