Design of measuring instrument with whole direct method for bed shear stress under two-dimensional water-flow co-action

To simulate the initial formation of sedimentary bedforms, constrained to be in hydraulically smooth turbulent flows under bedload conditions, a numerical model based on Large Eddy Simulation (LES) in a doubly periodic domain has been developed. The numerical model comprises three parts. Given the instantaneous bed geometry, the bed shear stress distribution is obtained from a Large-Eddy-Simulation (LES) method coupled with an Immersed-Boundary-Method (IBM). Flux is estimated by the van Rijn’s formula [1]. Finally, evolution of the bed surface is described by the Exner equation. “Two-dimensional bed” [2] and “three-dimensional bed” models employ, respectively, transversely averaged bed shear stress and instantaneous local shear stress to estimate the bedload flux. Based on this model, the evolution of an initial sand wave has been successfully computed. Compared to the “two-dimensional” [2] model, the three-dimensional model leads to a slightly slower propagation and a smaller sand wave. The tendency of the sand wave evolution in three-dimensional model is two-dimensional during the simulated interval.

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A Moment-Based Chezy Formula for Bed Shear Stress in Varied Flow

Water ◽

10.3390/w13091254 ◽

2021 ◽

Vol 13 (9) ◽

pp. 1254

Author(s):

Mohamed Elgamal

Keyword(s):

Shear Stress ◽

Water Flow ◽

Vertical Integration ◽

Numerical Models ◽

Calibration Coefficient ◽

Bed Shear Stress ◽

Flow Conditions ◽

Velocity Scale ◽

Moment Models ◽

New Formula

Despite its limitations, the Chezy bed shear stress formula is commonly used in depth-averaged flow numerical models as closure for estimating mutual tractive stresses with underneath boundaries. This paper proposes a novel moment-based formula that could be considered a revised version of the Chezy formula and can be used to estimate local variations of the bed shear stress under more complex and varied flow conditions with accelerating–decelerating flow fields. The formula depends on two velocity scales: the depth-averaged velocity, Uo, and a new moment-based velocity scale, u1. The new formula is calibrated using 10 experiments for flow over fixed bedforms, and the calibration coefficient is found to linearly correlate with h/Δ and h/zo ratios. The formula is also applied for the case of air flow across a negative step, jet water flow downstream a gate, and 2D water flow downstream an oblique negative step, and reasonably satisfactory agreement with the measured data is found. The new formula could be used in vertically averaged and moment models to disclose part of the information already lost by the vertical integration procedure.

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A comparison of two-dimensional and three-dimensional flow structures over artificial pool-riffle sequences

Canadian Journal of Civil Engineering ◽

10.1139/cjce-2017-0274 ◽

2017 ◽

Vol 44 (12) ◽

pp. 1084-1098 ◽

Cited By ~ 1

Author(s):

Elham Fazel Najafabadi ◽

Hossein Afzalimehr ◽

Jueyi Sui

Keyword(s):

Shear Stress ◽

Velocity Gradient ◽

Channel Wall ◽

Reynolds Shear Stress ◽

Three Dimensional ◽

Flow Structures ◽

Bed Shear Stress ◽

Two Dimensional ◽

Three Dimensional Flow ◽

Secondary Currents

Experiments have been carried out in a flume with one 2D pool-riffle sequence and one 3D pool-riffle sequence, respectively. Objectives of this study are to determine whether or not the convergence of lateral flow exists. Variations of the near-bed shear stress have been studied. The characteristics of the secondary currents along a pool-riffle sequence have been investigated. Results showed that for the 3D pool-riffle sequence, the near-bed velocity decreases along convective deceleration flow (CDF) and increases along convective acceleration flow (CAF), respectively. It is found that the shear velocities estimated from the slope of the velocity gradient in the inner layer, decrease in the CDF section, and increase in the CAF section in the 3D pool-riffle sequences. The Reynolds shear stress is highest at the CDF section along longitudinal lines with distances of 10 cm and 20 cm away from the channel wall.

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Correction: Development of a Two-Dimensional Wall Shear Stress Sensor for Wind Tunnel Applications

AIAA Scitech 2019 Forum ◽

10.2514/6.2019-2045.c1 ◽

2019 ◽

Author(s):

Brett Freidkes ◽

David A. Mills ◽

Casey Keane ◽

Lawrence S. Ukeiley ◽

Mark Sheplak

Keyword(s):

Shear Stress ◽

Wind Tunnel ◽

Wall Shear Stress ◽

Two Dimensional ◽

Stress Sensor ◽

Shear Stress Sensor ◽

Wall Shear

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Methods and computer program documentation for determining anisotropic transmissivity tensor components of two-dimensional ground-water flow

Open-File Report ◽

10.3133/ofr86227 ◽

1986 ◽

Cited By ~ 11

Author(s):

M.L. Maslia ◽

R.B. Randolph

Keyword(s):

Computer Program ◽

Ground Water ◽

Water Flow ◽

Two Dimensional ◽

Ground Water Flow ◽

Anisotropic Transmissivity

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Efficiency prediction for storage chambers using computational fluid dynamics

Water Science & Technology ◽

10.2166/wst.1996.0202 ◽

1996 ◽

Vol 33 (9) ◽

pp. 163-170 ◽

Cited By ~ 4

Author(s):

Virginia R. Stovin ◽

Adrian J. Saul

Keyword(s):

Fluid Dynamics ◽

Computational Fluid Dynamics ◽

Shear Stress ◽

Particle Tracking ◽

Critical Value ◽

Complex Geometries ◽

Bed Shear Stress ◽

Breadth Ratio ◽

Computational Fluid Dynamics Cfd ◽

Simulated Flow

Research was undertaken in order to identify possible methodologies for the prediction of sedimentation in storage chambers based on computational fluid dynamics (CFD). The Fluent CFD software was used to establish a numerical model of the flow field, on which further analysis was undertaken. Sedimentation was estimated from the simulated flow fields by two different methods. The first approach used the simulation to predict the bed shear stress distribution, with deposition being assumed for areas where the bed shear stress fell below a critical value (τcd). The value of τcd had previously been determined in the laboratory. Efficiency was then calculated as a function of the proportion of the chamber bed for which deposition had been predicted. The second method used the particle tracking facility in Fluent and efficiency was calculated from the proportion of particles that remained within the chamber. The results from the two techniques for efficiency are compared to data collected in a laboratory chamber. Three further simulations were then undertaken in order to investigate the influence of length to breadth ratio on chamber performance. The methodology presented here could be applied to complex geometries and full scale installations.

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The Departure from Equilibrium of Turbulent Boundary Layers

Aeronautical Quarterly ◽

10.1017/s0001925900004418 ◽

1968 ◽

Vol 19 (1) ◽

pp. 1-19 ◽

Cited By ~ 8

Author(s):

H. McDonald

Keyword(s):

Boundary Layer ◽

Shear Stress ◽

Kinetic Energy ◽

Stress Distribution ◽

Boundary Layers ◽

Turbulent Boundary Layers ◽

Two Dimensional ◽

Pressure Distributions ◽

Momentum Integral ◽

State Examination

SummaryRecently two authors, Nash and Goldberg, have suggested, intuitively, that the rate at which the shear stress distribution in an incompressible, two-dimensional, turbulent boundary layer would return to its equilibrium value is directly proportional to the extent of the departure from the equilibrium state. Examination of the behaviour of the integral properties of the boundary layer supports this hypothesis. In the present paper a relationship similar to the suggestion of Nash and Goldberg is derived from the local balance of the kinetic energy of the turbulence. Coupling this simple derived relationship to the boundary layer momentum and moment-of-momentum integral equations results in quite accurate predictions of the behaviour of non-equilibrium turbulent boundary layers in arbitrary adverse (given) pressure distributions.

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