scholarly journals Numerical Study for Near-Bed Variables in Velocity-Skewed Oscillatory Sheet Flow Transport

2017 ◽  
Vol 2017 ◽  
pp. 1-10
Author(s):  
Xin Chen ◽  
Zichao Zhang ◽  
Yong Li ◽  
Xiaoyan Shi
Keyword(s):  
Sediment Concentration ◽  
Sediment Flux ◽  
Phase Model ◽  
Phase Lag ◽  
Bed Sediment ◽  
Sheet Flow ◽  
Fall Velocity ◽  
Two Phase ◽  
Sediment Size ◽  
Flow Transport

The near-bed sediment concentration and vertical sediment flux are important in sediment transport mechanics, but they are known much less than the horizontal sediment flux, especially for fine sediment in unsteady flows. A developed two-phase model is applied to study the near-bed sediment concentration, vertical sediment flux, and the relevant total sediment amount for the velocity-skewed oscillatory sheet flow transport. With the sediment concentration hindered fall velocity, the classical reference concentration formulas conducted by Engelund and Fredsoe (1976) and Zyserman and Fredsoe (1994) are utilized for the comparison with the two-phase model and illustration of the phase-lag and sediment size effects in near-bed sediment concentration and vertical sediment flux. The concentration and vertical flux predicted by the two-phase model agree well with experimental data and are better than empirical formulas. Furthermore, the sediment size effect for pick-up flux function over starved bed is shown to be quite different from that containing sufficient sediment in oscillatory flows.

scholarly journals Investigation of sheet-flow processes based on novel acoustic high-resolution velocity and concentration measurements

2015 ◽  
Vol 767 ◽  
pp. 1-30 ◽  
Author(s):  
Thibaud Revil-Baudard ◽  
Julien Chauchat ◽  
David Hurther ◽  
Pierre-Alain Barraud
Keyword(s):  
Large Scale ◽  
Reynolds Shear Stress ◽  
Sediment Flux ◽  
Ensemble Averaging ◽  
Sheet Flow ◽  
Two Phase ◽  
Interface Position ◽  
Suspension Layer ◽  
The Mean ◽  
The Impact

AbstractA new dataset of uniform and steady sheet-flow experiments is presented in this paper. An acoustic concentration and velocity profiler (ACVP) is used to measure time-resolved profiles of collocated 2C velocity ($u,w$) and sediment concentration and to measure the time evolution of the bed interface position. Ensemble averaging over 11 similar experiment realisations is done to evaluate the mean profiles of streamwise velocity, concentration, sediment flux and Reynolds shear stress. The repeatability, stationarity and uniformity of the flow are carefully checked for a Shields number ${\it\theta}\approx 0.5$ and a suspension number of $S=1.1$. The mean profile analysis allows to separate the flow into two distinct layers: a suspension layer dominated by turbulence and a bed layer dominated by granular interactions. The bed layer can be further subdivided into a frictional layer capped by a collisional layer. In the suspension layer, the mixing length profile is linear with a strongly reduced von Karman parameter equal to 0.225. The Schmidt number is found to be constant in this region with a mean value of ${\it\sigma}_{s}=0.44$. The present results are then interpreted in terms of existing modelling approaches and the underlying assumptions are discussed. In particular, the well-known Rouse profile is shown to predict the concentration profile adequately in the suspension layer provided that all the required parameters can be evaluated separately. However, the strong intermittency of the flow observed in the bed layer under the impact of turbulent large-scale coherent flow structures suggests the limitations of averaged steady two-phase flow models.

Phase-lag effects in sheet flow transport

2006 ◽  
Vol 53 (5-6) ◽  
pp. 531-542 ◽  
Author(s):  
Benoît Camenen ◽  
Magnus Larson
Keyword(s):  
Phase Lag ◽  
Sheet Flow ◽  
Lag Effects ◽  
Flow Transport

scholarly journals MODELING COARSE SAND TRANSPORT UNDER SKEWED OSCILLATORY FLOW USING A CFD-DEM APPROACH

2018 ◽  
pp. 18
Author(s):  
Yashar Rafati ◽  
Zhen Cheng ◽  
Xiao Yu ◽  
Tian-Jian Hsu ◽  
Joseph Calantoni
Keyword(s):  
Sediment Transport ◽  
Surf Zone ◽  
Regional Scale ◽  
Breaking Waves ◽  
Coarse Sand ◽  
Sand Transport ◽  
Sheet Flow ◽  
Two Phase ◽  
Coastal Morphology ◽  
Flow Transport

Onshore/offshore sediment transport in the nearshore is an important mechanism driving the evolution of coastal morphology. The so-called sheet flow is a transport regime, in which the flow forces are intense such that a large amount of transport occurs in a concentrated layer near the bed. Onshore transport is often associated with flow skewness/asymmetry. In the nearshore zone, due to the bottom slope and wave shoaling, the wave velocity tends be onshore skewed before breaking in the surf zone. For breaking waves, the velocity asymmetry (or acceleration skewness) may also play a key role in determining net sediment transport. Understanding the net sediment transport rate in response to wave skewness/asymmetry is fundamental to a better prediction of sediment transport in regional scale morphodynamic models. In this study, we used an Euler-Lagrange two-phase model to study sheet flow transport of coarse sand under oscillatory flows subject to velocity/acceleration skewness.

Predictions of vertical sediment flux in oscillatory flows using a two-phase, sheet-flow model

2012 ◽  
Vol 48 ◽  
pp. 2-17 ◽  
Author(s):  
Xiao Yu ◽  
Tian-Jian Hsu ◽  
James T. Jenkins ◽  
Philip L.-F. Liu
Keyword(s):  
Flow Model ◽  
Sediment Flux ◽  
Sheet Flow ◽  
Two Phase ◽  
Oscillatory Flows

scholarly journals Critical conditions of bed sediment entrainment due to debris flow

2004 ◽  
Vol 4 (3) ◽  
pp. 469-474 ◽  
Author(s):  
M. Papa ◽  
S. Egashira ◽  
T. Itoh
Keyword(s):  
Shear Stress ◽  
Debris Flow ◽  
Erosion Rate ◽  
Sediment Concentration ◽  
Critical Conditions ◽  
Bed Shear Stress ◽  
Bed Sediment ◽  
Sediment Size ◽  
Flume Tests ◽  
Sediment Entrainment

Abstract. The present study describes entrainment characteristics of bed material into debris flow, based on flume tests, numerical and dimensional analyses. Flume tests are conducted to investigate influences of bed sediment size on erosion rate by supplying debris flows having unsaturated sediment concentration over erodible beds. Experimental results show that the erosion rate decreases monotonically with increase of sediment size, although erosion rate changes with sediment concentration of debris flow body. In order to evaluate critical condition of bed sediment entrainment, a length scale which measures an effective bed shear stress is introduced. The effective bed shear stress is defined as total shear stress minus yield stress on the bed surface. The results show that critical entrainment conditions can be evaluated well in terms of Shields curve using the effective bed shear stress instead of a usual bed shear stress.

scholarly journals Multi-dimensional rheology-based two-phase model for sediment transport and applications to sheet flow and pipeline scour

2016 ◽  
Vol 28 (5) ◽  
pp. 053305 ◽  
Author(s):  
Cheng-Hsien Lee ◽  
Ying Min Low ◽  
Yee-Meng Chiew
Keyword(s):  
Sediment Transport ◽  
Phase Model ◽  
Sheet Flow ◽  
Two Phase

A Study of Silt Erosion on Inner Buckets of Pelton Turbines

2014 ◽  
Vol 716-717 ◽  
pp. 644-649
Author(s):  
Su Wei ◽  
Wen Wu Song ◽  
Fu Jie ◽  
Cao Yong
Keyword(s):  
Flow Velocity ◽  
Sediment Concentration ◽  
Continuous Phase ◽  
Two Phase ◽  
Pelton Turbine ◽  
Coupled Calculation ◽  
Sediment Size ◽  
Fluid Analysis ◽  
Motion Characteristics ◽  
Silt Erosion

A 3-D model of pelton turbine bucket was built to investigate the motion characteristics of sediment particles in pelton turbines and the erosion caused by the movement. With the assistance of fluid analysis software FLUENT, A continuous phase turbulence model was estimated by the Euler equation which achieved convergence and the selected coupled calculation for solid-liquid two-phase flow with DPM model was built. It can be draw from the numerical analysis that, with the same size and sediment concentration, the inner bucket wall would suffer from the greater erosion by the relatively greater flow velocity; under the same condition of flow velocity and sediment concentration, the more serious erosion was caused by the bigger sized sediments; and the greater sediment concentration led to greater erosion, given the same flow velocity and sediment size. Based on the study, it showed that the erosion of inner wall of buckets was mainly affected by sediment size and concentration, as well as flow velocity.

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