On the vortex formation in the mixing layer behind dunes

Müller, Andres; Gyr, Albert

doi:10.1080/00221688609499314

Cited by 95 publications

(95 citation statements)

References 26 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…Many previous studies have suggested that the macroturbulence associated with dunes is www.intechopen.com important in controlling the stability of the bed forms and the entrainment and transport of the sediments. It has been suggested that this macroturbulence has its origin in KelvinHelmoltz instabilities in the separating shear layer (Best 2003;Kostaschuk and Church 1993;Muller and Gyr 1987). In particular, Best (2003) and Hyun et al (2003) provide whole field quantification using particle image velocimetry .…”

Section: Temporal and Spatial Flow Over Dunesmentioning

confidence: 99%

“…Muller and Gyr (1982) used fluorescent dye, a light sheet and video to visualize the flow. Nezu et al (1994) used both dye and hydrogen bubbles in conjunction with video to study turbulent structures over dunes, and Bennett and Best (1995) took long exposure photographs of small neutrally buoyant particles to view the paths of fluid particles.…”

Section: Experimental Studies Limitations Of Some Of the Studies Rementioning

confidence: 99%

See 1 more Smart Citation

Bed Forms and Flow Mechanisms Associated with Dunes

Balachandar¹,

Reddy²

2011

Sediment Transport - Flow and Morphological Processes

View full text Add to dashboard Cite

Section: Temporal and Spatial Flow Over Dunesmentioning

confidence: 99%

Section: Experimental Studies Limitations Of Some Of the Studies Rementioning

confidence: 99%

Bed Forms and Flow Mechanisms Associated with Dunes

Balachandar¹,

Reddy²

2011

Sediment Transport - Flow and Morphological Processes

View full text Add to dashboard Cite

“…Although flow over dunes has been extensively studied in field experiments (Matthes 1947;Jackson 1976;Flemming 1978;Gabel 1993;Kostaschuk & Church 1993;Bennett & Best 1995;Babakaiff & Hickin 1996;Kostaschuk & Villard 1996;Roden 1998;Carling et al 2000;Kostaschuk 2000;Best et al 2001), fixed 2D dunes have been the focus of the studies in laboratory experiments (Müller & Gyr 1986;Nelson et al 1993;Kadota & Nezu 1999;Schmeeckle et al 1999;Venditti & Bennett 2000;Hyun et al 2003;Balachandar et al 2007;Balachandar & Patel 2008), numerical simulations (Yoon & Patel 1996;Schmeeckle et al 1999;Yue et al 2005;Polatel et al 2006;Yue et al 2006;Stoesser et al 2008;Grigoriadis et al 2009;Omidyeganeh & Piomelli 2011), as well as theoretical studies (McLean & Smith 1986;Nelson & Smith 1989;McLean et al 1999). A comprehensive review of literature on dunes is given by Best (2005).…”

Section: Introductionmentioning

confidence: 99%

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

Omidyeganeh

Piomelli

2013

J. Fluid Mech.

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 flow over a series of three-dimensional dunes at laboratory scale (Reynolds number based on the average channel depth and streamwise velocity was 18,900) using the Lagrangian dynamic eddy-viscosity subgrid-scale model. The bedform three-dimensionality was imposed by shifting a standard two-dimensional dune shape in the streamwise direction according to a sine wave. The statistics of the flow are discussed in ten cases with in-phase and staggered crestlines, different deformation amplitudes and wavelengths. The results are validated qualitatively against experiments. The three-dimensional separation of flow at the crestline alters the distribution of wall pressure, which in turn may cause secondary flow across the stream, which directs lowmomentum fluid, near the bed, toward the lobe (the most downstream point on the crestline) and high-momentum fluid, near the top surface, toward the saddle (the most upstream point on the crestline). The mean flow is characterized by a pair of counterrotating streamwise vortices, with core radius of the order of the flow depth. However, for wavelengths smaller than the flow depth, the secondary flow exists only near the bed and the mean flow away from the bed resembles the two-dimensional case. Staggering the crestlines alters the secondary motion; the fastest flow occurs between the lobe and the saddle planes, and two pairs of streamwise vortices appear (a strong one, centred about the lobe, and a weaker one, coming from the previous dune, centred around the saddle). The distribution of the wall stress and the focal points of separation and attachment on the bed are discussed. The sensitivity of the average reattachment length, depends on the induced secondary flow, the streamwise and spanwise components of the channel resistance (the skin friction and the form drag), and the contribution of the form drag to the total resistance are also studied. Three-dimensionality of the bed increases the drag in the channel; the form drag contributes more than in the two-dimensional case to the resistance, except for the staggered-crest case. Turbulent-kinetic energy is increased in the separated-shear layer by the introduction of three-dimensionality, but its value normalized by the plane-averaged wall stress is lower than in the corresponding twodimensional dunes. The upward flow on the stoss side and higher deceleration of flow on the lee side over the lobe plane lift and broaden the separated-shear layer, respectively, affecting the turbulent kinetic energy. Permanent repository link

show abstract

“…Various conjectures were advanced to explain their occurrence (Jackson 1976;Müller & Gyr 1986;Nezu & Nakagawa 1993;Kadota & Nezu 1999;Best 2005a) ;Omidyeganeh & Piomelli (2011) confirmed the conjectures by Müller & Gyr (1986) and Best (2005a) and showed that they are due to horseshoe vortices of size comparable to the flow depth originating in the separated-shear layer.…”

Section: Introductionmentioning

confidence: 63%

“…The strong ejection that occurs behind the horseshoe head and between its legs causes the impingement of a nearly circular jet on the surface, made visible by the divergence of velocity-fluctuation vectors, similar to what was observed for 2D dunes (Omidyeganeh & Piomelli 2011). This impingement causes the upwelling of the surface known as a "boil" (Matthes 1947;Jackson 1976;Müller & Gyr 1986;Nezu & Nakagawa 1993;Babakai↵ & Hickin 1996;Kadota & Nezu 1999;Best et al 2001;Best 2005a,b). Figure 17 shows the probability of boil events occurring at the surface, selected by requiring that the planar divergence…”

Section: Boil Eventsmentioning

confidence: 98%

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

Omidyeganeh

Piomelli

2013

J. Fluid Mech.

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

On the vortex formation in the mixing layer behind dunes

Cited by 95 publications

References 26 publications

Bed Forms and Flow Mechanisms Associated with Dunes

Bed Forms and Flow Mechanisms Associated with Dunes

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

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

Contact Info

Product

Resources

About