Distribution characteristics of inertial sediment particles in the turbulent boundary layer of an open channel flow determined using Voronoï analysis

2017 ◽  
Vol 32 (3) ◽  
pp. 401-409 ◽  
Author(s):  
Xin Liu ◽  
Chunning Ji ◽  
Xiaoli Xu ◽  
Dong Xu ◽  
John J.R. Williams
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Channel Flow ◽  
Open Channel ◽  
Open Channel Flow ◽  
Distribution Characteristics ◽  
Sediment Particles

PIV Study of Separated and Reattached Open Channel Flow Over Surface Mounted Blocks

2008 ◽  
Vol 130 (6) ◽  
Author(s):  
Martin Agelinchaab ◽  
Mark F. Tachie
Keyword(s):  
Boundary Layer ◽  
Shear Layer ◽  
Channel Flow ◽  
Open Channel ◽  
Open Channel Flow ◽  
Reynolds Stresses ◽  
Mean Flow ◽  
Mean Velocity ◽  
High Background ◽  
The Mean

A particle image velocimetry is used to study the mean and turbulent fields of separated and redeveloping flow over square, rectangular, and semicircular blocks fixed to the bottom wall of an open channel. The open channel flow is characterized by high background turbulence level, and the ratio of the upstream boundary layer thickness to block height is considerably higher than in prior experiments. The variation of the Reynolds stresses along the dividing streamlines is discussed within the context of vortex stretching, longitudinal strain rate, and wall damping. It appears that wall damping is a more dominant mechanism in the vicinity of reattachment. In the recirculation and reattachment regions, profiles of the mean velocity, turbulent quantities, and transport terms are used to document the salient features of block geometry on the flow. The flow characteristics in these regions strongly depend on block geometry. Downstream of reattachment, a new shear layer is formed, and the redevelopment of the shear layer toward the upstream open channel boundary layer is studied using the boundary layer parameters and Reynolds stresses. The results show that the mean flow rapidly redeveloped so that the Clauser parameter recovered to its upstream value at 90 step heights downstream of reattachment. However, the rate of development close to reattachment strongly depends on block geometry.

scholarly journals Pressure forces on sediment particles in turbulent open-channel flow: a laboratory study

2014 ◽  
Vol 757 ◽  
pp. 458-497 ◽  
Author(s):  
Mohammad Amir ◽  
Vladimir I. Nikora ◽  
Mark T. Stewart
Keyword(s):  
Channel Flow ◽  
Open Channel ◽  
Pressure Sensors ◽  
Open Channel Flow ◽  
Stereoscopic Particle Image Velocimetry ◽  
Spherical Particles ◽  
Temporal Scales ◽  
Particle Correlation ◽  
Sediment Particles ◽  
Drag And Lift

AbstractAn experimental investigation into the fluctuating pressure acting on sediment particles on the bed of an open-channel flow was carried out in a large laboratory flume for a range of flow depths and bed slopes. The pressure measurements were made using 23 spherical particles instrumented with differential pressure sensors. These measurements were complemented with simultaneous measurements of the velocity field using high-resolution stereoscopic particle image velocimetry. The pressure statistics show that the standard deviations of the drag and lift fluctuations vary from 2.0 to 2.6 and from 2.5 to 3.4 times the wall shear stress, respectively, and are dependent on relative submergence and flow Reynolds number. The skewness is positive for the drag fluctuations and negative for the lift fluctuations. The kurtosis values of both drag and lift fluctuations increase with particle submergence. The two-particle correlation between drag and lift fluctuations is found to be relatively weak compared to the two-point drag–drag and lift–lift correlations. The pressure cross-correlations between particles separated in the longitudinal direction exhibit maxima at certain time delays corresponding to the convection velocities varying from 0.64 to 0.72 times the bulk flow velocity, being very close to the near-bed eddy convection velocities. The temporal autocorrelation of drag fluctuations decays much faster than that for the lift fluctuations; as a result, the temporal scales of lift fluctuations are 3–6 times that of drag fluctuations. The spatial and temporal scales of both drag and lift fluctuations show dependence on flow depth and bed slope. The spectral behaviour of both drag and lift fluctuations is also assessed. A $\def \xmlpi #1{}\def \mathsfbi #1{\boldsymbol {\mathsf {#1}}}\let \le =\leqslant \let \leq =\leqslant \let \ge =\geqslant \let \geq =\geqslant \def \Pr {\mathit {Pr}}\def \Fr {\mathit {Fr}}\def \Rey {\mathit {Re}}f^{-11/3}$ slope is observed for the spectra of the drag fluctuations over the majority of the frequency range, whereas the lift spectra suggest two scaling ranges, following a $f^{-11/3}$ slope at high frequencies and $f^{-5/3}$ behaviour at lower frequencies.

Experiments on particle—turbulence interactions in the near–wall region of an open channel flow: implications for sediment transport

1996 ◽  
Vol 326 ◽  
pp. 285-319 ◽  
Author(s):  
Y. Ninto ◽  
M. H. Garcia
Keyword(s):  
Flow Velocity ◽  
Channel Flow ◽  
Open Channel ◽  
Vertical Component ◽  
Open Channel Flow ◽  
Viscous Sublayer ◽  
Wall Region ◽  
Mean Flow ◽  
Sediment Particles ◽  
Near Wall

A high-speed video system was used to study the interaction between sediment particles and turbulence in the wall region of an open channel flow with both smooth and transitionally rough beds. In smooth flows, particles immersed within the viscous sublayer were seen to accumulate along low-speed wall streaks; apparently due to the presence of quasi-streamwise vortices in the wall region. Larger particles did not tend to group along streaks, however their velocity was observed to respond to the streaky structure of the flow velocity in the wall region. In transitionally rough flows particle sorting was not observed. Coherent flow structures in the form of shear layers typically observed in the near-wall region interacted with sediment particles lying on the channel bottom, resulting in the particles being entrained into suspension. Although there has been some speculation that this process would not be effective in entraining particles totally immersed in the viscous sublayer, the results obtained demonstrate the opposite. The entrainment mechanism appears to be the same independent of the roughness condition of the bottom wall, smooth or transitionally rough. In the latter case, however, hiding effects tend to preclude the entrainment of particles with sizes finer than that of the roughness elements. The analysis of particle velocity during entrainment shows that the streamwise component tends to be much smaller than the local mean flow velocity, while the vertical component tends to be much larger than the local standard deviation of the vertical flow velocity fluctuations, which would indicate that such particles are responding to rather extreme flow ejection events.

scholarly journals Development of River Meander Model

2020 ◽  
Vol 3 (1) ◽  
Author(s):  
Levent Yilmaz
Keyword(s):  
Boundary Layer ◽  
Velocity Profile ◽  
Channel Flow ◽  
Open Channel ◽  
Open Channel Flow ◽  
Suspended Sediments ◽  
Flow Region ◽  
Boundary Layer Theory ◽  
Meandering Channels ◽  
Meander Model

In the studies of open-channel flow with suspended sediments, used aconstant of Von Karman κ in a model for velocity profile. The augmentation parameters have been added by various researchers in more recentdevelopment of the boundary-layer theory of meander development. In thisresearch new parameters will be included because of the existence of theturbulent flow region in meandering channels because of boundary-layertheory.

Experimental Study of Shallow Open Channel Turbulent Flows Over Rough Walls

2014 ◽  
Author(s):  
B. Nyantekyi-Kwakye ◽  
E. E. Essel ◽  
S. Clark ◽  
M. F. Tachie
Keyword(s):  
Boundary Layer ◽  
Experimental Study ◽  
Reynolds Number ◽  
Channel Flow ◽  
Open Channel ◽  
Open Channel Flow ◽  
Reynolds Stresses ◽  
Freestream Velocity ◽  
The Mean ◽  
Bed Roughness

An experimental study was undertaken to investigate the effects of bed roughness on the turbulence characteristics of shallow open channel flows. The measurements were performed in a recirculating open channel flow over a reference smooth bed and a three-dimensional rough bed (36-grit sandpaper). The velocity measurements were conducted using a high resolution particle image velocimetry (PIV) system. The Reynolds number based on the depth of flow (h) and freestream velocity (Ue) varied from 21000 to 30000 and the Froude number ranged from 0.46 to 0.65. Two smooth bed experiments were conducted to investigate the effect of Reynolds number on the open channel flow. The mean velocities and Reynolds stresses for the two smooth cases were observed to be weakly dependent on Reynolds number. The effect of bed roughness was observed to penetrate into the outer layer of the boundary layer. The results show that bed roughness significantly increased the skin friction coefficient, wake parameter, boundary layer parameters, as well as the mean velocity, Reynolds stresses and the energy budget terms. A two-point correlation analysis showed that the coherent structures were also significantly modified by bed roughness.

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