Hydraulic parameters in channels with wall vegetation and gravel bed

Afzalimehr, Hossein; Sui, Jueyi; Moghbel, Razieh

doi:10.1016/s1001-6279(10)60029-7

Cited by 15 publications

(6 citation statements)

References 18 publications

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“…In the smaller z/H v , the no intermittency is observed for all cases and the effect of bed roughness is the determining factor in the near bed region. Generally, in the near bed region of gravel bed channels, the effect of bed roughness exceeds the patch-produced vortexes [53][54][55]. According to the results of this research, the intermittency and anisotropy of the turbulence are associated with the non-Gaussian distribution of instantaneous velocity.…”

Section: Temporal Characteristics Of Turbulence In the Mixing Layermentioning

confidence: 60%

Characteristics of Turbulence in the Downstream Region of a Vegetation Patch

Kazem

Afzalimehr

Sui

2021

Water

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In presence of vegetation patches in a channel bed, different flow–morphology interactions in the river will result. The investigation of the nature and intensity of these structures is a crucial part of the research works of river engineering. In this experimental study, the characteristics of turbulence in the non-developed region downstream of a vegetation patch suffering from a gradual fade have been investigated. The changes in turbulent structure were tracked in sequential patterns by reducing the patch size. The model vegetation was selected carefully to simulate the aquatic vegetation patches in natural rivers. Velocity profile, TKE (Turbulent Kinetic Energy), turbulent power spectra and quadrant analysis have been used to investigate the behavior and intensity of the turbulent structures. The results of the velocity profile and TKE indicate that there are three different flow layers in the region downstream of the vegetation patch, including the wake layer, mixing layer and shear layer. When the vegetation patch is wide enough (Dv/Dc > 0.5, termed as the patch width ratio, where Dv is the width of a vegetation patch and Dc is the width of the channel), highly intermittent anisotropic turbulent events appear in the mixing layer at the depth of z/Hv = 0.7~1.1 and distance of x/Hv = 8~12 (where x is streamwise distance from the patch edge, z is vertical distance from channel bed and Hv is the height of a vegetation patch). The results of quadrant analysis show that these structures are associated with the dominance of the outward interactions (Q1). Moreover, these structures accompany large coherent Reynolds shear stresses, anomalies in streamwise velocity, increases in the standard deviation of TKE and increases in intermittent Turbulent Kinetic Energy (TKEi). The intensity and extents of these structures fade with the decrease in the size of a vegetation patch. On the other hand, as the size of the vegetation patch decreases, von Karman vortexes appear in the wake layer and form the dominant flow structures in the downstream region of a vegetation patch.

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Section: Temporal Characteristics Of Turbulence In the Mixing Layermentioning

confidence: 60%

Characteristics of Turbulence in the Downstream Region of a Vegetation Patch

Kazem

Afzalimehr

Sui

2021

Water

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“…Setayesh and Afzalimehr showed that Reynolds stress distribution displays a concave form for emergent vegetation and the best method of shear velocity estimation of application of Reynolds stress [20]. For constant flow depth, and equal water surface and bed slopes for vegetation banks over gravel bed, Afzalimehr et al found that for the aspect ratio of W/h = 4, the maximum velocity occurs under water at a water depth of y/h = 0.46, and its difference with flow velocity near water surface is 50% [21]. Furthermore, in natural channels and W/h = 7, the maximum velocity in the central axis is located at the water surface, and for the near bank it is located on average at a water depth of y/h = 0.50.…”

Section: Introductionmentioning

confidence: 99%

Comparison of Velocity and Reynolds Stress Distributions in a Straight Rectangular Channel with Submerged and Emergent Vegetation

Mofrad,

Afzalimehr,

Parvizi

et al. 2023

Water

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Vegetation in rivers and streams plays an important role in preventing erosion and improving bank stability. Comparison between emergent vegetation (bank vegetation) and submerged vegetation, in terms of velocity and Reynolds stress distributions, for the same aspect ratio and flow discharge, has received limited attention in the literature. This study investigates the velocity and Reynolds stress, as well as the log law for submerged and emergent vegetation in a laboratory flume and compares the results for a different set up with different sediment size and aspect ratio but the same discharge. The results indicate that the influence of submerged vegetation on the secondary currents generation is less than emergent vegetation. In addition, the log law application is valid for both submerged and emergent vegetation cases, however, it is valid up to y/h = 0.75 for emergent vegetation (in which the vegetation cover in banks is partly out of the water) but up to y/h = 0.25 for vegetation bank. For both submerged and emergent vegetation, Reynolds stress distribution presents a convex form but with a different turning point. Comparison of the results with those in an artificial pool over submerged vegetation and low aspect ratio (<5) keeps almost the same form for velocity and Reynolds stress distributions but decreases the turning point in Reynolds stress distribution. For the submerged vegetation cover, the location of zero shear stress superposes that of maximum velocity, but for the emergent vegetation approaching the bank vegetation and shifting the maximum velocity towards the bed, the location of zero shear stress approaches the bed.

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“…In recent years, many researches have been conducted in vegetated streams due to the significant role played by vegetation in erosion, sediment transport and resistance to flow. Review of literature reveals that there are many studies on submerged vegetation [10][11][12] and flexible vegetation [13,14]. Some researchers mentioned that the maximum Reynolds stress and turbulence intensity occurred approximately at the deflected vegetation height [15][16][17][18].…”

Section: Introductionmentioning

confidence: 99%