Three-Dimensional Flow Characteristics in Slit-Type Permeable Spur Dike Fields: Efficacy in Riverbank Protection

This paper focuses on finding efficient solutions for the design of a highly permeable pile spur (or slit type) dike field used in morphologically dynamic alluvial rivers. To test the suitability of different arrangements of this type of permeable pile spur dike field, laboratory experiments were conducted, and a three-dimensional multiphase numerical model was developed and applied, based on the experimental conditions. Three different angles to the approach flow and two types of individual pile position arrangements were tested. The results show that by using a series of slit-type spurs, the approach velocity of the flow can be considerably reduced within the spur dike zone. Using different sets of angles and installation positions, this type of permeable spur dike can be used more efficiently than traditional dikes. Notably, this type of spur dike can reduce the longitudinal velocity, turbulence intensity, and bed shear stress in the near-bank area. Additionally, the deflection of the permeable spur produces more transverse flow to the opposite bank. Arranging the piles in staggered grid positions among different spurs in a spur dike field improves functionality in terms of creating a quasi-uniform turbulence zone while simultaneously reducing the bed shear stress. Finally, the efficacy of the slit-type permeable spur dike field as a solution to the riverbank erosion problem is numerically tested in a reach of a braided river, the Brahmaputra–Jamuna River, and a comparison is made with a conventional spur dike field. The results indicate that the proposed structure ensures the smooth passing of flow compared with that for the conventional impermeable spur structure by producing a lower level of scouring (low bed shear stress) and flow intensification.

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Numerical and experimental study on turbulence statistics in a large fan-stirred combustion vessel

Experiments in Fluids ◽

10.1007/s00348-021-03212-9 ◽

2021 ◽

Vol 62 (5) ◽

Author(s):

M. E. Morsy ◽

J. Yang

Keyword(s):

Isotropic Turbulence ◽

Burning Velocity ◽

Three Dimensional ◽

Flow Characteristics ◽

Turbulence Models ◽

Initial Pressure ◽

Dynamics Modeling ◽

Turbulence Statistics ◽

Experimental Conditions ◽

Measured Velocity

Abstract Particle image velocimetry (PIV) has become a popular non-intrusive tool for measuring various types of flows. However, when measuring three-dimensional flows with two-dimensional (2D) PIV, there are some uncertainties in the measured velocity field due to out-of-plane motion, which might alter turbulence statistics and distort the overall flow characteristics. In the present study, three different turbulence models are employed and compared. Mean and fluctuating fields obtained by three-dimensional computational fluid dynamics modeling are compared to experimental data. Turbulence statistics such as integral length scale, Taylor microscale, Kolmogorov scale, turbulence kinetic energy, dissipation rate, and velocity correlations are calculated at different experimental conditions (i.e., pressure, temperature, fan speed, etc.). A reasonably isotropic and homogeneous turbulence with large turbulence intensities is achieved in the central region extending to almost 45 mm radius. This radius decreases with increasing the initial pressure. The influence of the third dimension velocity component on the measured characteristics is negligible. This is a result of the axisymmetric features of the flow pattern in the current vessel. The results prove that the present vessel can be conveniently adopted for several turbulent combustion studies including mainly the determination of turbulent burning velocity for gaseous premixed flames in nearly homogeneous isotropic turbulence. Graphic abstract

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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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Comparison of Methods for Bed Shear Stress Estimation in Complex Flow Field of Bend

Water ◽

10.3390/w12102753 ◽

2020 ◽

Vol 12 (10) ◽

pp. 2753

Author(s):

Liyuan Zhang ◽

Faxing Zhang ◽

Ailing Cai ◽

Zhaoming Song ◽

Shilin Tong

Keyword(s):

Shear Stress ◽

Flow Field ◽

Single Point ◽

Three Dimensional ◽

Bed Shear Stress ◽

Complex Flow ◽

Three Dimensional Flow ◽

Stress Estimation ◽

Log Law ◽

Flow Field Measurement

Bed shear stress is closely related to sediment transport in rivers. Bed shear stress estimation is very difficult, especially for complex flow fields. In this study, complex flow field measurement experiments in a 60° bend with a groyne were performed. The feasibility and reliability of bed shear stress estimations using the log-law method in a complex flow field were analyzed and compared with those associated with the Reynolds, Turbulent Kinetic Energy (TKE), and TKE-w′ methods. The results show that the TKE, Reynolds, and log-law methods produced similar bed shear stress estimates, while the TKE-w′ method produced larger estimates than the other methods. The TKE-w′ method was found to be more suitable for bed shear stress estimation than the TKE method, but the value of its constant C2 needed to be re-estimated. In a complex, strong, three-dimensional flow field, the height of the measurement point (relative or absolute) should be re-estimated when a single point measurement is used to estimate the bed shear stress. The results of this study provide guidance for experimental measurement of bed shear stress in a complex flow field.

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Bed Shear Stress Influence on Local Scour Geometry Properties in Various Flume Development Conditions

Water ◽

10.3390/w11112346 ◽

2019 ◽

Vol 11 (11) ◽

pp. 2346 ◽

Cited By ~ 3

Author(s):

Kiraga ◽

Popek

Keyword(s):

Shear Stress ◽

Sediment Transport ◽

Mutual Influence ◽

Three Dimensional ◽

Critical Shear Stress ◽

Water Structure ◽

Correlation Coefficients ◽

Bed Shear Stress ◽

Hole Dimensions ◽

Bed Material

Numerous approaches in sediment mobility studies highlighted the key meaning of channel roughness, which results not only from bed material granulation but also from various bed forms presence, caused by continuous sediment transport. Those forms are strictly connected with the intensity of particle transport, and they eventuate from bed shear stress. The present paper comprised of local scours geometric dimensions research in three variants of lengthwise development of laboratory flume in various hydraulic properties, both in “clear-water” and “live-bed” conditions of sediment movement. Lots of measurements of the bed conformation were executed using the LiDAR device, marked by a very precise three-dimensional shape description. The influence of the bed shear stress downstream model on scours hole dimensions of water structure was investigated as one of the key factors that impact the sediment transport intensity. A significant database of 39 experimental series, lasting averagely 8 hours, was a foundation for delineating functional correlations between bed shear stress-and-critical shear stress ratio and geometry properties of local scours in various flume development cases. In the scope of mutual influence of bed shear stress and water depth, high correlation coefficients were attained, indicating very good and good functional correlations. Also, the influence of bed shear stress and the total length of the scour demonstrated a high correlation coefficient.

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Numerical Investigation on Wave Induced Vortex Dynamics Around Cylindrical Pile With Considering Varying Keulegan-Carpenter Number

Volume 7A: Ocean Engineering ◽

10.1115/omae2017-61948 ◽

2017 ◽

Author(s):

M. Mohammad Beigi Kasvaei ◽

M. H. Kazeminezhad ◽

A. Yeganeh-Bakhtiary

Keyword(s):

Shear Stress ◽

Vortex Shedding ◽

Vortex Dynamics ◽

Three Dimensional ◽

Surface Model ◽

Bed Shear Stress ◽

Wave Flume ◽

Horseshoe Vortices ◽

Free Surface Model ◽

Wave Induced

Three-dimensional numerical simulation of regular waves passing over cylindrical monopile has been conducted to investigate the vortex dynamics. To do so the rectangular wave flume and monopile is modeled on a solver, available in the open-source CFD toolkit OpenFOAM®. The solver applied RANS equations with VOF method for tracking free surface. Model validation has been done by comparison numerical results with the experimental ones and admissible agreement has been seen. Computations have been done for three cases with different pile diameters consequently for different Keulegan-Carpenter numbers (KC). The vorticity field around the pile was investigated as well as vortices by means of Q criterion. It was seen that by increasing KC number, horseshoe vortices will be formed and vortex shedding will be happened. Moreover, Bed shear stress around the pile has been extracted and it has been seen that, the bed shear stress is influenced by KC value which result of existence of horseshoe vortices and vortex shedding.

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MEASUREMENT OF BED FRICTION IN TIDAL INLETS

Coastal Engineering Proceedings ◽

10.9753/icce.v15.98 ◽

1976 ◽

Vol 1 (15) ◽

pp. 98 ◽

Cited By ~ 4

Author(s):

A.J. Mehta ◽

R.J. Byrne ◽

J.T. DeAlteris

Keyword(s):

Shear Stress ◽

Friction Factor ◽

Gulf Coast ◽

Flow Characteristics ◽

Bed Shear Stress ◽

Stress Regime ◽

Cross Sectional ◽

The Times ◽

The Stability ◽

Bed Friction

The flow characteristics and the stability of a tidal inlet are governed, among other factors, by the channel bed friction. In order to determine the bed shear stress regime and the frictional characteristics, near-bed velocity profiles were obtained at the throat sections of two inlets, John's Pass and Blind Pass, on the Gulf Coast of Florida. A specially designed steel cage with five current meters in a vertical array was used to obtain the profiles in the bottom one meter of the flow. The profiles were found to be logarithmic but it is noted that, especially near the times of slack water, the effect of inertia becomes significant. However, during the major part of the flood or ebb flow period, frictional effects are dominant. In the fully rough regime of flow, the bed-shear stress - velocity relationship is found to follow the square law, with a constant, characteristic friction factor and Manning's n for each inlet. This friction factor is used in hydraulic formulas, based on uniform, steady open channel flow relationships, to obtain the tidal prism - throat cross-sectional area ratio, which is then compared with that obtained from flow discharge measurements. Agreements and discrepancies in the comparison are discussed. The relationship between the bed shear stress at incipient motion and the grain size at the bed is reviewed, and it is noted that the observed relationship at the two inlets does not agree with the well-known correlation of Shields for uniform sandy beds.

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Formation of Sand Ripples Under Turbulent Flow Simulated by LES

ASME 2010 3rd Joint US-European Fluids Engineering Summer Meeting: Volume 1, Symposia – Parts A, B, and C ◽

10.1115/fedsm-icnmm2010-30574 ◽

2010 ◽

Author(s):

Yan Cui ◽

John C. Wells ◽

Y. Quoc Nguyen

Keyword(s):

Shear Stress ◽

Numerical Model ◽

Three Dimensional ◽

Sand Wave ◽

Bed Shear Stress ◽

Two Dimensional ◽

Dimensional Model ◽

Three Dimensional Model ◽

Eddy Simulation ◽

Large Eddy

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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Flow Characteristics in an Airlift Membrane Bioreactor

Chemical Product and Process Modeling ◽

10.2202/1934-2659.1403 ◽

2009 ◽

Vol 4 (5) ◽

Cited By ~ 1

Author(s):

Amirhossein Khalili ◽

MR Mehrnia ◽

Navid Mostoufi ◽

Mohammad Sarrafzadeh

Keyword(s):

Shear Stress ◽

Membrane Bioreactor ◽

Fluid Model ◽

Membrane Surface ◽

Three Dimensional ◽

Flow Characteristics ◽

Liquid Level ◽

Two Fluid Model ◽

Two Fluid

Effect of changing the liquid level in an airlift membrane bioreactor of 0.7 m height, 0.24 m width and 0.18 m depth was studied both experimentally and by simulation. Three-dimensional simulations of the airlift membrane bioreactor were carried out at two different liquid levels above the membrane. The simulations were based on the two-fluid model with the standard k? model for the turbulence. The results showed that by lowering the liquid level, the quality of mixing and uniformity of the velocity distribution of liquid phase in the riser would be improved while the shear stress on the membrane surface would be reduced. Higher shear stress on the membrane surface at high levels of liquid minimizes the extent to which particles settle on the membrane, thus, fouling will be reduced and flux of liquid through membrane will be enhanced. Moreover, it was shown that by lowering the liquid level, the fraction of air in the downcomers becomes lower.

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Modelling of three-dimensional flow velocities in a deep hole in the East Channel of the Mackenzie Delta, Northwest Territories

Canadian Journal of Civil Engineering ◽

10.1139/l07-054 ◽

2007 ◽

Vol 34 (10) ◽

pp. 1312-1323 ◽

Cited By ~ 8

Author(s):

Bahram Gharabaghi ◽

Chris Inkratas ◽

Spyros Beltaos ◽

Bommanna Krishnappan

Keyword(s):

Shear Stress ◽

Three Dimensional ◽

Bed Shear Stress ◽

Mackenzie Delta ◽

Stress Distributions ◽

Deep Hole ◽

Flow Conditions ◽

Scour Hole ◽

Scour Holes ◽

The Stability

The Mackenzie River has several anomalous deep scour holes in a number of river channels in its delta. Proposed gas pipeline crossings have renewed interest in studying the stability of these scour holes. The main goal of this research project was to study flow velocity and bed shear stress distributions for a 30 m deep hole in the East Channel of the Mackenzie Delta as a first step toward assessing the stability of the scour hole and the risk of its migration during various flow conditions. In this study, a three-dimensional (3D) finite element flow model, FLUENT, using the renormalization group (RNG) k-ε turbulence model (where k is the turbulent kinetic energy and ε is the turbulence dissipation rate) was set up for the scour hole and calibrated using detailed measurements of 3D flow velocities, obtained with an acoustic doppler current profiler. The numerical model was then applied to predict flow velocity and bed shear stress distributions in and around the scour hole for three flow conditions (720, 1000, and 1400 m3/s). Results indicate that two vortices are formed in the river elbow above the scour hole. As the flow rate changed, the sizes of the vortices varied. The region upstream of the hole experienced the greatest magnitudes of bed shear stress.Key words: computational fluid dynamics, finite element, bed shear stress, deep hole, flow reversal.

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