Measurement of fluid velocity development behind a circular cylinder using particle image velocimetry (PIV)

Goharzadeh, Afshin; Molki, Arman

doi:10.1088/0143-0807/36/1/015001

Cited by 13 publications

(8 citation statements)

References 14 publications

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“…For all the cases (A-D), small vortices were formed behind each vegetation element in the sparse patch (L/d = 3) which is termed as Primitive Karman vortex street (PKV), however no large-scale vortex streets were generated. These results have also been observed by previous investigators (Goharzadeh and Molki, 2014;Takemura and Tanaka, 2007). Large-scale vortex streets (LKV) were generated the downstream of the dense patch (L/d = 0.35) in Figure 10(a-d).…”

Section: Velocity Contours Distributionsupporting

confidence: 89%

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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Section: Velocity Contours Distributionsupporting

confidence: 89%

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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“…For the sparse emergent vegetation experiment (Figure c), primitive von Kármán vortex streets were observed behind the individual circular vegetation patch, whereas large von Kármán vortex streets were observed for the dense emergent vegetation experiment (Figure a). Such types of turbulent shedding behaviours behind circular patches have also been investigated in previous studies (Goharzadeh & Molki, ; Takemura & Tanaka, ). For sparse vegetation (Figure c,d), the intensity of wake formation was low compared with the dense vegetation experiments (Figure a,b).…”

Section: Resultssupporting

confidence: 58%

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

Ghani

Anjum

Pasha

et al. 2019

River Research & Apps

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In the present study, flow around circular and staggered vegetation patches was investigated numerically. For turbulence modelling, the Reynolds-averaged Navier-Stokes technique and Reynolds stress model were adopted. The numerical model was validated with the experimental data using varying vegetation density and flow velocities. The simulated results of mean stream-wise velocities were in close agreement with the experimental results. The results show that the mean stream-wise velocity in the downstream regions of vegetation patches were reduced, whereas the velocity in the free stream regions were increased. The influence of neighbouring and staggered vegetation patches on the flow was observed. The vegetation patches with larger nondimensional flow blockage (aD = 2.3, where a is the frontal area per volume of patches, and D is the diameter of vegetation patches) offered more turbulence when compared to the patches with a smaller flow blockage (aD = 1.2). Larger turbulence in the form of kinetic energy and turbulent intensity was recorded within the vegetation as well as the regions directly behind the patches. Negative Reynolds stresses were observed at the top of submerged vegetation. The turbulence characteristics peaked at the top of vegetation, that is, z/h = 1.0 (where z is the flow depth, and h is the vegetation height), which may be migrated vertically as the frontal area of the vegetation patch is increased. This high frontal area also increased stream-wise velocity above the vegetation, leading to an increased variation in turbulence around the vegetation canopy.

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“…For comparison, the time‐averaged velocity field behind a circular cylinder with periodic Kármán vortex shedding shows two symmetrically placed counterrotating standing vortices attached to the cylinder and streamlines parallel to the main flow past the reattachment point (Goharzadeh & Molki, ). The time‐averaged flow behind an inclined flat plate is similar, but the clockwise recirculation region at the leading edge is considerably larger than the anticlockwise recirculation region at the trailing edge (Breuer & Jovičić, ; Yang et al, ).…”

Section: Wake Flow Dynamicsmentioning

confidence: 99%

Evolution of an Atmospheric Kármán Vortex Street From High‐Resolution Satellite Winds: Guadalupe Island Case Study

et al. 2020

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Vortex streets formed in the stratocumulus‐capped wake of mountainous islands are the atmospheric analogues of the classic Kármán vortex street observed in laboratory flows past bluff bodies. The quantitative analysis of these mesoscale unsteady atmospheric flows has been hampered by the lack of satellite wind retrievals of sufficiently high spatial and temporal resolution. Taking advantage of the cutting‐edge Advanced Baseline Imager, we derived kilometer‐scale cloud‐motion winds at 5‐min frequency for a vortex street in the lee of Guadalupe Island imaged by Geostationary Operational Environmental Satellite‐16. Combined with Moderate Resolution Imaging Spectroradiometer data, the geostationary imagery also provided accurate stereo cloud‐top heights. The time series of geostationary winds, supplemented with snapshots of ocean surface winds from the Advanced Scatterometer, allowed us to capture the wake oscillations and measure vortex shedding dynamics. The retrievals revealed a markedly asymmetric vortex decay, with cyclonic eddies having larger peak vorticities than anticyclonic eddies at the same downstream location. Drawing on the vast knowledge accumulated about laboratory bluff body flows, we argue that the asymmetric island wake arises from the combined effects of Earth's rotation and Guadalupe's nonaxisymmetric shape resembling an inclined flat plate at low angle of attack. However, numerical simulations will need to establish whether or not the selective destabilization of the shallow atmospheric anticyclonic eddies is caused by the same mechanisms that destabilize the deep columnar anticyclones of laboratory flows, such as three‐dimensional vertical perturbations due to centrifugal or elliptical instabilities.

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Measurement of fluid velocity development behind a circular cylinder using particle image velocimetry (PIV)

Cited by 13 publications

References 14 publications

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

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 characteristics in an open channel with staggered vegetation patches

Evolution of an Atmospheric Kármán Vortex Street From High‐Resolution Satellite Winds: Guadalupe Island Case Study

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