Bend Flow Research Articles

Flow Characteristics at a River Diversion Juncture and Implications for Juvenile Salmon Entrainment

Flow structures at a river diversion juncture are complex and have been studied extensively. Their impact on the juvenile salmon entrainment into the side channel, however, is less investigated, and based mostly on empiricism. In this study, a Eulerian fish tracking model is developed and used in conjunction with a 3D flow solver to quantitatively evaluate the implications of complex flow characteristics at typical junctures on fish entrainment. First, the flow model is validated with the available experimental data, key flow structures are examined using the results, and their implications for fish entrainment are discussed. Next, the numerical fish tracking model is used to show that the cross-sectional fish distribution immediately upstream of a juncture is an important factor that controls fish entrainment efficiency. Fish entrainment efficiency curves are developed for different flow diversion ratios and fish distribution patterns and used to shed light on the reasons behind some field-observed fish entrainment patterns. Further, the model is used to show that the secondary flow in a river bend may have a significant impact on fish entrainment at flow junctures, in agreement with field observations. Finally, a submerged vane is demonstrated to be a potential management option to locally generate secondary flows upstream of a juncture to achieve the desired fish entrainment property.

Liquid Energy Reduction with Centrifugal Rotating Motion

This article provides equation for calculating the pressure loss for a fluid and energy for a rolling ball moving in a logarithmic spiral from the action of inertial forces. Classical formulas give incorrect results when calculating coils with a changing twist radius. The calculation of the parameters of the fluid flow in the spiral bend and in the blades of the centrifugal impeller can now be determined only by numerical methods of calculation and, as such, formulas reflecting the energy losses associated with inertial forces do not yet exist. Based on the results of experimental and theoretical work, formulas were obtained that describe the energy losses of a liquid and a ball, when they move along a logarithmic spiral. For the correct derivation of formulas for a moving fluid, it was first necessary to obtain formulas for a rolling ball and a material point. The movement in a logarithmetic spiral is the basis for the movement of particles in a vortex.

Influence of Negatively Buoyant Jets on a Strongly Curved Open-Channel Flow Using RANS Models with Experimental Data

Experimental and numerical studies of flow structures in a strongly curved 135-degree laboratory flume were carried out to investigate the influence of negatively buoyant jets using the finite volume method. The performance results of three different turbulence models were investigated by comparing the numerical results with the experimental measurements. The present study demonstrates that fully 3D numerical models are capable of simulating the primary flow pattern in a strongly curved channel with the presence of a negatively buoyant jet. The comparison also shows that the k-omega SST model can satisfactorily predict some of the smaller flow features in bend flow, such as the inner bank circulation cell and the overall form of the vorticity distributions. It was found that the flow distribution and the strength of secondary flow vary due to the interaction between the jet mixing behavior and the secondary flow in the channel bend. The presence of negatively buoyant jets attenuated the development of the outer bank cell as salinity increased. In the inner bank region, flow separation was strengthened by the participation of the negatively buoyant jets.

Flow and sediment transport in a sharp river bend using a 3D-RANS model

Flow dynamics and sediment transport in a river bend have recently been studied using experimental and numerical investigations. A three-dimensional numerical modeling model named NaysCUBE was used in this study to describe the flow pattern and process of sediment transport in a sharp river bend as a complement to the prior work of the physical hydraulic model. The model uses the RANS equation to simulate flow where a fully complex 3D flow is governed. Despite the limitations of the RANS model, NaysCUBE well reproduces the flow pattern and turbulence phenomena in a movable bed channel with sharp curvature. Compared with data from a prior experiment, the morphological adjustment is simulated sufficiently. The three-dimensional flow structures are useful for determining the appropriate countermeasures for local scouring and riverbank protection.

Can the mechanoreceptional setae of a feeding‐current feeding copepod detect hydrodynamic disturbance induced by entrained free‐floating prey?

AbstractCopepods that catch prey using feeding currents beat their cephalic appendages to generate flow entrainment, and detect the presence of nearby prey through the mechanoreceptional setae on the antennules and other appendages. It remains unclear whether the feeding current can be used by the copepod to gain information about its surroundings by sensing when the current is disturbed by nearby particles. In this article, we present a numerical model to address how much the presence of free‐floating prey can alter the feeding current velocity field, and how these prey‐induced disturbances modify setal deformation patterns. We prescribe the beating strokes of the feeding appendages, and quantify the changes in the bending flows across the setae and setal deformations due to the prey entrainment. We find that, first, the seta bends more due to the time‐averaged velocity component of the feeding current, while filtering out the oscillatory component. Second, 100 μm diameter free‐floating prey do not induce any noticeable change in deformations of the proximal and distal setae unless they are less than 10 or 5.5 prey radii from the antennules, respectively. Larger prey cause bigger flow disturbances than small prey, which are expected to be even harder to detect. Last, if setae are responsive to changes in deformation relative to the deformations in the absence of prey, the distal seta may have long‐ranged sensitivity to assist in detection of prey near the proximal seta, but if setae are responsive to absolute changes in deformation, both setae have very short‐ranged sensitivity.

Sensitivity and Uncertainity Analysis of Flow Velocity Estimation Using Gene Expression Programming Model in Curved Channels

Prediction of velocity is an important parameter in curved channels. Recently, artificial intelligent methods are developing than the common costly and time-consuming experimental and numerical methods in estimation of flow variables. In the present study, Gene expression programming (GEP) model as developed genetic programming model is used to predict the flow velocity in the channel with a sharp 90° bend. Different input parameter combinations are examined in order to finding the optimum model then the model efficiency are evaluated in estimation of the flow velocity in training and testing phases. By comparing the results of the GEP model with experimental data, there is an acceptable accordance between results with the root mean square error (RMSE) values of 0.828 and 0.8197 in the training and testing phase. The results show that the input parameters of (r,q) (polar points coordinate and the flow discharge) are the most effective parameters in bend flow pattern surveying. With increasing the flow discharge, the model error at the end section of the bend in the outer channel wall is decreased. Also a practical and reliable relationship is proposed by the GEP model and the sensitivity of suggested equation to each of input parameter is evaluated. Furthermore, the uncertainty of the proposed GEP model in the velocity prediction is assessed and different confidence bounds are introduced.

The effect of discharge on head loss with straight and bend flow directions in the pipeline

Piping flow is a way of transportation to carry material from one place to another. A problem in pipelines is a head loss. This head loss can affect pipe capacity and reduce flow discharge. Structure or geometry of pipelines will affect energy due to the roughness of pipe walls, friction, bends, joints and energy decreases with the length of passed pipe. Head loss in the piping system includes major and minor energy losses. The objective of this research is to determine the magnitude of major and minor head losses and to determine the relationship between discharge and velocity, pressure height, and the influence of geometric network structure. The variation of flowed discharge is 0.5 liter/second, 2.5 liter/second, 3 liter/second and 4 liter/second. The research is experimental research conducted in the laboratory. The test design uses a pipeline with a length of 6 m, a width of 1.20 m, and a dimension of 64 mm. The results showed that an increase in flow rate (Q) followed by an increase in flow velocity (v) will increase Reynold’s (Re) number so that the head loss in the pipeline will increase. The increasing of Reynold’s (Re) number will decrease the value of the friction coefficient. Structure or geometric of the line also influences the pattern of flow. In a straight pipe, the velocity of flow is large but the pressure height is small compared to the bend pipe flow where the velocity of flow is small but the pressure height is larger.

Incipient Motion of Gravel Bedload Considering the Secondary Flow in Bend

The transport of gravel bedload in river bend is one of the basic problems of river dynamics. However, both the complicated bend flow structure and the stochastic bedload transport make explaining the problem theoretically difficult. Flow is the power of the bedload transport, so obtaining the precise theoretical flow structure is fundamental. Through considering the velocity-dip phenomenon and giving the matched boundary conditions, we have obtained the completed three-dimensional bend flow structure in the previous study. Combining the flow structure and the influences of the two-way exposure, we did further research on the incipient motion of the gravel bedload in bend in this paper. It turns out that, because of the existence of the secondary flow, the particle in bend forced by both the longitude and the transverse velocities in the plane. The two-way velocities form an intersection angle which influences the incipient velocity and direction of the particle movement. Moreover, the non-uniform distribution of the bend flow structure along the cross-section decides the differences of the intersection angle, incipient velocity, transport speed of the bedload in the bed surface. Then, the above differences result in the change of the sediment gradation and partition behaviour of the bedload transport.

Three-dimensional numerical simulation of flow in continuous bend under the influence of piers

With the development of social economy, more and more cities plan to build various kinds of Bridges in curved rivers to construct urban traffic network. The Realizable k-ε turbulence model and VOF method were used to capture the free water surface, Simple algorithm was used for coupling calculation to simulate the flow characteristics of continuous bend with piers placed at 45° forward bend section. Simulation results show that: (1) under the condition of continuous curve, set in the horizontal surface slope will change the channel distribution of piers, bridge piers and curve superposition, the piers downstream transverse surface slope significantly improved, but the bridge pier near area, on the other hand, because of the water resistance of piers, bridge pier influence and affect the part of the balance of the bend, transverse surface slope value is only under the condition of no pier 1/2;(2) The high longitudinal flow velocity area is more concentrated, the high velocity center moves down to the bottom of the channel, and the central position of the circulation structure moves to the convex bank, which can aggravate the scouring of the convex bank.

An Analysis of Carcass Layer Erosion in Un-Bonded Flexible Offshore Pipework

In this paper, a simplified model for erosion in un-bonded flexible pipes caused by the sand entrained in the produced fluid is established. Flow field analysis is performed based on the governing equations of the continuous fluid and the discrete particles. A two-way coupled Eulerian-Lagrangian approach is employed to solve the gas-solid flow in the pipe bend. To eliminate the influence of the length of the straight pipe section on the stability of the flow field in the pipe, the flow field distribution under different lengths is analyzed to determine the optimal straight pipe length. Six commonly used erosion models are adopted to predict the erosion rate. After comparing the prediction results with experimental data, the most accurate Oka model is selected to calculate the effect of the fluid and structure parameters on erosion. Effects of particle parameters and pipe structural parameters on the erosion rate of curved flexible pipes are numerically fitted, and the quantitative description is given.

A Review of Numerical Simulations of Secondary Flows in River Bends

River bends are one of the common elements in most natural rivers, and secondary flow is one of the most important flow features in the bends. The secondary flow is perpendicular to the main flow and has a helical path moving towards the outer bank at the upper part of the river cross-section, and towards the inner bank at the lower part of the river cross-section. The secondary flow causes a redistribution in the main flow. Accordingly, this redistribution and sediment transport by the secondary flow may lead to the formation of a typical pattern of river bend profile. It is important to study and understand the flow pattern in order to predict the profile and the position of the bend in the river. However, there are a lack of comprehensive reviews on the advances in numerical modeling of bend secondary flow in the literature. Therefore, this study comprehensively reviews the fundamentals of secondary flow, the governing equations and boundary conditions for numerical simulations, and previous numerical studies on river bend flows. Most importantly, it reviews various numerical simulation strategies and performance of various turbulence models in simulating the flow in river bends and concludes that the main problem is finding the appropriate model for each case of turbulent flow. The present review summarizes the recent advances in numerical modeling of secondary flow and points out the key challenges, which can provide useful information for future studies.

Curvature induced intensification of biodiesel synthesis in miniature geometry

In the present study, mini-serpentine reactors of different R/D ratios are tested for mass transfer limited transesterification reaction to produce biodiesel. Experiments are carried out in three test sections made of glass capillary of id 2 mm with different R/D ratios and results are compared with a straight test-section of similar dimension. Yield increases almost 1.26 times in the presence of bend (serpentine geometry), as it induces the secondary flow in the liquid film surrounding the slug. Reverse flow in bend generates eddies surrounding the slug, known as Dean Vortices. This counter-flow enhances the transport rate significantly. An optimum Fatty Acid Methyl Ester (FAME) yield of 98 % is observed in serpentine test-section with R/D ratio 3 in just 1.18 min of residence time. Percentage FAME yield relies upon the prevalence of shape and size of long slugs or slender short slugs in subsequent tubes. FAME yield diminishes for the first case and enhancement is observed in the latter case.

Bending curvatures of subducting plates: old versus young slabs

SUMMARY By combining scaled laboratory experiments and numerical simulations, this study presents a quantitative analysis of the bending radius (RB) of subducting slabs within the upper mantle, taking into account the effects of age (A). Based on a half-space cooling model, we constrain the density (ρ), viscosity (η) and thickness (h) of slabs as a function of A, and develop representative models to estimate RB for different A. Laboratory subduction models produce visually contrasting bending curvatures for young (A = 10 Ma), intermediate (A = 70 Ma) and old (A = 120 Ma) slabs. Young slabs undergo rollback, resulting in a small bending radius (scaled up RB ∼ 150 km), whereas old slabs subduct along a uniformly dipping trajectory with large bending radius (RB ∼ 500 km). Equivalent real scale computational fluid dynamic simulations reproduce similar bending patterns of the subducting slabs, and yield RB versus A relations fairly in agreement with the laboratory results. We balance the buoyancy driven bending, flexural-resistive moments and viscous flow induced suction moment to theoretically evaluate the rate of slab bending. The analytical solution suggests an inverse relation of the bending rate with A, which supports our experimental findings. Finally, slab geometries of selected natural subduction zones, derived from high-resolution seismic tomographic images have been compiled to validate the experimental RB versus A regression. We also discuss the subduction settings in which this regression no longer remains valid.

Numerical investigation of electrostatic effect on particle behavior in a 90 degrees bend

Particle behavior in a turbulent circular-sectioned 90° bend under electrostatic field at three air flow rates (1600 L/min, 1100 L/min and 950 L/min, the corresponding bulk Reynolds numbers are 58,000, 40,000, 34,000) is simulated by a Large Eddy Simulation-Lagrangian particle tracking technique (LES-LPT) method coupled with electrostatic field model by Coulomb’s law. This numerical simulation is dedicated to study the electrostatic effect on particle behavior and erosion occurred in the dilute particle-laden bend flow. Forces considered acting on particles includes drag, lift, gravity and electrostatic force. Results obtained for the fluid phase are in good agreement with experimental and numerical data. Predictions show that electrostatic field does affect the particle motion in the pipe bend. At higher air flow rate with higher electrostatics at the inner arc the increasement of impact angle is lower than that at lower flow rate with lower electrostatics. The same conclusion can be found at the outer arc. In addition, electrostatic effect does increase particle-wall impact velocity while such trend decreases with flow rate. Erosion rate increases with increasing air flow rate, which is independent of electrostatics. However, given the same flow rate, the electrostatics reduces the occurrence of erosion at the bend. The erosion rate under electrostatic effect is found to approach that without electrostatics as the flow rate increases. Therefore, the effect of electrostatics on erosion decreases with the air flow rate.

Flow Structure in a River Bend in the Cryolithozone

Rivers of the cryolithozone are under consideration. The structure of open-water and ice-covered flows in this zone is determined by moderate river falls, high sinuosity of rivers, especially delta branches, and long freeze up periods. The basic relationships describing the open-water and ice-covered flows in straight reaches of rivers are presented. Special attention is paid to modern studies of features of flow in a river bend.

A preliminary study of the properties of potassium phosphate magnesium cement-based grouts admixed with metakaolin, sodium silicate and bentonite

In karst areas, the water inflow in underground pipelines often shows the features of large and high flow rate that is extremely difficult to treat. Due to long hardening time, poor bonding of the interface and low retained rates during dynamic water filling, the ordinary inorganic grouting materials are easy to lead to sealing failure. Magnesium phosphate cement has the characteristics of good interfacial bond and quick solidification, which is very appropriate for karst piping sealing. In the study, a water-resistant scour grouting material based on potassium dihydrogen phosphate, light burnt magnesium oxide, metakaolin, sodium silicate, and bentonite is developed. This grouting material is a modification of potassium magnesium phosphate cement and some of the MgO and KH2PO4 is replaced by metakaolin (0–30%). Then, these three materials make up the gel material system. The fresh grouts designed water-binder ratio is 1 and the material is sodium silicate and (0–6%) modified with bentonite (10%). The properties of the grouting material including compressive strength and bending strength (after 1 day, 3 days, 7 days, 14 days, and 28 days), setting time, viscosity, and flow distance are studied. We used X-ray diffraction and scanning electron microscope to study the microscopic properties of a hardened grouts. Our experimental results show that the MgO/KH2PO4 (molar ratio), sodium silicate and metakaolin affect the compressive strength, bending strength, gel time, and viscosity of the grouting material. The addition of metakaolin reduces the early strength and the fluidity of the grouting materials, but the grout with 20% metakaolin has a higher 28-day strength. The sodium silicate reduces the setting time and rheological property of the grouting materials but increases their strength.

Numerical analysis of global and local performance variations of proton exchange membrane fuel cell with different bend layouts and flow directions

Abstract In this work, a three-dimensional multi-component transport CFD model is established to discuss the discrepancies of local distributions under channels and ribs based on the serpentine flow field. Globally, increment of activation loss in the gas diffusive layer takes more effects on catalytic activity than decrease of oxygen concentration. Locally, current density under the channels and ribs is more affected by activation loss and oxygen concentration, respectively. Then the performance of four serpentine flow fields with different bend layouts and flow directions were compared according to the mean value and variance of current density and membrane water content on the cathode membrane surface. The results show that the current density on the membrane surface of the serpentine flow field with non-overlapping bends is more uniform and the standard deviation is about 6.25% lower than that of the overlapping bend. Co-flow has some advantages in uniformity of water content distribution on the cathode membrane surface, and the standard deviation is about 12.6% lower than that of the counter-flow. For large-scale and multi-channels serpentine flow field, the serpentine flow field with non-overlapping bends and co-flow has better application than other three types.

A three-dimensional numerical study of flow characteristics in strongly curved channel bends with different side slopes

The influence of channel side slope on flow in strongly curved channel bends is studied numerically. The performances of five different turbulence models are investigated. Comparison to experimental measurements demonstrates that the fully 3D numerical model can reliably simulate a channel bend flow field. Among the tested turbulence models, the realizable k − e model performed best. The present study also demonstrates that the realizable k − e model can satisfactorily predict smaller flow features in bend flow, such as the outer-bank circulation cell. The validated model is employed to carry out additional computations for channel bends with different side slopes. It is found that the number, position, and strength of secondary flow cells varies with the channel side slope, with corresponding influence on flow distribution and flow vorticity.

Effect of water and air injection on reduction of bend scour

In the proposed method, air and water were injected into the 180° bend flow from both sides of a perforated tube to overcome curvature-induced secondary flows by creating a non-rigid barrier. The experimental results showed that the secondary flows were deviated from the outer bend causing a reduction in the maximum scour depth along the bend. The navigable width may also be increased by shifting the maximum scour depth from the outer wall to the centerline. On the other hand, the maximum scour depth was reduced by decreasing the distance between the perforated tube and the outer wall. For example, the maximum scour depth in the water and air injection main experiments at 130° section of the bend and two tube distances of 2.5 cm and 5 cm decreased by 88%, 91%, 63%, and 45%, respectively. With the increase in the Froude numbers, the maximum scour depth has increased.

PSO-tuned support vector machine metamodels for assessment of turbulent flows in pipe bends

PurposeComputational fluid dynamics (CFD) technique is the most commonly used numerical approach to simulate fluid flow behaviour. Owing to its computationally, cost-intensive nature CFD models may not be easily and quickly deployable. In this regard, this study aims to present a support vector machine (SVM)-based metamodelling approach that can be easily trained and quickly deployed for carrying out large-scale studies.Design/methodology/approachRadial basis function and ε^*-insensitive loss function are used as kernel function and loss function, respectively. To prevent overfitting of the model, five-fold cross-validation root mean squared error is used while training the SVM metamodel. Rather than blindly using any SVM tuning parameters, a particle swarm optimisation (PSO) is used to fine-tune them. The developed SVM metamodel is tested using various error metrics on disjoint test data.FindingsUsing the SVM metamodel, a parametric study is conducted to understand the effect of various factors influencing the behaviour of the turbulent fluid flow in the pipe bend with CFD simulation data set. Based on the parametric study carried out, it is seen that the diametric position has the most effect on dimensionless axial velocity, whereas Reynolds number has the least effect.Originality/valueThis paper provides an effective PSO-tuned SVM metamodelling approach, which may be used as a significant cost-saving approach to quickly and accurately estimate fluid flow characteristics that, in general, require the use of expensive CFD models.