Flow characteristics of an offset jet over a surface mounted square rib

Nyantekyi-Kwakye, Baafour; Tachie, Mark F.; Clark, Shawn P.

doi:10.1080/14685248.2016.1174779

Cited by 9 publications

(7 citation statements)

References 36 publications

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“…The apparent dominant spectra peaks at low frequencies (f 4 0.5 Hz) in Figure 12, illustrates the dominance of large-scale structures. The present observation corroborates reports by Dey et al 23 and Nyantekyi-Kwakye et al 43 for a submerged plane and 3D offset jets, respectively. Within the symmetry plane, the present result was qualitatively similar for all the test cases investigated.…”

Section: Turbulent Scalessupporting

confidence: 93%

“…In addition, the present results depict that the turbulent structures are more temporally correlated within the recirculation and developing region compared to the reattachment region of the flow. This is due to the breakdown of turbulent structures when the discharged jet reattaches to the bottom of the channel, which supports previous observations by Nyantekyi-Kwakye et al 43 Figure 17 shows the computed integral length scales using equation ( 8) with streamwise distance. Figure 17(a) reveals the dominance of larger turbulent structures within the recirculation region of the flow-an observation that corroborates the high energy levels reported in previous section at the early development of the jet.…”

Section: Turbulent Scalessupporting

confidence: 88%

“…23 and Nyantekyi-Kwakye et al. 43 for a submerged plane and 3D offset jets, respectively. Within the symmetry plane, the present result was qualitatively similar for all the test cases investigated.…”

Section: Resultsmentioning

confidence: 98%

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Large-scale motion of submerged offset jets issuing from sharp-edged rectangular nozzles

Nyantekyi-Kwakye

2020

Proceedings of the Institution of Mechanical Engineers, Part C:

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The mean flow, turbulence characteristics, and dynamics of large-scale vortices are investigated for an offset jet issuing from different nozzle expansion ratios using a four-receiver acoustic Doppler velocimeter. The jet was discharged from sharp-edged rectangular nozzles with expansion ratios of 0.24, 0.49, 0.75, and 1.00 at Reynolds number of 5.3 × 104. The decay rate of the maximum mean velocity decreased with increasing expansion ratio due to suppressed lateral entrainment of ambient fluid. The acoustic Doppler velocimeter proved capable of providing high-quality data to investigate the energy spectrum and turbulent structures embedded in the flow. Large-scale vortices dominated the recirculation region compared to the reattachment and developing regions of the jet. Increasing the expansion ratio resulted in larger order of magnitude of the vortices within the recirculation region. The turbulent structures stretched in the lateral direction in regions where smaller-sized structures existed in the streamwise direction and vice versa.

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Section: Turbulent Scalessupporting

confidence: 93%

Section: Turbulent Scalessupporting

confidence: 88%

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Large-scale motion of submerged offset jets issuing from sharp-edged rectangular nozzles

Nyantekyi-Kwakye

2020

Proceedings of the Institution of Mechanical Engineers, Part C:

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“…As the gap length increases, scatter plot forms an elongated shape with the major axis inclined to the second and fourth quadrants, Q2 (ejection) and Q4 (sweep). Uneven distribution of velocity fluctuations indicates the anisotropic nature of the turbulence field and specifically dominance of sweep and ejection represents the existence of turbulent coherent structures (Nyantekyi‐Kwakye et al., 2016; Sambrook Smith et al., 2005). The size of the scatter plot remains consistent when the flow structures are fully developed, i.e., increasing the gap length does not further enhance the turbulence levels.…”

Section: Resultsmentioning

confidence: 99%

Turbulent Coherent Flow Structures to Predict the Behavior of Particles With Low to Intermediate Stokes Number Between Submerged Obstacles in Streams

You

Tinoco

2023

Water Resources Research

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Transport of particles in rivers is a fundamental process in aquatic ecosystems relevant to various engineering and scientific problems, such as the removal of polluted particles, transport of organisms, optimal sampling of organic matter and sediment transport (McQueen et al., 2021;Prada et al., 2021;Shi et al., 2021). Since Elghobashi (1994) first defined the order of interaction between particle and turbulence based on volume fraction and time scales, flow physics became a significant aspect to understand the transport mechanism of particulate matter. For instance, microplastic pollution, which causes detrimental effect on aquatic biota and requires effective management strategies, can also be analyzed based on the close relation between flow and particulate matter (McCormick et al., 2014). Common obstacles in freshwater such as branches, logs, and hydraulic structures, are identified as local hotspots of particles as the obstacles create flow structures and influence their retention in water (Carmen et al., 2021;Kapp & Yeatman, 2018;Prada et al., 2020). Similarly, laboratory studies have been carried out to quantitively measure the transport and retention of drifting particles and devise effective removal techniques (Boos et al., 2021;Miehls et al., 2020;Palmer et al., 2004).Despite the wide application and numerous studies on particle transport, the knowledge about their interactions with aquatic ecosystems is still lacking due to the difficulties of analyzing continuous flow and discrete particles simultaneously. Immersed obstacles such as vegetation, bedforms, and hydraulic structures, complicate the analysis by introducing specific ranges of flow structures which affect transport of particles (Chung et al., 2021;Le Ribault et al., 2021;Soleimani & Ketabdari, 2020). Laboratory and numerical studies often simplify the complicated geometry and arrangement of such obstructions to understand how submerged obstacles disturb the flow, and questions remain on how to thoroughly account for the effects of transport mechanism of particles (Follett et al., 2021;Park & Hwang, 2019). Such simplifications include assumptions that replicate either cavity flow or porous flow media.Cavity flow is a classical problem that investigates how flow structures evolve in the presence of submerged obstacles with a simplified geometry. Depending on the aspect ratio of the cavity, the flow is categorized into: (a) closed cavity flow with a shear layer reattached to the bottom, (b) open cavity flow with the cutout bridged

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“…In river flows, surface roughness can result from the composition of the riverbed, localized scouring and subsequent sediment transport and deposition (Piqué et al, 2016;Su & Lu, 2016). Surface roughness plays a crucial role in the formation and evolution of coherent structures in turbulent flows (Medjnoun et al, 2023;Nyantekyi-Kwakye et al, 2016). The presence of roughness elements on a surface can disrupt the smooth flow of fluid, leading to the generation of coherent structures (Nyantekyi-Kwakye et al, 2019).…”

Section: Introductionmentioning

confidence: 99%

Turbulent structures beneath semi-submerged simulated ice cover over smooth and rough bed in a shallow channel

Nyantekyi-Kwakye,

Saeedi

2024

Preprint

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The effect of bed roughness on shear layer separation and the structure of turbulence in a shallow channel is evaluated. A planar particle velocimetry system is used to conduct detailed instantaneous velocity measurements beneath the simulated ice cover. The results show that although surface roughness modifies near-wall turbulence, once shear layer separation occurs, it becomes the controlling parameter of turbulence for flow shallow channels. The instantaneous velocity field show elongated separated shear layer underneath the cover for flow over the smooth bed compared to the rough bed. For the current shallow channel, the bed roughness significantly reduced the size of the separation bubble at the undersurface of the cover. The instantaneous size of the separated bubble expands and contracts depicting intense shear layer flapping at the undersurface of the cover, and this is dominant for the smooth bed flow. Close to the leading edge of the cover, the instantaneous spanwise vorticity magnitude shows dominance of small-scale instabilities akin to the Kelvin-Helmholtz type instability at interface of the separated shear layer. The Q-criterion and swirling strength revealed that separation of the shear layer generated large-scale vortices of varying length scale when compared to the bed roughness. The bed roughness promotes near-wall turbulence with elevated levels of Reynolds stresses compared to the smooth bed. However, at the undersurface of the cover, the high levels of turbulence were controlled by the flow separation. Compared to the bed roughness, a wide range of integral length scales are estimated within the separated shear layer, which contributed significantly to the generation of Reynolds stresses.

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Flow characteristics of an offset jet over a surface mounted square rib

Cited by 9 publications

References 36 publications

Large-scale motion of submerged offset jets issuing from sharp-edged rectangular nozzles

Large-scale motion of submerged offset jets issuing from sharp-edged rectangular nozzles

Turbulent Coherent Flow Structures to Predict the Behavior of Particles With Low to Intermediate Stokes Number Between Submerged Obstacles in Streams

Turbulent structures beneath semi-submerged simulated ice cover over smooth and rough bed in a shallow channel

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