Flow dynamics in the wakes of low-aspect-ratio wall-mounted obstacles

Hajimirzaie, Seyed M.; Buchholz, James

doi:10.1007/s00348-013-1616-1

Cited by 15 publications

(15 citation statements)

References 33 publications

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“…Given that the shape of the emerged part of the mussel in the present study is relatively close to that of a semiellipsoid, some discussion is needed on the possible reasons for the large discrepancy between the dominant wake frequency predicted by the present simulation (St w = 0.32) and that observed past semiellipsoids with a similar AR value. It is relevant to mention that in the same semiellipsoid experiments, Hajimirzaie and Buchholz (2013) reported St w ≈ 0.35 for D/h ≈ 1 where the antisymmetric mode dominates. There are several differences in the flow conditions and geometry that can favor a stronger antisymmetric mode for high D/h values.…”

Section: Wake Regionmentioning

confidence: 81%

“…Several relevant experimental studies were conducted to investigate the hydrodynamics of flow past wall‐mounted, submerged, idealized‐shape obstacles (e.g., Hajimirzaie & Buchholz, 2013; Hajimirzaie et al, 2012; Martinuzzi & AbuOmar, 2003; Okajima, 1982; Okamoto & Sunabashiri, 1992; Okamoto & Uemura, 1991; Pattenden et al, 2005; Savory & Toy, 1986, 1988; Shamloo et al, 2001; Sumner et al, 2004). In particular, the eddies generated around fully submerged, low‐aspect‐ratio obstacles (e.g., streamline and transverse‐oriented semiellipsoids, vertical cylinders, and hemispheres) and the wake structure of these obstacles bear important similarities with those observed for isolated, partially burrowed mussels.…”

Section: Review Of Experimental and Numerical Investigationsmentioning

confidence: 99%

“…For a square cylinder with AR = 0.5 and a thin incoming boundary layer, Sattari et al (2010) reported St w = 0.33. Hajimirzaie and Buchholz (2013) reported St ≈ 0.185 for semiellipsoids with AR = 0.67–0.89, D/h ≈ 4 and a thin boundary layer at the location of the obstacle.…”

Section: Wake Regionmentioning

confidence: 99%

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Flow and Entrainment Mechanisms Around a Freshwater Mussel Aligned With the Incoming Flow

Constantinescu

Zeng

2020

Water Resources Research

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The paper uses information from eddy-resolving simulations to characterize flow and turbulence around freshwater mussels at the organism scale. The focus is on the simplest case of a partially burrowed, isolated mussel aligned with the incoming flow in an open channel. The wake structure and the capacity of the flow to displace the mussel from the bed substrate and to induce local scour around the mussel are investigated as a function of the ratio between the height of the exposed part of the mussel, h, and the total mussel height, d, and as a function of the filtration velocity ratio (VR) between the incoming channel flow velocity, U 0 , and the mean velocity inside the excurrent siphon, U e. As opposed to the flow past most surface-mounted obstacles where the bed shear stresses are reduced in the wake of the body, the capacity of the flow to induce bed erosion behind isolated mussels aligned with the flow is relatively large because of strong downwelling motions inside the horizontal separated shear layers. These flow features are associated with the formation of counterrotating base vortices of unequal coherence that induce upwash behind the mussel. The total circulation of the base vortices increases with increasing h/d and VR. Though both symmetrical and antisymmetrical shedding are observed in the wake, the antisymmetrical mode dominates, and its strength increases with increasing VR. The nondimensional streamwise force acting on the emerged part of the mussel's shell increases with increasing h/d and VR. Finally, the paper discusses the effects of varying h/d and VR on the dynamics and dilution of the jet of filtered water originating in the excurrent siphon, which is important to understand how mussels affect mixing and water quality (e.g., nutrient availability and phytoplankton concentration) in natural streams.

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Section: Wake Regionmentioning

confidence: 81%

Section: Review Of Experimental and Numerical Investigationsmentioning

confidence: 99%

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Flow and Entrainment Mechanisms Around a Freshwater Mussel Aligned With the Incoming Flow

Constantinescu

Zeng

2020

Water Resources Research

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“…where St denotes the dimensionless Strouhal number; it is recalled also that d c denotes the boulder diameter and U dc denotes the boulder approach velocity averaged over the boulder height. A review of reported studies with flow and obstacle characteristics that are most similar to those herein yielded a range of St = 0.14-0.24 for the wake structures and St = 0.17-0.3 for the stoss structures such as the HSV (Ettema et al, 2006;Hajimirzaie et al, 2014;Hajimirzaie & Buchholz, 2013;Lacey & Rennie, 2012;Okamoto, 1982;Paik et al, 2007). Therefore, the commonly used value of St = 0.20 was considered hereafter to estimate T BE .…”

Section: 1029/2018jf004753mentioning

confidence: 84%

Boulder Array Effects on Bedload Pulses and Depositional Patches

et al. 2018

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The influence of boulders in high gradient gravel‐bed rivers can be significant. Yet few studies have isolated their role in regulating bedload. It is hypothesized that boulder relative submergence and the corresponding eddies developing around boulders affect the frequency of bedload pulsations and the location of sediment deposits. Results show the occurrence of two distinct timescales in bedload exiting a boulder array, which were identified via time series analysis. These are the small‐scale periodicity, PS, and the large‐scale periodicity, PL. PS was identified in the range of 4–6 min and is believed to result from congested bedload movement due to reduced conveyance area within the array. PL was identified in the range of 8–46 min. It is suggested that PL corresponds to large bedload releases around boulders, which the authors consider to be caused by feedbacks between boulder eddies and bedload deposits. It is also found that boulder submergence and Froude number, Fr, influence the location of predominant deposition. At High Relative Submergence, deposition occurs in the boulder wake regions. At Low Relative Submergence, deposition instead occurs upstream of boulders in locations that depend on Fr. For Fr < 1, material deposits in the stoss of boulders due to the necklace structure of the horseshoe vortex. However, for Fr > 1, material deposits at the flanks of boulders due to the influence of local wave crests around boulders. The trapping efficiency of boulders reduces the dimensionless mean bedload transport rate by three orders of magnitude compared to conditions without boulders.

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“…The relative importance of the aforementioned factors may vary across different scenarios. 3, [26][27][28][29] So far, most of the existing studies address the influence of only one or two factors, and, therefore, the integrated effect of several parameters is still not fully understood. 2,3 Some interesting flow phenomena have been revealed by previous studies, such as the U-shaped horseshoe vortex system originating in front of a cylinder and extending downstream from either side of the cylinder; the flow separation from the leading edge of the top and side faces of the cylinder; the downward-directed flow from the top of the cylinder (viz., the downwash) and the recirculation region in the near-wake behind the cylinder.…”

Section: Introductionmentioning

confidence: 99%

Direct numerical simulation of flow around a surface-mounted finite square cylinder at low Reynolds numbers

Zhang

Cheng

et al. 2017

Physics of Fluids

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With the aid of direct numerical simulation, this paper presents a detailed investigation on the flow around a finite square cylinder at a fixed aspect ratio (AR) of 4 and six Reynolds numbers (Re = 50, 100, 150, 250, 500, and 1000). It is found that the mean streamwise vortex structure is also affected by Re, apart from the AR value. Three types of mean streamwise vortices have been identified and analyzed in detail, namely, “Quadrupole Type” at Re = 50 and Re = 100, “Six-Vortices Type” at Re = 150 and Re = 250, and “Dipole Type” at Re = 500 and Re = 1000. It is the first time that the “Six-Vortices Type” mean streamwise vortices are reported, which is considered as a transitional structure between the other two types. Besides, three kinds of spanwise vortex-shedding models have been observed in this study, namely, “Hairpin Vortex Model” at Re = 150, “C and Reverse-C and Hairpin Vortex Model (Symmetric Shedding)” at Re = 250, and “C and Reverse-C and Hairpin Vortex Model (Symmetric/Antisymmetric Shedding)” at Re = 500 and Re = 1000. The newly proposed “C and Reverse-C and Hairpin Vortex Model” shares some similarities with “Wang’s Model” [H. F. Wang and Y. Zhou, “The finite-length square cylinder near wake,” J. Fluid Mech. 638, 453–490 (2009)] but differs in aspects such as the absence of the connection line near the free-end and the “C-Shape” vortex structure in the early stage of the formation of the spanwise vortex.

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Flow dynamics in the wakes of low-aspect-ratio wall-mounted obstacles

Cited by 15 publications

References 33 publications

Flow and Entrainment Mechanisms Around a Freshwater Mussel Aligned With the Incoming Flow

Flow and Entrainment Mechanisms Around a Freshwater Mussel Aligned With the Incoming Flow

Boulder Array Effects on Bedload Pulses and Depositional Patches

Direct numerical simulation of flow around a surface-mounted finite square cylinder at low Reynolds numbers

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