Flow Partitioning in Rectangular Open Channel Flow

Hydraulic engineers often divide a flow region into subregions to simplify calculations. However, the implementation of flow divisibility remains an open issue and has not yet been implemented as a fully developed mathematical tool for modeling complex channel flows independently of experimental verification. This paper addresses whether a three-dimensional flow is physically divisible, meaning that division lines with zero Reynolds shear stress exist. An intensive laboratory investigation was conducted to carefully measure the time-averaged velocity in a rectangular open channel flow using a laser Doppler anemometry system. Two innovative methods are employed to determine the locations of division lines based on the measured velocity profile. The results clearly reveal that lines with zero total shear stress are discernible, indicating that the flow is physically divisible. Moreover, the experimental data were employed to test previously proposed methods of calculating division lines, and the results show that Yang and Lim’s method is the most reasonable predictor.

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Effect of aspect ratio on developing and developed narrow open channel flow with rough bed

Canadian Journal of Civil Engineering ◽

10.1139/cjce-2017-0458 ◽

2018 ◽

Vol 45 (9) ◽

pp. 780-794 ◽

Cited By ~ 2

Author(s):

Minakshee Mahananda ◽

Prashanth Reddy Hanmaiahgari ◽

Ram Balachandar

Keyword(s):

Kinetic Energy ◽

Aspect Ratio ◽

Channel Flow ◽

Open Channel ◽

Reynolds Shear Stress ◽

Open Channel Flow ◽

Flow Region ◽

Channel Flows ◽

Open Channel Flows ◽

Rough Bed

This study attempts to unravel the effect of aspect ratio on the turbulence characteristics in developing and fully developed narrow open channel flows. In this regard, experiments were conducted in a rough bed open channel flow. Instantaneous 3D velocities were acquired using an acoustic Doppler velocimeter at various locations along the centerline of the flume. The variables of interest include the mean components of the flow velocity, turbulence intensity, wall normal Reynolds shear stress, correlation coefficient, turbulence kinetic energy, and anisotropy. A new correlation between the equivalent roughness and velocity shift from the smooth wall logarithmic equation as a function of aspect ratio is proposed. Aspect ratio was found to influence the velocity characteristics throughout the depth in the developing flow region, while the effects are confined to the outer layer for fully developed flows. New equations to describe the variation of turbulence intensities and turbulent kinetic energy are proposed for narrow open channel flows. Reynolds stress anisotropy analysis reveals that level of anisotropy in narrow open channel flow is less than in wide open channel flows. Finally, a linear regression model is proposed to predict flow development length in narrow open channel flows with a rough bed.

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Turbulence structure of a reattaching mixing layer

Journal of Fluid Mechanics ◽

10.1017/s0022112081000670 ◽

1981 ◽

Vol 110 ◽

pp. 171-194 ◽

Cited By ~ 130

Author(s):

C. Chandrsuda ◽

P. Bradshaw

Keyword(s):

Boundary Layer ◽

Shear Stress ◽

Reynolds Shear Stress ◽

Mixing Layer ◽

Three Dimensional ◽

Flow Region ◽

Turbulent Energy ◽

Turbulence Structure ◽

Hot Wire ◽

Recirculating Flow

Hot-wire measurements of second- and third-order mean products of velocity fluctuations have been made in the flow behind a backward-facing step with a thin, laminar boundary layer at the top of the step. Measurements extend to a distance of about 12 step heights downstream of the step, and include parts of the recirculating-flow region: approximate limits of validity of hot-wire results are given. The Reynolds number based on step height is about 105, the mixing layer being fully turbulent (fully three-dimensional eddies) well before reattachment, and fairly close to self-preservation in contrast to the results of some previous workers. Rapid changes in turbulence quantities occur in the reattachment region: Reynolds shear stress and triple products decrease spectacularly, mainly because of the confinement of the large eddies by the solid surface. The terms in the turbulent energy and shear stress balances also change rapidly but are still far from the self-preserving boundary-layer state even at the end of the measurement region.

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Closure to “Three-Dimensional Open Channel Flow”

Journal of the Hydraulics Division ◽

10.1061/jyceaj.0005392 ◽

1980 ◽

Vol 106 (3) ◽

pp. 457-458

Author(s):

Chao-Lin Chiu ◽

David E. Hsiung ◽

Hsin-Chi Lin

Keyword(s):

Channel Flow ◽

Open Channel ◽

Three Dimensional ◽

Open Channel Flow

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The Effect of Habitat Structure Boulder Spacing on Near-Bed Shear Stress and Turbulent Events in a Gravel Bed Channel

Water ◽

10.3390/w12051423 ◽

2020 ◽

Vol 12 (5) ◽

pp. 1423

Author(s):

Amir Golpira ◽

Fengbin Huang ◽

Abul B.M. Baki

Keyword(s):

Shear Stress ◽

Habitat Structure ◽

Open Channel ◽

Reynolds Shear Stress ◽

Three Dimensional ◽

Quadrant Analysis ◽

Bed Shear Stress ◽

Gravel Bed ◽

Restoration Practices ◽

Ejections And Sweeps

This study experimentally investigated the effect of boulder spacing and boulder submergence ratio on the near-bed shear stress in a single array of boulders in a gravel bed open channel flume. An acoustic Doppler velocimeter (ADV) was used to measure the instantaneous three-dimensional velocity components. Four methods of estimating near-bed shear stress were compared. The results suggested a significant effect of boulder spacing and boulder submergence ratio on the near-bed shear stress estimations and their spatial distributions. It was found that at unsubmerged condition, the turbulent kinetic energy (TKE) and modified TKE methods can be used interchangeably to estimate the near-bed shear stress. At both submerged and unsubmerged conditions, the Reynolds method performed differently from the other point-methods. Moreover, a quadrant analysis was performed to examine the turbulent events and their contribution to the near-bed Reynolds shear stress with the effect of boulder spacing. Generally, the burst events (ejections and sweeps) were reduced in the presence of boulders. This study may improve the understanding of the effect of the boulder spacing and boulder submergence ratio on the near-bed shear stress estimations of stream restoration practices.

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