Open Channel Junctions Research Articles

New Findings of Flow Velocity and bed Shear Stress at an Open Channel Junction

New Findings of Flow Velocity and bed Shear Stress at an Open Channel Junction

Three-Dimensional Numerical Simulation of a Two-Phase Supercritical Open Channel Junction Flow

This study investigates the computational fluid dynamics (CFD) modeling of supercritical open channel junction flow using two different turbulence models: k-ω shear stress transport (SST) and k-ω SST scale-adaptive simulation (SAS), in conjunction with Volume of Fluid (VOF) and mixture multiphase models. The efficacy of these models in predicting the intricate free surface fluctuation and free surface elevation in a supercritical junction is evaluated through a comprehensive analysis of time-averaged free surface data obtained from CFD simulations and Light Detection and Ranging (LIDAR) measurements. The dimensionless Reynolds (Re) and Froude (Fr) numbers of the investigated scenario were Fr = 9 and Re = 5.1 × 104 for the main channel, and Fr = 6 and Re = 3.3 × 104 for the side channel. The results of the analysis demonstrated a satisfactory level of agreement with the experimental data. However, certain limitations associated with both CFD and LIDAR were identified. Specifically, the CFD performance was limited by the model’s incapacity to consider small-scale turbulent effects and to model air bubbles smaller than the cell size while the LIDAR measurements were limited by instrument range, inability to provide insight into what is happening below the water surface, and blind spots. Nonetheless, the k-ω SST turbulent model with the VOF multiphase model most closely matched the LIDAR results.

3D Numerical Simulations of the Bed Evolution at an Open-Channel Junction in Flood Conditions

3D Numerical Simulations of the Bed Evolution at an Open-Channel Junction in Flood Conditions

Numerical Investigation of the Optimum Angle for Open Channel Junction

Numerous natural and artificial streams, including those for irrigation ditches, wastewater treatment facilities, and conveyance structures for fish movement, have open channel confluences. The flow dynamics at and around the junction are intricate; in particular, immediately downstream of the junction, the flow creates a zone of separation on the inner wall along with secondary recirculation patterns. The structure of this complicated flow depends on several factors, including the flow rates in both channels, the angle of confluence, the geometry of the channels, including the longitudinal slope and bed discordance, the roughness of the boundary, and the intensity of the turbulence. It also has a significant impact on bed erosion, bank scouring, etc. The objective of the current work is to calculate the velocity profile and the separation zone dimensions for four angles (30o, 45o, 60o, and 75o) through the simulation process, and the best angle using a three-dimensional model. This work gives a detailed application of the numerical solution (Finite Volume) via Flow 3D software. Results for two flow discharge ratios, q*=0.250 and q*=0.750 were shown; the numerical model and the experimental results agreed well. The findings are consistent with past research and demonstrate how the main channel flow pattern is affected by changes in the channel crossing angle, as well as how greater separation zones are produced in the main channel when the flow discharge ratio q* (main channel flow divided by total flow) is smaller. Analysis revealed that the separation zone's smallest diameter will be at the 75ocrossing angle. Doi: 10.28991/CEJ-2023-09-05-07 Full Text: PDF

Flow Dynamics and Pollutant Transport at an Artificial Right-Angled Open-Channel Junction with a Deformed Bed

Artificial open-channel junctions have sharp corners and a smaller width-to-depth ratio. Despite numerous studies on channel junctions, knowledge on turbulent structures and their role in mixing at artificial junctions is lacking. To fill this research gap, the present study uses a large-eddy simulation (LES) model to investigate the three-dimensional (3D) turbulent structures and their role in pollutant transport at a right-angled laboratory open-channel junction with a deformed bed. The deformed-bed junction represents a quasi-equilibrium condition and consists of a scour zone and deposition bar. The numerical model is validated against experimental data of the velocity field and turbulent kinetic energy. Comparisons of the flow field between the flat-bed condition and quasi-equilibrium deformed-bed condition showed a reduced flow separation zone and less developed recirculating gyre in the latter case because of the strong secondary currents. The coherence of the turbulent structures was drastically disrupted at the deformed-bed junction because the Kelvin-Helmholtz (KH) instability results in more randomly oriented residuals. In contrast, the breakdown of the shear layer at a flat-bed junction displayed the trail of the arch-shaped vortices. The role of turbulent structures in pollutant transport is elucidated by using a neutrally buoyant conservative tracer. Large turbulent structures associated with the KH instability help the tracer evolve faster at the deformed-bed junction.

Three-Dimensional Numerical Simulation of the Flood-Wave Propagation at a Combining Open-Channel Junction

Three-Dimensional Numerical Simulation of the Flood-Wave Propagation at a Combining Open-Channel Junction

Experimental investigation and one-dimensional (1D) dynamic modelling of steady flow through a levee breach

Accurate prediction of levee breach flow is crucial to the mitigation of floods, and for timely breach closure. In this work, flow in an idealized levee breach has been studied for the case of a trapezoidal embankment. Flow data including water depths, surface velocities, and flow discharges were obtained from 28 experiments considering different cases of breach width and main channel downstream water depth. Ultrasonic sensors were used to record the water depth in the channel and the breach. The water surface velocity was measured using a particle tracking velocity method. A one-dimensional dynamic model based on the conservation of mass and momentum in two control volumes was developed by drawing similarities between levee breach flows and diverging open channel junction flows. The proposed model shows satisfactory performance against two independent datasets.

Reduction of the Flow Separation Zone at Combining Open-Channel Junction by Applying Alternate Suction and Blowing

The flow separation zone (FSZ) is one of the main flow characteristics of the combining open channel junction and is associated with energy dissipation. Bed shear stress in the contracted flow region increases as the channel’s effective width is reduced. Reduction of the FSZ at the junction to improve efficiency is desirable. The present numerical study focuses on the effect of continuous suction and blowing perturbations in reducing the FSZ at a right-angled open channel junction. The flow field is simulated using computational fluid dynamics (CFD) software. The numerical model is validated by comparing the simulated velocity field, water surface elevation, and energy loss for the unperturbed junction flow with corresponding experimental results available in the literature. The continuous suction and blowing perturbation is generated by a sinusoidal function with zero net discharge and is applied through a rectangular slit. Three different slit locations are considered downstream of the junction. The simulated results (time-averaged) show that the sinusoidal perturbation is effective in reducing the dimensions of the FSZ and, consequently, the energy loss and bed shear stress. The results demonstrate the enhanced effectiveness in reducing the energy loss when the slit is more proximate to the junction for the chosen flow configuration and the sinusoidal perturbation characteristics. The results of the time-averaged depth ratios show only a marginal reduction due to the flow perturbation.

Experiment-Based CFD Simulation of Flow Pattern at Open-Channel Junctions

This paper proposes a numerical 3D flow pattern at the 90° equal-width open-channel junction. The Reynolds stress turbulent model (RSM) is applied to simulate the turbulent flow which is analyzed as a one-phase steady state. The Shumate’s experimental findings are used to test the validity of developed numerical model. Comparison of the simulation results and the experimental data has indicated a close proximity between the flow patterns of the two sets. The average prediction error also showed a range between 3.5 and 10%. Effects of the discharge ratio on the separation zone characteristics have illustrated an inverse relation, where an increase in discharge ratio will entail a decrease in the length and width of the separation zone. The shape index of separation zone has an average value 0.18. Comparison analysis further revealed that the increase in the discharge ratio will lead to a decrease in the maximum value of the bed shear stress. In addition, it clearly provides a powerful numerical model for the flow pattern analysis.

Comparison between Numerical, Analytical, and Field Solutions with Experimental Data for 90º Open Channel Junctions

Junction in open channel flow points out any side water secession from natural or artificial channels. In the last decades, comprehensive theoretical and experimental investigations on the dividing flow in open channel junctions have been executed to understand the characteristics of this separating flow. In this research, a three-dimensional turbulence model by fluent software used to replicate the flow characteristics of a 90o open channel junctions for two geometries. One is with equal width and horizontal bed and the other is field canal junction with irregular section. The modeling is based on the Navier-Stokes equation and κ-ω turbulent model. Comparing prepared to the numerical solution, the analytical model and the field works with published experimental data. The comparison showed that the numerical solution gave good agreements with maximum discrepancy 1.620% for rectangular sections and 0.718% for irregular sections than the published experimental data. The analytical solution gave a large error than numerical with a maximum discrepancy of 2.95% for the rectangular section and 11.485% for irregular sections than the published experimental data. A proposed relation between discharge ratio with upstream Froude number and depth ratio for the irregular section is suggested. The proposed equation has a maximum discrepancy equal to 0.433% with reference to the field data recorded.

Numerical modelling of open channel junctions using the Riemann problem approach

ABSTRACTThe solution of an extended Riemann problem is used to provide the internal boundary conditions at a junction when simulating one-dimensional flow through an open channel network. The proposed approach, compared to classic junction models, does not require the tuning of semi-empirical coefficients and it is theoretically well-founded. The Riemann problem approach is validated using experimental data, two-dimensional model results and analytical solutions. In particular, a set of experimental data is used to test each model under subcritical steady flow conditions, and different channel junctions are considered, with both continuous and discontinuous bottom elevation. Moreover, the numerical results are compared with analytical solutions in a star network to test unsteady conditions. Satisfactory results are obtained for all the simulations, and particularly for Y-shaped networks and for cases involving variations in channels' bottom and width. By contrast, classic models suffer when geometrical channel effects are involved.

Velocity Field Simulation of Open-Channel Junction Using Artificial Intelligence Approaches

Open-channel junctions are one of the most significant and practical structures in hydraulic engineering. Due to erosion in the contraction zone and sediment deposition in the separation zone, the ability to know the flow velocity in each point’s coordinate of the junctions’ main channel is a vital topic in designing them. This study aims at modeling the flow velocity in junctions using the coordinates of each point (x*, y*, and z*) and the main channel upstream to downstream discharge ratio (q*). In the modeling procedure, four powerful and well-known simulation models, namely radial basis neural network (RBNN), gene expression programming (GEP), group method of data handling (GMDH), and nonlinear regression model are used. One of the main goals of the present study is to develop accurate, simple, and explicit equations for simulation of the junctions’ main channel velocity to use in practical situations. So that, all of the input variables are dimensionless to use in designing procedure of junctions with any scales. The results showed that using a simple and practical equation, GEP model with mean square error (MSE) value of 0.055 is more accurate in predicting longitudinal velocity in open-channel junctions than RBNN, GMDH, and the regression models with MSE values of 0.063, 0.075, and 0.103, respectively.

Discharge and flow field simulation of open channel sewer junction using artificial intelligence methods

One of the most important parameters in designing of sewer structures is the ability to accurately simulation the discharge and velocity field of them. Among the various sewer receiving inflow methods, open channel junctions are mostly occurring. Because of the separation and contraction zone that occur at the open channel junctions, the fluid flow has a complex behavior. Modeling is carried out by Radial Basis Function (RBF) neural network, Gene Expression Programming (GEP), and Multiple Non-Linear Regression (MNLR) methods. Finding the optimum situation for GEP and RBF models are done by examining the various mathematical and linking functions for GEP and different number of hidden neurons and spread amount for RBF. In order to use the models in practical situations, three equations were conducted by using the RBF, GEP, and MNLR methods in modeling the longitudinal velocity. Then, the surface integral of the presented equations is used to simulate the flow discharge. The results showed that the GEP and RBF method perform significantly better than the MNLR in open channel junction characteristics simulations. The GEP method has higher performance in modeling the longitudinal velocity field compare with the RBF. However, the RBF presented more reliable results on the discharge simulations.

Comparative 1D and 3D numerical investigation of open-channel junction flows and energy losses

Abstract The complexity of open channel confluences stems from flow mixing, secondary circulation, post-confluence flow separation, contraction and backwater effects. These effects in turn result in a large number of parameters required to adequately quantify the junction induced hydraulic resistance and describe mean flow pattern and turbulent flow structures due to flow merging. The recent development in computing power advances the application of 3D Computational Fluid Dynamics (CFD) codes to visualize and understand the Confluence Hydrodynamic Zone (CHZ). Nevertheless, 1D approaches remain the mainstay in large drainage network or waterway system modeling considering computational efficiency and data availability. This paper presents (i) a modified 1D nonlinear dynamic model; (ii) a fully 3D non-hydrostatic, Reynolds-averaged Navier–Stokes Equations (RANS)-based, Computational Fluid Dynamics (CFD) model; (iii) an analysis of changing confluence hydrodynamics and 3D turbulent flow structure under various controls; (iv) a comparison of flow features (i.e. upstream water depths, energy losses and post-confluence contraction) predicted by 1D and 3D models; and (v) parameterization of 3D flow characteristics in 1D modeling through the computation of correction coefficients associated with contraction, energy and momentum. The present comprehensive 3D numerical investigation highlights the driving mechanisms for junction induced energy losses. Moreover, the comparative 1D and 3D study quantifies the deviation of 1D approximations and associated underlying assumptions from the ‘true’ resultant flow field. The study may also shed light on improving the accuracy of the 1D large network modeling through the parameterization of the complex 3D feature of the flow field and correction of interior boundary conditions at junctions of larger angles and/or with substantial lateral inflows. Moreover, the enclosed numerical investigations may enhance the understanding of the primary mechanisms contributing to hydraulic structure induced turbulent flow behavior and increased hydraulic resistance.

Modeling of Unsteady Flow through Junction in Rectangular Channels: Impact of Model Junction in the Downstream Channel Hydrograph

Open channel junctions are encountered in urban water treatment plants, irrigation and drainage canals, and natural river systems. Junctions are very important in municipal sewerage systems and river engineering. Adequate theoretical description of flow through an open channel junction is difficult because numerous variables are to be considered. Equations of junction models are based on mass and momentum or mass and energy conservation. The objective of this study is to compare two junction models for subcritical flows. In channel branches, we solve numerically the Saint-Venant hyperbolic system by combining Preissmann scheme and double sweep method. We validate our results with HEC-RAS using Nash and Sutcliffe efficiency. In junction models, equality of water stage and complete energy conservation equation from HEC-RAS are compared. Outcome of the research clearly indicates that the complete conservation energy model is more suitable in flow through junction than equality of water stage model in serious situations.

Comparison of genetic programming and radial basis function neural network for open-channel junction velocity field prediction

The ability to accurately predict the velocity field in open-channel junctions has a significant impact on the designing process of many hydraulic structures, such as irrigation and drainage channels and sewer networks. The gene expression programming (GEP) and radial basis function neural network (RBF-NN) methods are developed in order to find a continuous spatial velocity description using discrete experimental measurements. By using the coordinates of each point and the tributary-to-main-discharge ratio of an open-channel junction, seven different input combinations are investigated. To find the optimum GEP model, various mathematical and linking functions are studied. The RBF-NN models are developed with various numbers of hidden layer nodes and amounts of spread. A comparison of the results indicates that both GEP and RBF-NN methods can accurately simulate flow in junctions. However, the GEP with root-mean-squared error (RMSE) of 0.2361 performs better than RBF-NN with RMSE of 0.2590. Owing to the higher accuracy and explicit output equation of the GEP, this method can be used in practical situations of predicting open-channel characteristics.

Numerical Investigation of Submerged Vane Effects on Flow Pattern in a 90° Junction of Straight and Bend Open Channels

Open-channel junctions have widespread application in civil and environmental engineering projects. A characteristic feature of flow in a junction is formation of a low-pressure zone with recirculating flow (with high sedimentation potential) accompanied by a high-velocity zone (with high erosion potential). A comprehensive numerical research study was done on submerged vanes to investigate their effect on flow pattern. This research was done in order to reduce sedimentation as well as erosion potential at the junction of bending and straight channels. Firstly, the numerical model was validated by previous studies. Secondly, flow pattern in a junction of bending and straight channels was evaluated numerically. Following that, effects of some geometrical characteristics, number and height of vanes and installation angle, were evaluated in relation to improved flow pattern. Finally, performance of vanes was investigated in terms of reducing maximum velocity after the junction with various discharge ratios. The results showed a comprehensive reduction in sedimentation of the junction as well as partial reduction of erosion potential. Evaluation of the results led to the recommendation of using two submerged vanes of height of 0.2h–0.3h and installation angle of 20°–30° in this type of channel. Results also determined that an installation angle of more than 40° and application of submerged vanes in channels by discharge ratios larger than 0.58 are not suggested.

Numerical Analysis of Stormwater Flow Conditions and Separation Zone at Open-Channel Junctions

AbstractOpen-channel junctions are critical design elements for many major and minor drainage infrastructures. Typical examples of these structural elements are encountered in stormwater drainage systems, urban water networks, irrigation, and natural or artificial waterways. The analysis of flow behavior and condition of those structures are of considerable use to engineers involved in the design and planning processes. However, these analyses are very challenging due to the interaction among the incoming junctional and main channel flow coupled with the functional parameters involved, such as the angle of confluence, channel width, cross-section, bed slope, flow direction, discharge, and wall roughness. Therefore, the aim of this paper is to illustrate the application of a finite volume/numerical analysis method to model stormwater flow conditions and separation zone at 45 and 90° of open-channel junctions. In general, the simulation results and analysis suggested that for a 90° junction the separation z...

Open channel junction velocity prediction by using a hybrid self-neuron adjustable artificial neural network

Determining the appropriate hidden layers neuron number is one of the most important processes in modeling the Multi-Layer Perceptron Artificial Neural Network (MLP-ANN). Despite the significant effect of the MLP-ANN neurons number on predicting accuracy, there is no definite rule for its determination. In this study, a new self-neuron number adjustable, hybrid Genetic Algorithm-Artificial Neural Network (GA-ANN), is introduced and its application examined on the complex velocity field prediction of an open channel junction. The results of GA-ANN were compared with those got by the Genetic Programming (GP) method as two applications of the Genetic Algorithm (GA). The comparisons showed that the GA-ANN model can predict the open channel junction velocity with higher accuracy than the GP model, with Root Mean Squared Error (RMSE) of 0.086 and 0.156, respectively. Finally the equation, obtained by applying the GA-ANN model, predicting the velocity at the open channel junction is presented.

Closure to “Experimental determination of free surface levels at open-channel junctions” by MARCIA MARIA LARA PINTO COELHO, J. Hydraulic Res. 53(3), 2015, 394–399

"Closure to “Experimental determination of free surface levels at open-channel junctions” by MARCIA MARIA LARA PINTO COELHO, J. Hydraulic Res. 53(3), 2015, 394–399." Journal of Hydraulic Research, 54(2), pp. 230–231