Roughness effect on turbulent flow structure beneath a simulated ice jam

Nyantekyi-Kwakye, Baafour; Pahlavan, Hoda; Clark, Shawn P.; Tachie, Mark F.; Dow, Karen

doi:10.1080/00221686.2018.1473298

Cited by 10 publications

(4 citation statements)

References 22 publications

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“…In recent times, particle image velocimetry (PIV) has gained prominence for conducting velocity measurements under simulated ice-covered flows due to its ability to map the spatial flow field. The present authors have conducted detailed PIV measurements to investigate turbulent structures beneath a simulated ice jam and reported the findings in Nyantekyi- Kwakye et al (2018). Based on the previous findings, the objective of the present experiment was to quantify the flow characteristics beneath a simulated rough ice jam using a high-resolution PIV for different discharges as well as upstream jam angles; and also assess the performance of traditional field measurement techniques (two-point, three-point, the six-tenths depth).…”

Section: R a F Tmentioning

confidence: 79%

“…Based on the configuration of jams, the flow beneath them is subjected to varying pressure gradients, such as favorable pressure gradient (FPG) and adverse pressure gradient (APG) within the upper and lower toe sections, respectively. The existence of different pressure gradients beneath the jam modifies the turbulent flow characteristics considerably compared to events in open water and uniformly ice-covered flows (Nyantekyi-Kwakye et al 2018).…”

Section: Introductionmentioning

confidence: 99%

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Effect of discharge and upstream jam angle on the flow distribution beneath a simulated ice jam

et al. 2019

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The velocity field beneath simulated rough ice jams under various upstream jam angles and discharge were investigated using a particle image velocimetry system. Three discharges were examined at 2.3 L/s, 3.4 L/s, and 4.0 L/s and two upstream ice jam angles were tested at 4° and 6°. Increasing the discharge resulted in high turbulence production beneath the jam. The adverse pressure gradient exerted on the flow increased the levels of the Reynolds shear stress. The measured velocities beneath the jam were used to assess the performances of three traditional field measurement techniques as well as the validity of the two-parameter power law. The two-point measurement technique performed remarkably well with the least mean bias error of 2.0%. The error associated with the different techniques showed their inability to accurately predict the average velocity under high discharge. The two-parameter power law accurately predicted velocity profiles within the equilibrium section of the jam, but failed within the boundary layers when the flow was subjected to a pressure gradient.

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Section: R a F Tmentioning

confidence: 79%

Section: Introductionmentioning

confidence: 99%

Effect of discharge and upstream jam angle on the flow distribution beneath a simulated ice jam

et al. 2019

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“…The displacement thickness and momentum thickness at the leading edge of the cascade decrease with the increase of roughness and show a trend of decreasing first and then increasing in the latter half. When the roughness is 74 μm, the displacement thickness, momentum thickness, and shape factor at the back of the cascade are the minimum (Wu and Piomelli, 2018;Rodriguez et al, 2017;Butler and Wu, 2018;Nyantekyi-Kwakye et al, 2019;Mendonca and Sharif, 2010;Xu et al, 2020;Zhou et al, 2021;Spalart and Watmuff, 1993;Li et al, 2020;Lee et al, 2018;Schlichting, 1936;Atmani et al, 2009;Goldfeld and Orlik, 2005;Back et al, 2009).…”

Section: Discussionmentioning

confidence: 99%

Effect of Cascade Surface Roughness on Boundary Layer Flow Under Variable Conditions

Liu

Zhou

et al. 2022

Front. Energy Res.

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Under the influence of many factors, the surface roughness of the cascade will change during turbomachinery operation, which will affect the boundary layer flow of the cascade. In this article, the effects of cascade surface roughness on boundary layer flow under variable conditions are analyzed by experiments and numerical simulation. The results show that with the increase of roughness, the total pressure loss coefficient of the cascade decreases first and then increases. The larger the Reynolds number is, the greater the total pressure loss coefficient is, and the sensitive area of loss change is changed. In the sensitive area, the roughness has a greater influence on cascade loss. There are separation bubbles at the suction front edge of smooth cascades. With the increase of roughness, the degree of turbulence increases, and the transition process is accelerated. When the roughness is between 74 and 150 μm, the separation bubble disappears and the separation loss decreases. In conclusion, the aerodynamic loss of the cascade increases with the increase of roughness, and the cascade efficiency decreases. However, roughness can restrain the flow separation and reduce the separation loss. The two have gone through a process of one and the other. When the roughness is 74 μm, the displacement thickness, momentum thickness, and shape factor at the back of the cascade are the minimum.

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“…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). It is a known fact that surface roughness generally increases the wall shear stress that initiates scouring along the riverbed.…”

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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Roughness effect on turbulent flow structure beneath a simulated ice jam

Cited by 10 publications

References 22 publications

Effect of discharge and upstream jam angle on the flow distribution beneath a simulated ice jam

Effect of discharge and upstream jam angle on the flow distribution beneath a simulated ice jam

Effect of Cascade Surface Roughness on Boundary Layer Flow Under Variable Conditions

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

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