Evaluation of Incipient Motion of Sand Particles by Different Indirect Methods in Erosion Function Apparatus

An experiment was carried out in an acrylic glass-sided re-circulating closed conduit with a rectangular cross section, which is similar in construction to an erosion function apparatus. An adjustable sand box, made of acrylic glass, was attached to the bottom of the conduit as the sand zone or the test section. The hydraulics of the flow in the erosion function apparatus is complicated due to the limited part of the non-smooth and erodible soil surface attached to the closed conduit. As the bed shear stress changes with the bed roughness, even though the flow velocity does not change, establishing a method to estimate the incipient motion is an important challenge for an erosion function apparatus. The present study was conducted to explore the incipient motion of sands from bed shear stress estimated by four different indirect methods on both the sand bed and the smooth bed installed in the erosion function apparatus. In the experiment, particle image velocimetry (PIV) was used to investigate flow dynamics and incipient motion in terms of dimensionless critical bed shear stress. The experimental results show that the bed shear stress estimated from the log-law profiles in the sand zone and the smooth zones are relatively higher than those of the other indirect methods. The dimensionless critical bed shear stress of threshold condition evaluated by all indirect methods was found in good agreement with those of previous results in both zones. The Manning roughness and Darcy–Weisbach friction coefficients were evaluated based on the critical shear velocity at the incipient motion. Although these coefficients were found slightly greater in the smooth zone than in the sand zone, in both zones, they showed good agreement with previous studies.

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Critical bed shear for initial movement of sediments on a combined lateral and longitudinal slope

Hydrology Research ◽

10.2166/nh.2004.0011 ◽

2004 ◽

Vol 35 (2) ◽

pp. 153-164 ◽

Cited By ~ 7

Author(s):

Subhasish Dey

Keyword(s):

Shear Stress ◽

Flow Direction ◽

Side Wall ◽

Shear Stresses ◽

Bed Shear Stress ◽

Conduit Flow ◽

Sloping Bed ◽

Stress Ratios ◽

Closed Conduit ◽

Initial Movement

An experimental study on critical bed shear-stress for initial movement of non-cohesive sediment particles under a steady-uniform stream flow on a combined lateral (across the flow direction) and longitudinal (streamwise direction) sloping bed is presented. The aim of this paper is to ascertain that the critical bed shear-stress on a combined lateral and longitudinal sloping bed is adequately represented by the product of critical bed shear-stress ratios for lateral and longitudinal sloping beds. Experiments were carried out with closed-conduit flow, in two ducts having a semicircular invert section, with three sizes of sediments. In laboratory flumes, the uniform flow is a difficult – if not impossible – proposition for a steeply sloping channel, and is impossible to obtain in an adversely sloping channel. To avoid this problem, the experiments were conducted with a closed-conduit flow. The critical bed shear-stresses for experimental runs were estimated from side-wall correction. The experimental data agree satisfactorily with the results obtained from the proposed formula.

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Experimental study of the turbulent boundary layer in acceleration-skewed oscillatory flow

Journal of Fluid Mechanics ◽

10.1017/jfm.2011.300 ◽

2011 ◽

Vol 684 ◽

pp. 251-283 ◽

Cited By ~ 62

Author(s):

Dominic A. van der A ◽

Tom O’Donoghue ◽

Alan G. Davies ◽

Jan S. Ribberink

Keyword(s):

Boundary Layer ◽

Shear Stress ◽

Reynolds Stress ◽

Oscillatory Flow ◽

Bed Shear Stress ◽

Flow Conditions ◽

Oscillatory Boundary Layer ◽

Layer Flow ◽

Momentum Integral ◽

Good Agreement

AbstractExperiments have been conducted in a large oscillatory flow tunnel to investigate the effects of acceleration skewness on oscillatory boundary layer flow over fixed beds. As well as enabling experimental investigation of the effects of acceleration skewness, the new experiments add substantially to the relatively few existing detailed experimental datasets for oscillatory boundary layer flow conditions that correspond to full-scale sea wave conditions. Two types of bed roughness and a range of high-Reynolds-number, $\mathit{Re}\ensuremath{\sim} O(1{0}^{6} )$, oscillatory flow conditions, varying from sinusoidal to highly acceleration-skewed, are considered. Results show the structure of the intra-wave velocity profile, the time-averaged residual flow and boundary layer thickness for varying degrees of acceleration skewness, $\ensuremath{\beta} $. Turbulence intensity measurements from particle image velocimetry (PIV) and laser Doppler anemometry (LDA) show very good agreement. Turbulence intensity and Reynolds stress increase as the flow accelerates after flow reversal, are maximum at around maximum free-stream velocity and decay as the flow decelerates. The intra-wave turbulence depends strongly on $\ensuremath{\beta} $ but period-averaged turbulent quantities are largely independent of $\ensuremath{\beta} $. There is generally good agreement between bed shear stress estimates obtained using the log-law and using the momentum integral equation, and flow acceleration skewness leads to high bed shear stress asymmetry between flow half-cycles. Turbulent Reynolds stress is much less than the shear stress obtained from the momentum integral; analysis of the stress contributors shows that significant phase-averaged vertical velocities exist near the bed throughout the flow cycle, which lead to an additional shear stress, $\ensuremath{-} \rho \tilde {u} \tilde {w} $; near the bed this stress is at least as large as the turbulent Reynolds stress.

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Comparison of Different Methods to Calculate Bed Shear Stress

Water Science & Technology ◽

10.2166/wst.1992.0187 ◽

1992 ◽

Vol 25 (8) ◽

pp. 131-140 ◽

Cited By ~ 5

Author(s):

M. R. Kabir ◽

H. Torfs

Keyword(s):

Shear Stress ◽

Velocity Profile ◽

Cross Section ◽

Friction Velocity ◽

Rectangular Cross Section ◽

Reference Level ◽

Bed Shear Stress ◽

Rough Bed ◽

Channel Slope

Precise velocity profile measurements were carried out in a fully developed, subcritical and supercritical flow on a smooth and a rough bed in a flume with a rectangular cross section. In both cases different approaches were used to calculate the friction velocity, u*, and comparisons were made. The influence of the reference level (hypothetical bed level) has been discussed. Friction velocities calculated from the velocity profile are very sensitive to the hypothetical bed level. For a smooth bed the determination of the reference level does not present any difficulties. However, for a rough bed this level shows dependency on the channel slope.

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TIME-DEPENDENT WAVE SHEAR STRESS

Coastal Engineering Proceedings ◽

10.9753/icce.v21.81 ◽

1988 ◽

Vol 1 (21) ◽

pp. 81

Author(s):

Suphat Vongvisessomjai

Keyword(s):

Shear Stress ◽

Suspended Sediments ◽

Measured Data ◽

Time Dependent ◽

Water Tunnel ◽

Shear Stresses ◽

Bed Shear Stress ◽

Measured Concentration ◽

The Third ◽

Good Agreement

A knowledge of bed shear stress induced by waves is required to understand dynamic processes of nearshore morphologies as a results of sediment transport. However, the information on the stress is still incomplete due to lack of measured data. The study analyzes the unsteady horizontally averaged shear stresses measured over mobile beds in a water tunnel. It is found from the analysis that the presence of the third and fifth harmonics in the shear stress is in good agreement with the measured concentration of suspended sediments.

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MEASUREMENT OF BED SHEAR STRESS UNDER WAVES

Coastal Engineering Proceedings ◽

10.9753/icce.v13.29 ◽

1972 ◽

Vol 1 (13) ◽

pp. 29 ◽

Cited By ~ 2

Author(s):

H.P. Riedel ◽

J.W. Kamphuis ◽

A. Brebner

Keyword(s):

Shear Stress ◽

Turbulent Flow ◽

Flow Regimes ◽

Wave Theory ◽

Bed Shear Stress ◽

First Order ◽

Turbulent Flow Regime ◽

Shear Plate ◽

Wave Boundary ◽

Good Agreement

Shear stress measurements on both smooth and sand roughened beds were carried out in an oscillating water tunnel using a flexurally supported shear plate. The range of simulated wave boundary layers covered practically any situation possible in the field or laboratory. In the laminar range good agreement is obtained with the theoretical shear stress calculated from first order wave theory. However, in the turbulent flow regimes the experimental data indicates that theory results in an overestimate of the shear force by 20-50%. Limits of laminar, smooth turbulent and rough turbulent flow regimes are determined and it appears that the rough turbulent flow regime may itself be subdivided into two sections, each having different turbulence characteristics.

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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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