Investigating the turbulent flow characteristics in an open channel with staggered vegetation patches

Ghani, Usman; Anjum, Naveed; Pasha, Ghufran Ahmed; Ahmad, Muhammad Masood

doi:10.1002/rra.3460

Cited by 22 publications

(12 citation statements)

References 41 publications

(46 reference statements)

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“…Specifically, as the patches became more clustered (smaller D and higher φ ), the velocity within the patch, U p , declined (Table 1). The decrease in U p could be more pronounced if the patch was placed directly in the wake of the upstream patch (e.g., Ghani et al, 2019). In addition, as clustering increased (decreasing D ), a smaller fraction of bed area contained patches (smaller φ p ).…”

Section: Resultsmentioning

confidence: 99%

Turbulence and Bed Load Transport in Channels With Randomly Distributed Emergent Patches of Model Vegetation

Shan

Zhao

Nepf

2020

Geophysical Research Letters

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Laboratory experiments explored the impact of vegetation patchiness on channel-averaged turbulence and sediment transport. Stems were clustered into 16 randomly distributed circular patches of decreasing diameter. For the same channel velocity, the sediment transport increased with total stem number but decreased as stems were clustered into smaller patch diameters, occupying a smaller fraction of the bed area. The channel-averaged turbulence, which also declined with increased clustering, was shown to be a good predictor for sediment transport at the channel scale. Previous models for uniform vegetation were adapted to predict both the channel-averaged turbulence and sediment transport as a function of the total number of stems and degree of clustering, represented by the fraction of bed covered by patches. This provides a way for numerical modelers to represent the impact of subgrid-scale vegetation patchiness on sediment transport.

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Section: Resultsmentioning

confidence: 99%

Turbulence and Bed Load Transport in Channels With Randomly Distributed Emergent Patches of Model Vegetation

Shan

Zhao

Nepf

2020

Geophysical Research Letters

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“…In Figure 1(b), the x-axis shows the streamwise flow direction, the y-axis shows the lateral direction, and the z-axis shows the vertical direction. The experiments were conducted both for dense and sparse vegetation cases with flow blockage (aD) of 2.3 and 1.2 (Dieter et al, 2014;Ghani et al, 2019a), respectively. All the experiments were performed with a discharge of 9 L/s.…”

Section: Methods and Materials 21 Experimental Data For Validation Pu...mentioning

confidence: 99%

3D numerical modeling of flow characteristics in an open channel having in-line circular vegetation patches with varying density under submerged and emergent flow conditions

Tariq

Ghani

Anjum

et al. 2022

Journal of Hydrology and Hydromechanics

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In the marine ecological system, the prime role of water management and durability of an ecosystem is being played by the vegetation patches. The vegetation patches in open channels can significantly affect the flow velocity, discharge capacity and hinder energy fluxes, which ultimately helps in controlling catastrophic floods. In this study, the numerical simulation for turbulent flow properties, i.e. velocity distribution, Reynolds stresses and Turbulent Intensities (TI) near the circular vegetation patches with progressively increasing density, were performed using the computational fluid dynamics (CFD) code ANSYS FLUENT. For examination of the turbulent flow features in the presence of circular patches with variable densities, Reynolds averaged Navier-Stokes equations, and Reynolds stress model (RSM) were employed. The numerical investigation was performed in the presence of in-line emergent and submerged patches having variable vegetation density in the downstream direction. Two of the cases were investigated with three circular patches having a clear gap to patch diameter ratio of La/D = 1 (where La is the clear spacing between the vegetation patches and D is the diameter of the circular patch), and the other two cases were analyzed with two patches having a clear gap ratio of La/D = 3. The case with a clear gap ratio (La/D = 3) showed 10.6% and 153% inflation in the magnitude of longitudinal velocity at the downstream of the sparse patch (aD = 0.8) and upstream of the dense patch (aD = 3.54), respectively (where aD is the flow blockage, in which “a” represents the patch frontal area and “D” represents the patch diameter). The velocity was reduced to 94% for emergent and 99% for submerged vegetation due to successive increase in vegetation density made by introducing a middle patch which reduced the clear gap ratio (La/D = 1). For La/D = 1, the longitudinal velocities at depth z = 15cm were increased by 319% than at depth z = 6cm at the downstream of the dense patch (aD = 3.54). Whereas it was observed to 365% higher in the case of La/D = 3. The magnitude of turbulent characteristics was observed 36% higher for submerged vegetation cases having a clear gap ratio of La/D = 1. The successive increase in the patch density reduced the Reynolds stresses, turbulent kinetic energy and turbulent intensities significantly within the gap region. The major reduction in the flow velocities and turbulent properties in the gaps provides a stable environment for aquatic ecosystems nourishment and fosters sediment deposition, and supports further vegetation growth.

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“…Choi and Kang (2006) implemented a Reynolds stress model (RSM) to replicate the turbulent flow structure in a large‐aspect ratio channel with partly placed submerged vegetation (SV). Several previous researchers implemented flow simulation techniques through a uniform array of vegetation to simulate the turbulent flow (Cui & Neary, 2008; Ghani, Anjum, Pasha, & Ahmad, 2019; Lopez & Garcia, 2001; Neary, 2003). The numerical studies on investigating the flow structures in vegetated open channels utilizing CFD tool FLUENT have also been reported (Anjum & Tanaka, 2020; Lima, Janzen, & Nepf, 2015).…”

Section: Introductionmentioning

confidence: 99%

Investigating the turbulent flow behaviour through partially distributed discontinuous rigid vegetation in an open channel

Anjum

Tanaka

2020

River Research & Apps

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Riparian vegetation does not only affect the channel flow carrying capacity, but also plays significant roles in water management, stream restoration, and river rehabilitation. This study numerically investigates the flow characteristics through longitudinally discontinuous rigid vegetation occupying half width of the channel, with the help of three-dimensional software FLUENT in which a Reynolds stress turbulence model was adopted. Three varying conditions of vegetation were considered comprising of vertically double-layered vegetation (DLV), submerged vegetation (SV), and emergent vegetation (EV) while keeping the same vegetation density, as well as a varying discharge condition against DLV was also tested. The results indicated that the flow distribution becomes more complex through DLV and SV followed by multiple layers with an inflectional instability in the vertical velocity profile around submerged canopy top, as compared to the flow through EV where the uniform distribution of flow over the canopy column was observed. The velocity in the canopy zone decreased considerably because of the resistance due to vegetation, which influenced the channel carrying capacity, in comparison to that in the non-vegetated zone. The flow velocities through the obstructed part of the channel, that is, canopy zone, in DLV arrangement reduced by a percentage difference of approximately 42 and 37% compared to that of SV and EV arrangements, respectively; whereas it was reduced by approximately 55% when the discharge was twice while keeping the same configuration of DLV. The inflectional instabilities and estimated mixing layer over the interfacial zone suggested a stronger lateral exchange of momentum for DLV configuration in comparison to that of SV and EV. Within the gaps between the patch zones, the flow velocity, turbulent kinetic energy, and turbulent intensity reduced significantly due to blockage effect and sheltering offered by the vegetation patches, signifying a positive flow response towards aquatic life and sediment deposition.

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Investigating the turbulent flow characteristics in an open channel with staggered vegetation patches

Cited by 22 publications

References 41 publications

Turbulence and Bed Load Transport in Channels With Randomly Distributed Emergent Patches of Model Vegetation

Turbulence and Bed Load Transport in Channels With Randomly Distributed Emergent Patches of Model Vegetation

3D numerical modeling of flow characteristics in an open channel having in-line circular vegetation patches with varying density under submerged and emergent flow conditions

Investigating the turbulent flow behaviour through partially distributed discontinuous rigid vegetation in an open channel

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